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

Abstract

Summary 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.