When compared to wild type littermates, knockout animals had a faster onset, greater incidence, and worsened severity of disease; increased radiographic evidence of bone destruction, increased histological joint inflammation, elevated in vitro release of Th1 cytokines from cultured splenocytes and increased systemic levels of Monocyte Chemotactic Peptide (MCP)-1 and TNF. This evidence concerns the gene CCL2 and inflammation.