Expansion of γδ⁺ T cells in BALB/c mice infected with Leishmania major is dependent upon Th2-type CD4⁺ T cells

T cells belong to either the αβ⁺ or γδ⁺ lineage as defined by their antigen receptor. Although both T-cell subsets have been shown to be involved in the immune response to the parasite Leishmania major, very little is known about possible interactions between these two populations. In this study, using a mouse model of infection with L. major, we showed that expansion of a subset of γδ⁺ T cells in vivo is dependent upon the presence of αβ⁺ CD4⁺ T cells. Moreover, this effect appears to be mediated via the secretion of lymphokines by CD4⁺ cells with a T-helper 2 (Th2) functional phenotype. Results showing that activation of Th2-type cells in mice treated with anti- immunoglobulin D antibodies or infected with Nippostrongylus brasiliensis also results in γδ⁺ T-cell expansion suggest that this effect of the Th2- type CD4⁺ cells is a general phenomenon not restricted to infection with L. major.