Activated T cells enter rat lymph nodes and Peyer's patches via high endothelial venules: survival by tissue-specific proliferation and preferential exit of CD8(+) T cell progeny

Activated T cells reach the lymph nodes via afferent lymphatics but it is u nknown to what extent they also enter them directly via high endothelial ve nules (HEV). Little is known about the mechanism mediating the proliferatio n of activated T cells within lymphoid tissues in vivo or the subsequent fa te of the progeny. Therefore, we stimulated rat T cells via TCR and CD28 in vitro and after injection identified them in the blood and the HEV of lymp hoid organs at several time points. In addition, the proliferation of these cells was studied after entering different lymphoid organs. Our results sh ow that, firstly, activated T cells continuously enter lymph nodes and Peye r's patches directly via HEV. Second, they proliferate within lymphoid orga ns, the rate significantly depending on the microenvironment. Third, mainly CD8(+) progeny are able to leave the tissues and re-enter the blood. Thus, the distribution of activated T cells circulating through the body can be regulated during entry, but also within the tissue by influencing their pro liferation and subsequent release.