ABSTRACT
CD4+ T cells mediating both delayed-type hypersensitivity (DTH) and acquired cellular resistance (ACR) were generated in mice after immunization with viable Listeria monocytogenes. In contrast, CD4+ T cells from mice immunized with killed L. monocytogenes in complete Freund's adjuvant were capable of mediating only DTH but not ACR. To determine the functional difference between T cells mediating DTH and T cells mediating ACR, we examined two different populations of T cells for profiles of lymphokine production after stimulation with a specific antigen in vitro. The production of interleukin-2 (IL-2) and IL-3 but not IL-4 was observed in both T cells mediating only DTH and those mediating DTH and ACR. In this respect, both types of T cells could be categorized into the TH1 population, and they produced macrophage chemotactic factor equally well. However, the production of gamma interferon (IFN-gamma) was observed only in T cells capable of mediating both DTH and ACR. This result was confirmed not only by an enzyme immunoassay specific for murine IFN-gamma but also by Northern (RNA) analysis for the detection of IFN-gamma mRNA. These results suggested that the TH1 population may be subdivided further into two distinct subsets and that the ineffectiveness of the killed bacterial vaccine may be partly explained by the dissociated development of T cell function.
