T lymphocytes isolated from naïve, unmanipulated mice, proliferate and secrete cytokines when cultured in vitro with allogeneic irradiated leukocytes. This in vitro response known as mixed lymphocyte reaction (MLR) is mediated by T cells recognizing intact donor MHC molecules on stimulator cells (direct allorecognition). It has been proposed that such primary in vitro T cell alloresponse is rendered possible by the high precursor frequency of naïve T cells capable of recognizing an allogeneic MHC molecule. On the other hand, it is possible that the MLR results from the presence of alloreactive memory T cells (TMEM) in naïve mice (endogenous TMEM). To address this question, we isolated naïve T cells and TMEM (CD4⁺ and CD8⁺) from unmanipulated BALB/c mice and tested their ability to mount a direct inflammatory response (using IL-2 and gIFN-ELISPOT assays) in vitro after exposure to irradiated B6 spleen cells. The presence of gIFN producing spots (100-200 spots/million T cells) was detected after 2 days only with CD8⁺ endogenous TMEM but not naïve T cells. Alternatively, a few IL-2 producing spots were detected after 4 days only with both naïve and endogenous CD4⁺ endogenous TMEM. Next, the same MLR assays were performed with T cell subsets from BALB/c mice having received a B6 skin allograft (5-7 weeks post-Tx). Again, no response was recorded with naïve T cells. In contrast, very high numbers of gIFN-producing spots (> 1,500 spots per million T cells) were detected with CD4⁺ and CD8⁺ TMEM (induced TMEM).

CITATION INFORMATION: Lee J, Benichou G. Contributions of Naive vs. Endogenous and Induced Alloreactive Memory T Cells in Mixed Lymphocyte Reactions. Am J Transplant. 2016;16 (suppl 3).

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