Host Defense Flashcards
(33 cards)
Host Defense
innate + adaptive immunity to eliminate microbes
5 types of microbes
- extracellular/intracellular bacteria
- fungi
- viruses
- parasites
Innate immunity
early defense, no memory generated
adaptive immunity
longer to develop, antigen-specific, have a memory response
How does extracellular bacteria destroy tissue
induce inflammation and some release toxins
What is the 1st line of defense against extracellular bacteria (innate immunity)?
phagocytosis (because phagocytes live in the same hood)
Alternative complement pathway
bacterial cell wall components can activate complement to lyse or opsonize bacteria. effective against extracellular bacteria
What is the first line of defense for adaptive immunity against extracellular bacteria
antibodies
Polysaccharide capsules
resist phagocytosis
inhibit alternative pathway complement activation
Septic Shock
often caused by gram neg bacteria (but some positive as well)
induce macrophages to release tumor necrosis factor and IL-1
Superantigens
bind to class II MHC proteins on antigen presenting cells and also to the Valpha and Vbeta chains on T cells, causing T cell activation
Response of innate immunity against intracellular bacteria
- not very effective
- NK cells are activated by IL-12, which produces interferon gamma to activate macrophages
Response of adaptive immunity against intracellular bacteria
DTH-like (type IV) reaction
- TH1 cells activated
- release interferon gamma
- activate macrophages
Granulomas in adaptive immunity against intracellular bacteria
Happens when the organisms persist for a long time
Activated macrophages surround microbes and form a granuloma
Mycobacterium
(causes TB and leprosy)
-inhibits fusion of phagosomes and lysosomes and may scavenge reactive oxygen intermediates to prevent bacterial killing
Listeria monocytogenes
disrupt phagosome, escapes into cytosol
Deleterious effects of immune response against intracellular bacteria
granuloma formation can really fuck with tissue function, especially if it’s in the lungs.
Viruses
obligate intracellular microbes that pirate host cell’s machinery
Cytopathic effect
when viruses lyse host cells
Innate immunity against viruses
Type 1 IFN (alpha and beta)
Type 1 IFN (alpha and beta)
upregulate expression of class I MHC activate NK cells
NK cells against viruses
Once the MHC 1 is gone they can kill the infected cell.
Humoral immunity against viruses
CTL is most effective
activate complement to lyse viral envelopes
prior exposure leads to B lymphocyte production
How does HIV evade immunity
has a ton of antigenic variable due to all the point mutations
infect and kill CD4+T cells, preventing immune response
