Granulocytes

Question 1

Granulocyte colony stimulating factor (GCSF)

Answer 1

• Stimulates granulocyte production
• Releases them from BM (loss of CXCR4)
• Is anti-apoptotic
• CXCR4 induces adhesion in BM and granulocyte retention, GCSF causes loss of CXCR4
• Re-expression of CXCR4 brings granulocytes back to BM
• 3-5% of granulocytes are in blood, the rest in BM
• Release of granulocytes from BM controlled in part by sympathetic NS

Question 2

Isolated neutropenia

Answer 2

• Tested w/ absolute neutrophil count (ANC)
• ANC = WBC x (SEGS + bands)
• Bands= immature PMNs, SEGS= mature PMNs
• Normal ANC is ≥1500, significant risk of infection <300 if due to marrow reserve pool depletion
• Almost never due to malignancy

Question 3

Propensity to infection in neutropenia

Answer 3

• Related to adequacy of marrow reserve pool and not to ANC
• ANC reflect propensity to infection only in the case of marrow failure (depleted reserve pool)
• If there is neutropenia (low ANC) but BM has reserves, there will not be infection
• If there is neutropenia and BM doesn’t have reserves, there will be infection
• In immune or destructive neutropenia, there is no relation btwn ANC and propensity to infection
• Must determine if neutropenia is causing infection of if its a secondary result of another global inflammatory process (AID such as RA or lupus)

Question 4

Margination and diapedesis

Answer 4

• Rolling along endothelium induced by selectins (weak interaction), adhesion induced by integrins (strong interaction)
• Diapedesis induced by actin cytoskeleton reorganization to squeeze btwn endothelium

Question 5

Chemotaxis

Answer 5

• Based on chemokine/cytokine gradient
• Actin polymerization and degradation responsible for movement
• Actin polymerizes in 8 second cycles and drives PMN shape change
• Actin extends pseudopod and pulls the cell forward

Question 6

Phagocytosis

Answer 6

• Fc receptor binds to Fc region on Ab (which is bound to Ag)
• Could also be complement opsonization
• Binding of the receptor leads to actin polymerization around the Ag
• Once Ag is engulfed in the phagosome killing will commence

Question 7

Bacterial killing

Answer 7

• Through O2 independent and O2 dependent mechanisms
• O2 independent: proteases and hydrolases in granules, antimicrobial peptides (defensins, cathelicidins)
• O2 dependent: respiratory burst
• Using NADPH + O2 to give superoxide (O2-), which will dismutate into H2O2 (NADPH oxidase)
• Respiratory burst is critical in killing bacteria and fungi (defects in it cause CGD- lack of NADPH oxidase)

Question 8

Myeloperoxidase (MPO)

Answer 8

• Nz synthesized by promyelocytes and packaged in the primary granules
• MPO used to combine Cl- w/ H2O2 to make HOCl (hypochloric acid, bleach)
• HOCl is the agent which kills bacteria and fungi

Question 9

Defects in superoxide generation of MPO

Answer 9

• CGD: deficient in Phox gene which is required for generation of superoxide radicals (leads to recurrent infections at epithelial surfaces)
• Dx w/ NBT test
• MPO deficiency leads to impairment in host defense to candida, but not staph aureus

Question 10

Clinical manifestations of neutropenia

Answer 10

• Gingivitis
• Mucosal ulcers
• Ab pain
• Abscesses
• Fevers