IgM-induced cell-mediated cytotoxicity with antibody and effector cells of human origin.

In vitro lysis of antibody-sensitized target cells by lymphocytes has been demonstrated in a number of systems (1–6). IgG has been implicated as the major antibody class involved in antibody-dependent cell-mediated cytotoxicity (ADCC)3 with human effector cells (1) and IgM had not been previously reported to be active with one recent exception (3). In contrast, independent investigations in three antigenic systems have demonstrated murine IgM to be active in ADCC with homologous effector cells (4–6). It should be pointed out that Wåhlin et al. (3) reported IgM- and IgG-induced cytotoxicity by using a sensitive plaque assay with rabbit antibody and human effector cells.4 Most investigations with human effector cells have been with heterologous antibodies for sensitization of the target cells. In order to evaluate the ability of human IgM to induce ADCC in an homologous system, we have used human heterophile antibody, which is entirely IgM (7) to sensitize 51Cr-labeled sheep erythrocytes (SRBC).