Immunization of cattle with a Leptospira borgpetersenii serovar hardjo-bovis vaccine results in the development of a recall response by WC1(+) gammadelta T cells and CD4(+) alphabeta T cells characterized by proliferation and interferon-gamma production. It was hypothesized that these two T cell subpopulations had largely redundant effector functions, principally differing in their requirements for activation. To test this, gene expression in cells proliferating to antigen were compared utilizing RT-PCR and bovine microarrays. Both T cell populations had similar transcript profiles for effector molecules, including IFN-gamma, FasL and granzyme B. In contrast, transcripts for costimulatory receptors and ligands were notably different following activation, as WC1(+) T cells expressed no or lower levels of transcripts for CD28 and CD40L, while CD4(+) T cells expressed substantial levels of both. However, both cell types had high levels of CTLA-4 transcript suggesting the cells may be regulated similarly following activation but differ in their need for and ability to provide costimulation. Microarray analyses to extend the number of genes examined revealed that while both subpopulations upregulated anti-apoptotic genes as well as those involved in cell activation and protein biosynthesis, overall there were limited differences between the two antigen-activated cell populations. Those genes that did differ were involved in cell signaling, protein production and intracellular protein trafficking. These results strengthen the hypothesis that these particular activated WC1(+) and CD4(+) T cells have overlapping effector functions and therefore may differ principally with regard to how they are recruited into immune responses.