Resistance to murine cutaneous leishmaniasis is mediated by TH1 cells, but disease-promoting CD4+ cells are different from TH2 cells.

A limiting dilution system has been used for quantitative analysis of antigen-reactive T cells producing interleukin (IL)2, IL4 and interferon (IFN)-gamma in the course of murine infection with Leishmania major. The precursor frequencies of CD4+ cells with the potential for production of IFN-gamma, which has been associated with TH1 cells, are much higher in resistant than in susceptible mice, whereas the reverse is found for CD4+ cells secreting IL4 which have been classified as TH2 cells. Our results allow a better understanding of the relative contribution of these cell types at various stages of disease and can be summarized as follows: (a) secretion of IL4 can be demonstrated in short-term clonal cultures of CD4+ cells from L. major-infected mice, (b) CD4+ cells releasing IL2, suggested to be a characteristic of TH1 cells that predominate in resistant mice, can also be detected in susceptible mice at any time of infection, (c) both IL2 and IL4 are released by the progeny of individual T cells from susceptible mice and (d) the kinetics of precursor frequencies in genetically susceptible mice protected against the disease by prophylactic treatment are different from those of congenitally resistant mice, thus indicating that the development of lymphokine-producing T cells and the establishment of protective immunity may be regulated differently in those mice. The data suggest that resistance to disease is correlated with the presence of IFN-gamma-producing TH1 cells, while susceptibility is associated with CD4+ cells that do not segregate into the TH1 or TH2 subset but display an overlapping pattern of lymphokine activities.