Autoantibodies constitute the hallmark of antineutrophil cytoplasmic antibody-associated vasculitis (AAV); however, CD4+ T cells play an essential role in the development of autoimmunity. Infection is associated with vasculitis, with Toll-like receptors (TLRs) a potential link between infection and autoimmunity. This study was undertaken to investigate the role of TLR ligation on cellular and humoral autoimmunity and glomerular injury in experimental myeloperoxidase (MPO)-induced AAV. METHODS: We analyzed autoimmune responses in wild-type mice immunized with MPO alone or coimmunized with MPO and a TLR-2 or TLR-9 ligand. The major vascular injury found in human disease, glomerulonephritis with focal necrosis, was triggered by administering a subnephritogenic dose of nephrotoxic serum.