Inflammasome-independent role of apoptosis-associated speck-like protein containing a CARD (ASC) in T cell priming is critical for collagen-induced arthritis

Abstract

Rheumatoid arthritis is an autoimmune disease with 1% prevalence in the industrialized world. The contributions of the inflammasome components Nlrp3, ASC, and caspase-1 in the pathogenesis of collagen-induced arthritis have not been characterized. Here, we show that ASC-/- mice were protected from arthritis, whereas Nlrp3-/- and caspase-1-/- mice were susceptible to collagen-induced arthritis. Unlike Nlrp3-/- and caspase-1-/- mice, the production of collagen-specific antibodies was abolished in ASC-/- mice. This was due to a significantly reduced antigen-specific activation of lymphocytes by ASC-/- dendritic cells. Antigen-induced proliferation of purified ASC-/- T cells was restored upon incubation with wild type dendritic cells, but not when cultured with ASC-/- dendritic cells. Moreover, direct T cell receptor ligation with CD3 and CD28 antibodies induced a potent proliferation of ASC -/- T cells, indicating that ASC is specifically required in dendritic cells for antigen-induced T cell activation. Therefore, ASC fulfills a hitherto unrecognized inflammasome-independent role in dendritic cells that is crucial for T cell priming and the induction of antigen-specific cellular and humoral immunity and the onset of collagen-induced arthritis.