Inability of EDTA to prevent damage mediated by cytolytic T-lymphocytes.

To analyze the nature of the target cell determinants recognized and bound by killer lymphocytes during lymphocyte-mediated cytolysis (LMC), the specific binding of serologically active tumor cell membrane fractions to cytotoxic T lymphocytes has been investigated. Particulate membrane fractions and soluble antigen preparations (extracted by papain or 3 M KCl) from tumor target cells were tested for their ability to inhibit the destruction of intact ⁵¹Cr-labeled target cells by killer lymphocytes in vitro. The effect of papain-solubilized tumor cell antigen on the binding of killer lymphocytes to tumor cell monolayers was also evaluated. Direct assays to determine the extent of binding of unlabeled or radioiodinated soluble antigen (extracted by papain or deoxycholate) to cytotoxic lymphocytes were carried out. In marked contrast to their serological activity, all of these particulate and soluble preparations failed to inhibit LMC or bind to killer lymphocytes in an immunologically specific way. It is suggested that killer lymphocytes recognize and bind to an antigenic complex whose organization is dependent upon the integrity of the target cell membrane.