lecture 10

Question 1

host immune response

Answer 1

• innate immunity
• adaptive immunity
• passive immunity

Question 2

innate immunity

Answer 2

• no antigen specificity
• no memory
• first line of defense because they are:
• -constantly present
• -operational immediately after viral infection
• -only immune defense available for first few days after viral infection

Question 3

innate immunity: important primary physical and chemical defenses

Answer 3

• GI tract

- respiratory tract

Question 4

innate defense of GI tract

Answer 4

• mucous membrane of oral cavity and esophagus are refractory to viruses
• acidity of the stomach
• alkalinity of the intestine
• layer of mucous covering gut
• lipolytic activity of bile
• proteolytic activity of pancreatic enzymes
• defensins (host defense peptides) with antiviral activity- modulate host immune response

Question 5

respiratory tract innate defenses

Answer 5

• mucociliary blanket
• temperature gradient: between nasal passages (33c) and alveoli (37C), plays important role in localization of infection, rhinovirus which infect nasopharynx and cause common cold replicate well at 33 C but grow poorly at 37, influenza shows inverse temp presence

Question 6

natural killer cells (NK cells)

Answer 6

-mediate death of virus infected cells via apoptosis

Question 7

cell pattern recognition receptors

Answer 7

• cells at portals of virus entry possess surface receptors (pattern recognition receptors) PRR that recognize specific pathogen-associated molecular patterns (PAMPS)
• one class of PRRs are the toll like receptors (TLRs) which cause phagocytosis, chemotaxis, inflammatory mediators, interferons

Question 8

interferons

Answer 8

• group of cytokines (complex glycoproteins) that are secreted in somatic cells in response to viral infections and other stimuli
• possess potent antiviral, immunomodulating, and anti-cancer properties
• not specific for virus
• RNA are stronger inducers of interferon than DNA
• orally inactive, should be administered parenteral (injection)

Question 9

types of interferons we care about

Answer 9

• type-I
• type-II interferon
• type-III
• IFN-alpha
• IFN-beta

Question 10

Type 1 interferons

Answer 10

• many types
• inhibit virus replication in host cells
• activate NK cells to kill infected cells
• increase expression of MHC-I molecules and antigen presentation
• stimulate different monocytes in dendritic cells
• maturation of dendritic cells
• stimulates memory T cell proliferation

Question 11

IFN-alpha

Answer 11

• leukocyte interferon

- produced in large quantities by plasmacytoid dendritic cells

Question 12

IFN-beta

Answer 12

• fibroblast interferon

- secreted by virus infected fibroblast

Question 13

type II interferon

Answer 13

• only one type, IFN-y
• mostly immunoregulatory
• produced by antigen-stimulated T cells and NK cells

Question 14

type-III interferon

Answer 14

• at least 3 types identified: IFN-lambda 1, IFN lambda 2, IFN lambda 3
• recently discovered
• expressed in response to viral infections and activation of TLRs
• primarily function as immunoregulator

Question 15

adaptive immunity

Answer 15

• humoral and cellular components
• humoral mediated principally by abs released from B lymphocytes
• cellular immunity mediated by T lymphocytes
• adaptive immunity is antigen specific, takes time (several days) to develop, mediated by lymphocytes that possess surface receptors specific to each pathogen
• long-term memory after infection
• internal viral antigens elicit protective cell mediated immune response
• surface cell antigens elicit protective humoral and CMI responses

Question 16

antibody mediated immunity (humoral immunity)

Answer 16

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

Question 17

antiviral effects of antibodies

Answer 17

• virus neutralization
• opsonization
• clumping of viruses (immunocomplex formation)
• activation of complement system
• antibody dependent cell mediated cytotoxicity

Question 18

virus neutralization

Answer 18

-neutralizing antibodies prevent virus attachment and entry into host cells, they bind to viral capsid or host envelope

Question 19

opsonization

Answer 19

• coating of virions with antibodies

- antibody coated virion is recognized and phagocytosed by macrophages, and sometimes by neutrophils

Question 20

cell-mediated immunity

Answer 20

• CD4+ recognizes microbial antigen in phagocyte
• CD8+ recognizes infected cell containing microbial antigen
• causes activation of macrophages, inflammation, stimulation of B lymphocytes, killing of infected cells

Question 21

evasion of immune response

Answer 21

• antigen plasticity
• antigen multiplicity
• negative cytokine regulation
• downregulation of MHC class I pathway
• inhibition of complement activation
• evasion of neutralizing antibodies
• latency
• cell-to cell spread of viruses
• inhibition of apoptosis

Question 22

antigen plasticity

Answer 22

• rapid changes in the structure of viral antigen, may be result of mutation, reassortment, or recombination
• due to change in antigen structure, virus may become resistant to immunity generated by previous infection

Question 23

antigenic multiplicity

Answer 23

-antigenic variants with little or no cross reactivity

Question 24

negative cytokine regulation

Answer 24

• virokines: homologs of cytokines/interferons produced by virus
• viroceptors: some viruses incode proteins that are homologous to the receptors