CD46 and rheumatoid arthritis: For example, concurrent signaling by the C3b/C4b‐binding complement regulator CD46 (membrane cofactor protein, MCP) and the C3aR expressed on CD4+ T cells has been proved to be a prerequisite for IFN‐γ production and human Th1‐cell induction 52, 53, 54, and dysregulation of CD46‐mediated costimulatory signals on T cells has been identified in chronic disease settings, including multiple sclerosis 55 and RA 52.