CD4 and rheumatoid arthritis: The SKG mice not only exhibit a loss in central and likely peripheral tolerance that can be molecularly dissected but they also recapitulate the paradoxical ability of RA CD4 T cells to differentiate into pathogenic effector cells despite impaired TCR signaling.49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 64, 76