Immuno: Evasion of Immune Responses Flashcards
What is antigenic variation?
display of new antigens (by a pathogen) that are not recognized by immune responses formed in response to previous infection.
Just For Fun!
Name the two influenza surface proteins that are the primary targets of antibody responses.
Neuraminidase and hemagglutinin
Are the antigenic drifts resulting in mutated neuraminidase and hemagglutinin a source of serious problems for the immune response?
Results in a new pandemic that is not terribly serious, probably because many of the determinants recognized by flu-specific T cells in previously infected cells have not been altered. So generating a new B cell response is very efficient.
Describe how recombination of influenza genome segments results in antigenic variation that is relatively troublesome.
A virus resulting from recombination of genome segments may now express a completely different version of either the hemagglutinin or neuraminidase surface proteins.
Describe how Trypanasomes use antigenic variation to evade immune responses.
Trypanasomes have genes that encode many “variant-specific glycoproteins” using a cassette system. Infecting trypanasomes generally express the predominant VSG.
Daughter trypanasomes begin to express a different VSG protein. Now the new VSG-bearing trypanasomes are able to escape the pre-formed immune response of the host until the host catches up. Each time the trypanasome re-infects a cell and replicates (re-organizes cassettes), the cycle starts over.
________ is a non-replicative state that some viruses can achieve in host cells. This involves the viral genome integrating into the host cell DNA.
Latency
Is there a way for the immune system to recognize a latent viral infection of host cells?
No sir.
What causes latent viruses to come out of hibernation and piss you off?
Stress.
Are latent infections ever cleared?
“Not likely”
How do superantigens work?
Cross-link MHC class II and TCR. Initiates massive production of cytokines. Cytokine production results in systemic toxicity and/or suppression of immune responsiveness.
HIV uses it genome as efficiently as any pathogen because of these two features:
1) uses all three reading frames
2) uses alternative splicing to create additional transcripts (same gene codes for multiple proteins depending on exon/intron splicing)
Explain briefly how HIV takes advantage of the host’s immune system during infection.
Uses chemokine receptor and CD4 as its cell surface receptors. Allows virus to target CD4+ T cells for infection.
Why are HIV infections considered to have a relative high rate of antigenic variation?
Reverse transcriptase has no proof-reading ability, it is a very error-prone enzyme. (reverse transcriptase copies viral RNA to create a ds-Provirus that is then integrated into host cell DNA)
Is HIV a T cell depleting infection?
Yes. The virus is cytopathic, and because its host cell is the CD4+ lymphocyte, it is T cell depleting.
Why can our immune responses not clear HIV?
1) antigenic variation that results because of the error rate of reverse transcriptase.
2) Latency: HIV proviruses integrate into host DNA and remain latent for long periods of time.
3) induction of acquired immunodeficiency
