Immunologic responses to a murine mammary adenocarcinoma. II. Monocyte effector activation by humoral factors.

Sera from DBA/2 mice bearing a syngeneic T1699 mammary adenocarcinoma not only induced specific antibody-dependent cellular cytotoxicity (ADCC) mediated by monocytes (and/or macrophages) but also armed (activated) such effector cells into specific killer cells in vitro. Removal of specific antitumor antibody (IgG2a subclass) by absorption with T1699 cells abolished ADCC activity at the level of target cell coating but did not alter the level of effector-arming activity. Fractionation on Sephadex G-20 indicated more than one factor capable of inducing specific monocyte-mediated lysis of target cells in vitro, including immune complexes, free IgG2a 7S antibody (ADCC), and another factor(s) with a molecular weight very close to that of 7S immunoglobulins.