CD4 and arthritic joint disease: Measurement of the mesenteric lymph node, however, showed that only 0.2% of B22a1+CD4+ T cells infiltrated this organ at peak day 10-indicating that the homing B22a1+CD4+ T cells did not occur at random and that the mesenteric lymph node is not involved in the arthritis-specific immune mechanisms, since these cells had retracted to approximate base levels again at day 20.