Inhibition of antibody-dependent cellular cytotoxicity by artificial immune complexes and pathological sera

Detection of immune complexes by inhibition of antibody-dependent cellular cytotoxicity (ADCC) is based on the principle that soluble complexes can compete with target cell-bound antibody for receptor (FcR) on cytotoxic lymphocytes. The objective of this study was to define a cytotoxicity system for the determination of soluble immune complexes in the sera of patients with inflammatory bowel disease (IBD). For this purpose, the conditions under which soluble complexes of rat serum albumin (RSA) and rabbit anti-RSA inhibited human K-cell mediated lysis of sensitized Chang cells were examined, on the assumption that the behaviour in the system of circulating immune complexes putatively present in inflammatory bowel disease is similar to that of artificial immune complexes. Inhibition of ADCC by a standard amount of artificial complex in different normal human sera was relatively uniform provided that the final concentration of the latter did not exceed 10% of the culture medium. In the absence of extraneous complexes, the effect of both normal and IBD sera on ADCC varied widely. Differential inhibition of ADCC by sera from patients with IBD and normal subjects was thus expressed as a function of ADCC in a standard batch of foetal bovine serum (FBS). Under these conditions differences between pathological (n=51) and normal (n=52) sera were highly significant (P