CD8 T cell-mediated pathogenicity in AA is linked to IFNg production and not cytolytic capacity

Summary: Abstract Body: Alopecia Areata (AA) is a prevalent autoimmune disease that presents as nonscarring hair loss. In AA, CD8 T cells accumulate around and within the hair follicle and have been identified as pathogenic effectors of disease. Our transcriptional analysis has revealed that CD8 T cells that infiltrate AA skin exhibit increased gene expression of cytolytic mediators, such as perforin and granzymes, and increased gene expression of the pro-inflammatory cytokine interferon gamma (IFNg). Given the close spatial relationship between CD8 T cells and the hair follicle end-organ target, our objective was to assess the relative contributions of CD8 T cell-derived molecules in the onset of disease. To address this, we used C3H/HeJ mice globally deficient in Prf1 (PKO), IFNg (IFNgKO) and IFNg-receptor (IFNgrKO). Although these global knockouts exhibited markedly different rates of AA development, we were able to leverage gene-deficient mice that developed AA from all groups to perform mechanistic studies. We assessed the relevance of CD8 T cell-derived perforin and IFNg in a C3H/HeJ murine model of AA, wherein pathogenic NKG2D+ CD8 T cells are flow-cytometrically sorted from the skin draining lymph nodes of AA mice, expanded in vitro, and then intradermally injected into naïve recipients. We observed that CD8 T cells from PKO AA mice were able to induce AA in a comparable manner to those from WT AA mice. Conversely, CD8 T cells from IFNgKO AA mice were unable to induce AA, suggesting that CD8 T cell-derived IFNg is critical for the initiation of disease. To further support this, we found that adoptive transfer of wild-type CD8 T cells into IFNgrKO global KO mice failed to induce AA. Overall, our findings suggest that perforin-mediated cytolysis is not required for the attack of the hair follicle, and that IFNg production is a crucial pathogenic effector mechanism employed by CD8 T cells in AA. Maddison Lensing¹, Samuel J. Connell¹, Otgonzaya Ayush¹, Ryan Reis¹, Payton Kahl¹, Joan Goverman², Ali Jabbari^{1, 3} 1. Department of Dermatology, University of Iowa Health Care, Iowa City, IA, United States. 2. University of Washington, Seattle, WA, United States. 3. Iowa City VA Medical Center, Iowa City, IA, United States. Adaptive and Auto-Immunity