Analysis of the human T cell responsiveness to purified antigens of Leishmania: lipophosphoglycan (LPG) and glycoprotein 63 (gp 63).

The responsiveness of peripheral blood lymphocytes from 15 cutaneous leishmaniasis patients and five healthy volunteers to purified surface antigens of Leishmania was studied. The following purified antigens were independently used as stimuli for lymphocyte proliferation in vitro: lipophosphoglycan of L. braziliensis, (Lb-LPG), lipophosphoglycan of L. mexicana (Lm-LPG), glycoprotein 63 of L. braziliensis (Lb-gp 63) and glycoprotein 63 of L. mexicana (Lm-gp 63). Among six patients tested with Lb-gp 63 and Lm-gp 63, two borderline responses and two positive responses were observed, respectively, all the others being negative. Lb-LPG and Lm-LPG induced positive responses in all patients tested (11 with Lb-LPG and five with Lm-LPG). A positive dose-response correlation was observed in the responses of the patients to both Lb-LPG and Lm-LPG. Significant differences (P less than 0.01) were found between the two groups (patients and healthy subjects) with regard to the responses to Lb-LPG. The proliferating cells after stimulation with Lb-LPG were shown to belong to the CD4+ T cell subset by flow cytometry. However, the following evidence suggests that the T cell responses were not induced by LPG itself but rather by protein contaminants in the LPG preparations: a highly purified Lb-LPG batch that had undergone additional purification induced positive responses in cells from only three out of six patients and a proteinase K-treated Lb-LPG batch did not stimulate any positive response among the same six patients.