Modulation of lymphocyte proliferation and immunoglobulin synthesis by interferon-gamma and "type I" interferons

Interferon (IFN)-alpha and IFN-beta ("type I" IFNs), but not IFN-gamma reduced phytohemagglutinin- or pokeweed mitogen (PWM)-induced proliferation in cultures of human mononuclear leukocytes. Proliferation induced by specific antigens (tuberculin PPD or tetanus toxoid) or by exogenous interleukin 2 (IL-2) was strongly inhibited by type I IFNs and, to a lesser extent, by IFN-gamma as well. Inhibition of proliferation in mitogen-stimulated cultures was not due to a reduced production of IL-2 or to an inhibition of IL-2 receptor expression. Type I IFNs inhibited immunoglobulin (Ig) production in PWM-stimulated unseparated mononuclear cells, whereas IFN-gamma enhanced Ig production in such cultures. In cultures of purified B cells type I IFNs caused a stimulation of Ig production and this B-cell differentiation factor (BCDF)-like activity of IFNs was synergistically enhanced in the presence of IL-2. IFN-gamma produced less BCDF-like activity than type I IFNs. These results show that in some instances type I IFNs can be more potent in affecting functions of cells of the immune system than IFN-gamma.     

Role of type I interferons during macrophage activation by lipopolysaccharide

Activation of macrophages by bacterial lipopolysaccharide (LPS) is accompanied by the secretion of type I interferons (IFNs) which can act in an autocrine manner. We examined the role of type I IFNs in macrophage responses to LPS using bone marrow-derived macrophages (BMM) from IFNAR1-/- mice, which lack a component of the type I IFN receptor and do not respond to type I IFNs. We found that, unlike wild-type (WT) BMM, LPS-treated IFNAR1-/- cells failed to produce nitric oxide (NO), or express inducible NO synthase (iNOS), indicating that type I IFNs are essential for all LPS-stimulated NO production in BMM. Exogenously added type II IFN (IFNgamma) rescued these responses in LPS-treated IFNAR1-/- BMM. In contrast to effects on NO, type I IFNs negatively regulated respiratory burst activity in LPS-primed BMM. We also found that while type I IFNs mediated the anti-proliferative effects of lower concentrations of LPS, at higher concentrations LPS acted in a type I IFNs-independent manner. Finally, we report that type I IFNs are a survival factor for BMM. Despite this, the ability of LPS to also prevent apoptosis in BMM was independent of type I IFNs. These findings highlight the diverse roles of type I IFNs in mediating LPS-stimulated macrophage responses.     

Type I IFN protects against murine lupus

Both the type I (IFN-alpha beta) and type II (IFN-gamma) IFNs have been heavily implicated in the pathogenesis of systemic lupus erythematosus. To test the relative roles of these systems, congenic lupus-prone MRL/CD95(lpr/lpr) (MRL/lpr) mice lacking the type I IFN receptor (IFN-RI), type II IFN receptor (IFN-RII), or both, were derived. As expected, deficiency for IFN-RII protected MRL/lpr mice from the development of significant autoimmune-associated lymphadenopathy, autoantibodies, and renal disease. However, deficiency for the IFN-RI surprisingly worsened lymphoproliferation, autoantibody production, and end organ disease; animals doubly deficient for IFN-RI and IFN-RII developed an autoimmune phenotype intermediate between wild-type and IFN-RII-deficient animals, all correlating with an ability of type I IFN to suppress MRL B cell activation. Thus, type I IFNs protect against both the humoral and end organ autoimmune syndrome of MRL/lpr mice, independent of IFN-gamma. These findings warrant caution in the use of type I IFN antagonists in the treatment of autoimmune diseases and suggest further investigation into the interplay between the types I and II IFNs during the ontogeny of pathogenic autoantibodies.     

Crystal structure of Zebrafish interferons I and II reveals conservation of type I interferon structure in vertebrates

Interferons (IFNs) play a major role in orchestrating the innate immune response toward viruses in vertebrates, and their defining characteristic is their ability to induce an antiviral state in responsive cells. Interferons have been reported in a multitude of species, from bony fish to mammals. However, our current knowledge about the molecular function of fish IFNs as well as their evolutionary relationship to tetrapod IFNs is limited. Here we establish the three-dimensional (3D) structure of zebrafish IFN?1 and IFN?2 by crystallography. These high-resolution structures offer the first structural insight into fish cytokines. Tetrapods possess two types of IFNs that play an immediate antiviral role: type I IFNs (e.g., alpha interferon [IFN-α] and beta interferon [IFN-β]) and type III IFNs (lambda interferon [IFN-λ]), and each type is characterized by its specific receptor usage. Similarly, two groups of antiviral IFNs with distinct receptors exist in fish, including zebrafish. IFN?1 and IFN?2 represent group I and group II IFNs, respectively. Nevertheless, both structures reported here reveal a characteristic type I IFN architecture with a straight F helix, as opposed to the remaining class II cytokines, including IFN-λ, where helix F contains a characteristic bend. Phylogenetic trees derived from structure-guided multiple alignments confirmed that both groups of fish IFNs are evolutionarily closer to type I than to type III tetrapod IFNs. Thus, these fish IFNs belong to the type I IFN family. Our results also imply that a dual antiviral IFN system has arisen twice during vertebrate evolution.     

The interferon system of teleost fish

Interferons (IFNs) are secreted proteins, which induce vertebrate cells into an antiviral state. In mammals, three families of IFNs (type I IFN, type II IFN and IFN-lambda) can be distinguished on the basis of gene structure, protein structure and functional properties. Type I IFNs, which include IFN-alpha and IFN-beta, are encoded by intron lacking genes and have a major role in the first line of defense against viruses. The human IFN-lambdas have similar biological properties as type I IFNs, but are encoded by intron containing genes. Type II IFN is identical to IFN-gamma, which is produced by T helper 1 cells in response to mitogens and antigens and has a key role in adaptive cell mediated immunity. IFNs, which show structural and functional properties similar to mammalian type I IFNs, have recently been cloned from Atlantic salmon, channel catfish, pufferfish, and zebrafish. Teleost fish appear to have at least two type I IFN genes. Phylogenetic sequence analysis shows that the fish type I IFNs form a group separated from the avian type I IFNs and the mammalian IFN-alpha, -beta and -lambda groups. Interestingly, the fish IFNs possess the same exon/intron structure as the IFN-lambdas, but show most sequence similarity to IFN-alpha. Recently, IFN-gamma genes have also been cloned from several fish species and shown to have the same exon/intron structure as mammalian IFN-gamma genes. The antiviral effect of mammalian type I IFN is exerted through binding to the IFN-alpha/beta-receptor, which triggers signal transduction through the JAK-STAT signal transduction pathway resulting in expression of Mx and other antiviral proteins. Putative IFN receptor genes have been identified in pufferfish. Several interferon regulatory factors and members of the JAK-STAT pathway have also been identified in various fish species. Moreover, Mx and several other interferon stimulated genes have been cloned and studied in fish. Furthermore, antiviral activity of Mx protein from Atlantic salmon and Japanese flounder has recently been demonstrated.     

Human primary immunodeficiencies of type I interferons

Type I interferons (IFN-alpha/beta and related molecules) are essential for protective immunity to experimental infection by numerous viruses in the mouse model. In recent years, human primary immunodeficiencies affecting either the production of (UNC-93B deficiency) or the response to (STAT1 and TYK2 deficiencies) these IFNs have been reported. Affected patients are highly susceptible to certain viruses. Patients with STAT1 or TYK2 deficiency are susceptible to multiple viruses, including herpes simplex virus-1 (HSV-1), whereas UNC-93B-deficient patients present isolated HSV-1 encephalitis. However, these immunological defects are not limited to type I IFN-mediated immunity. Impaired type II IFN (IFN-gamma)-mediated immunity plays no more than a minor role in the pathogenesis of viral diseases in these patients, but the contribution of impaired type III IFN (IFN-lambda)-mediated immunity remains to be determined. These novel inherited disorders strongly suggest that type I IFN-mediated immunity is essential for protection against natural infections caused by several viruses in humans.     

Expression of a novel murine type I IFN in the pancreatic islets induces diabetes in mice

IFN-kappa belongs to a recently identified subclass of type I IFNs. In this study, we report the cloning and preliminary characterization of the murine homologue of IFN-kappa. The gene encodes a 200-aa protein which is 38.5% homologous to human IFN-kappa. Murine IFN-kappa contains four cysteines in analogous positions to those observed in the IFN-alpha and an additional fifth unique cysteine, C174. The murine gene is located on chromosome 4, where other type I murine IFN genes, IFN-alpha and IFN-beta, are clustered. This region is syntenic with human chromosome 9 where the gene encoding IFN-kappa and the type I IFN gene cluster are found. Mouse IFN-kappa is expressed at low levels in peritoneal macrophages and its expression is up-regulated by dsRNA and IFN-gamma. Similar to previously reported transgenic mice carrying type I and type II IFNs, transgenic mice overexpressing murine IFN-kappa in the beta cells of the pancreas develop overt diabetes with hyperglycemia. Histological characterization of pancreatic islets from these transgenic mice showed inflammatory infiltrates with corresponding destruction of beta cells.     

Simultaneous production of IFN-gamma, IFN-alpha/beta and nitric oxide in peritoneal macrophages from TDM-treated mice

Peritoneal macrophages (PM) were isolated from mice treated with Dimycolate of Trehalose (TDM), a glycolipid extracted from the cell wall of Mycobacterium tuberculosis. PM from TDM-treated mice (TDM-PM) were shown to secrete consistent amount of IFN-gamma, which was not detectable in control Resident-PM (Res-PM), as revealed by ELISA. In addition, biologically active IFN was detected in the supernatants of TDM-PM, whereas no IFN production was found in those of control Res-PM. The addition of specific antisera to PM cultures revealed the simultaneous production of both type I and II IFNs in TDM-PM cultures. No reciprocal regulation in the production of IFN-gamma and IFN-alpha/beta was found in these cultures. In parallel, nitric oxide (NO) production was measured in TDM-PM cultures by detecting nitrites (NO2-). TDM-PM cultures accumulated high amounts of NO2- which decreased to the level of Res-PM in the presence of NMMA, an inhibitor of NO-synthases. In vitro, neither type I nor type II IFNs were involved in the stimulation of NO production. The capacity of macrophages to simultaneously secrete IFN-gamma, IFN-alpha/beta and NO upon in vivo TDM-treatment could be of particular relevance for the defense process of innate immunity in which macrophages play a crucial role.     

Dissection of a type I interferon pathway in controlling bacterial intracellular infection in mice

Defence mechanisms against intracellular bacterial pathogens are incompletely understood. Our study characterizes a type I IFN-dependent cell-autonomous defence pathway directed against Legionella pneumophila, an intracellular model organism and frequent cause of pneumonia. We show that macrophages infected with L. pneumophila produced IFNβ in a STING- and IRF3- dependent manner. Paracrine type I IFNs stimulated upregulation of IFN-stimulated genes and a cell-autonomous defence pathway acting on replicating and non-replicating Legionella within their specialized vacuole. Our infection experiments in mice lacking receptors for type I and/or II IFNs show that type I IFNs contribute to expression of IFN-stimulated genes and to bacterial clearance as well as resistance in L. pneumophila pneumonia in addition to type II IFN. Overall, our study shows that paracrine type I IFNs mediate defence against L. pneumophila, and demonstrates a protective role of type I IFNs in in vivo infections with intracellular bacteria.     

Distinct evolution process among type I interferon in mammals

Interferon (IFN) is thought to play an important role in the vertebrate immune system, but systemic knowledge of IFN evolution has yet to be elucidated. To evaluate the phylogenic distribution and evolutionary history of type I IFNs, 13gen omes were searched using BLASTn program, and a phylogenetic tree of vertebrate type I IFNs was constructed. In the present study, an IFNδ-like gene in the human genome was identified, refuting the concept that humans have no IFNδ genes, and other mammalian IFN genes were also identified. In the phylogenetic tree, the mammalian IFNβ, IFN?, and IFNκ formed a clad e sepa rate f rom the other mammalian type I IFNs, while piscine and avian IFNs formed distinct clades. Based on this phylogenetic analysis and the various characteristics of type I IFNs, the evolutionary history of type I IFNs was further evaluated. Our data indicate that an ancestral IFNα-like gene forms a core from which new IFNs divided during vertebrate evolution. In addition, the data suggest how the other type I IFNs evolved from IFNα and shaped the complex type I IFN system. The promoters of type I IFNs were conserved among different mammals, as well as their genic regions. However, the intergenic regions of type I IFN clusters were not conserved among different mammals, demonstrating a high selec tion pressure upon type I IFNs during their evolution.