Distinct mast cell responses in male and female SJL mice underlie sex dimorphic EAE susceptibility

Females are more to susceptible many autoimmune diseases. In multiple sclerosis (MS), not only is there a 3-4 fold increase in disease incidence, but there are sex-determined differences in the average age of onset and clinical course. Yet the cellular and molecular underpinnings of this sex-dimorphism have remained undefined. The SJL mouse model of MS recapitulates these differences in that female mice exhibit higher incidence, more severe disease, and a more consistent relapsing-remitting pattern than their male counterparts. This difference in disease susceptibility corresponds to qualitatively distinct anti-myelin Th cell cytokine responses. Whereas females generate pro-inflammatory Th1/Th17-dominant responses, the response in males is Th2-skewed and non-pathogenic. In this application we provide evidence that type 2 innate lymphoid cells (ILC2s) exert a male-specific protective influence. Best studied in allergic airway models, ILC2s are c-kit+ and are essential for inducing Th2 immunity through production of IL-13. Based on preliminary data, we propose that in males, mast cell activation in immunized mice elicits production of ILC2 activating factors such as IL-33 that promote ILC2 functionality. The inability to generate a robust IL-33 response in females leads to a functional deficit in ILC2 activity. Mast cells (c-kit+ FcεR1+) are one important source of IL-33 in vivo and although there is no sex-dependent difference in androgen receptor (AR) expression, testosterone directly induces Il33 only in male-derived cells. We propose a previously unknown and sex-specific role for both mast cells and ILC2s as important attenuators of the pro-inflammatory Th17 response in EAE. Furthermore, these data suggest a cellular and molecular target of testosterone and identify a potential mechanism of action for testosterone-mediated protection in CNS autoimmune disease. Specific Aim 1: Determine the cellular source (s) of IL-33 in immunized male mice. Using IL-33- reporter mice, these experiments will define the cell types expressing IL-33 and when and where IL-33 is produced. Specific Aim 2: Determine how testosterone influences IL-33 expression in mast cells and other cells. We will ask if testosterone induces epigenetic changes at the Il33 locus conferring changes in chromatin accessibility. IL-33 gene expression will be evaluated in mice treated with testosterone or AR antagonists. Specific Aim 3: Explore the contributions of sex determining genes on ILC2 and mast cell function in EAE. The potential effect of sex hormones and sex chromosomes on ILC2 and mast cell gene expression and function will be examined using four core genotype mice, which allow dissection of hormone-related vs. other sex chromosome effects.