CORRELATES OF MUCOSAL IMMUNITY AND UPPER RESPIRATORY
TRACT INFECTIONS IN GIRLS
Lauren Corbett1, Cameron Muir2, Izabella A. Ludwa1, Matthew Yao1, Brian W.
Timmons3, Bareket Falk1, Panagiota Klentrou1
1 Faculty of Applied Health Sciences, Brock University, Ontario, Canada
2Centre for Neuroscience, Department of Psychology, Brock University, Ontario, Canada
3Children’s Exercise & Nutrition Centre, McMaster University, Ontario, Canada
Running Title: Correlates of Immunity in Girls
Panagiota Klentrou, PhD
Department of Physical Education and Kinesiology
Faculty of Applied Health Sciences
St. Catharines, Ontario
Canada L2S 3A1
Tel: (905) 688-5550 ext 4538
Fax: (905) 688-8364
In this study we examined whether salivary hormones, physical activity and adiposity
were correlated with secretory immunoglobulin A (sIgA) and frequency of upper
respiratory tract infections (URTI) in 43 early-pubertal and 59 late-pubertal girls.
Physical activity was measured using accelerometers and relative body fat was assessed
using bioelectrical impendence. Resting saliva samples were obtained between 1500 and
1800hr and assayed for sIgA, cortisol and testosterone. Participants completed a one-
month health log to record URTI frequency. Early-pubertal girls were more physically
active, had less adiposity, but lower concentrations of sIgA than late-pubertal adolescents
(122.7±91.6 vs 201.9±102.9 pg/ml, respectively). The frequency of URTI was similar in
the two groups. Neither sIgA nor URTI were correlated with salivary hormones, physical
activity or adiposity within the early-pubertal girls. In the late-pubertal group, sIgA was
negatively associated (r=-0.44; p≤0.05) with cortisol, and positively associated (r=0.41;
p≤0.05)?? with the testosterone to cortisol ratio. These results suggest that mucosal
immunity increases with pubertal maturation, while higher cortisol is associated with
lower mucosal immunity in adolescents.
Keywords: Secretory immunoglobulin A; cortisol, testosterone; accelerometry; adiposity
The mucosal immune system protects surfaces of the respiratory tract that are exposed to
the environment, and is considered to be the first barrier to colonization by pathogenic
micro-organisms causing upper respiratory tract infections (URTI).1 Secretory
Immunoglobulin A (sIgA), is the main immunological defence mechanism of mucosal
surfaces and aids in immune defence by inhibiting the attachment and replication of
micro-organisms, and is also capable of neutralizing certain viruses and toxins.2 It is
currently under debate what intrinsic and/or extrinsic environmental factors moderate
sIgA levels, in children or adults, subsequently influencing the frequency of URTI.
Such suspect factors include physical and psychological stress.3-5 For instance,
moderate levels of physical activity have been associated with a lower incidence of URTI
in children, whereas adolescents who spent less time in sport activities reported a
significantly higher frequency of URTI.3,4 However, all these studies have used
subjective measures of physical activity, which are likely to misrepresent actual levels of
physical activity. Consequently, the true relationships between physical activity and
URTI incidence have yet to be determined. Conversely, psychological activation of the
hypothalamic-pituitary-adrenal axis, triggering the secretion of cortisol may lead to
immunosuppression.6 Although some studies have shown that higher levels of stress
exposure are associated with lower levels of sIgA,7, 8 no direct relationship has been
found between sIgA and cortisol in adults.9 In children, very few studies have examined
the relationship between cortisol and either sIgA or URTI.10, 11 The study by Cieslak et
al. failed to find significant correlations between sIgA and cortisol in fifth grade students
but found cortisol levels to be significantly associated with the frequency of URTI.10 In
addition, due to testosterone’s anabolic and cortisol’s catabolic effects, the ratio of
testosterone to cortisol (T:C) has often been used as an indicator of the anabolic/catabolic
balance in the body,12,13 yet none of these hormone relationships have ever been
examined in children and adolescents, especially with consideration of mucosal immunity
Body composition, and more specifically adiposity, has been associated with
mucosal immunity in youth. This is an important observation because a growing
proportion of our youth are either overweight or obese.14 However, very few studies have
examined whether or not adiposity is related to immune function in children, and girls in
particular. Juvenile obesity has been associated with elevated counts of most types of
circulating immune cells, suggesting the presence of low-grade systemic inflammation.15
Obese children have been shown to exhibit lower levels of sIgA than normal-weight
children.16 Nieman et al. reported that salivary IgA concentration was positively
correlated with the sum of two skinfolds in a heterogeneous group of children, but not
when expressed as a ratio of total protein or as a secretion rate.17 Others found no
significant relationship between adiposity and sIgA, yet still reported that obese children
had a higher incidence of URTI than normal-weight children.10 Jedrychowski et al. also
found that overweight children with a high body mass index (BMI>20) experienced a
two-fold higher risk of respiratory infections than children with a BMI<20, independent
of physical activity levels but adiposity per se was not measured in their study.18
Given the relationships between adiposity and mucosal immunity provided above,
it is possible that higher incidence of URTI in overweight and obese children could be
due, at least in part, to a relatively inactive lifestyle. However, given the lack of evidence
regarding the relationship between objectively measured physical activity levels and
mucosal immunity or incidence of URTI, this possibility requires further investigation.
Particularly, since girls are reported to be less physically active and have greater relative
body fat than boys, they may be more vulnerable to URTI. Indeed, girls report more
sickness days than boys, especially in adolescence, possibly due to the menstrual cycle.4
The overall purpose of this study was to examine correlates of sIgA and frequency of
URTI in early-pubertal girls and late-pubertal adolescents. Associated factors included: a)
salivary levels of cortisol, testosterone, and T:C, b) physical activity measured by
accelerometry, and c) adiposity as determined by relative body fat.
This project and all related protocols were approved by the Brock University Human
Ethics Review Board and the Hamilton Health Sciences/McMaster University Faculty of
Health Sciences Research Ethics Board. Subjects were recruited from local health care
facilities, recreation programs, newspaper advertisements, and through word of mouth
throughout south-western Ontario, Canada. Young females who had received a flu shot
within twelve months of testing were excluded from the study. The study was conducted
October to May, during the Northern hemisphere Fall to Spring. Any medication taken
for treatment of illness was recorded.
A total of 102 younger and adolescent girls volunteered to participate in the study.
Two cohorts were recruited: girls, aged 8-11 years, and adolescents, aged 14-16 years.
The younger girls were pre- or early-pubertal (30 girls of Tanner stage I and 13 girls of
Tanner stage II). The adolescents were late-pubertal (45 adolescents of Tanner stage IV
and 14 adolescents of Tanner stage V). All adolescents were also post-menarcheal with
self-reported regular menstrual cycles.
All participants were invited for a single visit to the laboratory during which all the
measurements and questionnaires were completed. Participants were instructed to avoid
drinks with caffeine, exhaustive physical activity for at least 12 hours prior to this visit,
and told to only consume a light snack within 4 hours prior to testing. Prior to
commencing assessment, all children were given an orientation of the laboratory
procedures. Once a comfortable rapport was established with each subject, sexual
maturity was self-assessed using the stages of sexual maturation developed by Tanner.19
The drawings of secondary sexual characteristics (pubic hair) used for this self-
assessment were taken from Taylor et al.20
Upon arrival, resting saliva samples were obtained (see below). Following this,
subjects were asked to consume 500ml of water and then, following about 30 min, to
void their bladders in order to standardize their hydration status prior to body
composition measurements. A complete anthropometric assessment was then performed
by the same investigator for all subjects. At the end of this visit, the researchers instructed
the subjects on the use of the accelerometer and the completion of the one-month health
log. The subjects were asked to return to the lab approximately one week after the initial
visit to give back the accelerometers and related data, and were provided with self-
addressed envelopes in order to mail the health log back once completed.
Participants were asked not to consume any food or drink for at least one hour prior to the
laboratory visit, when saliva collection was administered first, and the mouth was not
rinsed with water prior to sampling, to avoid altering resting sIgA levels. One milliliter of
unstimulated whole mixed saliva was collected from each subject using salivettes
(Sarstedt Inc., Quebec, Canada) placed in the mouth and subjects were instructed to
moisten/chew lightly on the swab for one minute. After sampling, the swabs were placed
directly into plastic tubes. After a two minute interval a second sample was collected
using the same procedure. All blood samples were taken consistently within the same
time frame between 1500 and 1900 hours eliminating issues with diurnal variations of the
hormones. This time frame was chosen for convenience to be afterschool and it
corresponds to the nadir of the diurnal rhythm of the hormones. After sampling, the
swabs were centrifuged for 10 minutes at 3500xg and the resulted saliva sample was
alliquotted into two separate 1.5 ml eppendorf tubes and stored at -80○C until analysis.
Mucosal sIgA was assayed in duplicate by commercially available ELISA kits
(Salimetrics, LLC, Pennsylvania, U.S.A). Due to recent evidence that concentrations of
sIgA, as measured by ELISA, may be affected by the use of salivettes21 a normal set of
standards was compared with a second set of standards (10 µl of standard in 4mL of 1X
sIgA diluent) that was run through a set of six salivettes, and centrifuged for 10 minutes
at 3500 rpm to separate the standards from the swabs. The two sets of standards were
then compared, and found to be no different. Cortisol and testosterone were assayed
using an in-house assay in the Department of Psychology at Brock University using
methods described elsewhere.22 Cortisol (R4866) and testosterone (R156/7) antibodies
and corresponding horseradish peroxidase conjugates were obtained from C. Munro
Clinical Endocrinology Laboratory (University of California Davis, USA). Steroid
standards were obtained from Steraloids Inc. (Newport, Rhode Island, USA). The intra-
assay and inter-assay coefficients of variation for each of the assays were: 7.1% and 6.3%
for sIgA, 6.5% and 6.8% for testosterone, and 7.8% and 6.5% for cortisol, respectively.
Height was measured to the nearest 0.1 cm (Ellard Instrumentation stadiometer, Monroe,
WA USA). Body mass and relative body fat were assessed by bioelectrical impedance
analysis (BIA) using the InBody520 (Biospace Inc., Beverly Hills, U.S.A). BIA has
emerged as an accurate and consistent tool that is inexpensive, noninvasive, portable, and
operationally simple.23 The InBody520 is a tetrapolar 8-point tactile electrode system that
uses a direct segmental multi-frequency (5, 50, and 500 kHz) bioelectrical impedance
method to analyze body composition in both the left and right arm and legs, and trunk.
The reliability and validity of this method has been demonstrated successfully in children
6 to 13 years of age.24 The BIA assessment took place approximately 45 minutes after
Physical activity was quantified using Actigraph GT1M accelerometers (formally known
as MTI/CSA accelerometers). The participants were instructed to wear the accelerometer
on the right hip from the moment they woke up until they went to sleep for 7 days
starting the day after their visit to the laboratory. As the accelerometers are not water-
proof, the participants were instructed to remove them if they went swimming or bathed.
Physical activity logs were used to record the times the accelerometer was removed as
well as to keep track of any type of structured physical activity. Only cases for which 10
hours of waking data were recorded for a minimum of three week-days and one weekend
day were used for analysis. The total count of minutes of combined moderate/hard/very
hard (MVH) was used to quantify daily physical activity. Epoch duration was 10 sec and
intensity was classified in accordance with age-appropriate cut-off points.25
Accelerometers provide an objective and valid method to assess physical activity in
Frequency of URTI
Frequency of URTI was determined using the one-month Health Log, as previously
described.28 The log quantifies the frequency and duration (number of days) of URTI.
Participants were asked to record any cold and flu symptoms each day of the month using
a set of codes provided with the log starting the day after their visit to the laboratory. This
method was chosen to eliminate participant bias when recording from memory. Parental
supervision was required for the younger subjects to ensure accurate recording of the
symptoms. The parents and/or participants were asked to return the health log once
completed. The total number of days with URTI symptoms was then calculated for each
subject, with days being counted only if two or more consecutive days of cold or flu
symptoms were reported.28
Due to the fact that testing took place between the months of October and June, an one-
way analysis of variance (ANOVA) was used on physical activity and all hormonal and
immunity variables to determine if there were any differences depending on the season in
which the participants were tested. Participants were grouped according to the season of
their testing into three groups: fall, winter and spring. No significant differences were
found in any of these variables according to season. Therefore, the data were pooled for
further analysis. A series of ANOVAs were then used to examine differences between
early-pubertal and late-pubertal girls. Partial correlation analyses, controlling for age,
were used to determine potential associations. In addition, a follow up analysis of
variance was used to examine potential differences within each age group between the
normal weight and the overweight and obese children as classified using the criterion of a
%BF ≥25 and a %BF ≥30, respectively. Data are expressed as mean ± standard deviation
(SD). An alpha level of ≤0.05 was used as the criteria for significance for all statistical
analyses, which were conducted using SPSS version 16.0 for Windows (SPSS Inc.,
As expected, there were significant differences between groups in height, body mass and
relative body fat (Table 1). There were no significant group differences in the frequency
of URTI but late-pubertal girls displayed higher concentrations of sIgA, cortisol, and
testosterone (Table 2). On the other hand, early-pubertal girls recorded significantly more
minutes of daily MHV physical activity than late-pubertal girls (Figure 1).
Within the group of early-pubertal girls, no significant correlations were found
between either of the immunity variables (URTI and sIgA) and daily minutes of MHV
physical activity, salivary hormones and relative body fat (Table 3). Within the group of
late-pubertal girls, sIgA was significantly and negatively correlated with cortisol, and
significantly and positively correlated with T:C (Table 3). In addition, daily minutes of
MHV physical activity was significantly and negatively correlated with cortisol (r=-0.51;
p≤0.05), but positively correlated with testosterone (r=-0.57; p≤0.05), and consequently
with T:C (r=79; p≤0.01) in the late-pubertal group.
Moreover, among the early-pubertal girls 8 of 43 (19%) were overweight and 10
of 43 (23%) were obese. Similarly, among the late-pubertal adolescents 11 of 59 (19%)
and 16 of 59 (27%) were obese. Consistently with our correlation analysis, the follow up
analysis of variance showed no significant differences in the frequency of URTI or sIgA
between the overweight or obese young females and their normal weight counterparts.
The overall purpose of this study was to examine factors associated with the frequency of
URTI and mucosal sIgA levels in early- and late-pubertal females. The strength of this
study is the simultaneous examination of immune status, objectively measured physical
activity and adiposity in both pre- and post-pubertal girls, and the first to consider the
possible relationship with salivary cortisol and testosterone, in this population. To our
knowledge, this is the first study of the relationship between immune status and physical
activity in children that used objective means (accelerometers) to quantify physical
activity. Not surprisingly, early-pubertal girls were more physically active, than late-
pubertal girls, yet the latter displayed higher concentrations of sIgA, cortisol, and
testosterone, suggesting a maturation effect on these variables. There were no group
differences in the frequency of URTI. No significant correlations were found between
either sIgA or URTI and physical activity, adiposity, and salivary hormones within the
group of early-pubertal girls while sIgA was negatively associated with cortisol, and
positively associated with the T:C ratio within the group of late-pubertal girls. In general,
these results suggest that pubertal development may have an effect on resting levels of
mucosal sIgA but not on URTI. While higher cortisol levels were associated with lower
levels of sIgA in late-pubertal girls, no correlation was apparent between cortisol and
Mucosal immunity and sIgA in particular, has been shown to gradually increase
during the first decade of life29,30 but there is no previous literature on differences in
sIgA and the incidence of URTI between younger and older children. The late-pubertal
girls also had significantly higher resting concentrations of cortisol and testosterone, than
the younger, early-pubertal girls. This is consistent with previous studies that have shown
salivary cortisol levels to increase with age in children and adolescents.31,32 Salivary
testosterone levels remain relatively stable during the preadolescent period (ages 6-9) in
young girls and rise rapidly between age 9 and menarche.33 After menarche the rate of
this increase declines, and there is a gradual rise during the teens, with adult levels
reached between 18 and 20 years of age.34,35 Despite these fluctuating levels of
hormones, their direct impact on the incidence of URTI remains unclear.
No significant associations were found between the immunity variables (sIgA or
URTI) and physical activity, salivary hormones and adiposity in the early-pubertal girls.
However, sIgA was negatively correlated with cortisol, and positively correlated with the
T:C ratio in the adolescents. Although it has been previously shown that salivary sIgA
appears to be down-regulated in individuals who have chronic exposure to psychological
stress,36 no direct relationship has been found between sIgA and cortisol in adults.9 Very
few studies have examined the relationship between cortisol and IgA in children. A study
on various behavioural states in preschoolers found no correlation between cortisol levels
and sIgA secretion.37 Furthermore, although both Cieslak et al.10 and Filaire et al.11 did
not find significant correlations between sIgA and cortisol in school children nor in
young, female gymnasts, Cieslak et al.10 reported that cortisol levels were significantly
associated with the frequency of URTI in fifth grade students. The present results do not
confirm this previous finding. This could be due to the fact that the correlation between
salivary cortisol and URTI reported by Cieslak et al.10 was found in boys and girls
together, while the present study focused on homogenous female groups. Evidence from
studies on chronic stress also support the hypothesis that higher levels of stress are
associated with lower levels of sIgA (8, 37) and this could explain the relationship
between sIgA and cortisol in our adolescent group.8,38
It is also widely accepted that physical activity declines throughout childhood and
adolescence, and this decline is associated with puberty onset.39-41 Consistent with these
previous reports, the younger girls in this study recorded a significantly greater amount of
time engaging in moderate, hard, and very hard activities than the adolescents. Although
it has been suggested that youth who are more active also experience fewer sickness
days3,4,10 there was no correlation between physical activity and URTI in either group in
our study nor was physical activity related to sIgA. Physical activity did, however,
demonstrate a positive correlation with testosterone and a negative correlation with
cortisol in the late-pubertal girls. Although our data cannot indicate cause and effect, it is
possible that regular physical activity of at least a moderate intensity may be protective
against markers of stress hormones, which in turn were found to relate to sIgA in this
group of adolescents. Furthermore, girls in the late-pubertal group appear, on average, to
be more overweight and less active and this could be problematic in the interpretation of
cortisol results. Higher salivary cortisol levels may not always reflect higher plasma
cortisol levels in obese individuals. However, although there were more obese
adolescents than early-pubertal girls and the percentage of overweight subjects in each
group was equal (19% for both early- and late-pubertal) no significant differences were
found between these obese and overweight females and their normal weight counterparts
and this is consistent with our correlation results. This of course may be due to the small
number of obese females in each group.
Regarding the relationship between adiposity and sIgA levels in children, while
the adolescents in our study had greater relative body fat than children, there were no
significant relationships between adiposity, sIgA and frequency of URTI, in neither
group. Previous studies on the effects of adiposity on immune function in children have
shown that overweight children have elevated leukocytes and other inflammatory
mediators, probably due to the production of these factors by the adipocytes and
suggesting the presence of low-grade inflammatory state.15,42 In terms of sIgA, Nieman
et al.17 found a significant correlation between adiposity and sIgA levels. Cieslak et al.10
found no significant relationship between adiposity and sIgA in fifth grade children, yet
the obese children had a higher frequency of URTI compared to normal weight children.
A limitation of both the present study and that by Cieslak et al.10 is that they used BIA to
estimate adiposity, a method with some disadvantages in assessing body fat, especially in
overweight and obese children. Nieman, on the other hand, used the sum of skinfolds to
assess adiposity. In any case although our findings add to the dearth of information on
this topic, it is clear that more work is needed in this area given the prevalence of
In summary, pubertal development seems to have an effect on mucosal sIgA
without a direct effect on the frequency of URTI. In addition, higher concentrations of
salivary cortisol were associated with lower sIgA in the late-pubertal girls. No significant
correlations were found between mucosal immunity and frequency of URTI and either
physical activity or adiposity, despite younger girls being significantly more active and
having less relative body fat than older adolescents.
We would like to thank the many participants and their parents, who were
enthusiastically involved in the project. This work was supported by the Social Sciences
and Humanities Research Council of Canada (SSHRC) and by Brock University.
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Table 1: Table 1: Anthropometric measures of early-pubertal and late-pubertal girls. Values
are means (standard deviation).
Early-pubertal (N=43) Late-pubertal (N=59)
Height (cm) 143.9 (11.0) 165.1 (6.2)*
Body mass (kg) 39.1 (9.5) 64.9 (16.3)*
Relative body fat (%) 23.2 (8.6) 28.3 (10.4)*
* P≤0.05 difference between groups
Table 2: Table 2: Frequency of Upper Respiratory Tract Infections (URTI),
mucosal/secretory Immunoglobulin A (sIgA), and salivary hormones in early-
pubertal and late-pubertal girls. Values are means (standard deviation).
sIgA (pg/ml) 122.7 (91.6) 201.9 (102.9)*
Cortisol (ng/ml) 2.00 (1.8) 3.2 (1.9)*
Testosterone (ng/ml) 0.14 (0.11) 0.33 (0.28)*
Testosterone to cortisol (ratio) 0.39 (1.70) 0.19 (0.13)
* P≤0.05 difference between groups
Table 3: Table 3: Partial correlation coefficients (r) controlling for age in early-pubertal
and late-pubertal girls.
sIgA (pg/ml) -0.31 -0.25
Relative body fat (%) 0.09 -0.01 0.26 0.09
MHV (min/day) -0.14 0.31 -0.15 0.31
Cortisol (ng/ml) 0.12 0.09 0.25 -0.44*
Testosterone (ng/ml) -0.11 0.21 -0.20 0.22
T:C (ratio) 0.06 0.10 -0.29 0.41*
*p≤0.05; URTI=Upper Respiratory Tract Infections; MHV=moderate/hard/very hard
activity; T:C=testosterone to cortisol ratio.
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Figure 1: Figure 1: Minutes of daily physical activity for pre-pubertal girls and late-
pubertal adolescents (*P<0.05).