Journal of Immunological Methods, 43 (1981) 121--129 121 Elsevier/North-Holland Biomedical Press ADCC ANALYSIS WITH THE COULTER COUNTER: A HIGHLY SENSITIVE, ULTRAMICRO ASSAY SUITABLE FOR CLINICAL AND EXPERIMENTAL APPLICATION A.M. ATTALLAH 1 and T.J. YEATMAN 2 Division of Pathology, Bureau of Biologics, FDA, Bethesda, MD 20205, U.S.A. (Received 26 November 1980, accepted 9 January 1981) Antibody-dependent cellular cytotoxicity (ADCC) is an in vitro immune mechanism implicated in several in vivo phenomena such as transplant rejection, tumor immunity and parasite elimination. We developed a method for detecting ADCC using the Coulter Counter and the Coulter Channelyzer that circumvents many of the disadvantages asso- ciated with existing assays for ADCC. Effector mononuclear cells were incubated with chicken red blood cell (CRBC) targets and anti-target antibody for 1--1.5 h. Killing was quantified by the Coulter Counter on the basis of size differences between effector and target cell nuclei. Using a 4 pl total volume we were able to detect cytotoxic levels of 55% when as few as 5000 effector cells were incubated with an equal number of target cells. This method for the detection of ADCC may be suitable for both clinical and research application. INTRODUCTION Antibody<lependent cellular cytotoxicity (ADCC) is phenomenon of cell- mediated immunity in which antibody~oated target cells are killed by Fc receptor-bearing leukocytes (Perlmann and Holm, 1969). The importance of ADCC has been substantiated by both human and animal studies. Recent investigations have indicated that this in vitro cytotoxic event correlates well with various in vivo immune states such as those associated with tissue damaging mechanisms in autoimmunity and with the immune response to tumors, transplants, parasitic infection and vitally modified cells (Hershey, 1973; Order et al., 1973; Bloom and David, 1976; Dumble et al., 1980). It has also been suggested that the monitoring of ADCC levels may prove to be effective in the prognosis of renal allograft survival (Dumble et al., 1980). Furthermore, ADCC activity seems to be a good indicator of immunosup- pression (Sasaki et al., 1979). The application of ADCC analysis, however, 1 Address reprint requests to Dr. A.M. Attallah, Bureau of Biologics, Bldg. 29, Room 521, 8800 Rockville Pike, Bethesda, MD 20205, U.S.A. 2 Timothy J. Yeatman is a first-year student at Emory University School of Medicine, Atlanta, GA, U.S.A. 0022-1759/81/0000---0000/$02.50 © Elsevier/North-Holland Biomedical Press