The fate of effector T cells in vivo is determined during activation and differs for CD4⁺ and CD8⁺ cells

Effector T cells generated in the mesenteric lymph nodes (mLN) are known to accumulate in mLN and the tissue drained by them after circulating in the blood. Their accumulation is due less to preferential entry into mLN but more to preferential proliferation within mLN. The factors regulating the proliferation of effector T cells in vivo are unclear, and it is unknown whether they are different for CD4⁺ and CD8⁺ effector T cells. Rat T cells from mLN or peripheral lymph nodes (pLN) were stimulated polyclonally via the TCR and CD28 and injected i.v. into congenic recipients. Using three-color flow cytometry and immunohistochemistry, they were identified in mLN, pLN, and blood over time, and proliferation was determined by measuring bromodeoxyuridine incorporation. Only effector mLN T cells showed a significantly increased proliferation rate after entry into mLN compared with that in pLN (2.4 ± 1.8% vs 0.8 ± 0.4%). Proliferation among the injected cells was higher when they had contact with dendritic cells within mLN (9.0 ± 4.3%) than when they did not (4.1 ± 2.1%). Furthermore, effector mLN T cells which were observed 56 days after injection maintained the capacity for preferential proliferation within mLN. Interestingly, CD4⁺ effector mLN T cells proliferated at a higher rate (4.8 ± 0.7%), remaining in mLN, whereas CD8+ effector mLN T cells proliferated at a lower rate (3.3 ± 1.0%) and were able to leave the mLN into the blood. Elucidating the factors regulating the proliferation of effector T cells in vivo will help to modify their distribution for therapeutic purposes.