WC1+ γδ T cell memory population is induced by killed bacterial vaccine

Limited studies have addressed the ability of 76 T cells to become memory populations. We previously demonstrated that WC1.1(+) gamma delta T cells from ruminants vaccinated with killed Leptospira borgpetersenii proliferate and produce IFN-gamma in recall responses. Here we show that this response is dependent upon antigen-responsive CD4 T cells, at least across transwell membranes; this requirement cannot be replaced by IL-2. The response was also dependent upon in vivo priming, since gamma delta T cells from leptospira vaccine-naive animals did not respond to antigen even when co-cultured across membranes from antigen-responsive PBMC. 76 T cells were the major antigen-responding T cell population for the first 4 wks following vaccination and replicated more rapidly than CD4 T cells. Primed WC1(+) 76 T cells circulated as CD62L(hi)/CD45RO(int),/CD44(lo), characteristics of Tcm cells. When stimulated with antigen, they decreased CD62L, increased CD44 and CD25, and had no change in CD45RO expression. These changes paralleled those of the leptospira antigen-responsive CD4 T cells but differed from those of 76 T cells proliferating to mitogen stimulation. This system for in vivo 76 T cell priming is unique, since it relies on a killed antigen to induce memory and may be pertinent to designing vaccines that require type 1 pro-inflammatory cytokines.