Mechanisms ofAntibody-dependent Cellular Cytotoxicity

cyte (HRBC) targets in suspension cultures indicative of abnormal intracellular postphagocytic killing. However, when phagocytosis was prevented by using a monolayer of antibody-coated HRBC targets, CGD monocytes, neutrophils, and lymphocytes exhibited normal ADCC activity. Similarly, antibody-coated HRBC targets in suspension could be lysed normally by CGD effector cells when phagocytosis was inhibited by the addition of in vitro colchicine. Extracellular lysis of autologous antibody-coated lymphoid cell targets in suspension was mediated normally by CGD effector cells. Thus, standard ADCC against HRBC targets in suspension is predominantly indicative of postphagocytic killing and, as such, is dependent upon a normal postphagocytic respiratory burst of oxidative metabolism which is deficient in CGD neutrophils and monocytes. Extracellular killing of sensitized targets does not appear to be dependent upon the generation of hydrogen peroxide (H202) and/or superoxide (O°) and is normal in CGD neutrophils and monocytes. Hence, by employing CGD leukocytes as investigative probes in ADCC, fundamental mechanisms of intracellular vs. extracellular expression of cytotoxicity have been delineated. Received for publication 6 July 1979 and in revised form 4 September 1979. INTRODUCTION Antibody-dependent cellular cytotoxicity (ADCC)' involves the destruction of sensitized target cells through the interaction of target-specific antisera with effector cell surface Fc receptors (1). Depending on the type of assay, antibody, target cells, and effector cells employed, the distinct ADCC activities of subpopulations of human leukocytes may vary. Thus, ADCC activity has been reported for neutrophils, monocytes, and Fc receptor-bearing (FcR+) T and nonT lymphocytes (1). ADCC against antibody-coated human erythrocyte (HRBC) targets in suspension culture has generally been felt to be mediated predominantly by phagocytic cells (i.e., neutrophils and monocytes) (2). As such, this assay system may primarily reflect postphagocytic intracellular lysis oftarget cells. Conversely, extracellular lysis is the predominant mode of cell killing when antibody-coated nucleated nonerythroid target cells are employed (1). The relative contribution of intracellular and extracellular events in ADCC in suspension culture are unclear. Additionally, the mechanisms of these two different modes of cytolysis as well as their potential interrelationship are presently speculative. In an attempt to further delineate the potential mechanisms ofADCC, the present study employed leukocytes from normal subjects and from patients with chronic granulomatous disease (CGD) as effector cells in ADCC assays against HRBC targets in suspension, autologous lymph' Abbreviations used in this paper: ADCC, antibodydependent cellular cytotoxicity; ALS, antilymphocyte serum; CGD, chronic granulomatous disease; E:T, effector to target; FcR+, Fc receptor-bearing; HRBC, human erythrocyte; 7S EA, bovine erythrocytes coated with IgG; TNP, trinitrophenol. TheJournal of Clinical Investigation Volume 65 January 1980 55-63 55 oid cell targets in suspension, and HRBC targets in monolayers. Phagocytic cells from CGD patients are deficient in NADPH oxidase activity and consequently lack phagocytosis-induced hydrogen peroxide (H202) and superoxide (O°) generation (3-5). We therefore used effector cells from these patients as investigative cellular probes in an attempt to delineate the importance of H202 and °2 and related mechanisms in intracellular and extracellular ADCC activity.