In recent years our knowledge of the role of B lymphocytes in the pathogenesis of rheumatoid arthritis (RA) has expanded and it is now thought that B cells have a more extensive role than was previously appreciated. They seem to play a pivotal role in the activation of synovial T cells and induction of cytokine secretion. CD20 antigen expressed on the surface of B cells is highly specific to B cells. The success of B cell depletion therapy by using the monoclonal antibody Rituximab, which targets CD20, further emphasized the importance of B cells in the pathogenesis of RA.