CD4 and rheumatoid arthritis: Disease-relevant CD4+ T cells isolated from the synovial membrane of patients with RA were also used as stimulators and found to be potent inducers of cytokine production in monocytic THP-1 cells [27], in monocytes from healthy donors [10,28] and in mononuclear cells isolated from synovial membranes of patients with RA [29].