Antibodies to Potato Virus Y Bind the Amyloid β Peptide

Article (PDF Available)inJournal of Biological Chemistry 283(33):22550-22556 · August 2008with29 Reads
DOI: 10.1074/jbc.M802088200 · Source: PubMed
Studies in transgenic mice bearing mutated human Alzheimer disease (AD) genes show that active vaccination with the amyloid β (Aβ) protein or passive immunization with anti-Aβ antibodies has beneficial effects on the development of disease. Although a trial of Aβ vaccination in humans was halted because of autoimmune meningoencephalitis, favorable effects on Aβ deposition in the brain and on behavior were seen. Conflicting results have been observed concerning the relationship of circulating anti-Aβ antibodies and AD. Although these autoantibodies are thought to arise from exposure to Aβ, it is also possible that homologous proteins may induce antibody synthesis. We propose that the long-standing presence of anti-Aβ antibodies or antibodies to immunogens homologous to the Aβ protein may produce protective effects. The amino acid sequence of the potato virus Y (PVY) nuclear inclusion b protein is highly homologous to the immunogenic N-terminal region of Aβ. PVY infects potatoes and related crops worldwide. Here, we show through immunocytochemistry, enzyme-linked immunosorbent assay, and NMR studies that mice inoculated with PVY develop antibodies that bind to Aβ in both neuritic plaques and neurofibrillary tangles, whereas antibodies to material from uninfected potato leaf show only modest levels of background immunoreactivity. NMR data show that the anti-PVY antibody binds to Aβ within the Phe4–Ser8 and His13–Leu17 regions. Immune responses generated from dietary exposure to proteins homologous to Aβ may induce antibodies that could influence the normal physiological processing of the protein and the development or progression of AD.


Antibodies to Potato Virus Y Bind the Amyloid
Received for publication, March 17, 2008, and in revised form, May 14, 2008 Published, JBC Papers in Press, May 27, 2008, DOI 10.1074/jbc.M802088200
Robert P. Friedland
, Johnathan M. Tedesco
, Andrea C. Wilson
, Craig S. Atwood
, Mark A. Smith
George Perry**, and Michael G. Zagorski
From the Departments of
Chemistry, and
Pathology, Case Western Reserve University, Cleveland, Ohio 44106, the
Department of Medicine, University of Wisconsin, and the Geriatric Research, Education and Clinical Center, William S. Middleton
Memorial Veterans Hospital, Madison, Wisconsin 53705, and the **University of Texas at San Antonio College of Sciences,
San Antonio, Texas 78249
Studies in transgenic mice bearing mutated human Alzhei-
mer disease (AD) genes show that active vaccination with the
) protein or passive immunization with anti-A
antibodies has beneficial effects on the development of disease.
Although a trial of A
vaccination in humans was halted
because of autoimmune meningoencephalitis, favorable effects
on A
deposition in the brain and on behavior were seen. Con-
flicting results have been observed concerning the relationship
of circulating anti-A
antibodies and AD. Although these
autoantibodies are thought to arise from exposure to A
also possible that homologous proteins may induce antibody
synthesis. We propose that the long-standing presence of
antibodies or antibodies to immunogens homologous
to the A
protein may produce protective effects. The amino
acid sequence of the potato virus Y (PVY) nuclear inclusion b
protein is highly homologous to the immunogenic N-terminal
region of A
. PVY infects potatoes and related crops worldwide.
Here, we show through immunocytochemistry, enzyme-linked
immunosorbent assay, and NMR studies that mice inoculated
with PVY develop antibodies that bind to A
in both neuritic
plaques and neurofibrillary tangles, whereas antibodies to mate-
rial from uninfected potato leaf show only modest levels of back-
ground immunoreactivity. NMR data show that the anti-PVY
antibody binds to A
within the Phe
and His
regions. Immune responses generated from dietary exposure to
proteins homologous to A
may induce antibodies that could
influence the normal physiological processing of the protein and
the development or progression of AD.
Despite great advances in our understanding of the genetics
and molecular biology of Alzheimer disease (AD),
we do not
fully understand why 99% of people with the disease are
affected. Although familial early-onset AD is caused by well
described mutations in the amyloid
) precursor (chromo-
some 21) and presenilins 1 and 2 (chromosomes 1 and 14) (1),
these mutations are responsible for only 1–2% of the cases of
the disease. The most important genetic risk factor for the
more prevalent (so-called sporadic) disease is the
4 allele of
apoE, which is well described and is responsible for 40
60% of the inherited risk. However, the
4 allele is likely not
causative, as approximately one-third of people with the dis-
ease do not have the gene, and many people with the gene do
not have the disease. (45% of apoE
4 homozygotes do not get
the disease by age 80 (2).)
Immunization with the A
peptide produces behavioral and
histopathological improvement in transgenic mice bearing
genes for human AD (3). In these transgenic mice, the A
cination paradigm is effective when administered either early in
life, before onset of behavioral or structural evidence of the
disease, or later, after disease onset (3). Because both active
vaccination with the A
peptide and passive immunization
with anti-A
antibodies have beneficial effects (4), the potential
for AD therapy is under active investigation (4). This vaccina-
tion approach has been thwarted by the development of auto-
immune meningoencephalitis in both mouse studies (5) and
human trials in the United States and Europe (6). However,
subjects who developed anti-A
antibody responses had
improved cognitive function and activities of daily living (7) as
well as clearance of the A
deposits (8). Hock and Nitsch (9)
have concluded that “in humans...antibodies against A
lated epitopes are capable of slowing progression of AD.” Cur-
rently ongoing Phase 3 clinical trials of A
must be completed before answers concerning the therapeutic
value of this approach can be obtained.
We propose that the mechanisms demonstrated by the A
immunization paradigm may also be operating lifelong, with-
out active or passive vaccination. Those individuals with higher
levels of the presumed naturally occurring anti-A
may be protected from developing AD. Conflicting studies have
been reported thus far on this possibility: increased (10 –12),
decreased (13–15), or unchanged (16) levels of anti-A
tibodies have been noted in studies of AD patients and control
subjects. Moir et al. (17) found that circulating autoantibodies
specific for A
oligomers are decreased in AD. It is not clear
whether the studies discussed above measured total circulating
* This work was supported, in wholeor in part, by National Institutes of Health
Grants R01-AG017173 and R01-AG027853. This work was also supported
by the Fullerton Family, the Joseph and Florence Mandel Research Fund,
the Nickman Family, Philip Morris USA, GOJO Corp., and the Institute for
the Study of Aging. The costs of publication of this article were defrayed in
part by the payment of page charges. This article must therefore be hereby
marked advertisement in accordance with 18 U.S.C. Section 1734 solely to
indicate this fact.
To whom correspondence should be addressed: Dept. of Neurology,
Case Western Reserve University School of Medicine, 10900 Euclid Ave.,
T504 SOM, Cleveland, OH 44122. Tel.: 216-368-1913; E-mail: robert.
The abbreviations used are: AD, Alzheimer disease; A
, amyloid
; PVY,
potato virus Y.
THE JOURNAL OF BIOLOGICAL CHEMISTRY VOL. 283, NO. 33, pp. 22550 –22556, August 15, 2008
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antibodies or only those antibodies that were not bound
to circulating A
(18). Also, the presence of circulating anti-A
antibodies may very well be modified by the presence of disease;
antibody studies have not yet been completed in longitu-
dinal studies of as yet unaffected subjects. It is also not clear if the
assays applied in these studies were sensitive to cross-reacting
antibodies. Thus, the active and passive A
immunization para-
digm suggests that the presence of circulating anti-A
may influence the development of AD. In the absence of A
cination, exposure to an immunogen that bears significant amino
acid sequence homology to A
could result in antibody produc-
tion that has either protective or detrimental consequences (as
illustrated by the studies mentioned above).
To explore this hypothesis, we identified a naturally occur-
ring protein that is highly homologous to the human A
tide and that is a nuclear inclusion b protein from a plant virus,
potato virus Y (PVY) strain N (tobacco veinal necrosis)
(BLAST, NCBI, and National Institutes of Health), to which
humans are commonly exposed. PVY is an RNA virus and a
member of the genus Potyvirus in the family Potyviridae (19,
20). It contains a single-stranded RNA molecule of 9 7 kb,
which is translated into a large precursor protein that is cleaved
into 10 mature proteins (21, 22). PVY infects solanaceous crops
(of the nightshade family) such as potatoes, peppers, tomatoes,
and tobacco. Potatoes are the fourth largest food crop in the world.
Infection with PVY limits crop yield but does not destroy all
growth. PVY is found worldwide, and it is estimated that 15% of
potato crops are infected. It is likely that some potatoes consumed
by humans are infected with PVY (23).
We report that antibodies to PVY bind to A
in solution and
in tissue sections. Data are presented illustrating the biochem-
ical nature of the binding of anti-PVY antibodies to the same
region of A
as is bound by therapeutic antibodies to the A
Antibody Production—50
g of peptide (27 amino acids from
positions 52 to 77 of PVY with cysteine on the N terminus) was
emulsified with 1:1 (v/v) Freund’s complete adjuvant for the
initial intraperitoneal injection, followed by a boost in Freund’s
incomplete adjuvant 2 weeks later, with monthly boosters
thereafter. Mice were also inoculated with A
and infected and
uninfected potato leaves. The positive control for PVY (catalog
no. LPC20001, Agdia, Inc., Elkhart, IN) was resuspended in 10
M citrate buffer containing 1 M urea and 0.1%
anol, spun at 14,000 g for 15 min to remove the particulates,
and then dialyzed against phosphate-buffered saline. The first
injection used Freund’s complete adjuvant, followed by a
booster 2 weeks later in Freund’s incomplete adjuvant and then
four more boosters at 1-month intervals with the latter adju-
vant. Equal volumes of the sample and Freund’s adjuvant were
emulsified for the injections.
Enzyme-linked Immunosorbent Assay Screening—Plates
were coated overnight with 10
or synthetic peptide in
sodium bicarbonate buffer (pH 9.6). Plates were rinsed and
blocked in 5% bovine serum albumin in Tris-buffered saline (50
M Tris-HCl and 150 mM NaCl (pH 7.6)) and 0.001% Tween 20
(pH 7.6), followed by incubation either with serum from the
mice injected with the synthetic peptide (35-1 through 36-3) or
with serum from the leaf-injected mice (37-1 through 38-3) at
dilutions of 1:20 and 1:50. Plates were developed with 2,2-azi-
nobis(ethylbenzthiazoline-6-sulfonic acid).
Immunocytochemistry—Hippocampal samples were ob-
tained from patients with clinically and histopathologically
confirmed AD (n 3; ages 76 –77) and controls (n 2; ages
48 67) (24). Tissue was fixed with methacarn (methanol/chlo-
roform/acetic acid, 6:3:1) overnight at 4 °C, dehydrated, and
embedded in paraffin. Endogenous peroxidase activity was
eliminated by incubation in 3% H
in Tris-buffered saline for
30 min. To reduce nonspecific binding, cells were incubated for
30 min with 1% normal goat serum in Tris-buffered saline.
After rinsing briefly with 1% normal goat serum, cells were
incubated overnight with primary antibody. Cells were
stained with the peroxidase anti-peroxidase method (29)
using 3,3-diaminobenzidine as a chromogen (Dako Corp.,
Carpinteria, CA).
NMR Spectroscopy—Commercially prepared anti-potato
virus IgG polyclonal antibody (Phyto Diagnostics, North
Saanich, British Columbia, Canada) was obtained as a solution
(5 m
M) in 50% ammonium sulfate and 100 mM phosphate
buffer. Uniformly
N-labeled A
-(1–40) and A
-(1–42) pep-
tides (recombinant peptides) were prepared in monomeric
form using procedures developed in our laboratory (25). In
brief, this procedure involved disaggregation of the A
(0.2–0.5 mg) by sonication in aqueous basic solution (pD 11, 0.2
ml, 10 m
M NaOD), followed by mixing with cold (5 °C) phos-
phate buffer solution (pH 7.5, 0.6 –1.0 ml, 5 m
M) containing
0.50 m
M perdeuterated Na
and 0.05 mM NaN
. The
amount of peptide and buffer varied in accordance with the
desired peptide concentration (50–200
M). To prevent aggre-
gation, peptide solutions were kept cold (5 °C), and NMR spec-
tra were obtained within 30 min of the sample preparation and
at 5 °C. A Varian 600-MHz Inova spectrometer equipped with
an HCN Bioprobe was used for data acquisition, and the two-
N heteronuclear single quantum coherence
experiments were recorded (on average) with 32 scans, 2048
complex points and the transmitter placed on the water signal
(26). The sweep widths were 6373.5 and 2000.0 Hz in the F
dimensions, respectively. Processing was done on PC or
Octane-2 (Silicon Graphics) computers equipped with the Felix
program (Accelrys).
Homology Sequencing—The amino acid sequences of A
the PVY nuclear inclusion b protein, an RNA-directed RNA
polymerase, are shown in Fig. 1. The N-terminal domain of
PVY is exposed to the exterior of the virion particle, enhancing
the likelihood that it is immunogenic (27, 28). PVY has 6 amino
FIGURE 1. Primary amino acid sequences of the A
-(1– 40) and A
-(1– 42)
peptides. The residues shown in red show homology to the PVY protein. The
sequence of the N-terminal region of the PVY strain is H
HQXXXXXANDTIDAGGSNK (where X is an unspecified amino acid on PVY)
(BLAST, NCBI, and National Institutes of Health).
Anti-potato Virus Y Antibodies and Amyloid
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acids (at positions 60 65) that share a high homology to the
N-terminal region of A
. This N-terminal region of A
dues 1– 40) has been demonstrated to be therapeutic in A
precursor protein-overexpressing animal models (29, 30). Also,
it is this region (residues 4 –10) of A
that is most highly immu-
nogenic for B cells (32). The three-dimensional structure of the
PVY protein is not yet known.
Enzyme-linked Immunosorbent Assay—To determine
whether antibodies generated following vaccination with the
PVY synthetic peptide labeled A
as well as the synthetic pep-
tide, enzyme-linked immunosorbent assay screening was per-
formed, which showed that antibodies made against the syn-
thetic peptide had a high affinity for both the synthetic peptide
and A
, whereas antibodies to the positive leaf control showed
a weaker affinity than the synthetic peptide antibody for both
and the synthetic peptide (Fig. 2). Lower levels of immuno-
reactivity were found using the antibodies to the control leaf
is associated with senile plaques, neurofibrillary tangles,
and neurons in AD (31); therefore, we tested whether mice
inoculated with the PVY synthetic peptide develop antibodies
that label A
in neuritic plagues as well as neurofibrillary tan-
gles (Fig. 3). The synthetic peptide antibody recognized senile
plaques, neurofibrillary tangles, and neurons. The positive con-
trol leaf antibody recognized neurofibrillary tangles, granulo-
vaculolar degeneration, and neurons in AD cases (Fig. 3). Neu-
ronal staining was observed in control cases for both the
synthetic peptide and control leaf antibodies.
NMR Spectroscopy—To explore the binding between the A
peptide and the anti-PVY polyclonal antibody, we undertook
NMR spectroscopic studies. The NMR peak assignments cor-
respond to monomeric A
peptide (25), and the sample prep-
aration protocol ensured that the A
peptides were monomeric
at the beginning the NMR experiments. Aggregation during
NMR data acquisition, particularly by the more aggregation-
prone A
-(1–42) peptide, was prevented by acquiring the data
at reduced temperatures (5 °C).
Fig. 4 shows the heteronuclear single quantum coherence
NMR spectra of uniformly
N-labeled A
-(1–40) and A
42) peptides. The spectra of the peptides alone are superim-
posed with those containing 1:50 molar eq of the anti-PVY anti-
body. Heteronuclear single quantum coherence spectroscopy,
which detects
H atoms directly attached to
N atoms, is a
standard NMR experiment for proteins and provides a finger-
print for the backbone. The narrow chemical shift dispersion in
H dimension (8.7 to 8.1 ppm) demonstrates that the pep-
tides adopt predominantly monomeric, random, extended
chain structures, consistent with previous studies (25, 33).
With the anti-PVY antibody, several amide-NH peaks have
different chemical shifts that are more confined to the polar
1–28 N-terminal residues and not within the hydrophobic
29 40 or 29 42 C-terminal peptide region. The residues
showing the most pronounced chemical movements include
, Arg
, Ser
, Tyr
, His
, Gln
, Lys
, Leu
, and Ser
the A
-(1–40) peptide and Phe
, Arg
, Ser
, His
, Gln
, Lys
, Ser
, and Asn
for the A
-(1–42) peptide.
Graphical depictions show that the
H and
N chemical shift
differences are localized within two regions, Phe
, which may constitute a binding pocket associated
within PVY (Figs. 5 and 6). Control studies showed that the
chemical shift movement upon addition of the anti-PVY anti-
body to the A
peptide solution was not caused by other com-
ponents (such as ammonium sulfate) present within the anti-
body solution. Because these studies utilized commercially
prepared anti-PVY antibody solutions, we were unable to con-
duct titrations at antibody concentrations greater than 1:50
FIGURE 2. Enzyme-linked immunosorbent assay data for plated synthetic
peptide (PVY-(52–77)) probed with each of the specified antisera (A) and
plated A
probed with each of the different antisera (B). PBS, phosphate-
buffered saline. Leaf material refers to leaf infected with PVY.
FIGURE 3. Antibodies raised against PVY-(52–77) (A) or the infected con-
trol (C) bind to neurofibrillary tangles, senile plaques, and neurons in AD
(B) and to neurons in control cases (D).
Anti-potato Virus Y Antibodies and Amyloid
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molar eq relative to peptide. However, even at these low con-
centrations, the anti-PVY antibody induced significant chemi-
cal shift movements, indicative of binding to the monomeric
The immunological approach to AD treatment has received
great attention in animal and human studies since the original
observations of Schenk et al. in 1999
(3). However, the role of immuno-
logical processes operating over a
lifetime in determining who gets the
disease has not been widely consid-
ered. If anti-A
antibodies are ben-
eficial in A
-overexpressing trans-
genic mice and humans with AD,
then the presence of antibodies pos-
sessing the ability to bind A
prevent or delay the onset of dis-
ease. A
-binding antibodies may
develop through natural mecha-
nisms, as autoantibodies often
develop with aging. Alternatively,
antibodies may be effec-
tively produced through immuno-
logical responses to immunogens
bearing sequence homology to A
such as PVY.
The aggregation and assembly of
the A
protein into amyloid depos-
its are major neuropathological
hallmarks of AD. The two predom-
inant forms of A
are X-40 and
X-42, with the latter protein being
more aggregation-prone and whose
overproduction has been linked to
many familial forms of AD. The A
peptide is a normal physiological
constituent that, from age-related
micro-environmental changes, can
undergo a conformational conver-
sion from soluble monomeric ran-
dom structures into aggregated
-pleated sheet structures, with the
latter forming neurotoxic soluble
aggregates (such as AD diffusible
ligands) and protofibrils and even-
tually precipitating as mature amy-
loid fibrils. It is now thought that
methods for preventing the A
formational conversions and fibril
formation could ameliorate the
effects associated with A
neurotoxicity in AD. Because mono-
meric and oligomeric species of A
exist in equilibrium in tissue culture
medium (34) and because the solu-
ble oligomers are now thought to be
the major culprit and resistant to proteolysis (35–37), the A
monomer may be the best therapeutic target for binding by an
amyloid inhibitor. Current FDA-approved AD drugs include
acetylcholinesterase inhibitors and an N-methyl-
antagonist that improves cognition and behavior but does not
reduce amyloid burden or delay progression.
Our NMR data demonstrate that the anti-PVY antibody
binds to monomeric A
. With our NMR sample preparation
FIGURE 4. Expanded
N heteronuclear single quantum coherence spectral regions showing the
backbone NH signals of the A
-(1– 40) and A
-(1– 42) peptides (50 mM) in aqueous phosphate buffer (5
M, pH 7. 3, 5 °C). Red peaks correspond to the peptides alone, whereas blue peaks are the peptides plus 1:50
molar eq of anti-PVY IgG polyclonal antibody. The peaks undergoing significant chemical shift movements are
FIGURE 5. Graphical representation of the
H chemical shift movements of the A
-(1– 40) and A
-(1– 42)
peptides with PVY.
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protocol (25), A
is monomeric, and the lack of any line width
changes is consistent with the anti-PVY antibody binding to
monomeric peptide. However, it is possible that the anti-PVY
antibody could also be binding with small amounts of soluble
aggregates, and further work to investigate this possibility is
currently under way in our laboratory. In contrast, significant
line width reductions were seen with binding to human
serum albumin, due to binding with A
oligomers (38). This
is exceptional given that the majority of proteins or small
molecules that reportedly bind to the A
peptide target the
soluble aggregates or early-stage amyloid fibrils (39, 40).
3 is an endogenous inhibitor of A
aggregation that
binds to pre-nuclear A
oligomers and blocks production of
the nucleation steps in amyloid formation (41). More recent
NMR studies showed that nicotine (42), human serum albu-
min (38), and the A
-binding alcohol dehydrogenase (43)
bind with soluble A
oligomers but not the monomers.
Because the binding we detected was promoted with subs-
toichiometric amounts (1:50) of the anti-PVY antibody, a
stronger binding may occur at higher antibody concentra-
tions. The binding seems localized within the Phe
peptide regions. The importance of the cen-
tral hydrophobic region for
-aggregation has been previ-
ously noted (44 47), and the core of the amyloid
structure is composed of Leu
(48). A major advan-
tage of the NMR approach is that it provides atomic level
details of protein structure and dynamics in solution that are
not available with other low resolution techniques. NMR
provides site-specific structural data that assist in the devel-
opment of specific amyloid inhibitors that select for the
monomeric form of the A
peptide. Recent work in mice
demonstrated that a 56-kDa soluble A
-(1–42) assembly
may be the actual culprit for initiating neuronal loss and
memory deficits (49); thus, an inhibitor with any therapeutic
value must prevent formation of
this or other toxic A
(39). It is generally though that
inhibitors that select for mono-
mers or dimers are good starting
These results show promise that
the anti-PVY antibody may be an
effective means of regulating A
behavior, particularly because such
a small relative molar ratio of anti-
body showed significant interaction
with the peptide. However, because
a polyclonal antibody was used, we
saw only a solution average of the
various forms of PVY present. As
such, further work is under way to
obtain a monoclonal antibody that
can be used to perform more con-
clusive and quantitative experi-
ments, including determination of a
binding constant and epitope-bind-
ing domains.
Tabira and co-workers (50) in
Japan have developed an oral vaccine for AD using a recombi-
nant adeno-associated viral vector carrying A
cDNA. The vac-
cine reduced A
deposits without causing lymphocytic infiltra-
tion in the brain. It was proposed that mucosal immunity leads
to safer immunological reactions to the vaccine. The lifelong
development of antibodies that cross-react with A
dietary exposure (such as PVY) to enhance clearance and
inhibit aggregation may be less likely to elicit an autoimmune
condition than late-life active vaccination because of the
chronic development of the antibody response and the involve-
ment of the immune system in the intestine, which is less likely
than parenteral administration to elicit a T cell response (32).
The immune system of the intestine enhances Th2 responses
and suppresses Th1 responses, leading to relatively less cell-
mediated immunity (32, 51). It has been proposed that immune
mechanisms involving Th2-dependent responses would be the
safest for an A
immune response in the setting of AD because
Th2-dependent mechanisms produce antibodies that are less
likely than those produced by Th1 responses to produce inflam-
mation (52). The oral route of vaccination has also been used in
studies in transgenic AD mice using transgenic potatoes
expressing five tandem repeats of A
-(1–42). Mice immunized
with A
with this edible vaccine made antibodies against A
and had reduced A
plaques in the brain (53).
The mechanisms by which anti-A
antibodies may have a
therapeutic effect include the following: 1) entry into the brain
and binding to oligomeric and fibrillar A
with microglial acti-
vation, eliciting Fc receptor-mediated phagocytic mechanisms
of removal of antibody-antigen complexes (52); 2) antibody-
mediated solubilization of fibrillar A
(32, 54); 3) stabilization
of the A
monomer, thus preventing the subsequent associa-
tion into the soluble aggregates; 4) binding of A
to antibody in
the circulation, enhancing clearance of A
from the brain (the
peripheral sink hypothesis) (55); 5) altered proteolysis of A
FIGURE 6. Graphical representation of the
N chemical shift movements of the A
-(1– 40) and A
-(1– 42)
peptides with PVY.
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(the ability of proteases that degrade A
ing enzyme, neprilysin, endothelin-converting enzyme, plas-
min, and insulin-degrading enzyme) (56) may be altered by
binding of A
to antibodies); and 6) hydrolysis of A
by circu-
lating autocatalytic IgM antibodies, as reported recently in
studies of AD cases and controls by Taguchi et al. (12). Lifelong
exposure to cross-reacting antibodies (such as PVY) that bind
to A
may have protective effects through all of these mecha-
nisms. This work is in keeping with current efforts to develop a
safe and effective vaccine for AD (52). Novel immunogens have
been developed that include the B cell epitopes of A
(the N
terminus) but lack T cell-reactive sequences (57). The absence
of a cellular immune response may provide for a safer therapy.
Plant viruses are found throughout the world, frequently
infect crops used for human consumption, and have no known
effects on human health. We propose that the development of
antibodies to PVY following oral exposure is protective against
the development of AD because of the beneficial effects of bind-
ing of the antibody to the A
protein. A model for this interac-
tion may be supplied by the relationship between vaccinia
infection (related to cowpox) and the resultant immunity to
variola (smallpox). There are naturally occurring proteins other
than PVY that bear significant homology to A
and that may
influence the development of AD. For example, several proteins
of Enterococcus contain sequences homologous to A
and National Institutes of Health). The mechanism we propose
may influence the pathophysiology of other conditions as well.
Antibodies developed in response to naturally occurring
plant or animal viruses, bacteria, or other agents may inter-
act with protein trafficking in the brain and blood to influ-
ence handling and deposition of pathological proteins. This
approach may be valuable for AD immunotherapy because of
the relatively low inflammatory potential with intestinal
immunogen delivery and the efficacy of antibody binding to
pathogenic A
It is of interest to note as well that circulating antibodies
against both unphosphorylated and phosphorylated Tau pro-
teins have also been observed (58), and active immunization
with a phosphorylated Tau epitope in P301L tangle model mice
reduced brain aggregated Tau and slowed progression of
behavioral deficits (59). Also, antibodies generated against sol-
uble oligomeric A
have been shown to neutralize oligomers of
the prion protein and
-synuclein, suggesting that shared
epitopes of these pathogenic proteins may play a role in several
neurodegenerative illnesses (52, 60).
Acknowledgments—The technical assistance of Peggy Harris is grate-
fully acknowledged. We are also grateful for the helpful comments of
Dr. Maureen McEnery and Gregory D. Friedland.
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  • Article · Feb 2009
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