T Cell Subsets and the Activation of γδ T Cells

Abstract

The T cell subsets in chicken are, in most respects, similar to those in mouse or human (Cooper et al. 1991; Arstila et al. 1994a). As in mammals, mature αβ T cells express either CD4 or CD8. The CD4⁺ αβ T cells function as helper T cells, recognizing antigens in a MHC class II-restricted way and producing cytokines upon activation (Chan et al. 1988). The αβ T cells expressing CD8 are poor producers of cytokines but exhibit T cell receptor (TCR)-dependent cytotoxicity. The αβ T cells can also be divided into two subsets on the basis of the Vβ gene segment utilized (Tjoelker et al. 1990; Lahti et al. 1991). There are two families of V genes in the TCR β locus, both containing several gene segments, and both subsets can be detected by a monoclonal antibody (Chen et al. 1988; Cihak et al. 1988; Char et al. 1990). Some studies have indicated differences between cells expressing Vβ1 or Vβ2 gene segments. For example, Vβ1⁺ cells are numerous in the intestinal epithelium and can support IgA responses. In contrast, Vβ2⁺ cells are rare in the intestinal epithelium and, either because of this or because of an unknown functional characteristic, are unable to provide help for IgA responses (Cihak et al. 1991).