Human T cell antigens involved in cytotoxicity against allogeneic or autologous chemically modified targets. Association of the Leu 2a/T8 antigen with effector‐target cell binding and of the T3/Leu 4 antigen with triggering

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Abstract
Monoclonal antibodies (mAb) recognizing human T cell differentiation antigens were employed to analyze the role of these antigens on T cell‐mediated cytotoxicity against autologous 2,4,6‐trinitrophenyl (TNP)‐modified targets. The OKT3/anti‐Leu 4 and anti‐Leu 2a/OKT8* mAb inhibited T cell‐mediated cytotoxicity against autologous or unrelated TNP‐modified targets, in the absence of complement and at the effector cell level. These cytotoxic effector cells were T3+, T8+, T11+, T4−. To analyze the role of the T3/Leu 4 and Leu 2a/T8 T cell differentiation antigens in the cytolytic process, we investigated the stages of this process that were inhibited by the OKT3/anti‐Leu 4 and anti‐Leu 2a/OKT8* mAb. Using: (a) visual adhesions, and (b) a single cell cytotoxicity assay in agarose, we observed that the OKT3 and anti‐Leu 4 mAb did not inhibit binding of effector cells to allogeneic targets or to autologous E rosette‐negative TNP‐modified targets, although they significantly inhibited both the proportions of target cells in conjugates that were lysed, and the 51Cr release. In contrast, the anti‐Leu 2a and OKT8* mAb blocked cytotoxicity by inhibiting binding of effector cells to the allogeneic or to autologous chemically modified targets. To further analyze the stages of the cytolytic process (adhesion; programming for lysis or lethal hit; and cytotoxic cell‐independent lysis) that were inhibited by these mAb, we employed the detachment and dispersion method. This method is based on the differential temperature requirements of adhesion (which occurred both at 37 °C or 20 °C) and of programming for lysis (which occurred at 37 °C but not at 20 °C). Operational adhesions were determined by the 51Cr‐release assay after dispersion of effector and target cells in a 10% solution of dextran (mol. wt. 500000). Programming for lysis was determined by the 51Cr‐release assay after detachment of effector‐target cell conjugates with 10 mM EDTA and dispersion in 10% dextran solution. Using this method we determined that mAb recognizing the Leu 2a/T8 antigen blocked cytotoxicity by inhibiting adhesion and binding of effector cells to target cells. These antibodies do not affect post‐adhesion stages of the cytolytic process. In contrast, the OKT3 and anti‐Leu 4 mAb inhibit a post‐adhesion step of the cytolytic process, that occurs before irreversible events of the programming for lysis stage have taken place.These results and other properties (lymphokine production, mitogenic properties) of the OKT3/anti‐Leu 4 mAb suggest that the T3/Leu 4 antigen may be associated with triggering of lethal hit (and triggering of T cell functions in general) and signal transfer or transduction. In contrast, the Leu 2a/T8 antigen appears to be involved in binding of effector to target cells and may contribute to the affinity of the effector cells for the target.

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