Modulation of human monocyte Fc receptor function by surface-adsorbed IgG.

Fc receptor-mediated phagocytosis was measured with monocytes subjected to various treatments. Monocytes exposed to IgG during their adherence, or after they had adhered to a surface, experienced functional impairment. This was manifested in the requirement of a higher antibody density on target particle for efficient phagocytosis, and in an enhanced susceptibility to inhibition by fluid-phase IgG. The impairment was found to be due to an interaction of IgG adhering to the surface with the Fc receptors. This effect could be induced with monomeric IgG, devoid of IgG aggregates or immune complexes. IgG coatings that resulted in inefficient Clq fixation promoted considerable functional impairment of monocytes within 1 hr. In addition, the prolonged contact of monocytes with polystyrene in the absence of IgG also led to a functional reduction. The study points to a compromised function of phagocytes exposed to artificial surfaces.