Butyrophilin 2A2 promotes T cell immunoregulation via CD45 phosphatase activation and protects against murine autoimmune glomerulonephritis and pregnancy loss

B7 costimulatory family member Butyrophilin 2A2 (BTN2A2) is predominantly expressed by antigen presenting cells and regulates T cell immunity, but molecular mechanisms are unclear. Using immunoblots analyzing TCR-initiated signaling intermediaries, co-immunoprecipitation studies, confocal microscopy, structural modeling-guided mutational analyses, and microscale thermophoresis, we demonstrate that BTN2A2 directly interacts with CD45RO, resulting in CD45 retention within the immune synapse during TCR activation. Recombinant BTN2A2 increases murine CD4+Foxp3+ regulatory T cells (Treg) and reduces T helper 17 (Th17) cells in vitro through mechanisms dependent on CD45 phosphatase activity. BTN2A2 therapy alleviates disease severity in murine nephrotoxic glomerulonephritis and autoimmune miscarriage while increasing Treg/Th17 ratios. Analyses of BTN2A2-deficient animals show exacerbation of disease associated with reduced Treg/Th17 ratios. BTN2A2 functions analogously on human T cells suppressing Th17, Th1 and Th2 responses while inducing Tregs. Together, our studies identify BTN2A2 as a modulator of CD45RO signaling in T cells, providing insight into how BTN2A2 regulates T cell-dependent immune responses including those mediating autoimmunity and transplant rejection. Butyrophilin 2A2 is a member of the B7 costimulatory family that is expressed on antigen presenting cells and is linked to the regulation of T cells. Here the authors implicate butyrophilin 2A2 in enhancement of CD45 phosphatase activity within the immunological synapse during T cell activation, leading to expansion of regulatory T cells and reduction of proinflammatory Th17 CD4 T cells.