HETEROGENEITY OF HELPER T-CELL SUBSETS IN PEYER PATCHES

The OX22 monoclonal antibody recognizes the high molecular weight form of the CD45 molecule on rat T cells encoded by the CD45RC exon of the leukocyte common antigen gene. Its expression on CD4+ T cells is asso ciated with virgin unprimed cells and primed cells which produce IL-2 and IFN-gamma on stimulation and participate in cell-mediated immune r eactions. This suggested that CD45RC expression may be useful as a phe notypic marker for cells expressing Th1 function. In view of our previ ous data indicating heterogeneity of T-cell helper function in differe nt lymphoid compartments in the gut, the helper activity of OX22-enric hed or OX22-depleted cell populations prepared from Peyer's patches (P P) of rats was compared. Following intestinal immunization with keyhol e limpet haemocyanin, PP cells were isolated and separated by panning. Recovery data indicated that the majority of T cells in rat PP expres s the OX22+ phenotype and, after separation, the OX22-enriched populat ion contained 4 times as many cells as the OX22-depleted population. F unctional studies revealed that both subsets were capable of providing cognate help for secondary IgM, IgG and IgA antibody responses indica ting that on this basis the CD45RC marker does not correlate with Th1 function in rats.