Immunity against viruses & parasites

Question 1

Describe what a virus is.

Answer 1

1. nonliving entity
   -genome (DNA/RNA), protein coat (capsid), other layers (ex. lipid envelope)
   -dont possess organelles
2. obligate intracellular parasites
   -cant synthesize proteins by themself
   -outside of host cell = dormant/inert
   -dont multiply by division = assembly line on host cell
3. virion
   -complete virus particle
   >nucleic acid core + capsid +/- ext envelope
   -infective form of virus
4. host specific
   -virus = selected for evading host immune resp
   -host = selected for resistance of virus induced disease

Question 2

Describe immunity to viruses (extra cellular/intracelluar).

Answer 2

1. extracellular
   -neutralization by Ab
   -phagocytosis
   -damage by effects of complement
2. intracellular
   -NK cells
   -CD8 cells
   -macrophages

Question 3

Describe innate immunity PRRs.

Answer 3

recognition of viral DNA/RNA - 2 systems
1. RIG1 & MDA5
-cytosol of nucleated cells
-recog dsRNA -> INFB gene activation
2. TLRs: 3, 7, 8, 9
-TLR3 - dsRNA
-TLR7 & 8 - single strand viral RNA
-TLR9 - unmethylated CpG (both virus & bacteria)

Question 4

Describe innate immunity interferons.

Answer 4

1. type I interferons (IFNa & IFNB)
   -made by virus infected cells within hrs of invasion
   -peak levels in first days
   -JAK/STAT signaling pathway

Question 5

Describe the major pathways of type I IFN antiviral actions.

Answer 5

1. protein kinase R (PKR)
2. 2’-5’ oligo A synthetase
3. GTPase

Question 6

Describe type I interferons.

Answer 6

1. type I interferons
   -IFNa -> plasmacytoid DCs
   >lymphocytes, monocytes, macrophages
   -IFNB -> virus infected fibroblasts
   -activate NK cells
   -monocytes -> DC
   -maturation of DC
   -transition from innate to adaptive resp

Question 7

Describe adaptive immunity - humoral response.

Answer 7

1. antibodies against capsid & envelope protein
   -prevent cell invasion by blocking absorption
   -stim phagocytosis
   -trigger complement mediated virolysis
   -cause viral clumping
2. antibodies against proteins expressed on infected cells
   -complement mediated cytolysis
   -ADCC

Question 8

Describe adaptive immunity - cellular response.

Answer 8

1. more imp in controlling viral disease
2. MHC I -> CD8
   -CD8+ cells may kill intracellular viruses without killing the infected cells
   -T cell derived IFNy & TNFa
3. activated macrophages -> IFNy
4. viruses can act as superantigens
   -nonspecific resp (Th2)

Question 9

Describe the evasion of immune response - virus.

Answer 9

diff viruses, diff strategies
1. RNA viruses -> small genome
-antigenic variation as main mechanism
2. DNA viruses -> larger genome
-neg cytokine reg
-interference w antigen processing pathways
-prevention of apoptosis
-NK evasion
-latency

Question 10

Describe antigenic variation.

Answer 10

influenza
1. genetic drift
-point mutations within genome
2. genetic shift
-reassortment of gene seg

Question 11

Describe interference with antigen processing pathways.

Question 12

Describe evasion of IR - viruses.

Question 13

Describe the immunity against parasites.

Answer 13

-diverse
-single cell to meters long

Question 14

Describe the immunity against protozoans.

Answer 14

1. innate immunity
   -similar mech to resp to bacteria
2. adaptive immunity
   -Th1 VS Th2
   -varies according w parasite & parasite/host adaptation
   [toxoplasma gondii penetrate cells thru molecular junctions in cell membrane & don’t trigger phagosome formation-> make performing like molecules to allow escape & invasion of other cells -> antibodies & complement can destroy extracellular toxoplasma & prevent spread]

Question 15

Describe immunity against helminths.

Answer 15

1. innate immunity
   -chitinases produced by mast cells, macrophages, neutrophils
   -cuticle -> chitin
2. adaptive immunity
   -predom Th2
   -2 types of targets:
   >larvae (tissue) -> eosinophilic -> destruction
   >adults (intestines or airways) -> IgE + cytokines -> expulsion
   eosinophil attach on helminth cuticle
   helminth in intestinal lumen
   resp against helminths in intestinal lumen = IgE (IgG) + cytokines

Question 16

Describe immunity against arthropods.

Answer 16

1. ticks, mosquitos, flies, fleas
   -saliva
   -Th2 -> IgE -> type I hypersensitivity
   -low molecular weight Ag -> haptens -> Th1 resp
   -vaccines target int Ag of tick
2. mange
   -demodex
   -CD8 cells, type IV hypersensitivity
   -absence of eosinophils = type I hypernot imp

Question 17

Describe immunity against parasites - escape mech.

Answer 17

-resistance to effector mechanisms
-avoid antigen recog
-block antigen recog & processing
-interfere w cell maturation & signaling
-enhance regulation
*trypanosoma sp. = VSG - variable surface glycoprotein
*helminth larvae

Question 18

Describe tuft cells.

Answer 18

-sense presence of intestinal helminths in intestinal lumen
-make lg amount of IL25 = recruit eosinophils & activate Th2 & ILC2 = secrete more IL13 & IL4
-IL25 = promotes hyperplasia of tuft cells & goblet cells
-increased gut motility & mucus production can expel helminthic skin