The correlation between delayed hypersensitivity, lymphocyte activation and protective immunity in experimental murine leishmaniasis.

The growth of Leishmania major and Leishmania mexicana lesions and the concomitant development of delayed-type hypersensitivity (DTH) to homologous or heterologous soluble antigen was studied in BALB/c and CBA/Ca mice. Although CBA/Ca mice are highly susceptible to L. mexicana, developing non-healing lesions, they are resistant to L. major; while BALB/c mice develop non-healing lesions when infected with either species. The development of resistance was associated with the acquisition of DTH which peaked at 48 h (L. major infected CBA/Ca mice). Non healing lesions were associated with either negative DTH (L. major infected BALB/c mice) or DTH that peaked at 24 h but had significantly subsided by 48 h (L. mexicana infected CBA/Ca and BALB/c mice). The latter response was associated with basophilic infiltration of the skin test site. Pre-irradiating (600 rad) CBA/Ca and BALB/c mice induced resistance against L. mexicana and L. major respectively in conjunction with the appearance of 48 h DTH to the homologous antigen. There was clear dissociation in the skin reactivity produced by the heterologous antigen. Thus L. major-derived antigen failed to produce DTH in L. mexicana infected mice of either strain. L. mexicana-derived antigen on the other hand produced a quicker response and of greater magnitude than the homologous antigen in L. major infected CBA/Ca mice. This correlated well with the strong cross-immunity induced by L. major in these mice to L. mexicana infection.