Dendritic cell expression of A20 preserves immune homeostasis and prevents colitis and spondyloarthritis

Dendritic cells (DCs), known to support immune activation during infections, may also regulate immune homeostasis in resting animals. Here we show that mice lacking A20 specifically in DCs spontaneously exhibited DC activation and expansion of activated T cells. DC-specific epistasis experiments using A20(fl/fl) Myd88(fl/fl) Cd11c-Cre compound mice revealed that A20 restricts both MyD88-independent signals, which drive DC and T cell activation, and MyD88-dependent signals, which drive T cell expansion. In addition, A20(fl/fl) Cd11c-Cre mice spontaneously developed lymphocyte-dependent colitis, sero-negative ankylosing arthritis and enthesitis, conditions stereotypical for human inflammatory bowel disease (IBD). These findings indicate that DCs require A20 to preserve immune quiescence and suggest that A20-dependent DC functions may underlie IBD and IBD-associated arthritides.