Myeloid cells exhibit excessive proliferation and infiltration into joint tissue of B6 miR-146a−/− mice, have increased phagocytic activity and produce excess cytokines such as IL-1β, IL-6 and CXCL1, leading to inflammation of synovial tissue and arthritis development (Figures 6–8). The gene discussed is CXCL1; the disease is arthritic joint disease.