TCR-gamma delta cells, a T cell subset present in the epithelial and lymphoid tissues, have been implicated in viral and bacterial infections. We have identified a TCR-gamma delta clone (TgI4.4) that, unlike TCR-alpha beta cells, recognizes a herpes simplex virus type 1 transmembrane glycoprotein, gI, in an MHC class I- and class II-independent fashion. The TCR of TgI4.4 is composed of rearranged V delta 8 (a V alpha 2 family member) and V gamma 1.2 variable genes, a heterodimeric pair not previously described. Furthermore, anti-V alpha 2 mAbs are sufficient to block recognition of the gI ligand. Strikingly, anti-gI Abs also are capable of blocking recognition, a phenomena that is very rare in TCR-alpha beta Ag recognition. Therefore, to dissect the mechanism involved in this unique form of Ag recognition, we constructed a mutant of gI, gIt, that lacks cell surface expression upon transfection into APCs. This form of gI was not sufficient for Ag presentation. In contrast, wild-type gI expressed in the Ag-processing mutant cell, RMA-S, is recognized by TgI4.4, suggesting that gI presentation occurs independently of classical Ag-processing pathways. In fact, through the use of a soluble recombinant gI molecule, gI-Ig, we show that TgI4.4 can recognize whole, unprocessed gI protein in the absence of any APCs. These results suggest that there exist alternate and novel forms of TCR Ag recognition, and that the TCR-gamma delta clone, TgI4.4, may represent a novel T cell subset that, during pathogenic challenge, may respond directly to Ags on the surfaces of bacteria and viruses.

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