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

Global gene expression profiling in infants with acute respiratory syncytial virus broncholitis demonstrates systemic activation of interferon signaling networks

BACKGROUND

Respiratory syncytial virus (RSV) is a leading cause of pediatric lower respiratory tract infections and has a high impact on pediatric emergency department utilization. Variation in host response may influence the pathogenesis and disease severity. We evaluated global gene expression profiles to better understand the systemic host response to acute RSV bronchiolitis in infants and young children.

METHODS

Patients (age ≤ 24 months) who were clinically diagnosed with acute bronchiolitis and who had a positive rapid test for RSV assay were recruited from the Texas Children's Hospital emergency department. Global gene expression of peripheral whole blood cells were analyzed in 21 cases and 37 age-matched healthy controls. Transcripts exhibiting significant upregulation and downregulation as a result of RSV infection were identified and confirmed in a subset of samples using RNA sequencing. The potential pathways affected were analyzed.

RESULTS

Blood was obtained from patients with acute RSV bronchiolitis (mean age 6 months). Of these, 43% were admitted to the hospital, 52% were given intravenous fluids and 24% received oxygen. Highly significant expression differences were detected in a discovery cohort of White infants (N = 33) and validated in an independent group of African-American infants (N = 19). Individuals with mild disease (N = 15) could not be distinguished from subjects with clinically moderate disease (N = 5). Pathway enrichment analyses of the differentially expressed genes demonstrated extensive activation of the innate immune response, particularly the interferon signaling network. There was a significant downregulation of transcripts corresponding to antigen presentation.

Hemophagocytosis causes a consumptive anemia of inflammation

Cytopenias of uncertain etiology are commonly observed in patients during severe inflammation. Hemophagocytosis, the histological appearance of blood-eating macrophages, is seen in the disorder hemophagocytic lymphohistiocytosis and other inflammatory contexts. Although it is hypothesized that these phenomena are linked, the mechanisms facilitating acute inflammation-associated cytopenias are unknown. We report that interferon γ (IFN-γ) is a critical driver of the acute anemia observed during diverse microbial infections in mice. Furthermore, systemic exposure to physiologically relevant levels of IFN-γ is sufficient to cause acute cytopenias and hemophagocytosis. Demonstrating the significance of hemophagocytosis, we found that IFN-γ acts directly on macrophages in vivo to alter endocytosis and provoke blood cell uptake, leading to severe anemia. These findings define a unique pathological process of broad clinical and immunological significance, which we term the consumptive anemia of inflammation.

Interferon-triggered transcriptional cascades in the oligodendroglial lineage: a comparison of induction of MHC class II antigen between oligodendroglial progenitor cells and mature oligodendrocytes

Interferon-gamma induces major histocompatibility complex class II (MHC-II) in proliferating oligodendroglial progenitor cells (OPC), but to a much lesser extent in mature oligodendrocytes. Interferon-beta has virtually no effects on MHC-II induction even in OPC. Interferon-gamma-mediated transcriptional induction of CIITA, a critical regulator of MHC-II induction, was 6-fold lower in mature oligodendrocytes than in OPC, and entirely dependent on promoter IV, suggesting that the transcriptional activity of promoter IV is down-regulated after differentiation. The distinct difference in MHC-II induction between interferon-gamma and interferon-beta is attributed to transient interferon-beta-mediated activation of STAT1-IRF1 signaling compared to the sustained interferon-gamma-mediated activation.

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.

Molecular analysis of G1B and G3A IFN gamma mutants reveals that defects in CIITA or RFX result in defective class II MHC and Ii gene induction

Class II major histocompatibility complex (MHC) genes and the invariant (Ii) gene are inducible by interferon-gamma (IFN gamma) but not by interferon-alpha and interferon-beta. The promoter regions of these genes contain three regulatory elements that mediate constitutive and IFN gamma-induced expressions; however, none of the DNA-binding proteins that interact with these elements are regulated by IFN gamma. Recently, a gene coding for a transactivator (CIITA) of class II MHC genes that complements a HLA-DR-negative immunodeficiency has been isolated. Using one IFN gamma mutant cell line (G3A) that is selectively defective in HLA-DR and Ii induction, four lines of evidence are presented to show that CIITA mediates the IFN gamma induction of HLA-DR and Ii genes. Analysis of another mutant line, G1B, indicates that the lack of DRA and Ii gene induction by IFN gamma is correlated with the lack of RFX DNA binding activity, thus providing the link between RFX and an IFN gamma response.

Successful treatment of primary progressive follicular mucinosis with interferons

Follicular mucinosis is a primary idiopathic disease or a secondary, lymphoma-associated dermatosis. An effective standard therapy for the benign group is unknown. We describe a patient with primary benign disseminated progressive follicular mucinosis who was successfully treated with recombinant interferon alfa-2b and interferon-gamma. Interferons might act by down-regulation of activated inflammatory cells and/or by induction of enhanced elimination of extracellular mucin via increasing phagocytosis by macrophages.

Granulocyte-macrophage colony-stimulating factor enhances macrophage accessory function in con A-stimulated T-cell proliferation

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been reported to augment various macrophage (M phi) functions, including antigen presentation in the antibody-producing response. We investigated the augmentative effect of GM-CSF on M phi A-cell activity in concanavalin A-stimulated T-cell proliferation. Pretreatment with GM-CSF of peritoneal M phi enhanced the T-cell proliferative response. This effect of GM-CSF was dose dependent and GM-CSF supplementation was needed at the beginning of M phi culture. We observed that GM-CSF induced M phi spreading and firm attachment accompanied with enlargement of the cytoplasm, but could not induce de novo expression of Ia antigen. GM-CSF treatment enabled M phi to produce more interleukin (IL)-1 and IL-6 upon stimulation with lipopolysaccharides or polyinosinic-polycytidylic acid, but was unable to stimulate M phi directly. This was confirmed by Northern blot analysis. These results indicate that GM-CSF augments M phi A-cell activity through the enhancement of the capacity of M phi to produce IL-1 and IL-6.