Antibody-dependent lysis of tumor cells in vivo. II. Elimination of chromium-51 as a measurement of cytolysis.

The effect of antibody on tumor cells was studied in vivo by measurement of the rate of elimination of 51Cr in A/J mice inoculated with labeled Ehrlich tumor cells. Mice receiving ip injections of tumor cells and normal serum eliminated 51Cr rapidly during the first 24 hours and at a much slower rate thereafter. This biphasic pattern of elimination was due to the fact that 51Cr predominantly labels small (less than 13,000 mol wt) intracellular molecules, which the mouse rapidly eliminates, whereas larger labeled molecules are eliminated slowly. Antibody to tumor cells significantly accelerated the elimination of 51Cr at concentrations that regularly suppressed tumor growth. Antibody also induced a faster elimination rate in mice treated with cobra venom factor but not in mice treated with silica or inoculated sc with the tumor cells. Unlabeled tumor cells inhibited antibody-induced 51Cr clearance in normal mice but not in proteose peptone-treated mice. These results suggested that peritoneal cells are required in the induction of antibody-dependent cytolysis in vivo. In addition, actively or passively alloimmunized mice exhibited a similar accelerated 51Cr elimination rate when inoculated with the appropriate labeled target cells.