The enigmatic specificity of gamma delta T cells

Interferon-gamma production by specific lung lymphocyte phenotypes in silicosis in mice

We recently described overproduction of interferon (IFN)-gamma by lung lymphocytes in mice with silicosis (11% of cells in air-control versus 19% of cells from silica-exposed mice; Davis and colleagues, Am. J. Respir. Cell Mol. Biol. 1999;20:813-824). We hypothesized that the increased IFN-gamma production might be due to selective enrichment of one lymphocyte phenotype. To test this hypothesis, small mononuclear cells from lung digest preparations of mice exposed 4 mo previously to cristobalite silica (70 mg/m(3), 12 d, 5 h/d) or to sham-air were stained for intracellular cytokines and surface antigen phenotypes, and examined by flow cytometry. Air-sham mouse lung digests included CD4(+) (16%) and CD8(+) (6%) T cells, gammadelta T-cell antigen receptor (TCR)(+) CD4(-)CD8(-) T cells (3%), natural killer (NK) cells (15%), B cells (6%), and macrophages (12%). The total number of lung lymphocytes was increased 1.7-fold in silicosis, but the phenotype frequencies did not change significantly. In the control lungs IFN-gamma was produced by three major phenotypes of lymphocytes: 5% of CD4(+) T cells, 5% of gammadelta-TCR(+) CD4(-)CD8(-) T cells, and 2% of NK cells. The percentage of each type producing IFN-gamma was increased 2- to 3-fold in silicosis. When multiplied by cell number, the increased percentages yielded a 3- to 5-fold increase in the total number of each IFN- gamma-producing phenotype in the lung. Our results demonstrate no selective phenotype enrichment but upregulated IFN-gamma production by at least three lymphocyte phenotypes. IFN-gamma may be an important signal driving lymphocyte differentiation and macrophage activation in silicosis.

TCR diversity in gammadeltaTCR+ hybridomas derived from mice given portal vein donor-specific pre-immunization and skin allografts

Portal venous (p.v.) immunization with multiple minor histoincompatible cells leads to antigen-specific increased skin allograft survival. GammadeltaTCR+ hybridoma cells, prepared from mesenteric lymphocytes of p.v. immunized animals, can adoptively transfer this increased graft survival to naive animals. We have analyzed VgammaVdelta gene usage, and TCR gamma-chain junctional diversity in gammadeltaTCR+ hybridomas from mice immunized with different antigen combinations by p.v. or conventional lateral tail vein (i.v.) immunization. Following p.v. immunization two independent sets of hybridoma cells were derived, one expressing a common gamma-chain junctional sequence which was also found in > 85% of the hybridomas derived following i.v. immunization, while the other set showed remarkable gamma-chain junctional sequence diversity. The diversity seen in these latter hybridomas was associated with the antigen specificity of the hybridoma cells. Cells expressing these 'unique' TCR junctional sequences were stimulated to produce cytokines both by hsp and by minor-histocompatibility-specific irradiated peritoneal cells. Cells expressing TCR with a common gamma-chain junctional sequence were stimulated to cytokine production by MHC-matched but minor-histocompatibility mismatched (as well as matched) peritoneal cells, but not by hsp. We suggest that p.v. immunization results in stimulation of both antigen-specific and non-specific regulatory gammadeltaTCR+ cells, which can be distinguished by gamma-chain TCR sequence diversity.