Project description:Influenza A viruses (IAV) cause seasonal outbreaks that pose a substantial burden on human health. They are also a zoonotic threat as avian and swine IAV can be a source for pandemic influenza. Receptor specificity is a critical determinant of tropism, host range and transmissibility of IAV and thus, plays a crucial role in zoonotic IAV infections1-3. Avian, swine and human IAV bind sialic acid on host cell glycans as their common receptor but differ in sialic acid specificity4,5. In contrast, bat IAV of the H17 and H18 subtypes cannot use sialic acid and require MHC class II complexes for host cell entry6-8. It is unknown how this difference in receptor specificity evolved and if dual receptor specificity for sialic acid and MHC class II is possible. Here, we show that human H2N2 IAV and related avian H2N2 possess dual receptor specificity. In addition to their known sialic acid-dependent entry they can use MHC class II as alternative entry pathway, independent of sialic acid. Of note, MHC class II from humans, pigs, ducks, swans and chickens but not from bats can mediate H2 IAV entry and the ability to use this alternative entry pathway is conserved in current Eurasian avian H2 IAV. Our results demonstrate that IAV can possess dual receptor specificity for sialic acid and MHC class II and suggest a role for MHC class II-dependent entry in zoonotic IAV infections.
Project description:Zoonotic influenza A viruses of avian origin can cause severe disease in individuals, or even global pandemics, and thus pose a threat to human populations. Waterfowl and shorebirds are believed to be the reservoir for all influenza A viruses, but this has recently been challenged by the identification of novel influenza A viruses in bats. The major bat influenza A virus envelope glycoprotein, haemagglutinin, does not bind the canonical influenza A virus receptor, sialic acid or any other glycan, despite its high sequence and structural homology with conventional haemagglutinins. This functionally uncharacterized plasticity of the bat influenza A virus haemagglutinin means the tropism and zoonotic potential of these viruses has not been fully determined. Here we show, using transcriptomic profiling of susceptible versus non-susceptible cells in combination with genome-wide CRISPR-Cas9 screening, that the major histocompatibility complex class II (MHC-II) human leukocyte antigen DR isotype (HLA-DR) is an essential entry determinant for bat influenza A viruses. Genetic ablation of the HLA-DR α-chain rendered cells resistant to infection by bat influenza A virus, whereas ectopic expression of the HLA-DR complex in non-susceptible cells conferred susceptibility. Expression of MHC-II from different bat species, pigs, mice or chickens also conferred susceptibility to infection. Notably, the infection of mice with bat influenza A virus resulted in robust virus replication in the upper respiratory tract, whereas mice deficient for MHC-II were resistant. Collectively, our data identify MHC-II as a crucial entry mediator for bat influenza A viruses in multiple species, which permits a broad vertebrate tropism.
Project description:Oligodendrocytes and their progenitors upregulate MHC pathways in response to inflammation, but the frequency of this phenotypic change is unknown and the features of these immune oligodendroglia are poorly defined. We generated MHC class I and II transgenic reporter mice to define their dynamics in response to inflammatory demyelination, providing a means to monitor MHC activation in diverse cell types in living mice and define their roles in aging, injury and disease.
Project description:A novel avian-origin H7N9 influenza A virus (IAV) emerged in China in early 2013 causing mild to lethal human respiratory infections. H7N9 originated from multiple reassortment events between avian viruses and carries genetic markers of human adaptation. Determining whether H7N9 induces a host-response closer to human or avian IAV is important to better characterize this emerging virus. Here we compared the human lung epithelial cell response to infection with A/Anhui/01/13 (H7N9) or highly pathogenic avian-origin H5N1, H7N7, or human seasonal H3N2 IAV.
Project description:The tumoricidal effects of CD8+T cells are well acknowledged, but how MHC Ib-restricted CD8+T (Ib-CD8+T) cells contribute to anti-tumor immunity remains obscure. Here, we show that infusion of MHC Ia+ cells to Kb-/-Db-/- mice induced the expansion of Ib-CD8+T cells in tumors and potently inhibited tumor progression. Such priming of Ib-CD8+T cells by MHC-Ia is not MHC haplotype restricted and MHC Ia tetramers alone can prime Ib-CD8+T cells for activation. The MHC Ia priming promoted Tbet expression in Ib-CD8+T cells and in absence of Tbet, such priming effect diminished. Importantly, these tumoricidal Ib-CD8+T cells are positive for CX3CR1, and exhibit rapid proliferation, high expression of cytotoxic factors, and prolonged persistence at tumor sites. Adoptive transfer of CX3CR1+Ib-CD8+T cells to wild type mice resulted in potent anti-tumor effects. Our findings unravel an uncharacterized function of MHC Ia molecules in immunoregulation and raise the possibility of using Ib-CD8+T cells in tumor immunotherapy.