S100A9 and Arthritis: Macrophage differentiation markers MNDA, MRP8 and MRP14, signaling molecules JAK3 and MAP kinase p38, receptors TNFR2/p75, CCR1 and CXCR4, integrin beta1, and the cytokines/chemokines interleukin (IL) 1beta and IL-8 have also been identified in patients with arthritis [27].