A large proportion of bovine T cells express the γδ T cell receptor and show a distinct tissue distribution and surface phenotype

The numbers, phenotype, and tissue distribution of γδ T cells in cattle were studied using two monoclonal antibodies (mAbs) which react with the bovine γδ T cell receptor (TCR). Both mAbs stained 20-40% of T cells in peripheral blood, and immunoprecipitated molecules of 44 and 36 kd (reduced) and 70-80 kd (non-reduced). In cattle the majority of circulating γδ T cells showed a distinct surface phenotype; they expressed T19, a 215 kd molecule described in sheep and cattle which marks only γδ T cells. Bovine γδ T cells were also CD2^-, CD4^-, and mostly CD8^-, and falled to express CD6, a molecule possibly involved in T cell activation. The distribution of γδ T cells in cattle lymphoid tissues differed markedly from that in humans, in that bovine γδ T cells were concentrated around lymph node trabeculae and were usually sparse or absent from the B cell and T cell domains of lymph nodes. Like most other species studied, γδ T cells in cattle were localized to epithelial surfaces, particularly within the skin and intestine, indicating that it was at these sites where γδ T cells functioned. Our results provide further evidence for the unusual localization, recirculation pattern, and phenotype of γδ T cells, and also show that some features of γδ T cells can differ quite markedly from species to species.