Melanoma differentiation-associated protein-5 (MDA-5) limits early viral replication but is not essential for the induction of type 1 interferons after Coxsackievirus infection

AbstractCoxsackievirus infections are associated with severe diseases such as myocarditis, meningitis and pancreatitis. To study the contribution of the intracellular viral sensor melanoma differentiation-associated protein-5 (MDA-5) in the host immune response to Coxsackievirus B3 (CVB3) we infected C57BL/6 and 129/SvJ mice lacking mda-5. Mice deficient in MDA-5 showed a dramatically increased susceptibility to CVB3 infection. The loss of MDA-5 allowed the virus to replicate faster, resulting in increased liver and pancreas damage and heightened mortality. MDA-5 was not absolutely required for the induction of type 1 interferons (IFNs), but essential for the production of maximal levels of systemic IFN-α early after infection. Taken together, our findings indicate that MDA-5 plays an important role in the host immune response to CVB3 by preventing early virus replication and limiting tissue pathology

An IFIH1 gene polymorphism associated with risk for autoimmunity regulates canonical antiviral defence pathways in Coxsackievirus infected human pancreatic islets

The IFIH1 gene encodes the pattern recognition receptor MDA5. A common polymorphism in IFIH1 (rs1990760, A946T) confers increased risk for autoimmune disease, including type 1-diabetes (T1D). Coxsackievirus infections are linked to T1D and cause beta-cell damage in vitro. Here we demonstrate that the rs1990760 polymorphism regulates the interferon (IFN) signature expressed by human pancreatic islets following Coxsackievirus infection. A strong IFN signature was associated with high expression of IFNλ1 and IFNλ2, linking rs1990760 to the expression of type III IFNs. In the high-responding genotype, IRF-1 expression correlated with that of type III IFN, suggesting a positive-feedback on type III IFN transcription. In summary, our study uncovers an influence of rs1990760 on the canonical effector function of MDA5 in response to an acute infection of primary human parenchymal cells with a clinically relevant virus linked to human T1D. It also highlights a previously unrecognized connection between the rs1990760 polymorphism and the expression level of type III IFNs.</p

Early and nonreversible decrease of CD161++ /MAIT cells in HIV infection

HIV infection is associated with immune dysfunction, perturbation of immune-cell subsets and opportunistic infections. CD161++ CD8+ T cells are a tissue-infiltrating population that produce IL17A, IL22, IFN, and TNFα, cytokines important in mucosal immunity. In adults they dominantly express the semi-invariant TCR Vα7.2, the canonical feature of mucosal associated invariant T (MAIT) cells and have been recently implicated in host defense against pathogens. We analyzed the frequency and function of CD161++ /MAIT cells in peripheral blood and tissue from patients with early stage or chronic-stage HIV infection. We show that the CD161++ /MAIT cell population is significantly decreased in early HIV infection and fails to recover despite otherwise successful treatment. We provide evidence that CD161++ /MAIT cells are not preferentially infected but may be depleted through diverse mechanisms including accumulation in tissues and activation-induced cell death. This loss may impact mucosal defense and could be important in susceptibility to specific opportunistic infections in HIV

Light-driven chloride transport kinetics of halorhodopsin

Despite growing interest in light-driven ion pumps for use in optogenetics, current estimates of their transport rates span two orders of magnitude due to challenges in measuring slow transport processes and determining protein concentration and/or orientation in membranes in vitro. In this study, we report, to our knowledge, the first direct quantitative measurement of light-driven Cl transport rates of the anion pump halorohodopsin from Natronomonas pharaonis (NpHR). We used light-interfaced voltage clamp measurements on NpHR-expressing oocytes to obtain a transport rate of 219 (± 98) Cl /protein/s for a photon flux of 630 photons/protein/s. The measurement is consistent with the literature-reported quantum efficiency of ∼30% for NpHR, i.e., 0.3 isomerizations per photon absorbed. To reconcile our measurements with an earlier-reported 20 ms rate-limiting step, or 35 turnovers/protein/s, we conducted, to our knowledge, novel consecutive single-turnover flash experiments that demonstrate that under continuous illumination, NpHR bypasses this step in the photocycle

An IFIH1 gene polymorphism associated with risk for autoimmunity regulates canonical antiviral defence pathways in Coxsackievirus infected human pancreatic islets

The IFIH1 gene encodes the pattern recognition receptor MDA5. A common polymorphism in IFIH1 (rs1990760, A946T) confers increased risk for autoimmune disease, including type 1-diabetes (T1D). Coxsackievirus infections are linked to T1D and cause beta-cell damage in vitro. Here we demonstrate that the rs1990760 polymorphism regulates the interferon (IFN) signature expressed by human pancreatic islets following Coxsackievirus infection. A strong IFN signature was associated with high expression of IFNλ1 and IFNλ2, linking rs1990760 to the expression of type III IFNs. In the high-responding genotype, IRF-1 expression correlated with that of type III IFN, suggesting a positive-feedback on type III IFN transcription. In summary, our study uncovers an influence of rs1990760 on the canonical effector function of MDA5 in response to an acute infection of primary human parenchymal cells with a clinically relevant virus linked to human T1D. It also highlights a previously unrecognized connection between the rs1990760 polymorphism and the expression level of type III IFNs

Immune dysregulation in patients with PTEN hamartoma tumor syndrome: Analysis of FOXP3 regulatory T cells

Background: Patients with heterozygous germline mutations in PTEN (phosphatase and tensin homologue deleted on chromosome 10) develop autoimmunity and lymphoid hyperplasia. Objectives: Since regulation of the phosphoinositol-3-kinase (PI3K) pathway is critical for maintaining regulatory T cell (Treg) functions we investigate Tregs in patients with heterozygous germline PTEN mutations (PTEN harmatoma tumour syndrome, PHTS). Methods: PHTS patients were assessed for immunological conditions, lymphocyte subsets, FOXP3+ Treg levels and phenotype. To determine the functional importance of phosphatases that control the PI3K pathway we assessed Treg induction in vitro, mitochondrial depolarization, and recruitment of PTEN to the immunological synapse. Results: Autoimmunity and peripheral lymphoid hyperplasia was found in 43% of 79 PHTS patients. Immune dysregulation in PHTS patients included lymphopenia, CD4+ T cell reduction and changes in T and B cell subsets. Although total CD4+FOXP3+ Treg numbers are reduced, frequencies are maintained in blood and intestine. Despite pathogenic PTEN mutations, the FOXP3+ T cells are phenotypically normal. We show that the phosphatase PHLPP downstream of PTEN is highly expressed in normal human Tregs and provides complementary phosphatase activity. PHLPP is indispensable for the differentiation of induced Tregs in vitro and Treg mitochondrial fitness. PTEN and PHLPP form a phosphatase network that is polarized at the immunological synapse. Conclusion: Heterozygous loss of function of PTEN in humans has an significant impact on T and B cell immunity. Assembly of the PTEN-PHLPP phosphatase network allows coordinated phosphatase activities at the site of T cell receptor activation, which is important for limiting PI3K hyperactivation in Tregs despite PTEN haploinsufficiency. </p

A Link Between a Common Mutation in CFTR and Impaired Innate and Adaptive Viral Defense

textabstractAcute respiratory virus infections predispose the cystic fibrosis (CF) lung to chronic bacterial colonization, which contributes to high mortality. For reasons unknown, respiratory virus infections have a prolonged duration in CF. Here, we demonstrate that mice carrying the most frequent cystic fibrosis transmembrane conductance regulator (CFTR) mutation in humans, ΔF508, show increased morbidity and mortality following infection with a common human enterovirus. ΔF508 mice demonstrated impaired viral clearance, a slower type I interferon response and delayed production of virus-neutralizing antibodies. While the ΔF508 mice had a normal immune cell repertoire, unchanged serum immunoglobulin concentrations and an intact immune response to a T-cell-independent antigen, their response to a T-cell-dependent antigen was significantly delayed. Our studies reveal a novel function for CFTR in antiviral immunity and demonstrate that the ΔF508 mutation in cftr is coupled to an impaired adaptive immune response. This important insight could open up new approaches for patient care and treatment