Genetic control of cell-mediated immunity in the rat. III. T cells restricted by the RT1.A locus recognize viable Listeria but not isolated bacterial antigens.

This study investigates the discordance between the restriction criteria required for the transfer of cellular resistance to Listeria monocytogenes (LM) and those for the transfer of delayed type hypersensitivity to Listeria antigens. Infective bacteria elicit both RT1.A-restricted T cells and RT1.B-restricted T cells. Both populations of T cells mediate lymphoblast localization and macrophage accumulation, which are reactions characteristic of delayed type hypersensitivity (DTH), and cause macrophage activation with rapid and efficient bacterial elimination, which is an expression of cellular resistance. If alcohol-killed Listeria organisms (pLMA) are injected, only the RT1.B-restricted T cell subset is triggered. Direct comparison of lymphoblast localization in LM infection sites and the expression of resistance revealed that efficient resistance may be mediated by small numbers of lymphoblasts and that below a certain threshold there is no correlation between lymphoblast localization and the level of resistance.