W2: WBCs Flashcards
how are WBCs split into 2 categories?
polymorphonuclear (granulocytes)
mononuclear
granulocytes include…
neutrophils (phagocytes)
eosinophils
basophils
mononuclear WBCs include…
lymphocytes
monocytes (phagocytes)
order smallest to largest WBC counts
basophils
eosinophils/monocytes
lymphocytes
neutrophils
neutrophils are elevated in…
bacterial infection
stress
exercise
myeloproliferative diseases e.g. leukaemia
lymphocytes are elevated in…
viral infection
lymphoproliferative diseases (e.g. lymphocytic leukaemia)
monocytes are elevated in…
infection
inflammation
tissue damage
monocytic leukaemia
eosinophils are elevated in…
allergy
intestinal parasites
hypereosinophilic syndrome
eosinophilic leukaemia
basophils are elevated in…
some myeloproliferative diseases
(esp chronic granulocytic leukaemia)
which 2 cell types can monocytes mature into?
macrophage
dendritic cell
neutrophil staining
granules are neutral-staining
eosinophil staining
granules stain w/ eosin (orange)
basophil staining
granules stain intensely w/ methylene blue
granulocyte maturation stages (neutrophils)
blasts
promyelocytes
myelocytes
metamyelocytes
‘band form’ neutrophils
neutrophils
granulocyte turnover
50-320 x 10^9/day
lifespan of a neutrophil
usually spend ~7h in peripheral blood (circulating & marginal pools)
migrate into tissues – last for ~20h, after which motility lost. Destruction by monocytes/macrophages.
Many also lost in GI tract.
marginal pools
stuck on inside of BVs
lifespan of eosinophils
8–12 h in circulation then 8–12d in tissues (thymus, lower GI tract,ovary, uterus, spleen & lymph nodes)
lifespan of basophils
few hrs-few days
function of neutrophils
destruction of invading bacteria & some fungi
how does a neutrophil perform its function? (2 steps)
- location by chemotaxis - motility up a conc grad
- phagocytosis = engulfing + killing
chemotaxis requires…
*vessel wall adhesion
*mmt up conc grad
motility of neutrophils
crawl
Amoeboid via pseudopodia.
Mechanism: chemotactic receptor-ligand binding followed by interaction of contractile proteins (e.g. actin & myosin)
phagocytosis is accompanied by a ‘respiratory burst’ in which there is…
Incr O2 consumption
Incr glycolysis
Uprating of bactericidal processes e.g. Myeloperoxidase (MPO) activity
Increased expression of some constituents, e.g. Alkaline phosphatase
stages of phagocytosis
1) Opsonisation w e.g. IgG /IgM Abs or complement.
2) Particle attachment, via a receptor for the opsonin
3) Pseudopodia enclose particle, which is ingested > phagosome
3) Fusion of granules into phagosome.
4) Microbial killing w/in 20m.
how do neutrophils trap & kill bacteria extracellularly?
prod web of DNA & proteases
helps prevent spread of infection
neutrophil nucleus structure
lobulate to aid deformability & motility
primary granules of neutrophils
discharge into phagosomes. Contain microbicidal proteins (eg MPO, hydrolases & lysozyme) for oxidative & non-oxidative killing
secondary granules of neutrophils
discharge into phagosomes and extracellularly. Contain hydrolases + chemotactic, opsonic & adhesion protein receptors e.g. Alkaline phosphatase, lysozyme & collagenase
tertiary granules of neutrophils
Contain e.g. alkaline phosphatase, gelatinase (involved in destruction of collagen), cathepsin (a protease)
defects of microbial killing: myeloperoxidase deficiency
Fairly common.
Partial or total.
Only 20% pts are immunocompromised. Oxygen free radicals (O-) & lysozyme
compensate.
Fungal infections are biggest prob.
other neutrophil disorders
Neonate neutrophils have only 20 – 27% chemotactic activity of adults , less in premature neonates.
Neutrophil function declines w age – chemotaxis and phagocytosis significantly impaired in elderly.
Abnormal neutrophils (e.g.hypogranular or agranular) found in myelodysplasia (“pre-leukaemia”), common in elderly
eosinophils
Eliminate helminth (= parasitic worm) infections by antibody-dependant cell-mediated toxicity (IgE) and are key mediators of allergic inflammation
Elevated in helminth infections and allergy
Normally found in thymus, lower GI tract, ovary, uterus, spleen and lymph nodes, but not usually in thelung except in the case of airborne allergy. Tissue eosinophils are several 100 x more numerous than blood eosinophils
Ab-dependent cell-mediated toxicity
a mechanism ofcell-mediated immune defence
effector cell of theimmune systemactivelylysesa target cell, whose membrane-surface Ags have been bound by specificAbs (IgE in the case of eosinophils)
Eosinophils – some constituents and their functions
Eosinophil cationic protein creates pores in mems of target cells allowing potential entry of other cytotoxic molecules to the cell & has anti-viral activity
Major Basic Protein (toxic to parasites & epithelial cells, causes release of histamine & heparin from basophils & mast cells)
Eosinophil-derived neurotoxin (has antiviral properties)
Eosinophil peroxidase is active against micro-organisms
Eosinophil degranulation causes significant local tissue damage
Eosinophil disorders
Hypereosinophilic syndrome – sustained unexplained eosinophilia > 1.5 x 109/l > 6 months.
Organ dysfunction due to eosinophilic infiltration (heart failure, skin & CNS disease etc)
Some cases are clonal (=Eosinophilic leukaemia)
In most cases the eosinophils are independent of GF control, = a myeloproliferative syndrome
A monoclonal pop of activated T lymphocytes may be found, producing excess IL5
Treatment attempts to limit organ damage by control of eosinophils using hydroxyurea, cytotoxic therapy, steroids.
Most cases are fatal
basophils
Mature in marrow for 2-7d, circulate for 2 weeks
mature in marrow and circulate in blood, mast cells mature in tissues.
major growth factor for basophils is IL-3, mast cells require Stem Cell Factor (SCF). Both contain heparin & histamine.
Basophils degranulate into internal phagosomes, mast cells discharge granules.
basophils - function
Basophils & mast cells orchestrate local immunologic & inflammatory reactions, esp. those involving parasitic infections. Secrete:
Histamine - chemotactic agent for eosinophils & is a vasodilator
Heparin - anticoagulant
Accum at site of allergic reactions, esp tick bites
key mediators of immediate hypersensitivity reactions e.g. asthma, urticaria & anaphylaxis
stim by e.g. IgE, IL-3, C5a, GM-CSF & insect venoms to release granule contents, esp histamine.
Basophil activation > release of numerous cytokines, e.g. IL-3, TNF-α & GM-CSF, IL-5,
IL-4.
Disorders of basophils
Marked basophilia common in CML
Basophilia to a lesser extent is found in other myeloproliferative disorders, e.g. myelofibrosis & Primary Proliferative Polycythaemia.
Basophil leukaemia vrare. Treatment difficult due to release of histamine and other granule contents.
Granulocyte function testing
Almost entirely limited to neutrophil function tests.
May be indicated in cases of:
Chronic bacterial infection
Increased susceptibility to bacterial infections
Therapy-resistant infections
Recurrent infections with nonpathogenic microorganisms
Abscesses of liver or lung
Rarely performed
Granulocytopenia (esp cyclic neutropenia) and defects of B cells or complement must be excluded first
Primary neutrophil dysfunction significant enough to cause clinical disease accounts for less than 6% of all primary immune deficiency
Nitroblue tetrazolium (NBT) dye reduction for Chronic Granulomatous disease.
Test of neutrophil respiratory burst (production of active oxygen species e.g. O-). Reduction of NBT to an insoluble blue compound by active neutrophils. Visual assessment (microscopy) of results.
Largely superceded by direct measurements of respiratory burst products using flow cytometry.
Can also test:
Motility by assessing ability to penetrate a filter membrane or observed movement across a glass slide
Phagocytosis:
Ingestion, e.g. by observing reduction in the number of free bacteria in a bacteria + neutrophil suspension
Killing, e.g. by observing the fall in numbers of ingested bacteria.
These functional assays are increasingly superceded by flow cytometry
monocyte structure
Kidney-shaped nucleus
Abundant grey-blue cytoplasm filled
w fine reddish granules
Many cytoplasmic enzymes, esp lysosyme,
peroxidase, esterases
Cytoplasmic vacuoles are evidence of phagocytosis
Amoeboid motility, exhibit chemotaxis
Accum at the site of inflammation
monocyte function
prod diff adhesins (adhesive glycoproteins) which facilitate adhesion to various surfaces, e.g. endothelial cells
APCs
Can phagocytose opsonised and non-opsonised particles (unlike neutrophils)
Can kill infected host cells (antibody-mediated cellular toxicity)
release many cytokines that stim other cells in IS
monocyte lifespan
Several months. Can differentiate into macrophages and dendritic cells (& are the only blood cell that can do this)
monocyte disorders
Lipid storage diseases, e.g. Gaucher’s disease, Niemann-Pick disease result from an accum of debris w/in macrophages – inherited impairment of degrad.
Cause permanent cellular and tissue damage, esp in brain, PNS, liver, spleen, and BM.
An increased number of monocytes (=monocytosis) occurs in chronic infections and inflammatory conditions, e.g. tuberculosis & Crohn’s disease
Monocytic leukaemia (Acute or Chronic)
defects of microbial killing: respiratory burst failure - esp NADPH oxidase
Inherited, metabolic failure of microbial killing
Some organisms live in the phagosome > persistent infections.
Non-oxidative killing partially compensates (= Chronic Granulomatous Disease (CGD).
defects of microbial killing: inherited/acquired defects in neutrophil adhesion/migration
Inherited defects v rare.
Acquired, e.g. leukaemia, diabetes, renal failure, > varying degrees of susceptibility to sepsis.