MACROPHAGE-ALLOANTIBODY-TARGET CELL INTERACTIONS

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Abstract
A new radioisotope assay for the quantitative assessment of macrophage-alloantibody-target cell interaction was studied. The assay, abrogation of complement lysis (ACL), is based on the observation that antibody-coated cells incubated with [mouse] macrophages become resistant to complement lysis. The degree of reduction in complement lysis, as measured by 51Cr release, can therefore be used to assess the extent of macrophage engulfment of the target cells. Previous incubation of macrophages with antigen-antibody complexes inhibited ACL, confirming that Fc receptors were necessary for ACL. However, the temperature dependence of ACL and the inability of many types of Fc receptor-bearing nonphagocytic cell populations to mediate ACL indicated that macrophage effector function after Fc receptor binding was essential for ACL. Microscopic assessment confirmed that the macrophage activity producing most of the ACL was engulfment of the cells, although certain observations suggested that a nonphagocytic effect of macrophages on the target cells may be detectable in ACL under certain circumstances. Macrophage activation strongly influenced the degree of ACL and of phagocytosis, the chief effect being not on the absolute number, but on the percentage of target cells engulfed by macrophages. The simplicity, objectivity and rapidity of ACL suggest that this will be a useful technique for exploring the role of macrophages in humoral alloimmunity.