B Cells Can Trigger the T-Cell-Mediated Autoimmune Response Against Melanocytes in Psoriasis.

Psoriasis vulgaris is a T-cell-mediated skin disease that may involve an autoimmune response against melanocytes. It develops through still unexplained pathomechanisms. Streptococcal tonsillopharyngitis is a major trigger of psoriasis onset and relapses. HLA-C*06:02 is the main psoriasis risk gene. Here we find that B cells isolated from streptococci-infected tonsils or peripheral blood of HLA-C*06:02+ psoriasis patients stimulate an HLA-C*06:02-restricted melanocyte-reactive Vα3S1/Vβ13S1 T-cell receptor (TCR) from a lesional psoriatic CD8+ T cell clone in an IFN-γ-enhanced manner. Patients' B cells furthermore induce proliferation of autologous blood CD8+ T cells. We identify several HLA-C*06:02-presented self-peptides in the immunopeptidomes we had isolated from four HLA-C*06:02 homozygous B-cell lines that stimulate the Vα3S1/Vβ13S1 TCR and differ from the melanocyte autoantigen recognized by this TCR. These data suggest that the proinflammatory environment of streptococcal tonsillopharyngitis may enable B cells to activate autoreactive CD8+ T cells that, owing to the polyspecificity of T-cell receptors, recognize several B-cell self-peptides presented by HLA-C*06:02 and subsequently cross-react against melanocytes in the skin, thereby triggering psoriasis. The capacity of B cells to stimulate a cross-reactive autoimmune response through HLA class I-presented B-cell peptides is a previously unknown mechanism in the induction of autoimmunity that could explain psoriasis onset and persistence.