neutrophils Flashcards
what percent are neutrophils in the blood
40-75
how many neutrophils are produced each minute
60 million
what is neutrophils half life
7hrs
where are neutrophils produced and stored
bone marrow
what are neutrophils crucial for
host defence against bacterial and fungal infection
what factors increase no of neutrophils
stress, injury, infection and cytokines
what do emergency cytokines do
switch off ebp alpha and increase granulocyte numbers
how do neutrophils kill bacteria
engulfment
what are rolling neutrophils tethered to
the blood vessels
3 stages of neutrophil movement
rolling, adhesions and crawling, transmigration
how is the movement of neutrophils controlled
neutrophils indergo a transient attachment to selectins
selectins interact with sugars on the surface of neutrophils with weak attachment to slow them down
once slowed down integrins bind to give fill arrest and firm adhesion
movement into tissues is driven by chemokines produced by inflammation
molecular players in rolling, firm adhesion, diapedis and chemotaxis
rolling - selectins and selectin counter receptors
firm adhesion - activated integrins and Ig like couterparts
diapedis - integrins and enothelial cell adhesion molecules
chemotaxis - integrins and chemokines/chemokine receptors
what is paracellular migration
movement between cells of the blood vessel wall
what is transcellular migration
movement through endothelial cells by engulfment
what are the 3 known selectins
e + p selectin and l selectins
what are beta 2 integrins
adhesion molecules, alpha beta heterodimers
diff alpha chain, common beta chain
exclusive to immune system
CD11a and CD11b are most important as they are major adhesion receptors
undergo conformational changes from low, med to high affinity via inside out signalling
usually found in low affinity states and are activated by chemokines
chemotaxis by neutrophils
allows neutrophils to chase infection
responds to sterile tissue injury in the liver
mediated by chemotatic factors / chemokines which bind to g protein coupled receptors on the neutrophils
results in polarisation and directed movement
chemotatic factors
platelet activating factors,
FMLP-N-formylated peptides from bacteria and mitochondria
C5a and C5 break down product, anaphlotoxin
how are g proteins activated
GTP replaces GDP
what are primary opsonins and what are they needed for
IgG, complement factor C3 fragment, C3b and C3bi
most microorganisms wont be phagocytosed without opsonins
pseudopods extend to cover the particle that is opsonised
opsonins are generated to mediate phagocytosis
IgG Fc receptors
the fab region reacts with the organism
the fc region interacts with the FcyR
what is necessary for complete digestion of bacteria
lysosomes
how does the phagosome help killing of bacterial through neutrophils
bacterium is phagocytosed by neutrophils
the phagosome fuses with azurophilic and specific granules
ph of the phagosome rises rises to activate the microbial response and the bacterium is killed
ph then decreases and fusion with lysosomes allows acid hydrolases to degrade the bacterium completely
the neutrophil dies by apoptosis and is phagocytosed by macrophages
respiratory burst and generation of reactive oxygen species:
when is the NADPH complex assembled?
where is the complex assembled?
why is super oxide acted upon?
where are reactive O2 species generated?
why does the conversion to reactive O2 need to be highly regulated?
what do further reactions lead to?
following the activation of neutrophils with diverse products, especially microbial derivatives
in the neutrophil that is to be oxidised
super oxide is to be acted upon to be converted to hydrogen peroxide which can be converted to other O2 species by iron
at the cell surface
if it wasnt highly regulated it would lead to a lot of tissue damage
formation of other antimicrobial reactive oxygen species such as hydroxyl radicals and hypochloras
what do membrane of granules contain
members of the NADPH complex
what do muts in the NADPH complex lead to
mutations in the complex lead to diseases as infection cannot be efficiently degraded
what is chronic granulomatous disease
a mut in the NOX2 of NADPH complex
recurring/persistant infection of soft tissue, lungs an other organs despite antibiotic treatment
symptoms = facial acne, inflam of nares, severe gingivitis, early pneumonia, excessive formation of granulomes in all tissue
treat with daily does of trimethoprim-sulfamethoxazole and INF-y to reduce frequency of infection
what are NETs (neutrophil extracellular traps)
an antimicrobial pathway of neutrophils
they decondense nuclear dna/chromatin and release them into the cytoplasm to mix with granule derived antimicrobial peptides before extending weblike structures into the extracellular environment
they trap and kill a variety of microbes
what do NETs require
reactive O2 species, granule proteins myeloperoxidase and neutrophil elastase
how do nets work
neutrophils activate and the NE is released from azurophilic granules into the cytosol and translocates to nucleus where it cleave the histone to decondense chromatin
myeloperoxidase consumes H2O2 to generate HOCl and other oxidants - required for translocation of NE to the nucleus during NETosis
what is NET deficiency associated with
susceptibility to fungal infection in patients with chronic granulomatous disease who do not generate reactive O2 species
