Binding of human recombinant 125I-interferon gamma to receptors on human cells

Recombinant human interferon gamma (rIFN-gamma) produced in Escherichia coli was labeled with 125I to study its binding to receptors of HeLa and lymphoblastoid cells. All the cell lines examined had receptors for rIFN-gamma, although the binding varied considerably among different cell lines. The binding of 125I-rIFN-gamma was competed up to 90% by the addition of unlabeled rIFN-gamma, although not by the addition of IFN-alpha or -beta. By adding increasing concentrations of unlabeled rIFN-gamma to binding assays containing a constant amount of 125I-rIFN-gamma, we determined a KD of 3.7 and 6.3 X 10(-10) M for its binding to Daudi and HeLa cells, respectively. About 13,000 receptors per cell were present in Daudi and 5,000 in HeLa cells. The Mr of the IFN-gamma/receptor complex was determined by cross-linking experiments to be about 125,000. This complex is smaller than the IFN-alpha/receptor complex that has a Mr of about 140,000. The rIFN-gamma receptor was down-regulated when HeLa cells were treated with this interferon, but not when these cells were treated with IFN-beta. These findings suggest that the receptors for IFN-alpha and -gamma differ in several characteristics. The turnover of the rIFN-gamma receptor was measured by inhibiting protein synthesis with cycloheximide and the half-life of this receptor was found to be 2 h. The unglycosylated rIFN-gamma was bound to cellular receptors with an affinity similar to that previously reported for natural IFN-gamma. The lymphoblastoid cell lines examined had high affinity receptors for rIFN-gamma, but did not respond to treatment with this IFN with an induction of the synthesis of the enzyme (2'-5')oligo(A) synthetase, whereas HeLa cells responded to rIFN-gamma. The reason for the lack of response of lymphoblastoid cells is presently unknown.     

Differential effects of type I IFN and IFN-gamma on the binding of tumor necrosis factor to receptors in two human cell lines

The effect of IFN-alpha and IFN-beta on the expression of cell surface receptors for tumor necrosis factor (TNF) was examined in two human cell lines. In HeLa cells, IFN-alpha and IFN-beta increased 125I-TNF binding, whereas in HT-29 cells these two IFN either slightly decreased or had no effect on 125I-TNF binding. In contrast, IFN-gamma increased 125I-TNF binding in both cell lines. Both IFN-alpha and IFN-beta exerted an antagonistic effect on IFN-gamma-induced stimulation of TNF receptor expression in HT-29 cells, but did not inhibit TNF receptor induction by IFN-gamma in HeLa cells. IFN-gamma and, to a lesser extent, IFN-beta were synergistic with TNF in producing cytotoxic/cytostatic activity in HT-29 cells. Despite the inhibitory effect of IFN-beta on the IFN-gamma-induced stimulation of TNF receptor expression, IFN-beta did not inhibit the synergistic enhancement of TNF cytotoxicity by IFN-gamma in HT-29 cells. The dissociation between the effects of IFN-beta on TNF receptor expression and on the cytotoxic activity of TNF in HT-29 cells suggests that TNF receptor modulation is not a major mechanism of synergism between IFN and TNF.     

Interferon receptor interaction. Internalization of interferon alpha 2 and modulation of its receptor on human cells

Studies reported earlier [ Joshi et al. (1982) J. Biol. Chem. 257, 13884-13887] have indicated that human interferon-alpha 2 (HuIFN-alpha 2) binds to a specific macromolecular receptor on human cells as identified by cross-linking with bifunctional cross-linking reagents and analysis by polyacrylamide gel electrophoresis. We have carried out experiments to investigate the fate of the interferon-receptor complex on the cell surface under conditions which lead to cellular response. As analyzed by cross-linking and gel electrophoresis, the interferon-receptor complex, formed on incubation with 125I-IFN-alpha 2 at 4 degrees C, persisted at the cell surface for several hours at 4 degrees C; however, if the cells were switched to 37 degrees C, there was a rapid decline in the complex, apparently due to a loss of the interferon receptors from the cell surface. This was associated with an internalization of the 125I-interferon as indicated by the fact that, on incubation at 37 degrees C, an appreciable fraction of the cell-associated interferon (approximately equal to 50%) became resistant to trypsin digestion, or dissociation on incubation in growth medium or low-pH buffer. A large fraction of the trypsin-resistant (internalized) 125I-labeled material migrated as intact interferon in polyacrylamide gels, and it was immunoprecipitated by anti-(HuIFN-alpha)antibodies but not by anti-(HuIFN-beta)antibodies. The bulk of the internalized 125I-interferon was recovered in a particulate fraction and, on cross-linking with disuccinimidyl suberate, a 150000-Mr complex could be detected. The results suggest that interferon may be internalized as a complex with the receptor, which may account for the loss of the interferon-receptors on the cell surface. This modulation of the IFN-alpha/beta receptors was induced by HuIFN-alpha and HuIFN-beta but not by HuIFN-gamma. The recovery of the IFN-alpha/beta receptors, lost upon incubation with HuIFN-alpha, took several hours and required protein synthesis. The significance of the results is discussed.     

The vaccinia virus soluble alpha/beta interferon (IFN) receptor binds to the cell surface and protects cells from the antiviral effects of IFN

Poxviruses encode a broad range of proteins that interfere with host immune functions, such as soluble versions of receptors for the cytokines tumor necrosis factor, interleukin-1 beta, gamma interferon (IFN-gamma), IFN-alpha/beta, and chemokines. These virus-encoded cytokine receptors have a profound effect on virus pathogenesis and enable the study of the role of cytokines in virus infections. The vaccinia virus (VV) Western Reserve gene B18R encodes a secreted protein with 3 immunoglobulin domains that functions as a soluble receptor for IFN-alpha/beta. We have found that after secretion B18R binds to both uninfected and infected cells. The B18R protein present at the cell surface maintains the properties of the soluble receptor, binding IFN-alpha/beta with high affinity and with broad species specificity, and protects cells from the antiviral state induced by IFN-alpha/beta. VV strain Wyeth expressed a truncated B18R protein lacking the C-terminal immunoglobulin domain. This protein binds IFN with lower affinity and retains its ability to bind to cells, indicating that the C-terminal region of B18R contributes to IFN binding. The replication of a VV B18R deletion mutant in tissue culture was restricted in the presence of IFN-alpha, whereas the wild-type virus replicated normally. Binding of soluble recombinant B18R to cells protected the cultures from IFN and allowed VV replication. This represents a novel strategy of virus immune evasion in which secreted IFN-alpha/beta receptors not only bind the soluble cytokine but also bind to uninfected cells and protect them from the antiviral effects of IFN-alpha/beta, maintaining the cells' susceptibility to virus infections. The adaptation of this soluble receptor to block IFN-alpha/beta activity locally will help VV to replicate in the host and spread in tissues. This emphasizes the importance of local effects of IFN-alpha/beta against virus infections.     

Interferon-gamma enhances expression of cellular receptors for tumor necrosis factor

Incubation of several human tumor cell lines with human interferon-gamma (IFN-gamma) increased the specific binding of subsequently added 125I-labeled recombinant human tumor necrosis factor (TNF). A similar increase in TNF binding was seen in murine L929 cells after incubation with murine IFN-gamma, but not after incubation with human IFN-gamma. Increased TNF binding to cells incubated with IFN-gamma was due to an increase in the number of TNF receptors, with no demonstrable change in binding affinity. In one out of two human cell lines tested, IFN-alpha and IFN-beta also produced increased TNF binding, albeit with a lower efficacy than IFN-gamma. A maximal increase in TNF binding was seen after about 6 to 12 hr of incubation with IFN. Increased TNF binding due to enhanced TNF receptor expression may contribute to the enhancement of TNF cytotoxicity seen in some tumor cell lines after INF treatment. Modulation of TNF receptor expression by IFN may also influence other biological activities of TNF.     

Alternative induction of alpha/beta interferons and gamma interferon by listeria monocytogenes in mouse spleen cell cultures

Production of interferon (IFN) by Listeria monocytogenes (LM) in nonimmunized mouse spleen cell cultures was studied. IFN-gamma defined by virtue of its acid stability and antigenicity was produced in spleen cell cultures obtained from ddY mice, C57BL/6 mice, and BALB/c mice in response to heat-killed (HK) LM within 24 hr. On the other hand, production of IFN-alpha/beta was demonstrated in spleen cell cultures obtained from one of four nude mice (BALB/c, nu/nu). Therefore, it is important to know the reason why the spleen cells of mice other than nude mice did produce only IFN-gamma, but did not produce IFN-alpha/beta in response to HK-LM. Spleen cells obtained from ddY mice were fractionated, and the cellular source for IFN production of either IFN-alpha/beta or IFN-gamma induced by HK-LM was investigated. IFN-gamma was produced only by a mixture of T lymphocytes (nylon wool-nonadherent, Thy-1-positive cells) and macrophages by HK-LM. Neither T lymphocytes nor macrophages alone produced IFN by HK-LM. Macrophage-depleted spleen cells produced neither IFN-gamma nor IFN-alpha/beta, but these cells acquired the ability to produce IFN-alpha/beta, not IFN-gamma, only when they had been treated with IFN-alpha/beta. A possible mechanism of both IFN-gamma and IFN-alpha/beta induction by Listeria in mouse spleen cell cultures is discussed.     

Internalization and degradation of receptor-bound interferon-gamma by murine macrophages. Demonstration of receptor recycling

Although the interferon-gamma (IFN-gamma) receptor on murine and human mononuclear phagocytes has been defined and partially characterized, very little data exists which describes the ultimate fate of receptor-bound ligand. The current studies were specifically designed to define the metabolic processes which act on murine recombinant IFN-gamma following its interaction with murine macrophages at physiologic temperatures. Ligand internalization was demonstrated by comparing binding of [125I]IFN-gamma to macrophages at 4 degrees C and 37 degrees C. When binding was carried out at 4 degrees C, 96% of the cell-associated [125I]IFN-gamma remained accessible at the plasma membrane and could be stripped from the cell by exposure to pronase. In contrast, at 37 degrees C, only 35% of the cell-associated radioactivity was pronase strippable. Macrophages degraded [125I]IFN-gamma into trichloroacetic acid-soluble material at 37 degrees C at a constant rate of 7000 molecules/cell/hr over a 12-hr time period. The amount of IFN-gamma degraded correlated with the amount of IFN-gamma bound to the cell surface. The receptor was neither up- nor down-regulated by ligand or by other agents known to regulate macrophage functional activity such as IFN-alpha, IFN-beta, lipopolysaccharide, or phorbol myristate acetate. The constant uptake of IFN-gamma by macrophages was due to the presence of an intracellular receptor pool (62% of the total receptor number) and to a mechanism of receptor recycling. Evidence for the latter was obtained using lysosomotropic agents which blocked degradation but not binding and internalization of ligand and caused the intracellular accumulation of receptor. By comparing the relationship between receptor occupancy and biologic response induction, two activation mechanisms became apparent. Induction of certain functions, such as H2O2 secretion, appeared to require only a single round of receptor occupancy. However, induction of more complex functions such as nonspecific tumoricidal activity appeared to require three to four rounds of receptor occupancy. These results thus support the concept that IFN-gamma internalization and receptor recycling are essential in the induction of nonspecific tumoricidal activity by macrophages.     

Cytokine-sensitive replication of hepatitis B virus in immortalized mouse hepatocyte cultures

We have previously shown that alpha/beta interferon (IFN-alpha/beta) and gamma interferon (IFN-gamma) inhibit hepatitis B virus (HBV) replication by eliminating pregenomic RNA containing viral capsids from the hepatocyte. We have also shown that HBV-specific cytotoxic T lymphocytes that induce IFN-gamma and tumor necrosis factor alpha (TNF-alpha) in the liver can inhibit HBV gene expression by destabilizing preformed viral mRNA. In order to further study the antiviral activity of IFN-alpha/beta, IFN-gamma, and TNF-alpha at the molecular level, we sought to reproduce these observations in an in vitro system. Accordingly, hepatocytes were derived from the livers of HBV-transgenic mice that also expressed the constitutively active cytoplasmic domain of the human hepatocyte growth factor receptor (c-Met). Here, we show that the resultant well-differentiated, continuous hepatocyte cell lines (HBV-Met) replicate HBV and that viral replication in these cells is efficiently controlled by IFN-alpha/beta or IFN-gamma, which eliminate pregenomic RNA-containing capsids from the cells as they do in the liver. Furthermore, we demonstrate that IFN-gamma, but not IFN-alpha/beta, is capable of inhibiting HBV gene expression in this system, especially when it acts synergistically with TNF-alpha. These cells should facilitate the analysis of the intracellular signaling pathways and effector mechanisms responsible for these antiviral effects.     

The interferon-gamma receptor in human monocytes is different from the one in nonhematopoietic cells

The receptor for interferon-gamma (IFN-gamma) on peripheral blood monocytes was characterized and was compared with that of human WISH cells. 125I-IFN-gamma was specifically bound to both cells; however, different binding characteristics were obtained. In the case of monocytes, Scatchard analysis gave an upward concave dependency curve, indicating either multiple binding sites or a negative cooperativity among the binding sites. In contrast, a linear Scatchard plot was obtained for the binding in WISH cells. Competition studies gave even more striking differences. Acid-treated IFN-gamma (95% inactivated) effectively competed with 125I-IFN-gamma for binding to the receptor on WISH cells, but not on monocytes. The significance of these differences was evaluated by analyzing the various biological activities of IFN-gamma in these two cell types. IFN-gamma was found to induce an antiviral state in WISH cells, but not in monocytes. Acid-treated IFN-gamma was found to be almost as active as IFN-gamma itself in inducing HLA-DR in WISH cells, but was almost completely inactive as an HLA-DR inducer in monocytes. It is proposed that these variations in biological activity stem from the presence of different receptors for IFN-gamma in monocytes and in WISH cells. Moreover it is suggested that the immunoregulatory functions of IFN-gamma in monocytes are related to the presence of a distinct IFN-gamma receptor in these cells.     

The antiviral response to gamma interferon

A role for alpha/beta interferon (IFN-alpha/beta) in the IFN-gamma antiviral response has long been suggested. Accordingly, possible roles for autocrine or double-stranded-RNA (dsRNA)-induced IFN-alpha/beta in the IFN-gamma response were investigated. Use was made of wild-type and a variety of mutant human fibrosarcoma cell lines, including mutant U5A cells, which lack a functional IFN-alpha/beta receptor and hence an IFN-alpha/beta response. IFN-gamma did not induce detectable levels of IFN-alpha/beta in any of the cell lines, nor was the IFN-gamma response per se dependent on autocrine IFN-alpha/beta. On the other hand, a number of responses to dsRNA [poly(I). poly(C)] and encephalomyocarditis virus were greatly enhanced by IFN-gamma pretreatment (priming) of wild-type cells or of mutant cells lacking an IFN-alpha/beta response; these include the primary induction of dsRNA-inducible mRNAs, including IFN-beta mRNA, and, to a lesser extent, the dsRNA-mediated activation of the p38 mitogen-activated protein (MAP) kinase(s). IFN-gamma priming of mRNA induction by dsRNA is dependent on JAK1 and shows biphasic kinetics, with an initial rapid (<30-min) response being followed by a more substantial effect on overnight incubation. The IFN-gamma-primed dsRNA responses appear to be subject to modulation through the p38, phosphatidylinositol 3-kinase, and ERK1/ERK2 MAP kinase pathways. It can be concluded that despite efficient priming of IFN-beta production, the IFN-alpha/beta pathways play no significant role in the primary IFN-gamma antiviral response in these cell-virus systems. The observed IFN-gamma priming of dsRNA responses, on the other hand, will likely play a significant role in combating virus infection in vivo.     

Two molecular forms of the human interferon-gamma receptor. Ligand binding, internalization, and down-regulation

The receptors for human interferon-gamma (IFN-gamma) on peripheral blood monocytes and various cells of nonhematopoietic origin were thoroughly characterized and compared. The receptors of all cell types exhibited a similar affinity for IFN-gamma (Kd approximately 1 x 10(-10) M), and in all cases receptor-mediated endocytosis and ligand degradation were demonstrated. However, the receptors differed in their molecular weights (95,000 in HeLa cells and 140,000 in monocytes, assuming a 1:1 ligand to receptor ratio) as concluded from experiments of cross-linking to 125I-IFN-gamma. Lower molecular weight species were obtained as well, particularly in monocytes. Such species could represent either degradation products or subunit structures. The monocyte and HeLa receptor responded differently to an excess of ligand. A significant receptor down-regulation was observed when monocytes were incubated with an excess of 125I-IFN-gamma, whereas no such down-regulation was observed in HeLa cells or in normal fibroblasts. This differential response was observed both in the presence or in the absence of a protein synthesis inhibitor. The receptor on monocytes was found to be acid-labile whereas that on HeLa cells was resistant to acid treatment. These and additional experiments indicate that the monocyte receptor is inactivated following internalization, whereas the HeLa receptor retains its structure and recycles back to the cell surface. The difference in the properties and fate of these two receptor subtypes is probably related to the differential functions of IFN-gamma in various cell types.     

Ligand-induced association of the type I interferon receptor components.

Two transmembrane polypeptides, IFNAR and IFN-alpha/Beta R, were previously identified as essential components of the type I interferon (IFN) receptor, but their interrelationship and role in ligand binding were not clear. To study these issues, we stably expressed and characterized the two polypeptides in host murine cells. In human cells, native IFN-alpha/beta R is a 102-kDa protein but upon reduction only a 51-kDa protein is detected. In host murine cells human IFN-alpha/beta R was expressed as a 51-kDa protein. Host cells expressing IFN-alpha/beta R bound IFN-alpha 2 with a high affinity (Kd of 3.6 nM), whereas cells expressing IFNAR exhibited no ligand binding. Upon coexpression of IFNAR and the 51-kDa IFN-alpha/beta R, the affinity for IFN-alpha 2 was increased 10-fold, approaching that of the native receptor. We show by cross-linking that both the cloned (51-kDa) and native (102-kDa) IFN-alpha/beta R bind IFN-alpha 2 to form an intermediate product, while IFNAR associates with this product to form a ternary complex. Hence, IFNAR and IFN-alpha/beta R are components of a common type I IFN receptor, cooperating in ligand binding. Ligand-induced association of IFNAR and IFN-alpha/beta R probably triggers transmembrane signaling.     

A large component of the antiviral activity of mouse interferon-gamma may be due to its induction of interferon-alpha

The finding that interferon-gamma (IFN-gamma) may require two rounds of protein synthesis to induce the antiviral state raises the possibility that this IFN may not be directly antiviral. We, therefore, examined the possibility that IFN-gamma induces one or both of the other IFNs (alpha and/or beta) which in turn induce the antiviral state. Evidence is presented showing that under certain conditions a large portion of IFN-gamma's antiviral activity in mouse L-929 cells is mediated by its induction of IFN-alpha based on the findings that: 1) the antiviral activity of IFN-gamma in cells at low densities can be blocked by poly and monoclonal antibody to IFN-alpha and, 2) IFN-alpha can be demonstrated in the supernatant fluids of IFN-gamma treated cells. This report raises the possibility that a major antiviral mechanism of IFN-gamma is via induction of IFN-alpha in the mouse system. If the majority of the antiviral activity of IFN-gamma is via induction of other IFNs, then the role and mechanism of IFN-gamma might have to be reevaluated.     

Epitope and functional specificity of monoclonal antibodies to mouse interferon-gamma: the synthetic peptide approach

Spleen cells from hamsters immunized with recombinant mouse interferon-gamma (IFN-gamma) were fused with mouse myeloma cells, resulting in the production of four anti-IFN-gamma monoclonal antibodies. Binding of 125I-IFN-gamma by these protein A-bound antibodies was specifically blocked by cold IFN-gamma. Binding by three of these antibodies was also blocked by a synthetic peptide corresponding to the N-terminal 1-39 amino acids of IFN-gamma, whereas a corresponding C-terminal (95-133) peptide had no effect on binding. The N-terminal specificity of these three antibodies was confirmed by their specific binding of 125I-N-terminal (1-39) peptide. One of the N-terminal specific monoclonal antibodies inhibited both antiviral and macrophage priming (for tumor cell killing) activities of IFN-gamma, whereas the other two had no effect on either biologic function. The selectivity of the inhibition of IFN-gamma function was not due to a differential ability of the N-terminal specific antibodies to bind IFN-gamma. Blocking experiments with cold IFN-gamma and N-terminal peptide suggest that the epitope specificities of the monoclonal antibodies could be determined by the conformational or topographic structure of IFN-gamma. An exact determination of the epitope specificity of the monoclonal antibody that inhibited IFN-gamma function could provide insight into the structural basis for the role of the N-terminal domain in the biologic function of IFN-gamma. Polyclonal antibodies to either the N-terminal or the C-terminal peptides also inhibited both the antiviral and the macrophage-priming activities of IFN-gamma. All of the antibodies that inhibited IFN-gamma function also blocked binding of IFN-gamma to membrane receptor on cells, whereas antibodies that did not block function also did not inhibit binding. The data suggest that both the N-terminal and the C-terminal domains of IFN-gamma play an important role in its antiviral and macrophage-priming functions, possibly in a cooperative manner.     

High endothelial venule morphology and function are inducible in germ-free mice: a possible role for interferon-gamma

Cytokines may facilitate lymphocyte traffic by modulating HEV structure and lymphocyte binding function in accordance with local tissue requirements. This study investigated whether the morphology of HEVs and their lymphocyte binding ligand are altered following antigenic challenge and evaluated the role of IFN-gamma in the induction of such changes. The morphology and lymphocyte binding function of mesenteric LN HEVs of GFM exposed to environmental pathogens were compared to those from GFM and conventional mice. Lymph nodes from all mice had microscopically identifiable HEVs. The morphology of HEVs from GFM was not uniform; many HEVs contained flat endothelial cells with sparse cytoplasm and prominent interendothelial gaps. The number of lymphocytes within the lumen and the HEV wall was low. In contrast, HEVs from GFME and conventional mice were characterized by cuboidal endothelial cells with plentiful cytoplasm and large numbers of lymphocytes in the vessel wall and lumen. There was no delineation of interendothelial cell borders. Lymphocyte binding to HEVs of lymph node sections from GFM was reduced (mean +/- SEM: 1.08 +/- 0.15) compared to that of conventional mice (1.91 +/- 0.20), P less than 0.003. GFME had augmented lymphocyte binding (2.23 +/- 0.26) to levels comparable with those of conventional mice. GFM injected intraperitoneally with IFN-gamma, IFN-alpha beta, or diluent resulted in minor changes in HEV morphology. By contrast, lymphocyte binding to HEV of GFM was more than doubled by the injection of IFN-gamma (1.95 +/- 0.25), P less than 0.01, but not IFN-alpha beta (0.54 +/- 0.07) or the relevant diluent controls (0.89 +/- 0.11, 0.56 +/- 0.06, respectively). It appears that the HEV binding ligand is inducible, and its expression is regulated by at least one immunomodulator, IFN-gamma. Although short-term exposure of HEVs to IFN-gamma influenced HEV function it caused only minor changes in morphology.     

Ligand-induced assembly and activation of the gamma interferon receptor in intact cells.

Functionally active gamma interferon (IFN-gamma) receptors consist of an alpha subunit required for ligand binding and signal transduction and a beta subunit required primarily for signaling. Although the receptor alpha chain has been well characterized, little is known about the specific role of the receptor beta chain in IFN-gamma signaling. Expression of the wild-type human IFN-gamma receptor beta chain in murine L cells that stably express the human IFN-gamma receptor alpha chain (L.hgR) produced a murine cell line (L.hgR.myc beta) that responded to human IFN-gamma. Mutagenesis of the receptor beta-chain intracellular domain revealed that only two closely spaced, membrane-proximal sequences (P263PSIP267 and I270EEYL274) are required for function. Coprecipitation studies showed that these sequences are necessary for the specific and constitutive association of the receptor beta chain with the JAK-2 tyrosine kinase. These experiments also revealed that the IFN-gamma receptor alpha and beta chains are not preassociated on the surface of unstimulated cells but rather are induced to associate in an IFN-gamma-dependent fashion. A chimeric protein in which the intracellular domain of the beta chain was replaced by JAK-2 complemented human IFN-gamma signaling and biologic responsiveness in L.hgR. In contrast, a c-src-containing beta-chain chimera did not. These results indicate that the sole obligate role of the IFN-gamma receptor beta chain in signaling is to recruit JAK-2 into the ligand-assembled receptor complex.     

The significance of alpha/beta interferons and gamma interferon produced in mice infected with Listeria monocytogenes

Interferon (IFN)-alpha/beta was induced in the circulation of mice infected intravenously with Listeria monocytogenes 24 to 72 hr after infection, but was not induced by the administration of heat-killed Listeria, listerial cell wall fraction (LCWF), or listerial soluble fraction. Appearance of IFN-alpha/beta showed a pattern similar to that of the growth of bacteria in the spleen and the liver of mice. IFN-alpha/beta production was abrogated by pretreatment of mice with anti-asialo GM1 antibody, antithymocyte serum, or hydrocortisone, but not with cyclophosphamide or carrageenan. Such treatments which suppressed IFN-alpha/beta production did not influence bacterial growth in the organs of mice in the early stage of Listeria infection. Administration of IFN-alpha/beta exogenously also did not. After 5 days of infection when the specific resistance against reinfection with Listeria was established, IFN-gamma but not IFN-alpha/beta was induced in the circulation 3 to 6 hr after stimulation with LCWF or reinfection with Listeria. IFN-gamma production was abrogated completely by cyclophosphamide and antithymocyte serum, and partially by hydrocortisone and carrageenan, but not by anti-asialo GM1 antibody in Listeria-infected mice treated with these agents before induction of IFN-gamma by LCWF. Presumably, IFN-alpha/beta might be produced by asialo GM1-bearing cells but IFN-gamma might not. However, IFN-gamma production was suppressed in Listeria-infected mice, when IFN-alpha/beta production had been inhibited by treatment with anti-asialo GM1 antibody or when the IFN produced had been neutralized with anti-mouse IFN-alpha/beta antibody. Therefore, it is conceivable that IFN-alpha/beta might be essential for the generation or the expression of antigen-specific T cells involving IFN-gamma production and acquired resistance during Listeria infection. In fact, the bacterial growth in the organs of mice in the early stage of infection was normal in IFN-alpha/beta-depleted mice but it resulted in the delay of T-cell-dependent elimination of bacteria from the organs of mice in the late stage.     

Modulation of monocyte type I transforming growth factor-beta receptors by inflammatory stimuli.

The regulatory mechanisms which control the wide array of cellular responses to transforming growth factor beta (TGF beta) are not understood. This report presents evidence that down-regulation of TGF beta receptors on human monocytes may be one mechanism by which the effects of TGF beta are regulated. Treatment of monocytes with interferon gamma (IFN gamma) and lipopolysaccharide for 18 h reduced monocyte receptor number (approximately 400/cell) in a dose-dependent fashion by 89 and 78%, respectively, as determined by 125I-TGF beta binding. Incubation with other cytokines (granulocyte-macrophage colony-stimulating factor, macrophage colony-stimulating factor-1, interleukin-1, tumor necrosis factor alpha) did not alter the amount of TGF beta bound. The decrease in 125I-TGF beta binding could not be attributed to competition for receptor sites by secreted TGF beta. Instead, the decline in binding was due to a loss of type I TGF beta receptors, the subtype primarily expressed by monocytes, with no decrease in receptor affinity. Lipopolysaccharide-induced receptor loss was rapid (1-4 h), in contrast to the prolonged (12 h) decline induced by IFN gamma. Loss of receptors was accompanied by a diminished ability of the cells to respond to TGF beta with an induction of TNF alpha mRNA. Thus, this monocyte system is the first example of a heterologous agent causing the down-regulation of TGF beta receptors with a concomitant decline in a TGF beta-stimulated function.     

Radiolabeling of the interferon-alpha receptor

The action of alpha interferon (IFN-alpha) is initiated by its binding to a specific cell-surface glycoprotein, the IFN-alpha receptor, which is not well characterized. IFN-alpha A was reacted with an 125I-labeled, cleavable, heterobifunctional reagent. The derivatized IFN-alpha A was bound to human Daudi cells and photoactivated, forming a covalent IFN/receptor complex of apparent molecular weight 130,000-140,000 by SDS-polyacrylamide gel electrophoresis. Cleavage of the complex produced a new 125I-labeled 110 kDa band, representing the 125I-labeled IFN-alpha receptor free of IFN-alpha. This result provides a better estimate of the apparent molecular weight of the IFN-alpha receptor, and also provides a tool for tracking the migration of the free receptor in SDS-polyacrylamide gel electrophoresis.     

Interferon-gamma is a strong modulator of NK susceptibility and expression of beta 2-microglobulin but not of transferrin receptors of K562 cells

The human cell line K562 was treated with human natural leukocyte interferon (IFN-alpha) and recombinant immune interferon (IFN-gamma). Cell cultures exposed to both types of IFNs displayed a reduced susceptibility to the cytotoxic activity of human PBL (NK activity). While this effect occurred preferentially at high doses of IFN-alpha, as little as 10 U/ml of IFN-gamma caused a marked decrease in susceptibility to NK-cell-mediated lysis. Using a monoclonal antibody against human beta2-microglobulin (beta2M) a low level of specific binding to K562 cells was detected. The binding increased after treatment with IFN-alpha (1.4-fold) and IFN-gamma (1.7-fold). The expression of transferrin receptors (TR) was not changed significantly. A hybrid cell line between K562 and a Burkitt's lymphoma-derived cell line displayed a similar pattern of response to IFN-alpha and IFN-gamma as did K562, when effects on NK susceptibility, beta2M expression, and TR expression were studied. The Burkitt's lymphoma line PUT showed no consistent changes in expression of beta2M and TR. These results demonstrate that IFN-gamma is highly efficient in modulating the NK susceptibility, and the expression of beta2M on K562. The presented data do not support a role for expression of TR as the only property that determines the degree of NK susceptibility, since there was no correlation between NK susceptibility and TR expression among the cell lines tested or when IFN-treated and untreated cells were compared.