Two subsets of human T lymphocytes expressing γ/δ antigen receptor are identifiable by monoclonal antibodies directed to two distinct molecular forms of the receptor

Two mAbs directed to the TCR-γ/δ were analyzed for their pattern of reactivity with CD3⁺WT31^- cell populations or clones. In normal individuals, the BB3 mAb reacted with ~2/3 of peripheral blood CD3⁺WT31^- lymphocytes, whereas δ-TCS-1 stained ~1/3 of such cells. In addition, the sum of the percentages of BB3⁺ and δ-TCS-1⁺ cells approximated the percentages of peripheral blood CD3⁺WT31^- lymphocytes in seven normal donors tested. Also, in peripheral blood-derived polyclonal CD3⁺WT31^- populations, cultured in IL-2, cells reacting with one or another mAb accounted for the whole cell population. On the other hand, only δ-TCS-1-reactive cells, but not BB3⁺ cells, could be detected in unfracionated as well as in CD4^-8^- thymocyte populations. Analysis of peripheral blood-derived CD3⁺WT31^- clones showed that 70% of 72 clones analyzed reacted with BB3 mAb, but not with δ-TCS-1, mAb. On the other hand, δ-TCS-1 mAb stained the remaining BB³- clones. Five clones expressing medium-low amounts of CDS antigen were BB3^- δ-TCS-1⁺. Both types of clones lysed the Fcγ receptor-bearing P815 target cell in the presence of anti-CD3 mAb (but not of mAb directed against HLA-DR, CD7 molecules, or TCR-α/β). In this cytolytic assay, BB3 mAb induced target cell lysis only by BB3⁺ clones, whereas δ-TCS-1 mAb was effective only with δ-TCS-1⁺ clones. The CD3-associated surface molecules expressed by BB3⁺ or δ-TCS-1⁺ clones were analyzed after cell surface iodination and immunoprecipitation with the corresponding anti-TCR mAb or with anti-CD3 mAb (in digitonin-containing buffer). In SDS-PAGE, molecules immunoprecipitated from 13 BB3⁺ clones displayed, under nonreducing conditions, a molecular weight of 80 kD (in some cases, a minor 38-kD band could be detected). Under reducing conditions, two major components of 44 and 41 kD (and a minor component of 38 kD) were detected. On the other hand, TCR molecules immunoprecipitated from 11 different δ-TCS-1⁺ clones appeared as a diffuse band of 41-44 kD, both under reducing and nonreducing conditions (under non reducing condition, an additional 38-kD band was present). Therefore, BB3⁺ cells express a disulphide-linked form of TCR-γ/δ whereas δ-TCS-1⁺ cells express a non-disulphide-linked form. TCR molecules immunoprecipitated from BB3⁺ clones and analyzed by two-dimensional electrophoresis were represented, under reducing conditions, by two bands of ~38 and 41 kD displaying a similar pI and a third more basic 44 kD band. Under nonreducing conditions, BB3-reactive molecules were represented by a single 80-kD band (displaying an intermediate pI with respect to that of the reduced chains). TCR molecules immunoprecipitated from δ-TCS-1⁺ clones were represented, in both reducing and nonreducing conditions, by a diffuse 41-44-kD band (in which, however, two distinct components could be detected). In addition, a poorly labeled band of lower molecular weight was present. All these molecules displayed a similar pI and a high charge heterogeneity. Since similar molecular patterns were consistently detected among all BB3⁺ as well as among all δ-TCS-1⁺ clones analyzed, we conclude that BB3 and δ-TCS-1 mAbs identify two distinct molecular forms of TCR-γ/δ expressed by two different peripheral blood T cell subsets.