The Female Reproductive Tract is a Sex-Specific Site for Rheumatoid Arthritis Specific Biomarkers 2334718

Abstract Introduction Women have a three-fold higher rate of rheumatoid arthritis (RA) as compared with men, and several reproductive factors are correlated with increased risk of RA in women. RA autoimmunity can develop when citrullinated (cit) proteins are generated at a mucosal surface by peptidylarginine deiminase (PAD) enzymes. Anti-citrullinated protein antibodies (ACPAs) are produced in the mucosa and when they become systemic they trigger joint inflammation. Neutrophil extracellular traps (NETs) can generate cit-proteins in RA patients and are present in mucosal surfaces, including the female reproductive tract (FRT). Shared mucosal sites have yet to explain the sex disparity in RA, leading us to hypothesize the FRT mucosa is a sex specific site of cit-protein generation, ACPA production, and NET formation. Methods Cit-proteins were identified by mass spectrometry from FRT fluid (FRTF) collected at day 25 of the menstrual cycle in RA positive women (RA+) and healthy controls (HC) and from mice during the estrous cycle. ACPA were quantified via the anti-CCP assay (humans) and from wild type (wt) and PAD2/4 double knockout (DKO) female mice using an in house ELISA specific to individual cit-proteins. NETs were visualized in mouse FRTF and from isolated neutrophils via confocal microscopy. Results RA+ women FRTF cit-proteins were elevated compared to HC with many cit-proteins also present in wt mouse FRTF. RA+ FRTF ACPA were significantly elevated compared to HC, while DKO mice had significantly decreased FRTF ACPA to cit-fibrinogen and NETs compared to wt. Conclusion The FRT is a sex-specific site of cit-protein generation, ACPA production, and NET formation. RA+ women have significantly elevated cit-proteins and ACPA compared to HC in FRTF. The wt mouse FRTF citrullinome is comparable to that of the human. ACPA specific to individual cit-proteins are quantifiable with our ELISA. Female PAD2/4 DKO show decreased ACPA production and NET formation compared to wt female mice. Funding Source Wyoming IDeA Networks for Biomedical Research Excellence (INBRE) Topic Categories Basic Autoimmunity (BA)