Sex differences in disease severity and immune responses in murine and human inflammatory arthritis

Background: Rheumatoid Arthritis (RA), a systemic autoimmune disorder of unknown etiology, disproportionately affects females at a 3:1 ratio compared to males. While biological sex differences in the immune system exist, sex-related differences in inflammatory and immune mediators of RA disease severity are undefined. Our objective was to characterize sex-related differences in immune responses in a murine collagen-induced arthritis (CIA) model and in human RA patients. Methods: In CIA compared to saline control mice, inflammatory disease severity was assessed using standardized clinical scores. Anti-collagen antibodies, neutrophil elastase, calprotectin/ S100A8/A9 heterodimer, CRAMP, MMP3, and MMP9 were quantified by ELISA in the sera and joint tissues. Cytokine/chemokine levels in sera and joints were assessed using a Luminex based-44-Plex Discovery Assay® Array. Immunophenotyping of mouse splenic T cells analysis was performed by flow cytometry. Proteomic profiling of serum samples from an established RA cohort (72 female and 19 male that were at least 84% ACPA+) was performed using an aptamer-based SomaScan platform. Results: We identified distinct sex-related differences in disease severity and pro-inflammatory profiles in the sera and joint tissues of CIA mice, with inflammatory responses that were male-skewed in the sera and female-skewed in the joints. Furthermore, we demonstrated heightened neutrophil activation markers and CD4 ⁺ T cell-mediated inflammatory responses in female CIA mice. Similar sex-related differences in neutrophil activation and leucocyte migration were identified in RA patients. Conclusions: Our study demonstrates novel sex differences in pro-inflammatory mediators and activities of neutrophils and CD4 ⁺ T cells associated with disease severity in CIA mice, and in human RA patients. These findings provide new insights into sex-related differences in immunological pathways associated with inflammatory arthritis, which may contribute to the sex disparity in RA pathogenesis.