Question

Influenza viruses gain entry into their host cells by attachment to N-acetylneuraminic acid residues on the cell surface, followed by receptor-mediated endocytosis. What effect would the following treatments have on attachment of the virion to a susceptible cell.

i.Treatment of the susceptible cell with neuraminidase

ii.Treatment of the susceptible cell with NH4 Cl to prevent lowering of lysosomal pH

iii. Treatment of the susceptible cell with actinomycin D, which prevents synthesis of messenger mRNA

b. What effect would these same treatments have on uncoating of the virion?

C. What effect would each of these treatments have on the burst size of an influenza infection?

Answer 1

Answer i) Since sialic acid is required for attachment to host cell and neuraminidase bind and cleave sialic acid, treatment with neuraminidase will remove surface sialic acid resulting in loss of influenza binding.

ii) After binding and entry via endocytosis, influneza virus needs to release its genome into cytosol of host cell which will be imported to nucleus for replication and transcription. For this influenza virus fuses its membrane with late endosomal membrane to release genome into cytosol. This fusion process is triggered by lowering of late endosomal pH. Treatment with NH4 Cl to prevent lowering of lysosomal pH will inhibit this fusion process, thus trapping the virus within the endosome.

iii) Since influenza virus have segmented RNA genome, and to replicate themselves they use host nucleus for synthesis of their RNA genomic segments. Treatment with actinomycin D, which prevents synthesis of messenger mRNA will also prevent synthesis of viral genomic RNA.

b) The uncoating of virus occurs in late endosome in case of influenza virus. Hence, neuraminidase will not affect uncoating process because viruses have already entered. However, treatment with NH4 Cl will affect the uncoating process because influenza virus fuses its membrane with late endosomal membrane to release genome into cytosol. Lowering the pH will stop this process. Treatment with actinomycin D will have no effect on uncoating because this process occurs upstream to the synthesis of viral genomic RNA.

C) The burst size of influenza infection will surely be affected with all of the above treatment. Neuraminidase treatment will inhibit virus binding, thus affecting release of virus, NH4Cl treatment will inhibit uncoting thus lowering the burst size and actinomycin D treatment will inhibit genome synthesis further lowering the burst size (may be zero depending upon the treatment).