GAMMA-DELTA T-CELLS CAN RECOGNIZE NONCLASSICAL MHC IN THE ABSENCE OF CONVENTIONAL ANTIGENIC PEPTIDES

Although T cells expressing the gamma delta Ag receptor (gamma delta c ells) have been found in all organisms with lymphoid systems, little i s understood about their immunologic function. It is known that T cell s that express the alpha beta Ag receptor (alpha beta cells) fight inf ection by recognizing foreign Ag as peptide presented by MHC molecules ; however, it is not known how gamma delta cells recognize Ag. Charact erization of ligands of the gamma delta cell Ag receptor (TCR) could l ead to a better understanding of gamma delta cell function. We have ch aracterized the ligand of the G8 gamma delta cell; we find that G8 gam ma delta cells are stimulated by T22, a nonclassical class I MHC molec ule. To study the involvement of peptides in gamma delta cell recognit ion, T22 was expressed in cells deficient in peptide transporter funct ion and in Drosophila cells, which can express MHC molecules without a ssociated peptides. We find no evidence that G8 gamma delta cells reco gnize peptides bound to T22. These results suggest that some gamma del ta cells, unlike alpha beta cells, may not be restricted to recognitio n of peptide-MHC complexes.