Structural analysis of gamma delta TCR using a novel set of TCR gamma and delta chain-specific monoclonal antibodies generated against soluble gamma delta TCR. Evidence for a specific conformation adopted by the J delta 2 region and for a V delta 1 polymorphism

Identification of guinea pig gammadelta T cells and characterization during pulmonary tuberculosis

Guinea pigs are an alternative small animal model for many disease studies. Here we describe a pan-gammadelta monoclonal antibody (anti-TCRdelta1) specific for the constant region of human T cell receptor delta chains that cross-reacts with a subpopulation of guinea pig (Cavia porcellus) lymphocytes. The phenotype and distribution of this subpopulation is consistent with the guinea pig gammadelta T cell subset. FACS analysis of fresh PBMC and splenocytes from naïve guinea pigs revealed the presence of a subset of cells that stained with the anti-TCRdelta1 mAb. The relative percentage of anti-TCRdelta1 positive cells in PBMC and tissues is similar to that described for gammadelta T cells in other species. Immunohistochemistry of tissues also revealed a distribution of anti-TCRdelta1 positive cells consistent with gammadelta T cells. These data are further supported by staining of a polyclonal guinea pig T cell line that became progressively CD4 and CD8 negative in long-term culture. Analysis of PBMC from guinea pigs following aerosol infection with virulent Mycobacterium tuberculosis revealed no apparent changes in the steady-state percentage of blood gammadelta+ T cells. Taken together, these data suggest that the anti-TCRdelta1 antibody recognizes the gammadelta T cell subset in guinea pigs. This reagent may be useful for examining gammadelta T cells in various disease models where the guinea pig is a more desirable model for study.

Allelic exclusion at the TCR delta locus and commitment to gamma delta lineage: different modalities apply to distinct human gamma delta subsets

Expression of a beta-chain, as a pre-TCR, in T cell precursors prevents further rearrangements on the alternate beta allele through a strict allelic exclusion process and enables precursors to undergo differentiation. However, whether allelic exclusion applies to the TCR delta locus is unknown and the role of the gamma delta TCR in gamma delta lineage commitment is still unclear. Through the analysis of the rearrangement status of the TCR gamma, delta, and beta loci in human gamma delta T cell clones, expressing either the TCR V delta 1 or V delta 2 variable regions, we show that the rate of partial rearrangements at the delta locus is consistent with an allelic exclusion process. The overrepresentation of clones with two functional TCR gamma chains indicates that a gamma delta TCR selection process is required for the commitment of T cell precursors to the gamma delta lineage. Finally, while complete TCR beta rearrangements were observed in several V delta 2 T cell clones, these were seldom found in V delta 1 cells. This suggests a competitive alpha beta/gamma delta lineage commitment in the former subset and a precommitment to the gamma delta lineage in the latter. We propose that these distinct behaviors are related to the developmental stage at which rearrangements occur, as suggested by the patterns of accessibility to recombination sites that characterize the V delta 1 and V delta 2 subsets.

Conservation of nonpeptide antigen recognition by rhesus monkey V gamma 2V delta 2 T cells

We have previously found that monkey Vgamma2Vdelta2(+) T cells mount adaptive immune responses in response to Mycobacterium bovis bacillus Calmette-Guérin infections. We have now analyzed rhesus monkey gammadelta T cell responses to nonpeptide Ags and superantigens. Like human Vgamma2Vdelta2(+) T cells, rhesus monkey gammadelta T cells are stimulated when exposed to prenyl pyrophosphate, bisphosphonate, and alkylamine Ags. Responsiveness was limited to gammadelta T cells expressing Vgamma2Vdelta2 TCRs. Rhesus monkey Vgamma2Vdelta2(+) T cells also responded to the superantigen, staphyloccocal enterotoxin A. Sequencing of the rhesus monkey Vgamma2Vdelta2 TCR revealed a strong sequence homology to human Vgamma2Vdelta2 TCR that preserves important sequence motifs. Moreover, chimeric TCRs that pair human Vgamma2 with monkey Vdelta2 and monkey Vgamma2 with human Vdelta2 retain reactivity to nonpeptide Ags and B cell lymphomas. A molecular model of the rhesus monkey Vgamma2Vdelta2 TCR has a basic region in the complementarity-determining region 3 binding groove that is similar to that seen in the human Vgamma2Vdelta2 TCR and preserves the topology of the complementarity-determining region loops. Thus, recognition of nonpeptide prenyl pyrophosphate, bisphosphonate, and alkylamine Ags is conserved in primates suggesting that primates can provide an animal model for human gammadelta T cell Ag responses.

Implication of gammadelta T cells in the human immune response to cytomegalovirus

In normal individuals, gammadelta T cells account for less than 6% of total peripheral T lymphocytes and mainly express T-cell receptor (TCR) Vdelta2-Vgamma9 chains. We have previously observed a dramatic expansion of gammadelta T cells in the peripheral blood of renal allograft recipients only when they developed cytomegalovirus (CMV) infection. This increase was long lasting (more than 1 year), was associated with an activation of gammadelta T cells, and concerned only Vdelta1 or Vdelta3 T-cell subpopulations. Analysis of gammadelta TCR junctional diversity revealed that CMV infection in these patients was accompanied by (a) a marked restriction of CDR3 size distribution in Vdelta3 and, to a lesser extent, in Vdelta1 chains; and (b) a selective expansion of Vdelta1 cells bearing recurrent junctional amino acid motifs. These features are highly suggestive of an in vivo antigen-driven selection of gammadelta T-cell subsets during the course of CMV infection. Furthermore, Vdelta1 and Vdelta3 T cells from CMV-infected kidney recipients were able to proliferate in vitro in the presence of free CMV or CMV-infected fibroblast lysates but not uninfected or other herpes virus-infected fibroblast lysates. This in vitro expansion was inhibited by anti-gammadelta TCR mAb's. These findings suggest that a population of gammadelta T cells might play an important role in the immune response of immunosuppressed patients to CMV infection.

An enlarged subpopulation of T lymphocytes bearing two distinct gammadelta TCR in an HIV-positive patient

Although T cell clone monospecificity is ensured by several allelic exclusion processes operating at either the genotypic or phenotypic levels, clones expressing two distinct alphabeta or gammadelta TCR have been described in several instances. Thus far, the origin of dual TCR-expressing cells and the homeostatic mechanisms controlling the size of this subset in the periphery remain poorly understood. In the course of a phenotypic analysis of gammadelta T cells in HIV-infected patients, we detected the presence of a T cell subset stained by both Vdelta2- and Vdelta3-specific mAb, which represented a large fraction (up to 16.5%) of gammadelta peripheral blood lymphocytes (PBL) in one HIV patient. The presence of two distinct functional delta chains on these cells was confirmed by phenotypic and molecular analysis of TCR transcripts expressed by Vdelta2+Vdelta3+ T cell clones derived from this patient. For 18 months, the absolute number of these cells varied similarly to the other PBL subsets, before becoming undetectable in blood samples. Moreover, most of these cells expressed CD8 receptors, which are classically found on activated, but not resting, gammadelta T cells. Taken together, these data suggest that dual TCR-expressing T cells are subjected to peripheral expansions and contractions presumably following antigen recognition, which would argue against a systematic counter-selection of these cells during peripheral antigen-driven responses.