Host response to viral infections -2 Flashcards
Innate immunity
- inhibition of virus infection by type 1 interferons
- NK cell-mediated killing of infected cells
Interferons
are cytokines produced and secreted by somatic cells in response to a variety of stimuli, including virus infection
what are the 3 classes of interferons
- IFN- alpha
- IFN-beta
- IFN-gamma
What are the type one IFNs and what do they do?
- alpha and beta
- cause an antiviral state in uninfected cells
- induce apoptosis in infected cells
- stimulate production of MHC class 1 proteins and proteasome proteins
IFN-alpha
- leukocyte interferon
- secreted by virus infected macrophages and other leukocytes
- not host specific
IFN-beta
- fibroblast interferon
- secreted by virus infected fibroblasts and epithelial cells
- host species specific
protein kinase
phosphorylates and inactivates a viral initation protein thereby preventing translation of viral mRNA
2-5 A synthesis
activates a ribonuclease that degrades viral mRNA
what are your type 2 IFNs
IFN-gamma; immune interferon
IFN-gamma
- secreted by: mitogens, antigens, or cytokine stimulate T cells and NK cells
- host specific
- no antiviral activity
Adaptive immune responses are directed against _____
viral capsid and envelope antigens
Internal viral antigens usually elicit ____
protective CMI responses
Surface antigens elicit___
protective humoral and CMI responses
Antibodies are effective against viruses only during the ________ stage of virus infection
extracellular
Virus neutralization
Neutralizing antibodies prevent virus attachment and entry into host cells
opsonization
coating of virons by IgG may facilitate pinocytosis and intracellular killing by macrophages and to limited extent neutrophils
clumping of viruses
reduces the number of infectious units available for cell invasion
complement activation
opsonization (C3b, iC3b, C4b) and possible direct lysis of enveloped viruses
lysis of virus-infects cells
cells expressing viral antigens on their surfaces are susceptible to antibody-mediated destruction via ADCC and complement-mediated cytolysis
CMI
- the intracellular replicative steps of viruses and virus-infected cells are major targets for CMI
- responses are more important in recovery from infections with non cytolytic viruses
Plasticity
rapidly changing surface antigenic structure by mutation, genetic reassortment or recombination
multiplicity
- antigenic variants with little or no cross- reactivity
- specific immunization against the common cold may not be feasible preventive strategy
immunosuppression
immunocompetent cells are either lysed or inactivated
virokines
-Epstein-Barr virus synthesizes a protein that is a homolog for IL-10, suppresses cytokine production by Th1 CD4 cells
viroceptors
the secreted cytokine receptor homologues may bind cytokines and function as competitive antagonists of the cytokine
