MHC class II proteins mediate sialic acid independent entry of human and avian H2N2 influenza A viruses.

Influenza A viruses (IAV) pose substantial burden on human and animal health. Avian, swine and human IAV bind sialic acid on host glycans as receptor, whereas some bat IAV require MHC class II complexes for cell entry. It is unknown how this difference evolved and whether dual receptor specificity is possible. Here we show that human H2N2 IAV and related avian H2N2 possess dual receptor specificity in cell lines and primary human airway cultures. Using sialylation-deficient cells, we reveal that entry via MHC class II is independent of sialic acid. We find that MHC class II from humans, pigs, ducks, swans and chickens but not bats can mediate H2 IAV entry and that this is conserved in Eurasian avian H2. 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.

Interdependent Impact of Lipoprotein Receptors and Lipid-Lowering Drugs on HCV Infectivity.

The HCV replication cycle is tightly associated with host lipid metabolism: Lipoprotein receptors SR-B1 and LDLr promote entry of HCV, replication is associated with the formation of lipid-rich membranous organelles and infectious particle assembly highjacks the very­low-density lipoprotein (VLDL) secretory pathway. Hence, medications that interfere with the lipid metabolism of the cell, such as statins, may affect HCV infection. Here, we study the interplay between lipoprotein receptors, lipid homeostasis, and HCV infection by genetic and pharmacological interventions. We found that individual ablation of the lipoprotein receptors SR­B1 and LDLr did not drastically affect HCV entry, replication, or infection, but double lipoprotein receptor knock-outs significantly reduced HCV infection. Furthermore, we could show that this effect was neither due to altered expression of additional HCV entry factors nor caused by changes in cellular cholesterol content. Strikingly, whereas lipid­lowering drugs such as simvastatin or fenofibrate did not affect HCV entry or infection of immortalized hepatoma cells expressing SR-B1 and/or LDLr or primary human hepatocytes, ablation of these receptors rendered cells more susceptible to these drugs. Finally, we observed no significant differences between statin users and control groups with regards to HCV viral load in a cohort of HCV infected patients before and during HCV antiviral treatment. Interestingly, statin treatment, which blocks the mevalonate pathway leading to decreased cholesterol levels, was associated with mild but appreciable lower levels of liver damage markers before HCV therapy. Overall, our findings confirm the role of lipid homeostasis in HCV infection and highlight the importance of the mevalonate pathway in the HCV replication cycle.