The persistence of parasites in mice cured of Leishmania mexicana infection was investigated by using immunosuppressive drugs and checking for the reappearance of lesions. BALB/c (susceptible) and C57BL/6 (partially resistant) mice infected with 10(4) amastigotes were treated with either thermotherapy or meglumine antimonate and subsequently immunosuppressed with either cyclophosphamide or hydrocortisone. Immunosuppression by either method caused lesions to reappear in both strains of mice regardless of the treatment used to produce clinical cure. In both strains of mice the proportion of animals developing lesions after immunosuppression was greater in the mice cured by the drug. The relevance of these findings to human therapy is discussed.

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.

This immunocytochemical study evaluates the presence of IgG1-4, IgA and IgE immunoglobulins in active lesions of 25 localized cutaneous leishmaniasis patients from three bioclimatic areas (Awa, Afa and Bsha) in Mérida State, Venezuela. All immunoglobulin isotypes except IgE were detected, with variable intensity, in one or more of the epidermal or dermal components of skin lesions. IgG1 and IgG2 were detected significantly more frequently than IgG3, IgG4 and IgA. The ranking of the isotypes according to frequency of detection was the same in all areas: IgG1 = IgG2 > IgG3 = IgG4 = IgA, but considered as whole, all isotypes were detected significantly more frequently in patients from the Awa area than in those from the Bsha area. The predominant expression of isotypes IgG1 and IgG2 suggests a preferential Th1 like immune response. Anti-Leishmania immunoserum stained only parasites and their debris, suggesting that most of the immunostaining was nonspecific.

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