Date on Master's Thesis/Doctoral Dissertation

8-2010

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Microbiology and Immunology

Committee Chair

Kosiewicz, Michele Marie

Author's Keywords

Systemic lupus erythematosus; Autoimmunity; Regulatory T cells; Sex differences; CD103

Subject

T cells; Disease susceptibility; Lupus; Sex factors in disease

Abstract

Females are more susceptible to autoimmune disease than males. In several mouse models of disease, castration of males exacerbates disease while androgen treatment ameliorates disease. These data suggest hormones can have an influence on disease susceptibility and progression. Regulatory T cells (Tregs), particularly the CD4+CD25+ Tregs, have been shown to be important in controlling autoimmune disease. Studies have shown that depleting regulatory T cells can cause severe autoimmune disease, and increasing regulatory T cell population size can protect from disease. We hypothesized that gender differences in regulatory T cell populations would correlate with differences in disease susceptibility. We used a spontaneous mouse model of systemic lupus erythematosus, (NZBxNZW)F1 (BWF1), in which only females develop full-blown kidney disease to investigate gender differences in regulatory T cell percentages and function between females and males and their relationship to disease development. First, we assessed differences in regulatory T cell function and number between young (before disease onset) female mice from four different strains, two autoimmune-prone strains, BWF1 and SJL, and two more autoimmune-resistant strains, CS7BL/6 and BALB/c. We found no differences in in vitro suppressive function by CD4+CD2S+ Tregs from any of the four strains when co-cultured with either syngeneic CD4+CD2Y responders and APCs or CS7BL/6 CD4+CD2Y responders and APCs. We did, however, find lower percentages of CD4+ cells that expressed Foxp3 (CD4+Foxp3+ cells) in the periphery of BWF1 mice when compared to the other three strains of mice. The CD4+CD2S+CDI03+ cells are a potent memory/effector subset of regulatory T cells that are better suppressors than CD4+CD2S+CDI03- Tregs both in vitro and in vivo. As found with the CD4+CD2S+ Tregs, we also found no differences in the suppressive function of CD4+CD2S+CD103+ cells from any of the four strains of mice. However, percentages of CD4+CD2S+CDI03+ cells were, again, decreased in the periphery of BWF1 mice compared to the other three strains. We found that reduced percentages of both CD4+Foxp3+ and CD4+CD2S+CD103+ cells in the periphery of BWF1 mice were not due to defects in either thymic production or homeostatic proliferation of these cells. These data suggest that it may be the decreased Treg:Teffector cell ratio, and not a defect in inherent suppressive function, that render BWF1 mice more susceptible to autoimmune disease. We next examined gender differences in regulatory T cell function and number between young female and male mice of the four strains. We found no differences in the suppressive ability of either CD4+CD25+ or CD4+CD25+CD103+ Tregs between females and males of any strain. BWF1mice were the only strain in which females had lower peripheral percentages of CD4+Foxp3+ cells than strain-matched males. Strikingly, females of all four strains had lower percentages of CD4+CD25+CD103+ cells in the periphery compared to strain-matched males. The lower percentages did not appear to be due to defects in either thymic production or homeostatic proliferation of the CD4+Foxp3+ or CD4+CD25+CDI 03+ cells in females of any strain studied. Taken together these data suggest that decreased percentages of Tregs in the periphery of female BWF1 mice compared to BWFI males and other mouse strains, and not an inherent defect in Treg suppressive function, may contribute to their increased susceptibility to systemic lupus erythematosus. Finally, we assessed regulatory T cell function and number in BWFI mice with established disease and compared age-matched (~32-36 weeks of age) sick (with proteinuria >_ 300 mg/dl) females, non-sick females and males. We found no differences in suppressive function of either CD4+CD25+ or CD4+CD25+CDI03+ cells from sick female, non-sick female or male mice when co-cultured with male CD4+CD2Y responders and male APCs in vitro. Surprisingly, we found significantly higher percentages of both CD4+Foxp3+ and CD4+CD25+CD103+ cells in the periphery of sick females that were nearly three times that seen in non-sick females and males. To evaluate the relationship between progression of disease and regulatory T cell function and number, we examined regulatory T cells at several time-points throughout disease development. The lower percentages of both CD4+Foxp3+ and CD4+CD25+CDI03+ regulatory cells found in young (9 week-old) pre-disease female BWFI mice compared to age-matched males disappeared as mice aged, i.e., by 20-24 weeks of age. We hypothesized that the 9 weeks time-point (before disease onset) may represent an important period during which having reduced proportions of the potent CD4+CD2S+CDI03+ Treg population could render females more susceptible to disease. To determine whether decreasing the CD4+CD2S+CDI03+ Tregs at this critical time-point could impact disease development later on, we depleted CD 1 03 + cells by administration of anti-CD 1 03 antibody bi-weekly then bi-monthly beginning at 8 weeks of age in female and male BWF1 mice. We found that CD 103+ cell depletion early on accelerated disease onset and death in female BWF1 mice, and dramatically increased disease incidence and death in male BWF1 mice. These data suggest that 9 weeks may be a critical time-point in disease development and that reduced regulatory T cell populations in young pre-disease mice may render female BWF1 mice more susceptible to disease or alternatively, that higher regulatory T cell numbers in young pre-disease mice may help protect male BWF1 mice from disease. The data presented in this dissertation suggest that reduced Treg:T effector cell ratios and not an inherent defect in regulatory function may cause increased susceptibility to autoimmune disease. It also suggests that the potent CD4+CD2S+CDI03+ regulatory T cell population may be more sensitive to hormonal influences, as females of all four strains studied had lower peripheral percentages of these cells than strain-matched males. Finally, these data suggest that the early pre-disease time-point in BWF1 disease progression represents a critical period of time where a reduction in regulatory T cells can accelerate disease and death.

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