Higher cytolytic efficiency of an IgG 2α than of an IgG 1 monoclonal antibody reacting with the same (or spatially close) determinant on a human high-molecular-weight melanoma-associated antigen

Abstract

Serological and immunochemical assays showed that the monoclonal antibody (MoAb) 225.28S, an IgG 2α, and the MoAb 653.40S, an IgG 1, react with the same (or spatially close) antigenic determinant expressed on a set of molecules carrying a high-molecular-weight human melanoma-associated antigen. Neither monoclonal antibody mediates complement-dependent lysis of cultured melanoma cells, but both of them specifically mediate lysis of target cells in an antiglobulin cytotoxic assay and in an antibody-dependent cell-mediated cytotoxicity (ADCC) assay. In the latter two assays the IgG 2α displays a higher lytic activity than the IgG 1. The differential lytic activity of the IgG 2α and IgG 1 monoclonal antibodies was detected also when the sensitivity of the ADCC assay was increased either by boosting the cytolytic activity of the effector cells or by enhancing the susceptibility to lysis of target cells.