The following statements were made about host–pathogen interactions during influenza virus infection:
A. Entry of the virus is mediated by the interaction of the HA-protein of the virus with sialic acid receptors on the airway epithelium.
B. CTLs are primed in the thymus to kill respiratory epithelial cells that present viral antigens on MHC-I molecules.
C. CTLs are primed in the thymus to kill respiratory epithelial cells that present viral antigens on MHC-II molecules.
D. Viral neuraminidase is required for the release of mature viruses from infected cells.
Which one of the following options represents the combination of all correct statements?

Correct option is D

Correct Answer:
(d) A and D only
Explanation:
Influenza virus entry is mediated by hemagglutinin (HA) binding to sialic acid receptors on respiratory epithelial cells (A).
Neuraminidase facilitates the release of newly formed virions by cleaving sialic acid residues, preventing viral aggregation at the cell surface (D).
CTLs are not primed in the thymus to recognize specific viral antigens; instead, priming occurs in peripheral lymphoid organs by antigen-presenting cells.
Information Booster :
· Influenza HA and neuraminidase are key viral surface glycoproteins.
· HA mediates attachment and entry, while neuraminidase enables viral spread.
· CTLs recognize viral peptides presented on MHC-I, but activation occurs outside the thymus.
· Antiviral drugs like oseltamivir target neuraminidase activity.
Additional Information (Incorrect Options):
Statement B: Incorrect because CTLs are primed in secondary lymphoid organs, not the thymus.
Statement C: Incorrect since CTLs recognize antigens on MHC-I, whereas MHC-II presents to CD4⁺ T cells.
Therefore, options including B or C are incorrect.