host defense

Question 1

host immune response against extracellular bacteria

Answer 1

kill extracellular bacteria

neutralize toxins

Question 2

how do extracellular bacteria mediate tissue destruction

Answer 2

induce inflammation

release toxins that kill host cells

Question 3

innate immune response to extracellular bacteria

Answer 3

phagocytosis by macrophages

alternative complement pathway activation via bacterial cell wall components

Question 4

adaptive immune response to extracellular bacteria

Answer 4

humoral immunity
IgG opsonizes and toxin-specific ABs neutralize
IgM and IgM activate classical complement
activated T helper cells secrete IFN gamme, which activates macrophages

Question 5

evasion of immunity by extracellular bacteria

Answer 5

polysaccharide capsules resist phagyctosis and inhibit complement activation
genetic variation of surface antigens keep microbes one step ahead of antigen-specific antibodies

Question 6

deleterious effects of immune response against extracellular bacteria

Answer 6

septic shock (hypotension and DIC) mediated by gram neg bacteria induced release of cytokines
bacteria also induce macrophages to release TNF and IL-1 –> septic shock effects
superantigens bind class II MHC on APCs and V chains on T cells –> activation T cells –> release cytokines –> septic shock-like clinical picture
rheumatic fever and poststreptococcal glomerulo-nephritis

Question 7

innate immune response to intracellular bacteria

Answer 7

phagocytosis NOT effective
macrophage secrete IL-12 –> TH1 immune response –> activation of NK cells –> NK cells secrete IFN gamma –> activation of macrophages at higher level
adaptive immunity required for full eradication of bacteria

Question 8

adaptive immune response to intracellular bacteria

Answer 8

DTH like type IV reaction:
TH1 cell activation –> release of IFN gamma –> activated macrophages
if macrophages cannot eliminate bacteria, form granulomas to prevent spread

Question 9

evasion of immunity by intracellular bacteria

Answer 9

inhibit fusion of phagosome and lysosome
scavenge ROS to prevent bacterial killing
disrupt phagosome and escape into cytosol –> class I MHC present antigens –> CTLs generated and kill infected cell

Question 10

deleterious effects of immune response against intracellular bacteria

Answer 10

granuloma formation via macrophages

Question 11

innate immune response against viruses

Answer 11

IFN alpha and beta –> antiviral effect on healthy cells –> upregulate class I MHC then killed by CTL AND activate NK cells that kill those with lower levels of class I MHC

Question 12

adaptive immune response against viruses

Answer 12

humoral immunity important if ABs are present from previous infection/vaccination
CTLs in absence of existing ABs

Question 13

evasion of immunity by viruses

Answer 13

alteration of antigens (point mutations, reassortants)
prevention of class I MHC expression
killing CD4 T cells, preventing immune response

Question 14

deleterious effects of immune response against viruses

Answer 14

CTLs can cause pathologic lesions
Hep B –> liver damage via CTLs
molecular mimicry and cross-reaction with host tissue

Question 15

innate immune response to parasites

Answer 15

not effective against parasites

parasites resistant to neutrophils and macrophages b/c of thick teguments

Question 16

evasion of immunity by parasites

Answer 16

conceal selves in tissue of intestinal lumen or protective cysts
coat surface with host proteins so not identified as foreign
outer surfaces inhibit complement-mediated damage
extracellular enzymes –> cleave membrane-bound antibody
varying of surface antigens
shed antigens spontaneously after binding AB

Question 17

deleterious effects of immune response against parasites

Answer 17

chronic parasite infections
liver fibrosis –> cirrhosis
immune complexes lodge in lymphatic channels –> severe lymphedema

Question 18

innate immune response to fungi

Answer 18

neutrophils –> phagocytosis –> lysosomal enzymes + ROS

Question 19

adaptive immune response to fungi

Answer 19

TH1 mediate immunity (CTLs)

also granulomas

Question 20

adaptive immune response to parasites

Answer 20

also not effective against parasites
if parasites survive in macrophages, CD4 T cells produce IFN gamme –> activate macrophages to higher levels
TH1 mediated immunity…??