Demonstration and partial characterization of the interferon-gamma receptor on human mononuclear phagocytes.

Abstract

Radioiodinated recombinant human interferon-gamma (IFN-y) bound to human monocytes, U937, and HL60 cells in a specific, saturable, and reversible manner. At 40C, the different cell types bound 3,000-7,000 molecules of IFNy, and binding was of comparable affinity (K. = 4-12 X 10 M-l). No change in the receptor was observed after monocytes differentiated to macrophages or when the cell lines were pharmacologically induced to differentiate. The functional relevance of the receptor was validated by the demonstration that receptor occupancy correlated with induction of Fc receptors on U937. Binding studies using U937 permeabilized with digitonin showed that only 46% of the total receptor pool was expressed at the cell surface. The receptor appears to be a protein, since treatment of U937 with trypsin or pronase reduced '251-IFNy binding by 87 and 95%, respectively. At 370C, ligand was internalized, since 32% of the cell-associated IFNy became resistant to trypsin stripping. Monocytes degraded '251-IFNy into trichloroacetic acid-soluble counts at 370C but not at 40C, at an approximate rate of 5,000 molecules/cell per h. The receptor was partially characterized by SDS-polyacrylamide gel electrophoresis analysis of purified U937 membranes that had been incubated with _251-IFNy. After cross-linking, the receptor-ligand complex migrated as a broad band that displayed an M, of 104,000±18,000 at the top and 84,000±6,000 at the bottom. These results thereby define and partially characterize the IFNy receptor of human mononuclear phagocytes.

Multiple mechanisms allowMycobacterium tuberculosisto continuously inhibit MHC class II-mediated antigen presentation by macrophages

“…In the absence of IFN-␥ and antigen, conditions that we used as a negative control, seven molecular species in the model were present in non-zero quantities: free IFN-␥ receptors, MHC class II mRNA, free intracellular and surface MHC class II molecules, self-peptides, and intracellular and surface self-peptide-MHC class II complexes. These results are consistent with the finding that cultured macrophages constitutively express several molecules relevant to antigen presentation at basal levels, including IFN-␥ receptors and MHC class II molecules (18,19).…”

The extracellular domain of the human interferon gamma receptor interacts with a species-specific signal transducer.

“…To determine the affinity of hIFN--y for the human and reported for a variety of human cells (3,7,16,36,51). Whether a particular IFN-,yR construct was expressed in L929 or SCC cells had no effect on its affinity for hIFN-y.…”

“…The hIFN-yR as expressed in murine somatic cell hybrids and transfected mouse cells has binding properties similar to those of the hIFN--yR on human cells (1,7,36,42). These findings, in conjunction with results of cross-linking experiments (7,19,36,40), suggest that in contrast to the interleukin-6 (26, 54) and granulocyte-macrophage colony-stimulating factor receptors (21, 24), a second IFN--yR chain is not involved in mediating high-affinity ligand binding.Human-murine somatic cell hybrids containing human chromosomes 6 and 21 (29), as well as human-hamster and human-murine somatic cell hybrids containing human chromosome 21 and transfected with hIFN--yR expression vectors (17, 28), respond to hIFN-y as measured by the induction of MHC class I antigen. These findings demonstrate that the human chromosome 21-encoded factor(s) is necessary for signalling by the hIFN-yR, at least with respect to histocompatibility antigen expression, and suggest that the signal transducer(s) and the IFN-yR must be from the same species.…”

“…The second is an undetermined species-specific signal transducer(s). To determine whether the human IFN-y receptor (hIFN--yR) IFN-,y binds with high affinity (Kd = 10-9 to 10-11 M at 4°C) to a 90-kDa glycoprotein receptor present in low numbers (102 to 104) on a wide variety of cell types (7,16,19,33,36,42,51). Human and murine IFN-y share 40%o amino acid sequence identity (22) and exhibit species specificity with respect to receptor binding (15, 52) and biological activity (14,22).…”

“…When this chromosome is present in human-murine somatic cell hybrids (29,41,43) or after transfection of the hIFN-yR gene into mouse cells (2), hIFN-,y binds with high affinity to the hIFN-yR but no biological response is elicited. The hIFN-yR as expressed in murine somatic cell hybrids and transfected mouse cells has binding properties similar to those of the hIFN--yR on human cells (1,7,36,42). These findings, in conjunction with results of cross-linking experiments (7,19,36,40), suggest that in contrast to the interleukin-6 (26,54) and granulocyte-macrophage colony-stimulating factor receptors (21,24), a second IFN--yR chain is not involved in mediating high-affinity ligand binding.…”