Specificity and function of Qa-1 restricted gamma delta T cells

Peptide antigens for gamma/delta T cells

γδ T cells express adaptive antigen receptors encoded by rearranging genes. Their diversity is highest in the small region of TCR V-J junctions, especially in the δ chain, which should enable the γδ TCRs to distinguish differences in small epitopes. Indeed, recognition of small molecules, and of an epitope on a larger protein has been reported. Responses to small non-peptides known as phospho-antigens are multi-clonal yet limited to a single γδ T cell subset in humans and non-human primates. Responses to small peptides are multi-clonal or oligo-clonal, include more than one subset of γδ T cells, and occur in rodents and primates. However, less effort has been devoted to investigate the peptide responses. To settle the questions of whether peptides can be ligands for the γδ TCRs, and whether responses to small peptides might occur normally, peptide binding will have to be demonstrated, and natural peptide ligands identified.

Unmodified and phosphorylated prolactin and gamma delta T cell development and function

This manuscript discusses our studies to date concerning the effects of unmodified prolactin (PRL) and phosphorylated PRL on immune function. Most of the discussion refers to effects of changing the ratio of these two forms in maternal PRL on gamma delta T cell development in rat pups in utero, but limited experiments where adult animals have been directly treated are also discussed. The manuscript begins with some general background on gamma delta T cells and the different forms of PRL and then proceeds to a discussion of experimental findings. Results demonstrate that the ratio of unmodified to phosphorylated PRL during rat pregnancy is crucial to normal epidermal gamma delta T cell development in the pup thymus. Elevation of phosphorylated PRL in the dams, by administration of a recombinant molecular mimic of phosphorylated PRL, produces a defect in epidermalgamma delta T cell seeding and subsequent function in the offspring. In contrast, a functional defect is not seen for uterine gamma delta T cells in the offspring, a finding likely reflective of the continued availability of precursors to these cells after the fetal period. Preliminary results from treatment of the NZB/NZW mouse model of lupus with the two forms of PRL suggest opposing effects of unmodified and phosphorylated PRL on one measure of the disease.

Host immune response to intracellular bacteria: A role for MHC-linked class-Ib antigen-presenting molecules

MHC-linked class-Ib molecules are a subfamily of class-I molecules that display limited genetic polymorphism. At one time these molecules were considered to have an enigmatic function. However, recent studies have shown that MHC-linked class-Ib molecules can function as antigen presentation structures that bind bacteria-derived epitopes for recognition by CD8+ effector T cells. This role for class-Ib molecules has been demonstrated across broad classes of intracellular bacteria including Listeria moncytogenes, Salmonella typhimurium, and Mycobacterium tuberculosis. Additionally, evidence is emerging that MHC-linked class-Ib molecules also serve an integral role as recognition elements for NK cells as well as several TCR alpha/beta and TCR gamma/delta T-cell subsets. Thus, MHC-linked class-Ib molecules contribute to the host immune response by serving as antigen presentation molecules and recognition ligands in both the innate and adaptive immune response to infection. In this review, we will attempt to summarize the work that supports a role for MHC-linked class-Ib molecules in the host response to infection with intracellular bacteria.

Response of murine gamma delta T cells to the synthetic polypeptide poly-Glu50Tyr50

Random heterocopolymers of glutamic acid and tyrosine (pEY) evoke strong, genetically controlled immune responses in certain mouse strains. We found that pE50Y50 also stimulated polyclonal proliferation of normal gamma delta, but not alpha beta, T cells. Proliferation of gamma delta T cells did not require prior immunization with this Ag nor the presence of alpha beta T cells, but was enhanced by IL-2. The gamma delta T cell response proceeded in the absence of accessory cells, MHC class II, beta 2-microglobulin, or TAP-1, suggesting that Ag presentation by MHC class I/II molecules and peptide processing are not required. Among normal splenocytes, as with gamma delta T cell hybridomas, the response was strongest with V gamma 1+ gamma delta T cells, and in comparison with related polypeptides, pE50Y50 provided the strongest stimulus for these cells. TCR gene transfer into a TCR-deficient alpha beta T cell showed that besides the TCR, no other components unique to gamma delta T cells are needed. Furthermore, interactions between only the T cells and pE50Y50 were sufficient to bring about the response. Thus, pE50Y50 elicited a response distinct from those of T cells to processed/presented peptides or superantigens, consistent with a mechanism of Ig-like ligand recognition of gamma delta T cells. Direct stimulation by ligands resembling pE50Y50 may thus selectively evoke contributions of gamma delta T cells to the host response.