CCL2 and Arthritis: In contrast to the reduced clinical severity of arthritis, however, a more vigorous immune response to immunization with collagen II seems to occur in TLR4 deficient mice, since both the serum concentrations of the proinflammatory cytokines IL-12p70, TNF alpha and MCP-1 (day 34) and the T cell responses against collagen II are higher in this group.