Involvement of Different CD4+T Cell Subsets Producing Granzyme B in the Immune Response toLeishmania majorAntigens

Abstract

The nature of effector cells and the potential immunogenicity ofLeishmania majorexcreted/secreted proteins (LmES) were evaluated using peripheral blood mononuclear cells (PBMCs) from healed zoonotic cutaneous leishmaniasis individuals (HZCL) and healthy controls (HC). First, we found that PBMCs from HZCL individuals proliferate and produce high levels of IFN-γand granzyme B (GrB), used as a marker of activated cytotoxic T cells, in response to the parasite antigens. IFN-γis produced by CD4+T cells, but unexpectedly GrB is also produced by CD4+T cells in response to stimulation withLmES, which were found to be as effective as solubleLeishmaniaantigens to induce proliferation and cytokine production by PBMCs from immune individuals. To address the question of regulatory T cell (Tregs) involvement, the frequency of circulating Tregs was assessed and found to be higher in HZCL individuals compared to that of HC. Furthermore, both CD4+CD25+and CD4+CD25−T cells, purified from HZCL individuals, produced IFN-γand GrB when stimulated withLmES. Additional experiments showed thatCD4+CD25+CD127dim/-Tregs were involved in GrB production. Collectively, our data indicate thatLmES are immunogenic in humans and emphasize the involvement of CD4+T cells including activated and regulatory T cells in the immune response against parasite antigens.