GAMMA-DELTA CELLS

Before TCR rearrangements, T cell progenitors are committed not only to the alphabeta and gammadelta T cell lineage but also to various subsets of both lineages. In the mouse, distinct gammadelta T cell subsets can develop in the fetal thymus, the adult thymus, or independently of a thymus, probably in intestinal epithelia. The two subsets that develop in the fetal thymus home to and are maintained throughout adult life in the skin and the mucosa of the uterus, vagina, and tongue. They are monospecific. This unusual restriction in receptor repertoires is the result of severe limitations in the generation of diversity in the fetal progenitors of these subsets and the thymic selection. After birth, one gammadelta T cell subset appears in the blood, spleen, and lymph nodes and one in the intestinal epithelia. The receptor repertoires of these subsets are characterized by the preferential usage of particular Vgamma gene segments and extensive junctional diversity. Several murine and human gammadelta T cell clones have been shown to recognize classical MHC class I and class II proteins or MHC class I-like proteins, and in very few cases the presented peptides are known. We suspect that the various murine gammadelta T cell subsets interact with different antigen presenting cells which utilize different antigen presenting proteins and reside in different tissues. The function of gammadelta T cells remains unknown. Preliminary results of experiments with gene knock out mice which lack either alphabeta T cells or gammadelta T cells or both suggest that gammadelta T cells do not function as helper cells in humoral immune responses but may complement alphabeta T cells in the defense against various microorganisms.