Resistance of BALB/c mice to Leishmania major infection is associated with a decrease in the precursor frequency of...

BALB/c mice are highly susceptible to infection with the protozoan parasite Leishmania major and develop a chronic fatal disease. They can, however, be manipulated to resist disease and this has been shown to correlate with increased expression of IFN-gamma mRNA and the absence of IL-4 mRNA in the draining lymph nodes and spleens of these animals. Here we show that anti-IL-4 or anti-CD4 treatment of BALB/c mice resulted in a reduction in the size of the lesion and in the number of parasites in the draining lymph nodes compared with untreated mice. The precursor frequency of CD4+ T cells proliferating in response to Leishmania antigens in vitro in the treated animals was not significantly different from untreated animals. Analysis of the lymphokines secreted by the clonal progeny of these cells showed that the precursor frequency of IL-4 secreting clones was at least 10-fold lower in animals treated with either mAb. However, there was no reciprocal increase in the precursor frequencies of IFN-gamma secreting clones. Comparisons of the total number of precursors of specific CD4+ cells secreting IFN-gamma showed that anti-CD4-treated animals, which are resistant to disease, had considerably fewer for the first 6 weeks than untreated mice with chronic disease. Protection of BALB/c mice was therefore associated with a reduction in the numbers of precursors of cells secreting IL-4 without a concomitant increase in the number of precursors of IFN-gamma secreting cells.