Enhancement of passive antilisterial immunity and change of Lyt phenotype following in vitro stimulation of murine lymphoid cells from immune donors.

To enhance the functional activity of the immune lymphoid cells required for passive antilisterial immunity, we cultured spleen cells from Listeria-immune mice in vitro with specific mitogens or listerial antigens and then transferred these cells into normal syngeneic mice. We assayed the level of passive immunity in these recipients either by their resistance to challenge with viable Listeria monocytogenes or by their delayed-type hypersensitivity (DTH) response to listerial antigens. In vitro stimulation with the T cell mitogens concanavalin A (ConA) and phytohemagglutinin (PHA) effectively enhanced passive immunity to viable Listeria. ConA stimulation of immune cells typically enhanced adoptive immunization 100- to 1000-fold. These ConA-stimulated immune lymphoid cells maintained their antigen specificity, since they provided no significant protection against Salmonella typhimurium. Although in vitro ConA stimulation resulted in markedly enhanced passive immunity to viable Listeria, the passive delayed-type hypersensitivity response to listerial antigens was not concurrently enhanced. Stimulation with certain preparations of listerial antigens also resulted in transfer of enhanced levels of adoptive immunity against viable Listeria. In cytotoxic assays utilizing monoclonal antibodies against the Lyt differentiation antigens, the ConA-stimulated immune T cells exhibited a different Lyt phenotype relative to nonstimulated immune T lymphocytes. Our results indicate that in vitro stimulation of Listeria-immune lymphoid cells leads to the differentiation as well as proliferation of antigen-specific T cells, suggesting that the in vivo development of immunity to Listeria monocytogenes is dependent not only on increased numbers of immune T lymphocytes, but also on the differentiation of these antigen specific T cells.