Recirculatory and sessile CD4(+) T lymphocytes differ on CD45RC expression

CD4(+) T cell subsets are unequally distributed in rat secondary lymphoid o rgans. Those with the memory phenotype CD45RC(low) Thy-1(-) L-selectin(-) a re present at a higher frequency in Peyer's patches (PP) than in lymph node s and spleen, and increase in numbers with age in all three tissues, partic ularly in the PP. Homing experiments revealed that CD4(+) T cells that reci rculate through secondary lymphoid organs are mainly CD45RC(high). It was a lso apparent that the ability of recirculating cells to enter different lym phoid organs varies; less cells enter PP than the spleen or lymph nodes. Ou r results also reveal the existence of a nonrecirculating population of CD4 (+) T cells in secondary lymphoid organs, which are predominantly, if not e xclusively, CD45RC(low), Our results show that secondary lymphoid organs di ffer in their CD4(+) T cell subset composition as a consequence of having d ifferent ratios of recirculatory:nonrecirculatory CD4(+) T cells, and these cells display a different CD45RC phenotype.