Binding, Endocytosis, and Degradation of Model Immune Complexes by Murine Macrophages at Various Levels of Activation

To determine if stimulation of macrophages enhances their capacity to recognize and process immune complexes, the binding, endocytosis, and degradation of soluble model immune complexes in murine macrophages have been measured. These complexes are composed of covalently crosslinked dimers and heavy oligomers of murine IgG antidinitrophenyl antibodies. Resident (unstimulated), inflammatory (thioglycolate-elicited), and activated (bacillus Calmette-Guerin-elicited) macrophages were studied. Cells elicited with either agent bound five times more dimers or heavy oligomers than did resident cells. Stimulated macrophages internalized and then degraded 50-60% of those heavy oligomers initially bound to the surface of the cell. Resident macrophages, however, were about 70% as efficient as stimulated cells at degrading intracellular complexes. Although dimers avidly bound to all three types of macrophages, they were internalized poorly and were degraded minimally. Intracellular complexes were degraded within lysosomes as determined by centrifugation of cell homogenates on Percoll gradients. Following endocytosis of heavy oligomers, Fc receptors on each type of macrophage were down-modulated to 30% of control levels.