Immunologic control of the ascites form of murine adenocarcinoma 755. V. Antibody-directed macrophages mediate tumor cell destruction.

An in vitro assay has been developed that mimics the potent in vivo protective capacity of B6 anti-AD755a serum in a passive therapy protocol. In the presence of small volumes of hyperimmune serum or IgG2a antibody, thioglycollate-elicited B6 mouse peritoneal cells (PEC) inhibit the growth of AD755 Cl.10 target cells and other cells provided that they express FLV-related antigens. When hyperimmune serum is replaced by normal serum, or elicited PEC from BALB/c mice are used, growth inhibition of the AD755 Cl.10 target cells is not seen. The latter is in accord with the inability to protect BALB/c mice with the anti-AD755a serum. Tumor cells to which antibody has been pre-bound are not inhibited by thioglycollate-elicited B6 PEC, analogous to the undiminished tumorigenicity of antibody-bound AD755a cells in vivo. These results, along with those presented in the accompanying papers, have led to the construction of a model to explain the specificity and mechanism of the potent in vivo passive protection characteristic of this system. The major features of this model are that the protective IgG2a antibody must first interact with an appropriate host effector cell, presumably of the monocyte/macrophage lineage, and that such an antibody-directed cell then binds to the tumor cell and effects its elimination, possibly by a phagocytic mechanism.