Quantification of Leishmania-specific T cells in human American cutaneous leishmaniasis (Leishmania braziliensis braziliensis) by limiting dilution analysis.

Limiting dilution analysis was used to estimate the frequency of Leishmania-specific T cells from the peripheral blood of 18 human cases of American Cutaneous Leishmaniasis (ACL). Sixteen patients had localized cutaneous leishmaniasis (LCL) and two were recovered LCL patients. In 10 patients with active disease and in two with healed lesions the Leishmania-specific T cell frequencies ranged from 1/10(5) to 1/10(3). In six patients no proliferation was detected after 21 days of cell culture. This finding points to very low precursor frequencies in the peripheral blood of these patients. A significant correlation was found between the two groups with low or high Leishmania-specific T cell frequencies and the lymphoproliferative responses to leishmanial antigens. The majority of the blast-like Leishmania-specific T cells showed a helper/inducer (CD4) phenotype.