IFITM3 restricts virus-induced inflammatory cytokine production by limiting Nogo-B mediated TLR responses.

Interferon-induced transmembrane protein 3 (IFITM3) is a restriction factor that limits viral pathogenesis and exerts poorly understood immunoregulatory functions. Here, using human and mouse models, we demonstrate that IFITM3 promotes MyD88-dependent, TLR-mediated IL-6 production following exposure to cytomegalovirus (CMV). IFITM3 also restricts IL-6 production in response to influenza and SARS-CoV-2. In dendritic cells, IFITM3 binds to the reticulon 4 isoform Nogo-B and promotes its proteasomal degradation. We reveal that Nogo-B mediates TLR-dependent pro-inflammatory cytokine production and promotes viral pathogenesis in vivo, and in the case of TLR2 responses, this process involves alteration of TLR2 cellular localization. Nogo-B deletion abrogates inflammatory cytokine responses and associated disease in virus-infected IFITM3-deficient mice. Thus, we uncover Nogo-B as a driver of viral pathogenesis and highlight an immunoregulatory pathway in which IFITM3 fine-tunes the responsiveness of myeloid cells to viral stimulation.

Interferon-Induced Transmembrane Protein 1 Restricts Replication of Viruses That Enter Cells via the Plasma Membrane.

The acute antiviral response is mediated by a family of interferon-stimulated genes (ISGs), providing cell-intrinsic immunity. Mutations in genes encoding these proteins are often associated with increased susceptibility to viral infections. One family of ISGs with antiviral function is the interferon-inducible transmembrane proteins (IFITMs), of which IFITM3 has been studied extensively. In contrast, IFITM1 has not been studied in detail. Since IFITM1 can localize to the plasma membrane, we investigated its function with a range of enveloped viruses thought to infect cells by fusion with the plasma membrane. Overexpression of IFITM1 prevented infection by a number of Paramyxoviridae and Pneumoviridae, including respiratory syncytial virus (RSV), mumps virus, and human metapneumovirus (HMPV). IFITM1 also restricted infection with an enveloped DNA virus that can enter via the plasma membrane, herpes simplex virus 1 (HSV-1). To test the importance of plasma membrane localization for IFITM1 function, we identified blocks of amino acids in the conserved intracellular loop (CIL) domain that altered the subcellular localization of the protein and reduced antiviral activity. By screening reported data sets, 12 rare nonsynonymous single nucleotide polymorphisms (SNPs) were identified in human IFITM1, some of which are in the CIL domain. Using an Ifitm1-/- mouse, we show that RSV infection was more severe, thereby extending the range of viruses restricted in vivo by IFITM proteins and suggesting overall that IFITM1 is broadly antiviral and that this antiviral function is associated with cell surface localization.IMPORTANCE Host susceptibility to viral infection is multifactorial, but early control of viruses not previously encountered is predominantly mediated by the interferon-stimulated gene (ISG) family. There are upwards of 300 of these genes, the majority of which do not have a clearly defined function or mechanism of action. The cellular location of these proteins may have an important effect on their function. One ISG located at the plasma membrane is interferon-inducible transmembrane protein 1 (IFITM1). Here we demonstrate that IFITM1 can inhibit infection with a range of viruses that enter via the plasma membrane. Mutant IFITM1 proteins that were unable to localize to the plasma membrane did not restrict viral infection. We also observed for the first time that IFITM1 plays a role in vivo, and Ifitm1-/- mice were more susceptible to viral lung infection. These data contribute to our understanding of how ISGs prevent viral infections.

Characterization in mice of the immunological properties of five allergenic acid anhydrides.

Occupational exposure to certain acid anhydrides, including trimellitic anhydride (TMA), maleic anhydride (MA), phthalic anhydride (PA), hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA), has been associated with the development of respiratory allergy or asthma. There is considerable debate about the mechanisms through which such chemicals may cause respiratory sensitization, particularly concerning a universal requirement for specific IgE antibody. Despite the controversy regarding an obligatory role for IgE, there is a growing consensus that chemical respiratory hypersensitivity is associated with the selective development of T lymphocytes with a type 2 (Th2) phenotype. In the current investigations we have characterized in mice the nature of immune responses provoked by prolonged topical exposure to five acid anhydrides. Under application conditions where similar overall immunogenicity was achieved, we have compared cytokine responses induced by PA, MA, HHPA and MTHPA with those provoked by concurrent exposure to TMA or to the reference contact allergen 2, 4-dinitrochlorobenzene (DNCB). Lymph node cells (LNC) draining the site of topical exposure to DNCB invariably expressed high levels of the type 1 cytokines interferon-gamma (IFN-gamma) and interleukin-12 (IL-12), but only low levels of the type 2 cytokines interleukin-4 (IL-4) and interleukin-10 (IL-10). In each experiment, TMA-activated LNC displayed the converse, type 2, phenotype of cytokine production. The other acid anhydrides in each case provoked a type 2 cytokine secretion profile, with comparable IL-10 expression but somewhat less vigorous IL-4 production compared with that observed following exposure to the reference respiratory allergen TMA. In every experiment relatively low levels of IFN-gamma and IL-12 were elaborated by acid anhydride-activated LNC, with the exception of PA-stimulated LNC that displayed increased amounts of IL-12 in comparison with other acid anhydrides. Thus, prolonged topical exposure of mice to five different acid anhydrides in each case resulted in the development of a predominantly Th2-type cytokine secretion phenotype, consistent with the ability of these materials to provoke asthma and respiratory allergy through a type 2 (possibly IgE-mediated) mechanism. Taken together with the results of previous investigations with a wider range of chemical allergens, these data suggest that induced cytokine secretion patterns or 'fingerprints' allow discrimination between contact and respiratory allergens and consequently represent a suitable approach to prospective evaluation of respiratory sensitization hazard.