Down-regulation of macrophage Ia mRNA expression by interferon (IFN)-alpha and IFN-beta mediated by de novo synthesized protein

Exogenous and endogenous type I interferons inhibit interferon-gamma-induced nitric oxide production and nitric oxide synthase expression in murine peritoneal macrophages

We investigated the effect of type I IFNs (IFN-alpha and IFN-beta) on IFN-gamma-induced nitric oxide (NO) production by murine peritoneal macrophages. It was found that exogenous and also endogenous type I IFNs suppressed IFN-gamma-induced NO production, cytosolic inducible NO synthase (iNOS) activity, and iNOS mRNA accumulation in macrophages. Furthermore, we show here that type I IFNs prevent the NO-mediated deterioration of mitochondrial respiratory activity in macrophages. These results seem to indicate a possible protective role of type I IFNs against the NO-mediated immunosuppressive and/or cytotoxic effect of macrophages.

Counteracting effect of interferon-alpha and -beta on interferon- gamma-induced production of nitric oxide which is suppressive for antibody response

We investigated the nitric oxide (NO)-mediated immunosuppressive activity of macrophages and the regulatory effect of type I (alpha and beta) interferons (IFNs) on IFN-gamma-induced NO production by macrophages. In the sheep red blood cell (SRBC)-specific secondary antibody response in vitro, the addition of macrophages to the culture of primed spleen cells substantially decreased the number of plaque-forming cells. The concentration of nitrite in the culture supernatant showed a positive correlation with the number of macrophages added in a dose- dependent manner, and the addition of NMMA, a potent inhibitor of NO production, resulted in the restoration of of the response. In addition, anti-IFN-gamma antibody abolished the ability of the immune culture supernatant to stimulate macrophages to produce NO. Therefore, the macrophage-dependent immunosuppression was due primarily to NO that was produced by macrophages in response to IFN-gamma derived from responding lymphocytes. The pretreatment of macrophages with IFN-alpha or -beta gave rise to a dramatic reduction of IFN-gamma-mediated NO production. In addition, the suppressive activity of these macrophages was much lower than that of untreated macrophages. These results indicate that type I IFNs can regulate the immune response by modulating IFN-gamma-induced production of immunosuppressive NO.

The role of interferon beta in human cytomegalovirus-mediated inhibition of HLA DR induction on endothelial cells

Human cytomegalovirus (HCMV), a member of the virus family Herpesviridae that is associated with extensive worldwide morbidity and mortality in immunocompromised hosts, inhibits interferon-gamma (IFN gamma)-mediated induction of human leukocyte antigen (HLA) class II antigens on endothelial cells. In this study, the ability of HCMV-infected endothelial cells to synthesize interferon-beta (IFN beta), and the role of IFN beta in HCMV-mediated inhibition of HLA class II induction, was investigated. As determined by an encephalomyocarditis virus protection assay, HCMV-infected endothelial cell culture supernatants contained 240 IU/ml of IFN type I activity, of which 99.9% was IFN beta, as compared to the absence of IFN beta in mock-infected culture supernatants. UV-irradiated supernatants from HCMV-infected cultures inhibited induction of HLA class II in noninfected cultures by 24%. This inhibition could be abolished with 500 NU/ml of anti-IFN beta antibody. Addition of anti-IFN beta antibody directly to HCMV-infected cultures mitigated but did not abolish HLA class II antigen inhibition. Dual immunohistochemistry for HCMV and HLA DR demonstrated that infected cells, in contrast to noninfected cells, were rarely induced to express HLA class II even in the presence of anti-IFN beta antibody. These findings suggest that HCMV inhibits induction of HLA class II antigens by IFN beta dependent and independent mechanisms.

Tumor-induced modulation of macrophage class II MHC molecule mRNA expression

Class II MHC protein expression in macrophages (M phi) is reduced during tumor growth. Because regulation of class II MHC proteins occurs during transcription, tumor growth may suppress class II MHC protein expression by suppressing mRNA. The decrease in class II mRNA may result from (i) a decrease in M phi responsiveness to an inducing agent, such as interferon-gamma (IFN-gamma), or (ii) an increase in M phi sensitivity to suppressing agents, such as prostaglandin E2 (PGE2). To determine how tumors induce suppression of class II mRNA, M phi were cultured in the presence of IFN-gamma with or without other factors, and Northern blot analyses were performed. Unstimulated normal host (NH) or tumor-bearing host (TBH) M phi do not express detectable class II mRNA. The addition of IFN-gamma induces class II mRNA expression in NH and TBH M phi, but class II mRNA expression is significantly lower in TBH M phi. Kinetic studies suggested that NH M phi class II mRNA is induced faster and in greater amounts than TBH M phi class II mRNA. There is a decrease in M phi class II mRNA stability during tumor growth that may account for the decreased induction by IFN-gamma. Lipopolysaccharide (LPS) suppresses class II mRNA induction in both NH and TBH IFN-gamma-treated M phi, but TBH M phi are more sensitive to its suppression. PGE2 and tumor-necrosis factor-alpha (TNF-alpha), two factors produced by LPS-stimulated M phi, were tested for their ability to modulate class II mRNA expression in NH and TBH IFN-gamma-treated M phi. PGE2 suppressed class II mRNA expression in both NH and TBH M phi. The addition of TNF-alpha to IFN-gamma-treated M phi suppressed class II mRNA in NH M phi but, surprisingly, had an additive effect on IFN-gamma-induced class II mRNA expression. TNF-alpha did not induce class II mRNA expression in TBH M phi in the absence of IFN-gamma. The cause of the reduced class II mRNA expression during tumor growth is a decreased response to IFN-gamma and an increased sensitivity to PGE2. This change may cause the observed suppression mediated by TBH M phi.

Suppression of macrophage Ia antigen expression by endogenous interferon-alpha/beta

Exogenous interferon-alpha (IFN-alpha) and interferon-beta (IFN-beta) (type I IFNs) are known to suppress the IFN-gamma-dependent expression of class II MHC (Ia) antigens on macrophages (M phi). We report here that the endogenous type I IFNs produced by M phi in response to IFN inducers regulate Ia expression of the M phi themselves. Coculture of M phi with IFN-gamma and polyinosinic-polycytidylic acid [poly(I):poly(C)] resulted in the reduction of Ia expression in comparison with those cultured without poly(I):poly(C). Pretreatment of M phi with poly(I):poly(C) or a bacterial lipopolysaccharide (LPS), which is also a potent IFN inducer, in vitro or in vivo, before being exposed to IFN-gamma was also effective in suppressing the Ia expression. Such suppression was abolished by the addition of anti-IFN-alpha/beta antibodies to the M phi culture along with IFN-gamma. M phi cultured with L-cell conditioned medium (LCM) containing M-CSF were less capable of expressing Ia antigens than those cultured without LCM. The Ia-expressing ability of LCM-treated M phi was also restored by the addition of anti-IFN-alpha/beta antibodies. M phi in the early stage of sterile inflammation were less responsive to IFN-gamma than those in the late stage. These results suggest that endogenous type I IFNs, which are produced in response to natural or synthetic IFN-inducers, regulate M phi Ia expression in an autocrinal manner.

Downregulation of Newcastle disease virus (NDV)-dependent IFN-alpha/beta production in macrophages by IFN-induced gene products of the locus If-1

We have found that in cultured mouse bone-marrow-derived macrophages (BMDM), endogenous IFN-beta specifically regulates Newcastle disease virus (NDV) induced interferon (IFN)-alpha/beta synthesis, possibly by influencing the activity of genes within the regulatory locus If-1. Comparison of anti-IFN-beta-treated BMDM from C57BL/6 mice and the congenic line B.6C-H28c carrying the high (h) or low (l) producer allele of If-1, respectively, revealed a much stronger response of the If-1l allele to exogenous IFN-alpha treatment. Twenty IU rIFN-alpha 4 were sufficient to induce nearly complete suppression of NDV-induced IFN-alpha and IFN-beta production in BMDM from B6.C-H28c mice, but had no effect on the IFN-alpha/beta response induced by Sendai virus, another member of the paramyxovirus group. Simultaneous treatment of BMDM with cycloheximide inhibited the suppressive effect of rIFN-alpha 4, indicating that IFN induced the expression of one or several new proteins encoded by gene(s) within the If-1l locus which are responsible for the NDV-specific downregulation of IFN-alpha/beta production. A time course analysis indicated that the suppressive activity of IFN-induced If-1l gene products took 12 h to develop. It was preceded by an opposite priming effect, leading to enhancement of the early IFN-alpha/beta response to NDV measured 5 h after infection. This priming effect in BMDM was, however, only visible during an 8-h period of IFN-alpha treatment, whereas in the continued presence of IFN for 12 h or longer, priming was superimposed by the inhibitory action of the If-1l gene products.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporin A regulates the expression of HLA-DR on human monocytes by two different mechanisms

Cyclosporin A (CsA), but not its nonimmunosuppressive analog cyclosporin H (CsH), inhibited the expression of HLA-DR in human monocytes. Induction of HLA-DR by interferon (IFN)-gamma in fresh monocytes was also inhibited by CsA and not by CsH. However, when monocytes were pretreated with either CsA or CsH for 16 hr prior to the addition of IFN-gamma, HLA-DR expression was increased, probably because of a cyclosporin-induced increase in the number of IFN-gamma receptors. Down-regulation of the HLA-DR mRNA by CsA was found to be dependent on continuous protein synthesis. IFN-alpha also inhibited the IFN-gamma-induced HLA-DR mRNA expression and showed synergy with CsA at low concentrations but not at high concentrations of the drugs. A common mechanistic element in the pathways of CsA and IFN-alpha is proposed.

Interferon-alpha and interferon-beta induce Ia expression in limited protein synthesis condition

We investigated the regulatory effect of interferons (IFNs) on macrophage (m phi) Ia antigen expression. Unlike type II IFN (IFN-gamma), type I IFNs (IFN-alpha and IFN-beta) were incapable of inducing the accumulation of Ia mRNA. However, when cultured with type I IFN plus cycloheximide (CHX), M phi accumulated significant amounts of Ia-specific mRNA, which was translated into Ia molecules expressed on the cell surface after the removal of CHX. Significant enhancement of Ia mRNA accumulation and the Ia expression were observed also in M phi stimulated with IFN-gamma plus CHX. Type I IFNs suppressed IFN-gamma-dependent Ia expression through the inhibition of Ia mRNA accumulation, but such suppression was not directed to the post-transcriptional step in M phi that had accumulated Ia mRNA in response to stimulation by type I or type II IFN plus CHX. These results seem to indicate that type I IFNs can induce Ia mRNA accumulation but that they also induce some inhibitory protein, the synthesis of which precedes it and is dominant, so that the Ia expression is masked.

Suppression of macrophage Ia antigen expression by endogenous interferon-alpha/beta

Exogenous interferon-alpha (IFN-alpha) and interferon-beta (IFN-beta) (type I IFNs) are known to suppress the IFN-gamma-dependent expression of class II MHC (Ia) antigens on macrophages (M phi). We report here that the endogenous type I IFNs produced by M phi in response to IFN inducers regulate Ia expression of the M phi themselves. Coculture of M phi with IFN-gamma and polyinosinic-polycytidylic acid [poly(I):poly(C)] resulted in the reduction of Ia expression in comparison with those cultured without poly(I):poly(C). Pretreatment of M phi with poly(I):poly(C) or a bacterial lipopolysaccharide (LPS), which is also a potent IFN inducer, in vitro or in vivo, before being exposed to IFN-gamma was also effective in suppressing the Ia expression. Such suppression was abolished by the addition of anti-IFN-alpha/beta antibodies to the M phi culture along with IFN-gamma. M phi cultured with L-cell conditioned medium (LCM) containing M-CSF were less capable of expressing Ia antigens than those cultured without LCM. The Ia-expressing ability of LCM-treated M phi was also restored by the addition of anti-IFN-alpha/beta antibodies. M phi in the early stage of sterile inflammation were less responsive to IFN-gamma than those in the late stage. These results suggest that endogenous type I IFNs, which are produced in response to natural or synthetic IFN-inducers, regulate M phi Ia expression in an autocrinal manner.