γδ T cell activation or anergy during infections: the role of nonpeptidic TCR ligands and HLA class I molecules

Vγ9Vδ2‐encoded T cell receptors (TCR) expressed by most human peripheral blood γδ T cells mediate the recognition of nonpeptidic phosphoantigens from various pathogens without any known requirement for HLA molecules. Functionally mature Vγ9Vδ2 T cells display a potent natural killer (NK) ‐like cytotoxic activity, share with NK cells the expression of inhibitory receptors for HLA class I molecules, and release a plethora of cytokines, most notably interferon‐γ and tumor necrosis factor α. Hence, through local activation, the early recruitment and stimulation of Vγ9Vδ2 T cells may promote efficient anti‐infectious immunity. However, a chronic overactivation of this T cell subset may result in immunopathology. The meeting held in St. Vincent, Val d'Aosta, Italy (symposium on γδ T cells in natural immunity to infections: a rationale for vaccine development organized by the World Foundation for AIDS Research and Prevention, the UNESCO, and the Italian National Research Council, December 2–4,1996) focused on the importance of γδ T cell activation and anergy for the pathogenesis of tuberculosis, malaria, and HIV infections. J. Leukoc. Biol. 62: 287–291; 1997.