2-Host Defense

Question 1

general principles

Answer 1

-host defense = innate + adaptive immunity
-5 types of microbes
-to cause disase must effectively evade host immune resp

Question 2

types of microbes

Answer 2

1. extracellular bacteria
2. intracellular bacteria
3. fungi
4. viruses
5. parasites

Question 3

distinct effector mechanisms

Answer 3

for optimal response by microbe
1. antibody vs intracell bacteria would be ineffective
2. CTL resp vs extracell bacteria useless

Question 4

extracellular bacteria

Answer 4

staphylococcus + streptococcus + neisseria + escherichia coli + clostridium

will cause tissue damage so inflamm and toxins released

host immune resp to kill bacteria and neutralize toxins

Question 5

innate immunity vs extracellular

Answer 5

1. phagocytosis most effective, first line defense
2. alternative complement pathway bc bacterial cell wall can activate

Question 6

adaptive vs extracellular

Answer 6

-best approach is antibody production via humoral immunity
-IgG opsonizes + toxin specific antibodies neutralize
-IgM/IgG act classical complement to lyse

Question 7

evasion of immunity

Answer 7

polysaccharide capsules resist phagocytosis and inhib alternative pathway complement

also genetic variation of surface antigens

Question 8

septic shock

Answer 8

gram neg and some gram pos bacteria induce macrophages to release tumor necrosis factor (TNF) and IL-1

Question 9

superantigens

Answer 9

bind class II MHC on APCs and to Valpha/beta chains on T cells = T cell activation
-so many activated that large # cytokines = septic shock like condition

Question 10

disease causing antibodies

Answer 10

1. rheumatic fever- induced by streptococcal Mm protein during pharyngeal infection binds sarcolemma proteins in heart = carditis
2. poststreptococcal glomerulonephritis- infection with streptococci = antibodies form immune complex with bacterial antigens > lodge in kidney = nephritis

Question 11

listeria monocytogenes and
mycobacteria

Answer 11

-survive/multiply in macrophages
-inaccessible to circulating antibodies
-allow to thrive in phagocytic cells

myco will inhibt fusion of phagosomes/lysosomes and may savenge ROS to prevent killing bacteria

listeria will disrupt phagosome so bacteria escapes into cytosol then CTLs generated

Question 12

innate vs intracellular

Answer 12

ineffective bc bacteria not killed when ingested
-NK cells act by IL-12 > prod interferon gamma to act macros but only some killed

need adaptive for full eradication

Question 13

adaptive vs intracellular

Answer 13

DTH like type IV reaction
-TH1 act > release interferon gamma > act macros
-macros will surround microbes to form granuloma to prevent spread

Question 14

viruses

general

Answer 14

obligate intracelllular microbes that priate host cell machinery

can lyse host cells = cytopathic effect

Question 15

innate vs virus

Answer 15

best defense = type 1 IFN = alpha and beta interferons
-upreg expression of class I MHC on host cells
-act NK cells to lyse early in infection
-block virus protein syn

Question 16

NK cells and viruses

Answer 16

viruses downreg class I MHC so NK cells are released from inhibition by absence of I MHC

enhanced by interferons

Question 17

adaptive vs viruses

Answer 17

IF antibodies present = humoral imm to prevent virus from binding target host, opsonize virus, act complement

NO antibodies = CTLs principal immune component, virus processed on class I MHC so CTLs effective

Question 18

viral evasion of immunity

Answer 18

1. HIV makes point mutations so antigenic variability, infects CD4 T cells
2. influenza - reassortants make antigenic alteration

also prevent class I MHC xpr of viral peptides so not lysed by CTLs

Question 19

deleterious effects viruses

Answer 19

1. hep B virus infection induce CTL resp that destroys liver, if immunodeficient then no liver damage
2. molecular mimicry- immune resp vs virus cross reacts with host tissue

Question 20

fungal disease

general

Answer 20

inc # of opportunistic fungal infections

AIDS, cancer (chemotherapy), transplants (immunosuppressants) high risk

immunity to fungi involves humoral and cell mediated

Question 21

innate vs fungi

Answer 21

neutrophils main mediators so phagocytosis

neutropenic indivs highly susceptible to fungal infections

Question 22

adaptive vs fungi

Answer 22

TH1 most important
-cryptococcus neoformans eliminated by CTLs
-intracellular fungus > granuloma formation

Question 23

parasites

general

Answer 23

protozoa and helminths/worms

complex life cycle so involved intermediate host like mosquitoes, ticks

Question 24

innate vs parasites

Answer 24

not very effective
-macros phagocytize protozoa but many orgs resistant to killing

outer layer of helminths act alternative complement but resistant to the effects
-resistant to neutrophils and macros bc thick teguments

Question 25

parasite evasion of immunity

Answer 25

-concealed by intestinal lumen or cysts
-coat with host proteins so not id as foreign
-outer surface inhibits complement
-extracell enz cleave membrane bound antibody
-vary suface antigens
-shed antigens spontaneously or after being bound by antibodys