HUMAN NEUTROPHIL RC-RECEPTOR-MEDIATED PHAGOCYTOSIS

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Neutrophils (PMN) collect in the synovial fluid of patients with rheumatoid arthritis and contribute to joint destruction by the release of inflammatory mediators and intracellular enzymes in response to the binding of IgG containing immune complexes to PMN Fc receptors. The transmembrane signals that trigger ingestion of these complexes, lysosomal enzyme release, and/or production of inflammatory mediators are not well understood. The PMN Fc receptor is a low avidity receptor which binds immune complexes and is antigenically and functionally distinct from the high avidity Fc receptor expressed on monocytes which avidly binds both monomeric and polymeric IgG. PMN, but not monocyte, Fc-receptor-mediated ingestion and lysosomal enzyme release can be enhanced by a low molecular weight cytokine derived from human mononuclear cell culture supernatants and rheumatoid synovial fluid. The action of this cytokine is inhibited by a monoclonal antibody (1C2) which recognizes neither the PMN Fc receptor nor the cytokine binding site. Certain agents (aliphatic alcohols, amphotericin B, tumor-promoting phorbol esters, and chemotactic peptides) which modify the microenvironment of the PMN Fc receptor mimic aspects of cytokine stimulation and can be used as models to probe PMN Fc receptor function. This project proposes to study the effect of these agents and cytokine on Fc-receptor-mediated ingestion by: 1) Determination of intrinsic changes in, and aggregation state of, PMN Fc receptors which efficiently transduce a phagocytic signal; 2) Determination of the cytoskeletal associations which contribute to the efficient transduction of a phagocytic signal; and 3) Determination of the cell activation mechanisms which result in membrane lipid changes affecting Fc-receptor-meldiated ingestion. PMN will be treated with the above phagocytosis modifying agents and the following paramaters assessed: Fc receptor aggregation and avidity; ligand-dependent and - independent Fc receptor internalization; cytoskeleton attachment of Fc receptors and 1C2 antigen; membrane fluidity; and protein kinase C activation and inositol phospholipid hydrolysis. These experiments will provide information on the functional modulation of the low avidity Fc receptor expressed on PMN which collect at inflammatory sites and which mediate clearance and destruction of immune complexes.