Augmentation of antibody-dependent cell-mediated cytotoxicity by anti-immunoglobulin. I. Relationship to target cell capping.

The effects of anti-immunoglobulin (anti-Ig) on the susceptibility of mouse B cells or alloantibody-coated thymocytes to lysis by human K cells were studied. Since anti-Ig caps readily, we examined in particular the relationship between the extent of capping of the target cells and their susceptibility to lysis by K cells. The effects varied with the anti-Ig concentration: dilute anti-Ig capped B cells poorly and induced K cell lysis very efficiently. Dilute anti-Ig could also augment alloantibody-induced ADCC: for example, anti-Thy-1 coated thymocytes, which were not lysed by K cells in the absence of anti-Ig, could be lysed extensively when dilute anti-Ig was present. High anti-Ig concentrations induced more extensive capping and less K cell lysis than more dilute anti-Ig, suggesting that capping does reduce susceptibility to K cells. Nevertheless, when the ability of K cells to lyse anti-Ig-coated targets was compared to that of complement, K cells were superior in two respects: (i) K cell lysis could be induced by low (subcapping) concentrations of anti-Ig, whereas complement lysis could not; and (ii) K cells could lyse even extensively capped targets to some extent, whereas such targets were highly resistant to complement. We conclude that (i) augmentation of ADCC by dilute anti-Ig can be demonstrated and may be useful in systems in which the first antibody induces ADCC poorly; and (ii) the K cell system could have a particular role in the lysis of antibody-coated cells or micro-organisms which cap readily.