Evasion of Immune Responses

Question 1

anitgenic variation

Answer 1

alteration of antigenic determinants that allow a pathogen to avoid immune responses that the host previously produced in response to that pathogen ex) memory response is less effective

Question 2

influenza virus surface proteins that are the primary immune response targets (neutralization response)

Answer 2

neuraminidase and hemagglutinin

Question 3

antigenic drift in influenza

Answer 3

the neuraminidase and hemagglutinin becomes mutated in other hosts and then reinfects human who has already experienced the flu. But since this flu virus has undergone genetic drift it will still cause systemic symptoms in the host.

influenza 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/immune patients have not been altered, so generating a new B cell response is very efficient and happens relatively quickly

Question 4

antigenic shift in influenza

Answer 4

influenza has a segmented ss RNA genome, if two different strains co-infect a host they can replicate simultaneously within the host and repackage genetic mutation from the opposite strain. This can lead to the virus expressing completely different strains of neuraminidase and hemagglutinin. So the resulting antigenically shifted virus can cause a new pandemic that causes much more severe disease that a viral strain that arose via antigenic drift

Question 5

Trypanasomes

Answer 5

Pathogens encode over 1,000distinct variant specific glycoproteins using a cassette system. Once the immune system combats one they will being to express another. Ex) African sleeping sickness-chronic recurrent condition. Eventually the continual immune responses lead to tissue damage including neural tissue damage and coma

Question 6

latency in herpes virus

Answer 6

initial virus infects the epithelial cells but then travels up the nerve serving that tissue and resides in the trigeminal ganglion. During latency period the virus genome resides within the episomal DNA in the trigeminal ganglion where it cannot be detected by the host. Some stimulus such as stress or illness will activate it again later.

Question 7

Another latency example

Answer 7

varicella coster-latent after chicken pox in dorsal root ganglion on one side of the body
Leads to shingles

Question 8

superantigens

Answer 8

cause cross linking of MHC class II leading to cytokine storms

Question 9

HIV lentivirus

Answer 9

type of retrovirus
encodes reverse transcriptase as well as an integrase
2 surface proteins-gp41 and gp120

Question 10

HIV uses _____ as cell surface receptors

Answer 10

CD4 and a chemokine receptor»>targets CD4 T cells

Question 11

T/F HIV reverse transcriptase has no proof reading capabilities

Answer 11

true

Question 12

cytopathic nature of HIV

Answer 12

kills host eventually through CD4 T cell depletion

Question 13

2 reasons immune response cannot clear HIV infection

Answer 13

1. anitgenic variation that results from the high rate of mutation due to lack of proof reading capabilities
2. latency: integrates into host genome and lies latent for long periods of time

Question 14

T/F HIV pt eventually develops SCID phenotype

Answer 14

true

Question 15

Why is HIV a nearly perfect pathogen?

Answer 15

1. anitgenic drift
2. latency
3. introduction of acquired immunodeficiency