Mesenteric lymph node T cells but not splenic T cells maintain their proliferative response to Concanavalin-A following peroral infection with Toxoplasma gondii

The suppression of T cell responsiveness which occurs after infection with Toxoplasma gondii in mice has been widely studied using spleen cells. Becau se the natural route of infection with T. gondii is the peroral route, Lye examined the proliferative responses of mesenteric lymph node (MLN) cells, in addition to spleen cells, to Concannvalin-A (Con-A) in mice perorally in fected with T. gondii. Proliferative responses of spleen cells were signifi cantly suppressed seven and ten days after infection when compared with spl een cells from uninfected mice (62% and 91% reduction, respectively). In co ntrast, proliferative responses of MLN cells from these infected mice did n ot differ from those of normal MLN cells. Since IFN-gamma-induced reactive nitrogen intermediate (RNI) production has been reported to play a major ro le in suppression of proliferative responses in spleen cells of infected mi ce, bye compared production of IFN-gamma and RNI by spleen and MLN cells fo llowing infection. MLN cells produced as much IFN-gamma as did spleen cells , but produced 70% less nitrite (ns a measure of RNI) after Con-A stimulati on. Proliferative responses of MLN cells were suppressed when co-cultured w ith spleen cells from infected mice, and addition of an inhibitor of RNI to these co-culture inhibited this suppression, suggesting that reduced RNI p roduction by MLN cells contributes to their maintenance of higher prolifera tive responses. These results demonstrated a clear difference in activity o f T cells in the MLN and spleen during the acute stage of the infection.