Relationship between murine macrophage Fc receptor-mediated phagocytic function and competency for activation for non-specific tumor cytotoxicity

Reconstitution of murine resident peritoneal macrophages for antibody-dependent cellular cytotoxicity by homologous serum Clq

Mouse resident peritoneal macrophages (PM) were reconstituted in their response to activation for antibody-dependent cellular cytotoxicity (ADCC) for sheep erythrocyte targets (SRBC) by subhemolytic dilutions of homologous or autologous sera. ADCC-responsive inflammatory PM were largely unaffected in their activation by exogenous serum. Augmentation of resident PM for ADCC by homologous serum was correlated with the complement-activating potential of the mouse monoclonal anti-SRBC IgG isotype in that serum augmented IgG gamma 2a greater than IgG gamma 2b much greater than IgG gamma 1. The active component of mouse serum was heat-labile at 56 degrees C for 30 min and was present in both C5-deficient AKR and C5-sufficient homologous C3H mouse sera. Western blot analysis of the cell lysates for Clq confirmed that oil-elicited and thioglycollate-elicited inflammatory PM had greater levels of endogenous Clq than did resident PM which correlated with their innate responsiveness for ADCC activation. Depletion of Clq from serum by immunoprecipitation with IgG antibody to Clq or by ion exchange chromatography removed the active reconstituting activity for ADCC. Purified mouse Clq (0.4 microgram) partially replenished the ADCC augmenting activity of Clq-depleted AKR mouse serum. SRBC targets preopsonized with IgG gamma 2a and purified mouse Clq (0.075-5.0 microgram/ml) fully reconstituted the ADCC response of resident PM similar to homologous serum indicating that the major active component of serum was Clq. Thus resident PM with low endogenous levels of Clq were reconstituted for ADCC by the addition of exogenous Clq, whereas inflammatory PM with sufficiently high endogenous levels of Clq were not further enhanced by exogenous Clq. Our findings indicate that Clq may provide an essential second signal in concert with Fc receptor binding of IgG to initiate ADCC activation of macrophages.

Triggering of interferon gamma-primed macrophages by various known complement activators for nonspecific tumor cytotoxicity

Five known complement activators were evaluated for their capacity to directly activate murine macrophages and to trigger activation of lymphokine primed macrophages for nonspecific tumor cytotoxicity. Bacterial lipopolysaccharide (LPS), Lipid A, polyinosinic-polycytidylic acid, cobra venom factor (CVF), and zymosan directly activated macrophages in a dose-dependent fashion at high concentrations. Subactivating concentrations of each of these agents were found to effectively trigger macrophages which were preprimed either by macrophage-activating factor or by murine recombinant interferon gamma for enhanced tumoricidal activity. An Fc receptor blockade with opsonized sheep erythrocytes abrogated LPS-mediated direct activation and triggering of interferon gamma-primed macrophages, but had no inhibitory effect on direct activation or triggering by CVF for nonspecific tumor cytotoxicity. This study characterizes the capacity of a diverse group of known complement activators to serve as second signal triggers for culmination of the activation process of interferon-primed macrophages for nonspecific tumoricidal activity. These findings suggest that complement activators may directly activate macrophages by stimulation of interferon beta production by macrophages for self-priming and, as we have shown, act as self-triggers. The putative role of macrophage-associated complement components in the activation process is discussed.

Activation of mouse macrophages for migration inhibition and for tumor cytotoxicity is mediated by interferon-gamma priming and triggering by various agents

The requirements for activation of C3HeB/FeJ mouse peritoneal macrophages to mediate migration inhibition from capillary tubes was compared with those conditions prerequisite for nonspecific tumor cytotoxicity. Both in vitro assays for macrophage activation were found to require a two-stage process that involved priming by murine recombinant interferon-gamma (IFN-gamma) and triggering by subactivating concentrations of bacterial lipopolysaccharide (LPS), Lipid A, Polyinosinic-polycytidylic acid (poly I:C), or cobra venom factor (CVF). A dose-related increase in both migration inhibition and tumor cytotoxicity was shown with increasing concentrations of IFN-gamma (3.0-50.0 U/ml) in synergistic combination with an LPS trigger. IFN-gamma alone produced low levels of migration inhibition or tumor cytotoxicity, only at higher concentrations, that was not attributable to LPS contamination. The concentrations of the various agents required for direct activation or triggering of IFN-gamma-primed macrophages were approximately 2- to 10-fold greater for migration inhibition than for tumor cytotoxicity. Our results indicate that the two-signal process of priming and triggering for mediating mouse macrophage nonspecific tumoricidal activity is also operative in migration inhibition from capillary tubes. Thus, under defined conditions with purified lymphokines, the migration inhibition assay appears to be a reliable alternate in vitro correlate of macrophage activation by IFN-gamma.