TNF and rheumatoid arthritis: The role of B cells in immunopathogenesis of RA has not been fully characterised but several possible mechanisms of action have been proposed; B cells may function as antigen presenting cells with co-stimulatory signals required for T cells CD4 regulation, as well they may secrete proinflammatory cytokines (TNF, IL6, other chemokines) and regulate immune response during RA contributing to the inflammation and bone erosions.