ADCC effector cells in a murine adenocarcinoma. I. Evidence for blood-borne bone-marrow-derived monocytes

The origin and identity of effector cells for anti-body-dependent cell-mediated cytotoxicity and/or growth inhibition (ADCC) found in the murine mammary adenocarcinoma T1699 were investigated. Non-phagocytic, non-adherent ADCC effector cells were identified in bone marrow, peripheral blood and the host fraction of the tumor but not from lymphoid organs. These cells were shown to be distinct from the specific growth-inhibitory "armed monocytes" also identified in situ. The ADCC effector cells possess low levels of EA Fc receptors and appear to express a macrophage-associated antigen. Both the bone-marrow and the in situ effector cells became phagocytic after overnight incubation, providing further evidence for the monocyte-macrophage lineage of these cells. The results suggest that bone-marrow-derived blood-borne monocytes are the principal ADCC effector cells localizing in the mammary adenocarcinoma T1699. The parallels between tumor-induced immunity and cellular resistance to infectious agents involving hypersensitivity reactions and blood-borne monocytes are discussed.