C1q regulates CD40 pathway on DCs and drives the Th1 polarization of T cells. DCs secrete C1q, which binds to C1q receptors (C1qR) on the surface of the DC. When antigen-specific T cells recognize cognate antigen on DCs, it results in CD40 ligation on the DC by CD40L on activated T cells. This induces the up-regulation of CD40 expression on DCs and the colocalization of C1q with CD40 and formation of a signaling complex. Increased phosphorylation of p38 and ERK1/2 occurs, resulting in increased production of IL-12. This further sustains the IFN-γ production from T cells.