The antagonism of sex chromosomes and sex hormones dictates outcomes in Th17 cell-mediated central nervous system autoimmunity.
Biological sex traits are shaped by the combined effects of both sex hormones and chromosomes. How these factors interact in sex-related autoimmune diseases, such as multiple sclerosis (MS), has been a subject of intense recent interest. Here, using the Four Core Genotype (FCG) mouse model, in which these two variables can be disentangled, we describe an antagonism between sex hormones and chromosomes that potently influences outcomes in T helper 17 (Th17)-driven progressive central nervous system (CNS) autoimmunity. Male gonadal hormones dampen disease severity, irrespective of sex chromosome complement, by promoting a Wnt/{beta}-catenin signaling program associated with a homeostatic, non-pathogenic Th17 phenotype. By contrast, XY chromosomal complement exacerbates Th17 pathogenicity in a recipient sex-dependent manner; we identify the X-linked molecule SUV39H1 as an inhibitor of inflammatory Th17 cell function. Unexpectedly, we found that hormonally and chromosomally female FCG Th17 cells induced far more severe disease than WT female counterparts despite being genetically identical, pointing to a parental imprinting effect in dictating Th17 cell pathogenicity. These latter investigations uncovered Runx2, a transcription factor previously linked to developmental programs, as a novel negative regulator of the pathogenicity of Th17 cells. Together, our findings establish biological sex as a multilayered regulator of Th17 pathogenicity, revealing distinct and sometimes opposing contributions of hormones, chromosomes, and parental inheritance.