Host Responses to Viral Infections

Question 1

LO 1. List effects of viruses on infected cells: CPE, syncytia, growth, apoptosis.

Answer 1

CPE (cytopathic effects): indirect damage = integration of viral genome, induction of mutations, inflammation, host cell responses; direct = diversion of cell’s energy, competition
Syncytia (cell fusion):
growth: diversion of energy to making viruses
apoptosis: cell lysis

Question 2

LO 2. Explain IFN response and “anti-viral state”.

Answer 2

interferons are secreted by infected cells. Type I IFN = antiviral, secreted w/I hours. Type II IFN: produced by T and NK cells
Anti-viral state is induced by IFNs- when cells bind IFNs, they block viral replication changing transcription, blocking proliferation, reducing metabolism, increasing antigen presentation

Question 3

LO 3. Distinguish between innate and adaptive anti-viral responses.

Answer 3

innate: immediate, non-specific (TLRs, helicases, IFN, DCs, macs, NKs, PMNs, cytokines, chemokines)
adaptive: acquired over time, specific (B and T cells, Abs)

Question 4

LO 4. Compare antibody characteristics produced in primary and secondary responses.

Answer 4

primary: low affinity, IgM
secondary: IgA, G; can be group specific or type specific

Question 5

LO 5. List and describe major cell types involved in anti-viral responses.

Answer 5

humoral: B lymphocytes

cell-mediated: T cells

Question 6

LO 6. Compare the efficacy of antibody versus cell-mediated immunity in the anti-viral response.

Answer 6

Abs bind to viral proteins, virions, or infected cells for complement-mediated, NK cell, or phagocyte killing

Question 7

LO 7. Explain means of virus evasion/manipulation of host defenses by various viruses. (8)

Answer 7

1. antigenic variation (point mutations, genome shuffling)
2. immune tolerance (molecular mimicry, immunotolerant)
3. restricted expression (latent infections)
4. virus produces inhibitors or decoys (cytokines, receptors, Abs)
5. down-regulation of host proteins (MHC I or adhesion molecules)
6. infection of immunoprivileged sites (brain)
7. direct infection of the immune system (HIV)
8. inhibition of apoptosis and cell cycle control