Characterization of a novel low affinity receptor for IFN-gamma on adherent human monocytes by radioligand binding studies and chemical cross-linking.
Freshly isolated monocytes in suspension express 2000 to 4000 high affinity receptors for IFN-gamma. Because monocytes change phenotypically as they migrate out of the circulation and adhere to extracellular matrix, modulation of the expression of IFN-gamma receptors may occur. In order to determine if adherence alone modulates the receptor for IFN-gamma, we have studied receptor expression in adherent human peripheral blood monocytes. Elutriation-purified monocytes were allowed to adhere to polystyrene overnight at 37 degrees C. These cells now expressed 1 to 2 x 10(5) low affinity (Ka = 10(8) liters/M) receptors for [125I]rIFN-gamma. Binding to this receptor was specific and saturable. The expression of these receptors occurred rapidly (within 3 h) after adherence and was not inhibited by cycloheximide treatment. Binding to the receptor was abrogated by treating cells with trypsin, but was enhanced after treatment with alkaline protease or proteinase K. mAb against the high affinity receptor did not block binding to the low affinity receptor on adherent cells. The low affinity receptor transduced a signal to the cell as measured by the IFN-gamma-induced enhancement in FcR for human IgG1. The structure of the receptor on adherent cells was investigated by chemical cross-linking techniques. A receptor-[125I]rIFN-gamma complex was observed by SDS-PAGE to have a Mr of 180,000 to 200,000. Reduction of this complex with 2-ME resulted in the loss of the high Mr complex and the appearance of a doublet of lower Mr of 68,000 and 82,000. In contrast, cross-linking of monocytes in suspension yielded a complex of 110,000 to 120,000 Mr, which was unchanged upon reduction. Upon adherence, human monocytes express large numbers of a novel receptor for rIFN-gamma which is capable of stimulating the cell. This receptor appears to be composed of at least two components which are disulfide linked and structurally differs from the high affinity receptor on nonadherent monocytes.
Finbloom
D S
DS
Department of Immunology, Walter Reed Army Institute of Research, Washington, DC 20307-5100.
Wahl
L M
LM
D000911:Antibodies, Monoclonal / Q000502:physiology; D002448:Cell Adhesion; D003432:Cross-Linking Reagents; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism* / Q000494:pharmacology; D007457:Iodine Radioisotopes; D009000:Monocytes / Q000378:metabolism*; D011869:Radioligand Assay; D011971:Receptors, Immunologic / Q000032:analysis* / Q000096:biosynthesis / Q000276:immunology; D017471:Receptors, Interferon; D011994:Recombinant Proteins; D013329:Structure-Activity Relationship
D000911:Antibodies, Monoclonal; D003432:Cross-Linking Reagents; D007457:Iodine Radioisotopes; D011971:Receptors, Immunologic; D017471:Receptors, Interferon; D011994:Recombinant Proteins; D007371:Interferon-gamma