6 - bacterial immunity Flashcards
features of innate protection
broad
low-level
fast
many different pathogens
features of adaptive immunity
slower
specific for a particular microorganism
high-level protection
innate recognition
recognises molecules that have common characteristics of bacteria but are foreign to the host
innate receptors are ..
pre-coded to recognise a limited repetoire of molecules
PAMPs
2 innate killing mechanisms
complement pathway
phagocytosis
how is alternitve pathway activated
recognisiton of cell surface proteins and polysaccharides eg LPS
how is classical complement pathway activated
triggered by antibodies (bound IgM or IgG) binding to antigens
how is lectin complement pathay activated
by carbohydrates like mannose and N-acetylglycosamine
early events of complement
different for each pathway but all generate a protease
e.g. C3 convertase
C3 component cleaves to form
C3a and C3b
C3b
bound to surface of bacteria
means response is localised (no collateral damage)
role of C5 convertase
cleaves C5 to C5a and C5b
which component of complement becomes MAC
C5b
which components of complement are the effectors
C3a and C5a
what is the main effect of C3a and C5a
promote inflammation
how to C3a and C5b promote inflmmation
bind to mast cells via their receptors
- cause degranulation and release of histamine
promote vasoldilation providing access to other immune cells
act as chemoattractants - signal to phagocytes
how does membrane attack complex (MAC) work
composed of some C9 subunits
forms a pore in target membrane
promotion of unregulated movement of ions across membrane
bacterial cell lysis
C1q deficiency
leads to sepsis and meningitis
C3 deficiency
leads to respiratory tract infections and meningitis
types of recognition for phagocytic killing
direct
indirect
direct recognition - phagocytes
via antibody receptors (Fc)
via C3b receptors
indirect recognition - phagocytes
PRRs
TLRs
type of PRR
embedded in membrane of phagocytic cell
structure of TLR
horseshoe - extracellular
dimerisation occurs intracellularly
describe TLR recognition –> signalling
PAMP binds dimerisation signalling cascade leads to activation of T factors e.g. NF-kappaB cytokine production inflammatory response
5 examples of cytokines
IL-1 IL-6 TNF-a Interferon-a interferon-B
role of IL-1
activates endothelial cells
causes fever
IL-6 role
proliferation of antiobody-producing B cells
effects of TNF-a
activates endothelial cells
causes fever
activates neutrophils
effects of interferon-a and interferon-B
anti-viral immunity
promotes CD4+ and CD8+
T cell response
interferon-a used to treat
Hep A/B viral
interferon-B used to treat
multiple sclerosis
effect of bacteria binding to TLR
triggers ingestion and uptake into the phagocyte
bacteria then enters the phagosome and fuses with the lysosome –> phagolysosome
killing mechanisms of phagolysosome
lowers pH
enzymes (lysozymes, proteases)
oxygen-free radicals
oxygen free radicals
e.g. hydrogen peroxide
superoxide
generated by phagocytic cell and put into phagosome
Coley’s toxins (1900-1910)
observed spontaneous recovery from bacterial infection?
developed concoction from bacterial cells
adaptive recognition
adaptive immune cells recognise antigens that are unique to an individual pathogen
common types of bacterial antigens on surface of bacterial cell
proteins
polysaccharides
2 MHC presentational pathways
protein escapes phagosome into cytosol
protein taken up into pahgosome
if protein antigen escapes phagosome …
antigen enters cytosol
proteins recognised and processed in the proteasome
proteins complexed with MHC I
fragments presented to and recognised by CD8+ T cells
if protein antigen is taken up into phagosome
protein is killed and processed inside phagosome by endocytosis of extracellular protein
complexed with MHC II
antigen fragments presented to and recognised by CD4+ T cells
role of CD8+ T cells
activated and kill host infectected cells by releasing toxins
toxins released by CD8+ T cells
perforin
granzymes
granulysin
CD8 T cells are critical during which two infections
tuberculosis
salmonellosis
role of CD4+ t cells
activate immune system
promote cytokine production
effects of cytokine production due to activation of CD4+ T cells
macrophage activation
inflammation
maturation of antibody response
role of CD4+ t cells
activate immune system
promote cytokine production
effects of cytokine production due to activation of CD4+ T cells
macrophage activation
inflammation
maturation of antibody response
4 protective mechanisms of antibodies
- complement pathway activation
- agglutination
- neutralisation
- opsonisation
how do antibodies activate complement
antibodies bound to bacteria form complexes with antigens
classical pathway
how do antibodies protect the body using agglutination
antibodies cause bacteria to stick together and clump allowing more effective cleaning by phagocytes
importance of neutralisation caused bby antibodies
defends cell from antigen
neutralises cells effect eg. the toxins
example of a neutralising antibody
diptheria antitoxin
neutralises biological effects of diptheria toxin
effect of antibodies against streptococcal pneumonia
antibodies cause agglutination, opsonisation and activation of complement
effect of antibodies against tetanus
antibodies neutralise toxin
