host response to viral infection

Question 1

3 general types of host immune response

Answer 1

innate, adaptive and passive (introduced into host by third party)

Question 2

innate immunity

Answer 2

no AG specificity or memory
first line of defense
operate immediately after viral infection

Question 3

NK cells

Answer 3

mediate death of virus infected cells via apoptosis, synthesize and release a variety of cytokines

Question 4

cellular pattern and recognition receptors

Answer 4

cells at portal of entry possess surface receptors (PRR) that recognize PAMPs
PRRS = TLR which do phagocytosis, chemotaxis, inflammatory mediators and interferons

Question 5

interferons

Answer 5

group of cytokines
antiviral, immunomodulating and anti cancer
generalized response
RNA virus is stronger induced of interferon than DNA virus
need to be admin by injection

Question 6

Type 1 IFN a

Answer 6

leukocyte interferon and produced in large quantities by the cell

Question 7

IFNb

Answer 7

fibroblast interferon, secreted by virus infected fibroblast

Question 8

roles of type 1 IFN

Answer 8

inhibit viral replication in host cell, activate NK cells to kill infected cells, increase expression of MHC 1 molecules and AG presentation, stimulate diff. of monocytes into dendritic cells, maturation of dendritic cells and stimulate memory T cell prolif.

Question 9

how do type 1 IFN inhibit viral replication

Answer 9

activate latent ribonuclease called RNAse L –> degrades viral RNA, induces synthesis of Mx proteins that bind and trap viral nucleocapsid and inhibit virus assembly, induce synthesis of protein kinase R which prevents initiation of translation of viral RNA

Question 10

type 2 IFN

Answer 10

only one type, IFN y – most immunoregulatory
-produced by AG stimulated T cells and NK cells

Question 11

type 3 IFN

Answer 11

IFN 1,2,3, recently discovered, expressed in response to viral infections and activation of TLR, primarily functions as immunoregulator

Question 12

adaptive immunity

Answer 12

humoral (B cells) and cellular (T cells), antigen specific, take days to develop, lymphocytes have surface receptors that are specific to each pathogen, long term memory, internal viral AG stimulate cell mediated immune (CMI) response, surface AG stimulate protective humoral and CMI response

Question 13

AB mediated immunity - humoral

Answer 13

AB may be directed against viral proteins on free virions (capsid or envelope) or against viral proteins expressed on surface of infected cells

Question 14

antiviral effects of AB (5)

Answer 14

1. neutralization: prevent virus attachment and entry into host cells, bind to viral capsid or envelope
2. opsonization: coating of virions with AB, AB coated virion is tagged for phagocytosis by macrophages
3. clumping of viruses (immunocomplex formation)
4. activation of complement
5. ADCC

Question 15

cell mediated immunity

Answer 15

CD 4 T helper lymphocytes and CD 8 cytotoxic T cells activate macrophages, inflammation, stim B lymphocytes and kill infected cells

Question 16

evasion of immune system

Answer 16

1. antigenic plasticity: rapid changes in the structure of viral AG, may be the result of mutation (AG drift), reassortment or recombination (AG shift), due to change in AG structure, the virus may become resistant to immunity
2. antigenic multiplicity: antigenic variants with little or no cross reactivity
3. negative cytokine regulation: virokines- some viruses synthesize proteins which are homologs of cytokines, viroceptors: some viruses encode proteins that are homologous to the receptors for cytokines – serves as COMPETITIVE ANTAGONIST
4. down regulation of MHC class
5. inhibition of complement activation
6. evasion of neutralizing AB
7. latency
8. cell to cell spread of virus
9. inhibition of apoptosis