IDENTIFICATION AND STRUCTURAL CHARACTERIZATION OF FC-GAMMA-RECEPTORS ON PULMONARY ALVEOLAR MACROPHAGES

Little is known about the structure of the cell surface receptors for the Fc portion of immunoglobulin G (Fc-gamma-R) on tissue macrophages. Studies on leukocytes indicate the existence of three classes of Fc-gamma-R, denoted I, II, and III. The purpose of this study was to structurally characterize Fc-gamma-R on alveolar macrophages obtained by bronchoalveolar lavage, comparing them with Fc-gamma-R of monocytes, neutrophils, and U937 cells. Flow-cytometric evaluation, utilizing anti-Fc-gamma-R class-specific monoclonal antibodies, showed that alveolar macrophages expressed three Fc-gamma-R classes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the immunopurified Fc-gamma-R molecules revealed the following apparent molecular mass for each Fc-gamma-R class: Fc-gamma-RI, 70 kDa; Fc-gamma-RII, 44 kDa; and Fc-gamma-RIII, 57-65 kDa. RNA blot analysis demonstrated a 1.7-kb transcript for Fc-gamma-RI, 2.5 and 1.6 kb transcripts for Fc-gamma-RII, and a 2.2 kb mRNA for Fc-gamma-RIII. Fc-gamma-RII displayed the high-responder/low-responder polymorphism. Fc-gamma-RIII did not express the neutrophil antigen-type specific structural polymorphism of the deglycosylated Fc-gamma-R molecule and appeared to be a transmembrane molecule.