Critical events in the irreversible uptake of soluble immune complexes by macrophages.

Small, soluble, IgG-containing complexes bind to phagocytes via Fc receptors on the cell membrane, in competition with IgG in the environment. Following attachment, the complexes rapidly rearrange themselves into larger aggregates by forming additional Ag-Ab bridges. The driving force for this rearrangement is a massive increase in the effective concentration of the complexes at the receptor-bearing surface. Aggregation precedes ingestion and probably constitutes the critical irreversible step which predisposes complexes to selective clearance from the circulation.