A monoclonal antibody (8H3) that binds to rat T lineage cells and augments in vitro proliferative responses

A murine monoclonal antibody, designated 8113, recognizes a cell surface antigen expressed exclusively on rat T lineage cells. 8113 antibody immunoprecipitated 180-, 120-, and 90-kD components from rat thymorytes as well as splenic T cells under nonreducing conditions. 8113 antibody specifically inhibited the binding of thymocytes to fibronectin. Furthermore, binding of rat thymocytes to immobilized synthetic peptide GlyArg-Gly-Asp-Ser-Pro-Cys-BSA was inhibited by 8113 antibody as was GlyArg-Gly-Asp-Ser-Pro-Cys, but not by Gly-ArgAla-Asp-Ser-Pro-Lys or Gly-Arg-Gly-Glu-Ser-Pro. Crosslinking of SH3 antigen on double-negative thymocytes and adult thymocytes, as well as splenic T lymphocytes by 8113 antibody and F(ab')2 fragments of goat antibodies to mouse immunoglobulin, led to an increase in the concentration ofcytoplasmic free Ca²⁺ due to the release of Ca²⁺ from intracellular stores as well as the influx of Ca²⁺ from extracellular sources. Expression of interleukin 2 receptor and subsequently cell proliferation was observed upon incubation of thymocytes and splenic T cells with 8113 antibody. Furthermore, 8113 antibody induced the proliferation of double-negative thymocytes. These data collectively indicate that a cell surface antigen, 8113, is involved in not only cell adhesion but also involved in the expression of immature as well as mature thymocytes.