Heterogeneity of helper T cell subsets in Peyer's 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 associated with virgin unprimed cells and primed cells which produce IL-2 and IFN-gamma on stimulation and participate in cell-mediated immune reactions. This suggested that CD45RC expression may be useful as a phenotypic marker for cells expressing Th1 function. In view of our previous data indicating heterogeneity of T-cell helper function in different lymphoid compartments in the gut, the helper activity of OX22-enriched or OX22-depleted cell populations prepared from Peyer's patches (PP) of rats was compared. Following intestinal immunization with keyhole limpet haemocyanin, PP cells were isolated and separated by panning. Recovery data indicated that the majority of T cells in rat PP express the OX22+ phenotype and, after separation, the OX22-enriched population contained 4 times as many cells as the OX22-depleted population. Functional studies revealed that both subsets were capable of providing cognate help for secondary IgM, IgG and IgA antibody responses indicating that on this basis the CD45RC marker does not correlate with Th1 function in rats.