Neonatal vaccination with bacillus Calmette–Guérin and hepatitis B
vaccines modulates hippocampal synaptic plasticity in rats
Qingqing Li, Fangfang Qi, Junhua Yang, Luwen Zhang, Huaiyu Gu, Juntao Zou, Qunfang Yuan, Zhibin Yao ⁎
Department of Anatomy and Neurobiology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou 510080, China
Received 20 March 2015
Received in revised form 8 August 2015
Accepted 19 August 2015
Immune activation can exert multiple effects on synaptic transmission. Our study demonstrates the inﬂuence of
neonatal vaccination on hippocampal synaptic plasticity in rats under normal physiological conditions. The
results revealed that neonatal BCG vaccination enhanced synaptic plasticity. In contrast, HBV hampered it.
Furthermore, we found that the cytokine balance shiftedin favour of the T helper type 1/T helper type 2 immune
response in BCG/HBV-vaccinated rats in the periphery. The peripheral IFN-γ:IL-4 ratio was positively correlated
with BDNF and IGF-1 in the hippocampus. BCG raised IFN-γ, IL-4, BDNF and IGF-1 and reduced IL-1β, IL-6, and
TNF-αin the hippocampus, whereas, HBV triggered the opposite effects.
© 2015 Elsevier B.V. All rights reserved.
The immune system plays a pivotal role in modulating nerve injury,
regeneration, and learning and memory, which has been ﬁrmly
established over the past two decades (Kohman & Rhodes, 2013;
Perry, 2004; Yirmiya & Goshen, 2011). Immune activation early in
life can signiﬁcantly affect the development of neural processes
(Bitanihirwe et al., 2010; Chen et al., 2013; Chugh et al., 2013; Ito
et al., 2010). Global coverage with bovis bacillus Calmette–Guérin
(BCG) and hepatitis B virus (HBV) vaccinations has reached more than
80% for neonates. It has been reported that neonatal vaccination with
BCG inhibited allergic airway inﬂammation in mice and may protect
against tuberculous meningitis (Freyne & Curtis, 2014; Shen et al.,
2008). In addition to BCG, the association between neonatal vaccination
with HBV and autism has also been researched (Gallagher & Goodman,
2010). However, the related reports regarding the role of neonatal vac-
cination have almost all been derived from studies conducted under
pathological conditions. The safety and side effects of neonatal vaccina-
tion are controversial and need to be evaluated in association with
physiological status (Demirjian & Levy, 2009; Hodgins & Shewen, 2012).
According to these reports, the correlation between neonatal vacci-
nation and neural developmental processes warrants investigation.
Although the related reports demonstrate that early-life immune acti-
vation affects brain development and is related to neurodegenerative
diseases, there has been no study reporting whether neonatal vaccina-
tion could inﬂuence brain development in a physiological manner.
Synaptic plasticity is the primary and sensitive model for investigating
brain development. Therefore, the purpose of this study was to investi-
gate the changes in hippocampal synaptic plasticity induced by neona-
Previous studies have demonstrated that BCG/HBV vaccination can
induce Th1/Th2 serum cytokine bias (Libraty et al., 2014; Ota et al.,
2002, 2004). The Th1/Th2 cytokine balance could modulate the expres-
sion of neurotrophins in the central nervous system (CNS) (Besser &
Wank, 1999). Based on previous reports, we suggested the hypothesis
that early-life vaccination may alter this normal developmental trajec-
tory of synapses via regulation of the expression of cytokines and
neurotrophins. Hippocampal synaptic plasticity was measured because
it is particularly sensitive to neuroinﬂammation (Min et al., 2009). In
this study, neonatal vaccinationwith BCG/HBV modulated hippocampal
synaptic plasticity, including long-term potentiation (LTP), spine densi-
ty and morphology, and the protein expression of synapses. Interesting-
ly, two opposite alterations of synaptic plasticity were observed to be
induced by BCG or HBV vaccination.
2. Materials and methods
Adult male and female Sprague Dawley (SD) rats (70 days) were
purchased from the Sun Yat-Sen University laboratory animal centre
Journal of Neuroimmunology 288 (2015) 1–12
Abbreviations: LTP, long-term potentiation; DG, dentate gyrus; BCG, bacillus
Calmette–Guérin; HBV, hepatitis B vaccination; CNS, central nervous system; BDNF,
brain derived neurotrophic factor; IGF-1, insulin-like growth factor 1; EPSP, excitatory
⁎Corresponding author at: Department of Anatomy and Neurobiology, Sun Yat-Sen
University, #74, Zhongshan No. 2 Road, Guangzhou 510080, China.
E-mail address: firstname.lastname@example.org (Z. Yao).
0165-5728/© 2015 Elsevier B.V. All rights reserved.
Contents lists available at ScienceDirect
Journal of Neuroimmunology
journal homepage: www.elsevier.com/locate/jneuroim
(Guangzhou, China) and were raised in same-sex pairs in a speciﬁc
pathogen-free facility. The colony was maintained under controlled
temperature (22 ± 2 °C) and artiﬁcial light under a 12-h cycle, with
water and food available ad libitum. After acclimation to breeding
conditions, males and females were paired into breeders. All experi-
mental protocols were approved by the Institutional Research Ethics
Committee at Sun Yat-Sen University.
2.2. Experimental design
The present study included four sets of newborns. The results of
hippocampal LTP in this study were based on set one; settwo conﬁrmed
morphology ﬁndings; synaptic protein levels were investigated in set
three; and set four was used for cytokine expression analysis. Each set
was included in three experiments,and every experiment was conduct-
ed at the age of 2,4, and 8 weeks. These experimental time points were
chosen because they are distributed across the important age span
when rats grow from juvenile into adults.
Newborn pups were randomly assigned to three experimental
groups and three matched control groups. They were administered
BCG, HBV, or a combination of BCG and HBV and were named the BCG
group, HBV group, and BH group, respectively. The control groups re-
ceived injections of sterile phosphate-buffered saline (PBS) following
the same protocol as that used in the matched experimental group.
Every experiment included six groups (three experimental groups and
three matched control groups) and the four sets of newborns were
conducted at the age of 2, 4, and 8 w, respectively.
Female rats were visually checked for conﬁrmation of pregnancy,
and male rats were removed from cages before the birth of pups
[postnatal day 0 (P0)]. Female pups were culled to 12 pups per litter
on P0, retaining two females and as many males as possible (Bilbo
et al., 2005). All subjects were males to avoid effects of hormonal varia-
tion in females (Cui et al., 2009).
The BCG and HBV vaccination procedures imitated those used for
human infant vaccinations (Marchant et al., 1999). BCG was adminis-
tered in a single dose at P0,and HBV was administered in a 3-dose series
at P0, P7, and P21. Freeze-dried living Bacillus Calmette–Guérin
(D2-BP302 strain, Biological Institute of Shanghai, Shanghai, China)
was suspended in sterile PBS. Newborn pups were injected intradermal-
ly in the back with 50 μl/rat of BCG suspension containing 10
forming units (CFU) or 50 μl of sterile PBS according to a previously de-
scribed procedure (Kiros et al., 2010). The dose was originally chosen
because it successfully induced an immune response and cytokine pro-
duction in the periphery. In the HBV group and matched CON group,
newborn pups were intraperitoneally injected with a total volume of
100 μl/rat of HBsAg-aluminium-vaccine (20 μg/ml, yeast-derived,
Kangtai Biological Pharmaceutical Company, China) containing ap-
proximately 2 μg HBsAg and an equal amount of PBS. The doses of
HBV (2 μg/rat) and BCG (10
CFU/rat) were chosen based on our pilot
experiments because they were effective without causing obvious
body weight changes (Table S1 and Table S2). Newborn pups in the
BH group were vaccinated with both the BCG and HBV procedures
mentioned above. The newborn pups in the CON groups matched to
the BH group received PBS injections with the same methods as those
used in the BH group. All male pups that underwent synaptic analyses
were weaned on P21 and caged separately in sibling pairs; the remain-
ing female pups were culled.
Newborn pups (2, 4, 8 w) were anaesthetised with urethane (20%
solution, 1.2 g/kg, i.p.) and positioned in a stereotaxic apparatus
(Stoelting Instruments, USA). Body temperature was maintained at
37.0 °C via an electric heating pad. A bipolar concentric tungsten
electrode (Concentric Bipolar Microelectrode, WPI, USA) was used to
stimulate the medial perforant path (coordinates: from bregma, AP,
−8.0 mm; ML, 4.4 mm; DV, 2–2.5 mm below the dura) in the left hemi-
sphere. The stimulating electrode was connected to the output of an
isolator (ISO-ﬂex, AMPI, Israel) connected with a stimulator (Axon
Digidata 1440 A, MDC, USA). A stainless steel, monopolar recording
electrode was inserted into the dentate gyrus (DG) granular cell
(coordinates: from bregma, AP, 3.5 mm; ML, 2.15 mm; DV, 2.5–3mm
below the dura (Süer et al., 2009)). The depths of the recording elec-
trode was optimised to maximise the excitatory postsynaptic potential
(EPSP), and a superimposed negative population spike (PS) was evoked
with a 0.1 mm step. Then the depth of stimulating electrodes were
adjusted to maximise the PS amplitude in response to the perforant
path stimulation. Two screws in the occipital bone were used as the ref-
erence and ground.
Evoked ﬁeld potentials were scored by a population spike (PS). The
test stimulation intensity that produced 50% of the maximum ampli-
tude of the PS was chosen, and the measured test pulse for different an-
imals was between 200 and 400 μA. The test stimuli were performed
every 30 s. Recordings were allowed to stabilise for 20 min, and the
high-frequency stimulation protocol (HFS, 20 trains of 15 pulses at
200 Hz with an inter-train interval of 5 s) was applied to induce LTP.
Following the delivery of the tetanic stimuli, application of the test
stimuli was continued for up to 60 min at 0.033 Hz. The percentage of
the ratio of EPSP slope to the basal value represented the level of
synaptic strength. A slope of EPSP change exceeding 20% was deﬁned
as a successful induction of LTP (Bliss & Collingridge, 1993). The magni-
tude of LTP was between 58 and 60 min in the last bin of the recording
session and was expressed as the percentage change from the PS base-
line. Values from the ﬁnal 2-min bin were compared between the
immunised group and the corresponding control group using Student's
2.5. DiOlistic labelling
Dendritic spine density and morphology in DG neurons were
assessed by quantifying spines in neurons labelled with the ﬂuorescent
dye (1-1′-Dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlo-
rate) DiI (CM-DiI, Sigma-Aldrich, USA) in 2-, 4-, and 8-w-old pups
(Erion et al., 2014). Pups were transcardially perfused with 4% parafor-
maldehyde and postﬁxed in the same ﬁxative for 1–2 days at 4 °C.
Coronal brain slices (200 μm free-ﬂoating) were cut on a vibratome
(Leica VT 1000S, Bannockburn, IL). Slices were rinsed and stored in
0.1 M phosphate buffer (PB) for DiI delivery. The gene gun bullets
were prepared according to a previously described method (Staffend
&Meisel,2011). Brieﬂy, 8 mg of gold particles (1.0 μm in diameter)
was mixedwith 2 mg of DiI (CM-DiI, Sigma-Aldrich, USA) and dissolved
in 300 μl of methylene chloride. After drying, the coated particles were
collected in 2 ml of water, vortexed on a sonicator for 5 min, and imme-
diately transferred to gene gun tubing with a 1-mm diameter (Bio-Rad).
The tube was held still for 1 h before slowly withdrawing the remaining
liquid. Then, we dried the tubing under a constant nitrogen ﬂow for
30 min. The tube was cut into small sections (2 cm in length) and stored
in a desiccated container at 4 °C for up to 1 month.For particle delivery,
slices were transferred to a Petri dish, and most of the PB was then re-
moved. The DiI-coated particles were delivered using the Helios Gene
Gun system (Bio-Rad) at a pressure of 150–180 psi. To prevent clusters
of large particles from landing on the tissue, causing non-speciﬁc label-
ling and preventing single-cell resolution, a membrane ﬁlter was
inserted between the gene gun and the brain sections. After delivery,
slices were incubated overnight in 0.1 M PB at 4 °C to a llow the diffusion
of the dye along the neuronal processes. Finally, the sections were
rinsed 3 times with PB before being mounted on slides and coverslipped
with 65% glycerine in 0.1 M PB.
2Q. Li et al. / Journal of Neuroimmunology 288 (2015) 1–12
2.6. Photography and confocal imaging
Image acquisition and analysis were performed in a systematic
manner by individuals who were blinded to the treatment. On the
same day, brain sections were imaged on a confocal microscope (LSM
710, Carl Zeiss, Germany) to acquire a stack of images (z-spacing,
1μm) of the apical dendrites from isolated DG granule neurons using
a 63x oil objective (N.A., 1.4) with a DPS of 568nm. Three to ﬁve second-
ary dendrites per neuron were imaged (1024 × 1024 pixels, x–y
scaling = 0.0952 μm/pixel), and at least three neurons per rat were col-
lected. All segments were imaged from secondary branches in theapical
dendritic tree at a similar distance from the cell body across genotypes.
Dendritic spine morphology was analysed using the Imaris software
package (Version 7.0, Bitplane Inc., St Paul, MN). Spine density was
determined by manually identifying spines. Spine area and length
were automatically measured in the 3D reconstructive stacks, which
can classify spines into stubby, mushroom, long thin, and ﬁlopodia on
the basis of suitable morphological categories.
2.7. Western blot
Hippocampal tissue was harvested from the vaccinated and control
pups at 2, 4, and 8 weeks (n = 4) and homogenised in ice-cold RIPA
lysis buffer containing (in mM) 50.0 Tris–HCl, 150 NaCl, 5.0 CaCl
, and 1% Triton X-100 in the presence of a protease inhibitor
mixture (1 mM PMSF, protease inhibitor cocktail; Sigma-Aldrich). The
lysates were then centrifuged at 12,000 g for 20 min at 4 °C after incu-
bation in ice for 30 min. The protein concentration was determined
using a BCA Protein Assay Kit (Beyotime). The samples (20 μlper
lane) were separated by 8% sodium dodecyl sulphate-polyacrylamide
gel electrophoresis (SDS-PAGE) and electro-transferred onto a
polyvinylidenediﬂuoride (PVDF) membrane (Bio-Rad Lab, Hercules,
CA, USA) at 60 V for 30 min and then 90 V for 1 h. Membranes were
blocked with 5% non-fat milk in TBS for 2 h at room temperature. The
following primary antibodies were used at the given concentrations:
synaptophysin (1:500; Sigma-Aldrich), PSD-95 (1:2000; Sigma-
Aldrich), NMDAR2A (1:1000; Millipore), NMDAR2B (1:1000;
Millipore), NMDAR1 (1:1000; Cell Signalling Technology), and
β-tubulin (1:1000; Beyotime). Membranes were then rinsed for
10 min three times in PBST (100 nM phosphate buffer, pH 7.5, contain-
ing 150 nM NaCl and 0.1% Tween-20) and incubated with a horseradish
peroxidase (HRP)-conjugated secondary antibody (1:5000; Sigma-
Aldrich) at room temperature for 2 h. Immunoblots were developed
on ﬁlms using the enhanced chemiluminescence technique (Pierce
Chemical Co., Rockford, IL, USA). The intensities of protein bands were
quantiﬁed and analysed using the NIH Image J software. All assays
were performed at least three times.
2.8. Enzyme-linked immunosorbent assay (ELISA)
The levels of IFN-γ, IL-4, TNF-α, IL-6, and IL-1βin serum and in
the hippocampus were assessed in duplicate via an ELISA kit
(Neobioscience Technology Co., Ltd) as described previously (Xia
et al., 2014a). The hippocampal samples were homogenised as de-
scribed above by Western blotting. The levels of neurotrophic factors
in the hippocampus were measured by an ELISA kit (Cusabio Life Sci-
ence Co., Ltd) according to an optimised manufacturer's protocol at 2,
4, and 8 weeks. Samples were homogenised on ice in buffer (pH 7.6)
containing (in mM) 50.0 Tris–HCl, 150 NaCl, 5.0 CaCl
, 0.02% NaN
and 1% Triton X-100 and then centrifuged at 17,000 ×gfor 30 min at
4 °C. The total hippocampal homogenate concentration was adjusted
to 4.5 mg/ml by using an Enhanced BCA Protein Assay Kit (Beyotime)
according to a previous report (Selenica et al., 2013). The prepared
plates were analysed by the microplate reader (BIO-TEk ELx800, USA)
at 450 nm.
2.9. Statistical analysis
Data are presented as the means ± SEM. Differences between
groups were evaluated by two-way (vaccination × time) ANOVA
followed by Bonferroni post-hoc test using SPSS 17.0. The analysis of
the correlation between the IFN-γto IL-4 ratio and BDNF/IGF-1 wasper-
formed using Pearson correlation analysis. Statistical signiﬁcance was
set to pb0.05, and analyses were performed using Graph Pad Prism
5.0 (GraphPad Software).
3.1. Neonatal vaccination and antibody levels
Each group of rats was administered BCG (BCG group), HBV (HBV
group), or a combination of BCG and HBV (BH group) on P0. The
serum anti-HBsAg antibody and anti-BCG titres of all control rats were
kept at a baseline level. There was a signiﬁcant increase in antibody
titres in the HBV/BCG vaccinated rats compared with their control
groups at all three time points (2, 4, and 8 weeks; Table S1 and
Table S2). The increase was also observed in the BH groups. No signiﬁ-
cant differences were observed in physical conditions, such as weight,
between the vaccinated rats and the controls (Table S1 and Table S2).
3.2. Neonatal vaccination affects hippocampal LTP in vivo
To investigate the effects of neonatal vaccination on synaptic plastic-
ity, we examined LTP in the DG area in vivo at 2, 4, and 8 weeks postna-
tal. Two-way ANOVA revealed signiﬁcant main effects of BCG (F
12.20, P = 0.002). Subsequent analysis revealed that BCG vaccination
facilitated the induction of hippocampal LTP at 2 weeks (166.20 ±
9.11%, p= 0.01, Fig. 1A and E) and 4 weeks (173.22 ± 7.27%,
p= 0.016, Fig. 1B and E) compared with the controls. There was no sig-
niﬁcant main effects of HBV, time or signiﬁcant interactions of
HBV × time. However, Subsequent analysis revealed that HBV vaccina-
tion inhibited hippocampal LTP at 8 weeks (126.12 ± 6.21%, p=0.017,
Fig. 1C and F). Interestingly, there was no signiﬁcant difference in LTP
between the BH group and the control group (Fig. 1D and G), which sug-
gested that these two vaccines may counteract each other to a certain
extent. Notwithstanding, these data indicated that neonatal BCG and
HBV vaccination indeed inﬂuenced the synaptic activity in the hippo-
campus; moreover, the initial effect of BCG vaccination occurred at 2
weeks, whereas that of HBV was delayed to 8 weeks.
3.3. Neonatal vaccination inﬂuences dendritic spine density on hippocam-
pal DG granule cells
Dendrites receive and process synaptic inputs from other neurons
(Kampa et al., 2007). To elucidate whether the cellular mechanisms of
LTP include the formation of new synapses or the remodelling of
existing synapses, numerous studies have examined the number and
structure of synapses following hippocampal LTP (Geinisman, 2000;
Urbanska et al., 2012). To determine the morphological basis for the
change in hippocampal LTP following neonatal vaccination, we investi-
gated spine density, length, and area in hippocampal granule neurons at
2, 4, and 8 weeks. DiOlistic labelling was used to label spines. Although
both neurons and neuroglia werelabelled with DiI, they could be clearly
distinguished on the basis of their morphological features (Cui et al.,
2010). Granule cell bodies, apical dendrites, several lateral and basilar
dendrites, and even dendritic spines could be recognised. There were
signiﬁcant main effects of BCG (F
= 4.03, P = 0.049), time
= 35.13, P = 0.000) and interaction of BCG × time (F
3.49, P = 0.039) on the density of spines. Moreover, signiﬁcant main
effects of BCG (F
= 10.89, P = 0.002) and time (F
P = 0.000) on the area of spines were observed. Subsequent analysis re-
vealed that BCG vaccination increased the spine density at 4 w (11.39 ±
3Q. Li et al. / Journal of Neuroimmunology 288 (2015) 1–12
1.33 10 μm
,n= 9 neurons, p= 0.001, Fig. 2B) and the spine area at 2
and 4 weeks (5.49 ± 0.26 μm
,p= 0.021; 13.72 ± 0.17, p= 0.032,
n= 9 neurons, Fig. 2C) compared with their controls. In contrast, HBV
vaccination reduced the spine density (HBV: F
= 4.86, P = 0.033,
= 9.85, P = 0.000) and area (time: F
P = 0.000, HBV × time: F
= 3.69, P = 0.033) at 8 weeks (HBV vs
CON: density: 5.00 ± 0.52 10 μm
,n= 10 neurons, p=0.01,
Fig. 2B. Area: 2.45 ± 0.15 μm
,n= 10 neurons, p= 0.015, Fig. 2C).
Consistent with previous ﬁndings, the BH group showed no signiﬁcant
difference in spine density or area (Fig. 2B and C). No signiﬁcant alterna-
tions were observed with respect to the spine length between any two
groups (Fig. 2D). Altogether, there is a close correlation between hippo-
campal LTP and dendritic spine number and structure, suggesting that
the functional and structural plasticity of synapses occurred simulta-
neously following neonatal vaccination. A total of three dendritic
segments per neuron, three neurons per pup, and three to ﬁve pups
were averaged to yield the mean spine density and area for each rat.
3.4. Neonatal vaccination changes the dendritic spine morphology on
hippocampal DG granule cells
The number of spines and their morphology have been demonstrat-
ed to be important for information processing and are associated with
hippocampal LTP (Geinisman, 2000; Urbanska et al., 2012). The plastic
changes in spine morphology reﬂecting the dynamic state of the correl-
ative synapse are responsible to some extent for neuronal circuitry
remodelling (Alvarez & Sabatini, 2007). Therefore, we assessed the
density of the dendritic spines according to their speciﬁc morphology
(ﬁlopodia, long thin, stubby, and mushroom) by DiOlistic labelling.
Our ﬁndings revealed that BCG caused a selective increase in mushroom
spines (BCG: F
= 5.21, P = 0.029, time: F
= 32.19, P = 0.000,
BCG × time: F
= 6.11, P = 0.022) on hippocampal DG granule
cells at 4 weeks (BCG vs CON: P = 0.017, Fig. 3B), whereas there was
a signiﬁcant reduction in the number of stubby spines (HBV: F
7.98, P = 0.009, time: F
= 22.59, P = 0.000, BCG × time: F
17.11, P = 0.002) in the HBV group at 8 weeks (HBV vs CON:
p=0.037,Fig. 3C). In line withthe previous results,no signiﬁcant differ-
ences were observed between the BH and CON groups (Fig. 3D). There-
fore, it was inferred that the selective increase or reduction in
mushroom and stubby spines, which have bigger heads, may contribute
to the alterations in overall spine density and area.
3.5. Neonatal vaccination affects the expression levels of synaptic proteins
in the hippocampus
Synaptophysin is the major integral membrane protein of synaptic
vesicles (Thiel, 1993). The main functions of synaptophysin are docking,
fusion, and endocytosis, otherwise known as membrane trafﬁcking
(Evans & Cousin, 2005). PSD-95, the major scaffolding protein contrib-
uting to the excitatory postsynaptic density (PSD) and a potent regula-
tor of synaptic strength, has been considered a key synaptic protein that
promotes synapse stability (Chen et al., 2011; Taft & Turrigiano, 2014). It
is known that the induction of hippocampal LTP requires synaptic acti-
vation of postsynaptic NMDA receptors (Citri & Malenka, 2008).
Fig. 1. Effects of neonatal vaccination with BCG, HBV, and BH on hippocampal LTP in vivo. (A) Representative traces (left) of PS before (basal) and after (60 min) HFS. BCG vaccination
facilitated the induction of hippocampal LTPat 2 weeks (A) and 4 weeks (B) compared with controls. In contrast, HBV vaccination inhibited the induction of LTP at 8 weeks (C) . BH vac-
cination caused no profound alterations at 2, 4, or 8 weeks compared with their controls (D). (E, F, and G) Summary histograms representing the effects of BCG (E), HBV (F), and
BH (G) vaccination on LTP at 60 min post-HFS. Data are presented as the means ± SEM and were analysed with two-way ANOVA followed by Bonferroni post-hoc test. n=6–7 for
each group. *pb0.05.
4Q. Li et al. / Journal of Neuroimmunology 288 (2015) 1–12
Fig. 2. Alterations in the dendritic spinelength, area, and densityof granule cellsin the DG of the rats vaccinated withBCG, HBV, and BH. (A) A DiOlisticassay was used to visualisedendritic
spines in granule cells.Individual granulecell at 2, 4, and 8 weeks, respectively (left), representative sections of lateral dendritesin the CON, BCG, HBV, and BH groups at 2, 4, and 8 weeks.
The magniﬁedimages are on the right. BCG vaccination increased thespine density at 4 weeks (B) and the spine area at 2 and 4 weeks (C) compared with the controls. Conversely, HBV
vaccination reducedthe spine area and densityat 8 weeks (B and C). BH-vaccinatedrats showed no signiﬁcant difference in spine density or area (B and C). No profound alterations were
observed inthe spine length between any two groups at any of thethree time points (D).Data are presented as the mean ± SEM and were analysed with two-way ANOVA followed by
Bonferroni post-hoc test. n= 9 neurons (3 dendritic segments per neuron, 3 neurons per pup, and 3 pups). *pb0.05 versusvehicle control. Scale bar, 10 μm (left), 5 μm(right).
Fig. 3. Alterations in the morphology of thedendritic spines in the hippocampusof vaccinated rats. (A)Representative photomicrograph depictsdifferent morphological subtypes of den-
driticspines in relation to the dendritic shaft.BCG vaccinationincreased the densityof mushroom spines at4 weeks (B). HBVvaccination decreased the densityof stubby spines at 8 weeks
(C). Data arepresented as the means± SEM and were analysed with two-wayANOVA followed by Bonferroni post-hoc test. n= 9 neurons(3 dendritic segments per neuron, 3 neurons
per pup, and 3 pups). For all graphs, *pb0.05 versus vehicle control and scale bar = 5 μm.
5Q. Li et al. / Journal of Neuroimmunology 288 (2015) 1–12
Therefore, we applied a Western blotting technique to assess whether
the synaptic proteins were subject to modulation by neonatal vaccina-
tion. It was demonstrated that BCG vaccination promoted the expres-
sion of hippocampal synaptophysin (BCG: F
= 12.29, P = 0.001,
= 13.22, P = 0.000. BCG vs CON: p= 0.002, Fig. 4B),
PSD-95 (BCG: F
= 5.90, P = 0.028, time: F
P = 0.000) and NMDAR2A (BCG: F
= 4.47, P = 0.043, time:
= 7.91, P = 0.002. BCG vs CON: p=0.01,Fig. 4F) at 4 weeks.
Fig. 4. NeonatalBCG, HBV, and BH vaccinations affect the expression ofsynaptophysin, PSD-95, NMDAR2A, NMDAR2B, and NMDAR1 in the hippocampus. (A,C, E, G and I) Representative
immunoblots of synaptic proteinsat 3 time points. BCGincreased the synaptophysin(B), PSD-95 (D) and NMDAR2A (F) protein levelsat 4 weeks comparedwith the controls.Conversely,
HBV vaccination reduced the synaptophysin, PSD-95, NMDAR2A, and NMDAR2B levels at 8 weeks (B, D, F and H). BH rats showed no signiﬁcant changes in synaptic proteins. Data are
presented as the mean ± SEM and were normalised to the matched control. Two-way ANOVA followed by Bonferroni post-hoc test. n= 4 per group. *pb0.05 and **pb0.01 versus
the control group.
6Q. Li et al. / Journal of Neuroimmunology 288 (2015) 1–12
Conversely, HBV vaccination decreased their expressions at 8 weeks
(synaptophysin: HBV: F
= 5.15, P = 0.031, time: F
P = 0.000. HBV vs CON: p= 0.012, Fig. 4F; PSD-95: NMDAR2A: HBV:
= 12.64, P = 0.002. HBV vs
CON: p= 0.000; NMDAR2B: HBV: F
= 5.61, P = 0.025, time:
= 14.02, P = 0.001. HBV vs CON: p= 0.042. Fig. 4B, D, F, and
H). No signiﬁcant changes wereobserved in these proteins in the hippo-
campus between the BH and control groups. The results indicated that
the alterations in the synaptic proteins may be associated with spine
density and morphology because PSD-95, which is one of the most
abundant PSD proteins, is involved in synapse maturation (El-Husseini
et al., 2000; Prange & Murphy, 2001).
3.6. Neonatal vaccination altersthe levels of cytokines and neurotrophins in
serum and the hippocampus
Cytokines and neurotrophins play a critical role in the process of
brain development under physiological/pathological conditions such
as synaptic plasticity (Erion et al., 2014). Therefore, we considered the
potential implications of the immune-related diffusible mediator in
modulating synaptic plasticity and neural network functioning.
Research in this ﬁeld has focused on several pro-inﬂammatory cyto-
kines, such as IL-1β, IL-6, and TNF-α, as having a detrimental effect on
neuronal function and synaptic plasticity (Spedding & Gressens,
2008). However, IFN-γ, IL-4, BDNF, and IGF-1 are regarded as neuro-
trophic factors (Yirmiya & Goshen, 2011). Therefore, we investigated
potential changes in the mediators related to immune activation and
synaptic plasticity. The levels of cytokines and neurotrophins are
shown in Table S3 (serum) and Table S4 (hippocampus). Our data re-
vealed that the BCG group displayed a neurotrophic expression proﬁle
of increased IFN-γ, IL-4, BDNF, and IGF-1 and decreased TNF-α, IL-1β,
and IL-6 at 2 and 4 w, whereas the HBV group exhibited a neurotoxic ex-
pression proﬁle of increased TNF-αand IL-6 and decreased IFN-γ,BDNF,
and IGF-1 at 8 w (see Fig. 5). Interestingly, the BH group exhibited no
signiﬁcant changes in serum molecules, but it exhibited slight alter-
ations in the hippocampus compared with the controls. According to
these data, the expression of cytokines and neurotrophins was altered
in both serum and the hippocampus after neonatal vaccination. More-
over, the altered trend was almost the same in serum and the hippo-
campus, which suggested that there wasan internal link between them.
3.7. Neonatal vaccination switches the bias of Th1 or Th2 in serum
Recent animal studies on ageing have indicated that hippocampal
neurogenesis is associated with a decrease in the Th1/Th2 bias
(Baruch et al., 2013). Therefore, to evaluate whether neonatal vaccina-
tion regulates the Th1/Th2 bias, we assessed the ratio of classical
serum cytokine IFN-γ(Th1) to IL-4 (Th2). Consistent with the previous
reports (Libraty et al., 2014; Marchant et al., 1999; Ota et al., 2002,
2004), our ﬁndings conﬁrmed that BCG induced a Th1-like response at
2 weeks (BCG: F
= 8.28, P = 0.007, time: F
= 3.8, P = 0.034,
BCG vs CON: p= 0.043, Fig. 6A). In contrast, HBV induced a Th2-like re-
sponse at 8 weeks (HBV: F
= 7.48, P = 0.01, time: F
P = 0.000, HBV vs CON:p=0.012,Fig. 6A). Moreover, no signiﬁcant dif-
ference was observed in the BH group. The association between the
Th1/Th2 bias and the central cytokine and neurotrophin milieu and,
thus, the impact on synaptic plasticity were further demonstrated by
the positive correlation between the IFN-γ:IL-4 ratio and BDNF (2 w:
= 0.572, p= 0.000; 4 weeks: r
= 0.507, p= 0.002; 8 weeks:
= 0.386, p=0.02;n= 36; Pearson correlation analysis; Fig. 6B)
and IGF-1 (2 weeks: r
= 0.518, p= 0.001; 4 weeks: r
p= 0.004; 8 weeks: r
= 0.131, p=0.446;n= 36; Pearson correlation
analysis; Fig. 6B) levels.Interestingly, the results showed decreased cor-
relation coefﬁcients between the IFN-γ:IL-4 ratio and BDNF and IGF-1
levels as time progressed.
Our ﬁndings support the hypothesis that neonatal vaccination with
BCG or HBV modulates hippocampal synaptic plasticity probably via
the neuro-beneﬁcial or neuro-detrimental expression proﬁles of hippo-
campal cytokines and neurotrophins. BCG vaccination facilitated the
induction of hippocampal LTP, increased the spine density and area,
elicited a selective increase in mushroom spines in the hippocampal
DG area, and elevated hippocampal synaptophysin, PSD-95, and
NMDAR2A protein levels. Conversely, HBV vaccination showed almost
inverse alterations of all these aspects. In this study, BCG induced a
Th1-like response followed by increased neurotrophins in the brain,
whereas HBV induced a Th2-like response followed by decreased
neurotrophins. In addition, positive correlations between the IFN-γ:IL-
4 ratio and BDNF and IGF-1 were observed. Interestingly, BH showed
no obvious shift to either a Th1 or Th2 response and no signiﬁcant inﬂu-
ence on synaptic plasticity.
LTP is the most extensively studied model of the cellular mecha-
nisms of synaptic plasticity (Bliss & Collingridge, 1993; Bliss & Lomo,
1973). In the present study, PP-DG LTP was determined based on the
particular sensitivity of the DG structure to both endogenous and
exogenous signals, such as immune activation and pro-inﬂammatory
cytokines, particularly IL-1βand TNF-a (Beattie et al., 2002; Di Filippo
et al., 2008). The present study demonstrated that neonatal BCG vacci-
nation transiently facilitated the induction of hippocampal LTP in rats.
However, HBV impaired hippocampal LTP. These data conﬁrm our spec-
ulation that altered immune status induced by vaccination modulates
hippocampal synaptic plasticity during early life, which is different
from immune activation models induced by LPS, poly (I:C), and
Escherichia coli (E. coli) under pathological conditions.
Dendritic spines are important and pleomorphic structures in the
collection, integration, and transmission of neural signals. Thus, the al-
terations of spine density and morphology may contribute to hippo-
campal LTP. We found that the changes in spine area and density
were consistent with the results of hippocampal LTP in the DG area. It
should be noted that only two subtypes of dendritic spines, namely,
stubby and mushroom (mature and stable, with bigger heads that
allow the passage of more current (Zhao et al., 2006; Urbanska et al.,
2012)), were altered in granule neurons in the DG area in BCG/
HBV-vaccinated rats (BCG rats/HBV rats), and no difference was
observed in immature dendritic subtypes (thin and ﬁlopodia) in either
experimental group. Together with spine density and area, the subse-
quent potential alterations in mature and efﬁcient spine subtypes may
contribute to the performance of hippocampal LTP in BCG and HBV
rats. Recent evidence suggests that activated immune cells secrete cyto-
kines and growth factors, which can modulate synaptic transmission
(Henneberger et al., 2005; Pickering et al., 2005) and alter dendritic
spine morphology (Schratt et al., 2006; von Bohlen und Halbach et al.,
2006). The opposite ﬁndings regarding spine density and morphology
between the BCG and HBV rats may be due to the different cytokine
and neurotrophin networks induced by neonatal vaccination with
In addition to the structural plasticity of dendritic spines, the func-
tional plasticity and molecular mechanisms involved in regulating syn-
aptic transmission also require exploration. Both of these mechanisms
may potentially contribute to the alterations in LTP observed in vacci-
nated rats. The synapse proteins, including synaptophysin, PSD-95,
and NMDA receptors, play an important role in synaptic plasticity
(Kamphuis et al., 1992; Liu et al., 2004; Monyer et al., 1992). Therefore,
the modulation of these proteins by immune activation may inﬂuence
synaptic transmission. Our ﬁndings showed that changes in synaptic
proteins were almost parallel to the changes in LTP, spine density, and
morphology. Based on these results, altered synaptic proteins induced
by vaccination may be another contributory factor to the induction of
hippocampal LTP observed in vaccinated rats. The BCG vaccination-
induced increase in spine density and synaptic proteins may represent
7Q. Li et al. / Journal of Neuroimmunology 288 (2015) 1–12
an enhanced excitatory synaptic connectivity in the early stage of
synaptogenesis. Accordingly, it has been reported that there was a
correlation between spine density, PSD-95, and the inﬂammatory
environment (Chugh et al., 2013; Jakubs et al., 2006). Although recent
studies have demonstrated that inﬂammatory cytokines participate in
physiological and pathological events depending on PSD-95 protein
level or NMDA receptor activation (Gardoni et al., 2011), how the
vaccination-related cytokine network modulates the expression of
synaptic proteins remains elusive.
The most important question for further study is the underlying
mechanism mediating synaptic transmission and structure and the po-
tential difference between the two vaccines. It has been reported that
early life events altered this normal developmental trajectory of the
brain, speciﬁcally synaptic plasticity, via their speciﬁc impact on cyto-
kine and neurotrophin expressions (Goshen et al., 2007; Yirmiya &
Goshen, 2011). Therefore, the hippocampal homogenate was collected
to determine the proﬁle of these mediators in relation to immune acti-
vation. IL-1β, IL-6, and TNF-a, which have been associated with cogni-
tive decline, inhibited synaptic plasticity and caused hippocampal LTP
impairment in previous studies (Balosso et al., 2008; Viviani et al.,
2003; Viviani et al., 2006). It has also been demonstrated that both
IL-4 and IFN-γcontribute to hippocampal LTP and neurogenesis
(Nolan et al., 2005; Zhu et al., 2011). In line with previous reports, our
results showed that the levels of IL-4 and IFN-γwere signiﬁcantly
Fig. 5. Neonatal BCG, HBV,and BH vaccination alters the levels of cytokines and neurotrophins in the hippocampus and serum.The levels of IL-1β, IL-6, TNF-α,IL-4,IFN-γ,BDNF and IGF-1
in serum(A, B and C) and the hippocampus (D,E, F, G, H and I) were normalised andanalysed at 2, 4, and8 weeks. In serum, BCGvaccination up-regulatedIL-4 at 4 weeks (B) andIFN-γat
2 weeks (A)and 4 weeks (B), whereasit down-regulatedIL-1βand TNF-αat2 weeks (A) and 4 weeks(B) and down-regulated IL-6 at4 weeks (B). HBV vaccination up-regulatedthe level
of IL-6 at 8 weeks (C), which decreasedthe level of IFN-γat 2 weeks (A),4 weeks (B), and 8 weeks (C)and decreased the level of IL-4 at 2 weeks (A) and 8 weeks (C). Alterationsin the
hippocampus werealmost consistentwith those in serum(D, E and F). BCG vaccination increased the expressionof BDNF and IGF-1 at 2 weeks(G) and 4 weeks (H),whereas HBV decrease
them at 8 weeks (I). Data are presented as the means ± SEM normalised to the controls and were analysed with two-way ANOVA followed by Bonferroni post-hoc test. n= 6 for each
group. *pb0.05, **pb0.01, and ***pb0.001 versus the control group.
8Q. Li et al. / Journal of Neuroimmunology 288 (2015) 1–12
increased in the hippocampus of BCG rats, whereas the levels of IL-1β,IL-
6, and TNF-a, known to be detrimental to LTP, were reduced.
Importantly, the concentrations of BDNF and IGF-1, which are thought
to enhance brain functional plasticity (Nolan et al., 2005), were up-
regulated in the BCG rats. In contrast to BCG, those levels declined in
the HBV rats. Interestingly, the BH rats showed no signiﬁcant alterations
in these cytokines and neurotrophins in the brain. These data indicated
that the alterations in synaptic plasticity regulated by the cytokine net-
work were accompanied by the alterations in neurotrophins, such as
IL-4, BDNF, and IGF-1, which modulate synaptic efﬁcacy and neurotrans-
mission (Figurov et al., 1996; Levine et al., 1995; Neal-Perry et al., 2014).
Previous studies have demonstrated that manipulations of individu-
al cytokines can modulate learning, memory, and synaptic plasticity.
However, there are many conﬂicting ﬁndings that have prevented a
clear understanding of the precise role of cytokines in synaptic plastici-
ty. Given the complexity of inﬂammatory signalling, we speculated that
it is primarily the cytokine network that contributes to the ﬁne-tuning
of neural transmission rather than an individual cytokine (Xia et al.,
2014a). In our study, the levels of cytokines in the hippocampus
displayed similar trend as those in the serum, which suggests a close co-
incidence between the brain and peripheral blood system. It has been
reported that peripheric cytokines may permeate into the CNS and
affect neuronal transmission directly (Banks, 2005). The interplay be-
tween cytokines and neurotrophins is complex. Neurotrophins can be
secreted by several types of immune cells, including T cells, microglia,
macrophages, and mast cells (Elkabes et al., 1996; Nakajima et al.,
2001). Cytokines in the CNS have crosstalk with resident immune cells
(e.g., microglia) and regulate their phenotypes and therefore alter
their local molecule production, including cytokines and neurotrophins
(Schwartz and Shechter, 2010).
BCG or HBV vaccination induced a shift toward a dominance of the
Th1 or Th2 response, respectively. Given that mediator-related
Fig. 6. Neonatal BCG, HBV, and BH vaccination alters the Th1/Th2 bias. BCG vaccination induced a Th1-like response, while HBV led to a Th2-like response in the periphery. Bars in
(A) represent the fold-change ofthe average concentration of IFN-γwith respect to that of IL-4 in each group in serum. Dataare presented as the means ± SEM normalised to the control
and were analysed with two-way ANOVA followed by Bonferroni post-hoc test. n= 6 for each group (A). Correlation analysis was performed using the serum IFN-γ:IL-4 ratio and the
hippocampal BDNF or IGF-1 level (B). Pearson correlation analysis (BDNF: 2 weeks, r
=0.572,pb0.01; 4 weeks, r
= 0.507, pb0.01; 8 weeks, r
= 0.386, pb0.05; IGF-1: 2 weeks,
=0.518,pb0.01; 4 weeks, r
= 0.472, pb0.01; n=36).
9Q. Li et al. / Journal of Neuroimmunology 288 (2015) 1–12
immunity in the hippocampus resulted from immune activation in the
periphery, the positive correlation between systemic Th1:Th2 ratios
and hippocampal neurotrophins bridges the vaccination and neurogen-
ic niche and explains the change in synaptic plasticity.
Furthermore, it has been conﬁrmed that the Th1/Th2 cytokine bal-
ance can modulate neurotrophin expression and, thus, affect neuronal
function (Besser & Wank, 1999). Thus, an integrated network is formed
between the extrinsic Th1/Th2 serum cytokines followed by intrinsic
CNS-derived cytokines and the neurotrophin network to build a
beneﬁcial/detrimental neurogenic niche. Therefore, we propose a hy-
pothesis that a systemic Th1/Th2 bias modulates central cytokines and
neurotrophins andthereby affects theneurogenic niche, which istightly
correlated with synaptic plasticity. Previous reports support this hy-
pothesis. It was reported that cognitive deﬁcit was related to decreased
Th1/Th2 balance in periphery and could be recoveredwhen the balance
was restored (Jakobsson et al., 2014; Palumbo et al., 2012). In addition
to this, inﬂuenza vaccines administered during pregnancy induced a
systemic Th1 bias and increased neurotrophins in both dams and their
offspring (Xia et al., 2014a; Xia et al., 2014b). Inour study, the probable
underlying mechanism of the Th1/Th2 bias modulating synaptic plastic-
ity was demonstrated by the following results: 1) BCG vaccination in-
duced a Th1 serum cytokine response and yielded beneﬁcial effects on
synaptic plasticity; conversely, HBV induced a Th2 bias and exerted det-
rimental effects; 2) the correlation analysis showed a positive correla-
tion between systemic Th1:Th2 ratios and hippocampal BDNF and
IGF-1 levels; 3) it has been demonstrated that BDNF and IGF-1 contrib-
ute to the enhancement of synaptic transmission (Figurov et al., 1996;
Levine et al., 1995; Neal-Perry et al., 2014); and 4) BH vaccination
showed no obvious shift in Th1 or Th2, and no signiﬁcant effects were
observed on synaptic plasticity. In summary, the possibility arises that
altered synaptic plasticity during early life may be modulated by the
balance of two forces, namely, intrinsic CNS-derived signals and
extrinsic signals that permeate to the CNS. However, the underlying
mechanism is complex and diverse. Other mechanisms may exist and
require further study, such as the neuro-protective or neurotoxic
microglial cells reactivity to TH1/TH2 response. Moreover, the implica-
tion of immune molecules, such as MHC of class I, toll like receptors
and complement system, which have been recently related to neonatal
synaptic plasticity, may contribute to the alteration of synaptic
Interestingly, we found a decline in the correlation coefﬁcients
between the IFN-γ:IL-4 ratio and BDNF and IGF-1 levels as time
progressed, which may explain why the effect on synaptic plasticity
induced by neonatal vaccination disappeared with age. Although we
speculated that the inﬂuence on synaptic plasticity induced by neonatal
vaccination was associated with Th1/Th2 bias accompanied by changes
in BDNF and IGF-1, other immune cells, such as regulatory T lympho-
cytes and local microglia affected by immune activation, also play criti-
cal roles in modulating synaptic plasticity (Lagranderie & Guyonvarc'h,
2014; Yong et al., 2011).
We found that the timing of the effect on synaptic plasticity was
different between the BCG and HBV rats. This may be due to immune
reactions, bacterial/virus antigens, or the humoral/cellular immune
response that contribute to different latencies. It is well known that
the cellular immune response is activated faster than the humoral
immune response under normal physiological conditions, which may
explain why BCG vaccination is more quickly effective in synaptic struc-
tures and transmission than HBV. However, the present analysis re-
mains speculative, and the reason for this speculation is considerably
complicated and requires further exploration.
In summary, we worked speciﬁcally with a model of neonatal vacci-
nation in rats that modulates hippocampal synaptic plasticity. The pres-
ent ﬁndings provide innovative information regarding the correlation
between neonatal vaccination and synaptic transmission. Moreover,
our data suggested that combinationsof different vaccines can mutually
interact (enhance or counteract). The mechanism of synaptic plasticity
modulation through neonatal BCG/HBV vaccination may be via systemic
Th1/Th2 bias accompanied by a speciﬁcproﬁle of cytokines and
neurotrophins in the brain. Our work highlights a critical role of
neonatal vaccination in synaptic plasticity outside of infectious disease
prevention, which suggests the necessity of further studies on the asso-
ciation of vaccination with brain development under normal physiolog-
The authors thank Prof. Huaiyu Gu and Prof. Juntao Zou for their
technical assistance, as well as Qunfang Yuan for technical guidance.
This work was supported by National Natural Science Foundation of
China (No. 31371130),and the Science and Technology Planning Project
of Guangdong Province, China (No. 2009B080701089). The authors
declare no competing ﬁnancial interests.
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