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Clinical and Diagnostic Laboratory Immunology, September 2003, p. 944-949, Vol. 10, No. 5
1071-412X/03/$08.00+0 DOI: 10.1128/CDLI.10.5.944-949.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Effects of Ovarian Steroids on Immunoglobulin-Secreting Cell Function in Healthy Women
Fabien X. Lü,1,2 Zhongmin Ma,1 Susie Moser,3 Thomas G. Evans,3 and Christopher J. Miller1,2,4*
California National Primate Research Center,1
Center for Comparative Medicine,2
Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine,4
Department of Internal Medicine, School of Medicine, University of CaliforniaDavis, Davis, California 956163
Received 11 February 2003/
Returned for modification 13 May 2003/
Accepted 20 June 2003

ABSTRACT
To determine the effect of the ovarian hormone cycle on immunity,
immunoglobulin-secreting cell (ISC) frequency and lymphocyte
subsets were examined in the blood of healthy women. We found
that immunoglobulin A (IgA)-secreting cells (IgA-ISC) were fourfold
more frequent than IgG-ISC in peripheral blood mononuclear cells
(PBMC). Further, the ISC frequency in PBMC was highest (
P <
0.05) during the periovulatory stage of the menstrual cycle.
Thus, endogenous ovarian steroids regulate the ISC frequency
and this may explain why women are more resistant to viral infections
and tend to have more immune-mediated diseases than men do.

TEXT
The strength and nature of immune responses differ between women
and men. Humoral and cellular immune responses in females are
stronger than those in males (
2). For example, female mice produce
stronger antibody and cell-mediated responses to immunization
than males do (
9,
34). Immunoglobulin M (IgM), but not IgG,
levels and CD4/CD8 T-cell ratios are significantly higher in
the blood of women than in that of men (
1,
19). Women also develop
autoimmune diseases at a much higher rate than men do (
36).
The precise reasons for the observed gender bias in these diseases
are unclear; however, it may be related to the generally stronger
immune responses of women. These observations clearly demonstrate
a role for ovarian steroid hormones in mediation of the immune
system.
Gender also influences the clinical course of many viral diseases. Females are more likely to develop a Th1-type response after viral exposure, except during pregnancy, when Th2 responses predominate (36). Female mice are more resistant to lethal vesicular stomatitis virus (3, 12), Coxsackie type B-3 virus (22), herpes simplex virus type 1 (4, 6), and Theiler's murine encephalomyelitis virus (18) infections. Further, in viral infections in which Th1 responses are known to produce immune-mediated pathology, such as lymphocytic choriomeningitis virus infections, females have a more severe disease. Clearly, ovarian sex hormones affect the nature and effectiveness of antiviral immunity.
We have demonstrated that the menstrual cycle stage has a dramatic effect on IgG and IgA levels in cervicovaginal secretions of macaques that is similar to the changes found in women (21). Further, in rhesus macaques the frequency of immunoglobulin-secreting cells (ISC) and antibody-secreting cells is significantly higher in systemic lymphoid tissues and the vaginal mucosa collected in the periovulatory period of the menstrual cycle than at other stages of menstrual cycle (20). The change in ISC frequency is not due to a change in the relative frequency of lymphocyte subsets, as this does not change during the menstrual cycle (23).
In the present study, we sought to confirm that cyclic changes in ovarian steroid hormone levels elicit similar changes in the ISC frequency of women. Thus, we determined the frequency of spontaneous IgG-secreting cells (IgG-ISC) and IgA-ISC in the peripheral blood mononuclear cells (PBMC) of healthy women volunteers throughout the course of several menstrual cycles. Criteria for participation in the study included an age of 30 to 45 years, no pregnancy at the time of entry into the study, no use of oral or parenteral hormonal contraceptives, no known health problems, hematocrits greater than 37% (normal range, 36 to 47%), and a recent history of regular menstrual cycles. There was no evidence of autoimmune disease, endocrine diseases, heart and vascular diseases, cerebrovascular disease, chronic obstructive pulmonary disease, allergy, gastrointestinal tract and liver diseases, kidney and urinary diseases, or alcohol or drug abuse in any of the volunteers. If a subject became pregnant during the study, she was withdrawn from the study. A urine pregnancy test was done a week prior to the start of the study. All of the women gave informed consent to participate in this study, which was approved by the University of CaliforniaDavis Institutional Review Board. Although all of the participants had hematocrits greater than 37% at entry into the study, hematocrit fluctuations occurred during the course of the study. Thus, individual blood samples were excluded if they had a hematocrit lower than 35% or there was evidence of infection, such as neutrophilia or lymphocytosis. Volunteers were also removed from the study if they came under a physician's care for allergy or infections during the course of the study or had a poor follow-up. On the basis of these criteria, six of the nine volunteers completed the study. The ages and hematology data of these six women volunteers at the time of enrollment are listed in Table 1. Peripheral venous blood (40 ml) was collected from each participant twice a week for 14 weeks. A standard multivitamin containing iron was supplied to all participants. PBMC were isolated by differential gradient centrifugation as previously described (20). A single midday voided urine sample was collected on Monday to Friday with a sterile collection cup and transferred to 15-ml conical centrifuge tubes. The urine samples were stored at -20°C within 15 min of collection and subsequently used to assess systemic levels of ovarian hormones. Daily urinary levels of estrone conjugates, pregnanediol-3-glucuronide, and follicle-stimulating hormone (FSH) ß subunit of all women were measured by enzyme immunoassay as previously described (21, 28).
Complete blood cell counts and three-color flow cytometry were
performed on each fresh heparinized venous blood sample by a
licensed medical technician. Anti-CD3
+-fluorescein isothiocyanate
(FITC), anti-CD4
+-phycoerythrin (PE), anti-CD8
+-peridinin chlorophyl
protein (PerCP), anti-CD20
+-PerCP, and anti-CD56
+-PE were obtained
from B-D Biosciences/PharMingen, San Jose, Calif. The three-color
staining combinations used were as follows: PE-CD4, PerCP-CD8,
and FITC-CD3 in one tube and FITC-CD3, PerCP-CD20, and PE-CD56
in the other tube. Numbers of CD4
+, CD8
+, CD20
+, and CD56
+ cells
were determined with a FACScalibur flow cytometer (Becton-Dickinson
Immunocytometry Systems, San Jose, Calif.). Data were analyzed
with FlowJo versions 3.6 and 4.1 (TreeStar, San Carlos, Calif.).
The ISC frequency in blood was enumerated by ELISPOT assay as
previously described, with the exception that anti-human immunoglobulin
was used as a detection reagent (Southern Biotechnology Associates,
Inc., Birmingham, Ala.) (
20).
ISC isotype frequency in blood.
As has previously been reported in rhesus monkeys (20) and humans (14), the frequency of IgA-ISC in PBMC was fourfold higher than the frequency of IgG-ISC (5.75 ± 0.47 IgG-ISC/105 PBMC versus 24.52 ± 2.08 IgA-ISC/105 PBMC; P < 0.05). Similar results were obtained when the data were analyzed to determine the number of ISC per 105 lymphocytes or the number of ISC per 105 B cells (19.40 ± 2.24 IgG-ISC/105 lymphocytes versus 82.64 ± 8.48 IgA-ISC/105 lymphocytes; P < 0.05; 30.25 ± 2.42 IgG-ISC/105 B cells versus 149.45 ± 14.50 IgA-ISC/105 B cells; P < 0.05) (Table 2). The frequencies of CD4+ and CD8+ T cells, neutrophils, lymphocytes, monocytes, eosinophils, CD20+ B cells, and CD56 + NK cells in all of the samples from the women were in the normal range (11, 17, 24, 25, 33) (Table 2).
Effect of menstrual cycle stage on ISC frequency.
Blood samples were collected twice a week, and the sampling
period extended over two or three complete menstrual cycles.
The inability to collect weekend urine samples made it difficult
to be certain of the day of ovulation in some individuals. To
be certain that samples were placed into the correct groups
for comparisons, only the data from one or two of the best-characterized
menstrual cycles of each woman were included in the analysis.
Group I included 27 samples collected between menstrual cycle
days -15 and -7 (Fig.
1). Thus, group I samples were collected
over a 9-day period in the follicular phase, when the levels
of both progesterone (PdG) and estrogen (E
1C) were relatively
low. Group II included 27 samples collected between menstrual
cycle days -5 and 1. Thus, group II samples were collected over
a 7-day period in the periovulatory stage, when E
1C levels were
high and PdG levels were low. Group III included 21 samples
collected between menstrual cycle days 2 and 12. Thus, group
III samples were collected over an 11-day period in the luteal
phase, when PdG levels were high and E
1C levels were low to
moderate. Only the samples collected during menstrual cycles
in which we could document a normal PdG and E
1C pattern (as
show in Fig.
1A) were included in the analysis. The frequency
of IgG- and IgA-ISC in the PBMC samples collected during the
follicular (group I), periovulatory (group II), and luteal (group
III) phases were compared by Duncan's new multiple-range statistical
method (Fig.
1B and C). The frequency of IgG-ISC in group II
PBMC samples was significantly higher than that in group I (
P < 0.025) and group III (
P < 0.016) PBMC samples (Fig.
1B). Similar results were found for IgA-ISC; the frequency of
IgA-ISC in group II PBMC samples was significantly higher than
that in group I (
P < 0.016) and group III (
P < 0.01) samples
(Fig.
1C). Thus, the frequency of ISC in PBMC samples collected
during the periovulatory stage was significantly higher than
that in PBMC samples collected at other stages of the menstrual
cycle. Representative results from an individual subject are
illustrated in Fig.
2. Note that the increased frequency of
ISC in blood was apparent when either the total number of lymphocytes,
PBMC, or B cells were used as the denominator. Thus, as has
been shown previously in female rhesus monkeys (
23), the changes
in ISC frequency were not due to altered frequencies in other
cell populations. The in vivo effect of ovarian hormones on
ISC frequency in women is consistent with published findings
demonstrating the enhancing effect of E
1Cs on the differentiation
of human antibody-secreting cells in vitro (
10,
26,
31).
Physiological levels of estrogen stimulate, while physiological
levels of PdG depress, B-cell maturation in both human and nonhuman
primate PBMC cultures (
10,
20,
26,
31). In rhesus monkeys, the
frequencies of ISC and antibody-secreting cells in genital tract
tissues and numerous systemic lymphoid tissues are significantly
affected by the stage of the menstrual cycle (
20). To date,
there have been no reports establishing an in vivo role for
ovarian steroids in the regulation of B-cell function in normal
women. In the present study, we show that the frequency of ISC
in PBMC of normal women was affected significantly by the stage
of the menstrual cycle in a manner very similar to that described
in female rhesus monkeys.
Note that in Fig. 2, the peak estrogen level in urine was not coincident with the highest ISC frequency in most of the cases. The ISC frequency peak occurred 2 days before the E1C level peak in urine. Presumably, this discordance exists because hormone levels in urine reflect the levels in serum on the previous day (8, 10).
E1C stimulates immunoglobulin-secreting activity by B cells in PBMC, and estrogen receptors are found on human macrophage lines (15), human CD8-positive peripheral T cells (7, 32), stromal cells derived from bone marrow of mice (29, 30), and mouse splenic lymphocytes (27). Estrogen stimulates interleukin-1 (IL-1) production by macrophages, and IL-1 levels in the plasma of women increase after ovulation (5, 16). Further, IL-1 can serve as either a B-cell growth factor or differentiation factor (13). Among human T cells, estrogen receptors are present only in T cells of the CD8+ suppressor/cytotoxic subset (32). Further, the effect of estrogen and progesterone on rhesus monkey B-cell physiology in vitro is mediated indirectly through CD8+ T cells (20). Thus, it is likely that B-cell immunity in women is regulated by CD8+ T cells under the influence of ovarian steroid hormones.
Elucidation of the precise cellular and molecular mechanisms by which sex hormones alter immune function is vital to understanding gender-based differences in autoimmunity (35, 36). Further, it has been difficult to elicit vaccine-induced protective immunity to sexually transmitted diseases in women. A better understanding of the role of sex hormones in promoting antibody secretion by B cells may lead to improved therapies for autoimmune diseases and vaccine strategies for the control of sexually transmitted diseases, including AIDS, in women.

ACKNOWLEDGMENTS
This work was supported by grants P51 RR 60169; R01 HD 33169,
and U 54HD 125.

FOOTNOTES
* Corresponding author. Mailing address: California National Primate Research Center, University of CaliforniaDavis, Davis, CA 95616. Phone: (530) 752-0447. Fax: (530) 752-2880. E-mail:
cjmiller{at}ucdavis.edu.


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Clinical and Diagnostic Laboratory Immunology, September 2003, p. 944-949, Vol. 10, No. 5
1071-412X/03/$08.00+0 DOI: 10.1128/CDLI.10.5.944-949.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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