Identification and characterization of T cell-stimulating antigens from Leishmania by CD4 T cell expression cloning

Abstract

Persistent immunity against Leishmania infections in humans is mediated predominantly by CD4+ T cells of the Th1 phenotype. Herein we report the expression cloning of eight Leishmania Ags using parasite-specific T cell lines derived from an immune donor. The Ags identified by this technique include the flagellar proteins α- and β-tubulin, histone H2b, ribosomal protein S4, malate dehydrogenase, and elongation factor 2, as well as two novel parasite proteins. None of these proteins have been previously reported as T cell-stimulating Ags from Leishmania. β-tubulin-specific T cell clones generated against Leishmania major amastigotes responded to Leishmania-infected macrophages and dendritic cells. IFN-γ enzyme-linked immunospot analysis demonstrated the presence of T cells specific for several of these Ags in PBMC from self-healing cutaneous leishmaniasis patients infected with either Leishmania tropica or L. major. The responses elicited by Leishmania histone H2b were particularly striking in terms of frequency of histone-specific T cells in PBMC (1 T cell of 6000 PBMC) as well as the percentage of responding donors (86%, 6 of 7). Ags identified by T cells from immune donors might constitute potential vaccine candidates for leishmaniasis.