Two monoclonal anti‐CD3 antibodies can induce different events in human T lymphocyte activation

Abstract

Two monoclonal antibodies, WT32 and CLB-T3/4.2a, directed against the CD3 complex were used to study the mechanism of activation of human peripheral T lymphocytes. WT32, a mouse monoclonal IgG_2a antibody with a low avidity (≫ OKT3) for the CD3 complex, effectively induces mitogenesis of purified T lymphocytes when used in the 1 ng-10 μg range in the presence of monocytes or recombinant interleukin 2 (IL 2). In contrast, CLB-T_3/4.2a, a mouse monoclonal antibody of the same isotype with a high avidity (< OKT3) for the CD3 complex, induces IL 2 receptor expression and IL 2 responsiveness only at very low concentrations (< 5 ng/ml), yet in the presence of monocytes this antibody induces proliferation within a similar dose range as WT32. Apparently, in the absence of accessory cells which can cross-link the antibody CD3 complexes, the binding properties (avidity) of an antibody and thereby the number of receptors that are occupied are important parameters for induction of IL 2 responsiveness. Furthermore, we show that Ca²⁺ mobilization only occurs when the cells are stimulated by saturating amounts of antibody, so that, when the conditions are optimal for the induction of IL 2 responsiveness, no Ca²⁺ mobilization will be detected.