Influenza A viruses are classified by their surface glycoproteins. The current seasonal influenza H3N2 subtype has which hemagglutinin (HA) and neuraminidase (NA) combination, and which host receptor does human-adapted influenza preferentially bind?

• A H3N2 with HA binding to sialic acid α-2,3-galactose in human nasopharynx
• B H3N2 HA binds ACE2 receptors on nasal epithelium
• C H3N2 with HA binding to sialic acid α-2,6-galactose residues on human upper respiratory tract epithelium (vs. avian viruses binding α-2,3-galactose) ✓
• D H3N2 HA specifically cleaves N-acetylneuraminic acid without receptor binding

Explanation

Human-adapted influenza A and B viruses preferentially bind sialic acid with α-2,6-galactose linkage (SA-α-2,6-Gal), which is predominantly expressed on upper respiratory tract epithelium (trachea, bronchi) in humans. Avian influenza viruses (e.g., H5N1, H7N9) preferentially bind α-2,3-galactose sialic acid linkages found in avian intestinal epithelium and deep in the human lower respiratory tract (alveoli), explaining their poor human-to-human transmissibility but severe pneumonia. Neuraminidase (NA) cleaves sialic acid to release newly formed viral particles; it does not mediate receptor binding.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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