Granular contents of Neutrophils and Platelets

Neutrophil Granules

Azurophilic (Primary) Granules

  • These are lysosomes that occur in all granulocytes, as well as in lymphocytes and monocytes.
  • In addition to expected lysosomal hydrolases, they also contain peroxidases (used to demonstrate azurophilic granules chemically).
  • Develop earlier than specific granules.
  • Stains blue/purple by Romanowsky stain.

Mnemonic: ABCDE MnOP

  1. Acid hydrolase
  2. BPI (Bactericidal Permeability Increasing) protein
  3. Cathepsin G
  4. Defensin
  5. Elastase
  6. Myeloperoxidase (MPO)

neutrophil granules

Specific (Secondary) Granules

  • Do not stain intensely with Romanowsky stain.
  • Smaller and more numerous than specific granules.

Mnemonic: COLA

  1. Collagenase
  2. Cathelicidin
  3. Oxidase (NADPH oxidase)
  4. Lactoferrin
  5. Alkaline phosphatase

Common to both Azurophilic and Specific Granules

  1. Lysozyme
  2. Phospholipase A2 (PLP A2)

Tertiary Granules

  • Cathepsin
  • Gelatinase

Defect in Neutrophil Granules

1. Alpha granule defect:

Myeloperoxidase (MPO) deficiency:

  • Most common neutrophil defect.
  • Microbicidal activity of neutrophil is delayed but not absent (defective HOCl formation).
  • Acquired form is seen in AML.

Chediak-Higashi Syndrome (CHS):

  • Defect in LYST (lysosomal transport) protein, encoded by CHS1 gene at 1q42.
  • Abnormal giant alpha granules, impaired chemotaxis and phagolysosome formation leading to severe bacterial infections.
  • Giant granules in: melanocytes and hair (oculocutaneous albinism), nerve tissue (peripheral neuropathy).

2. Specific granule defect (SGD):

  • Misnomer
  • Defect of both primary and specific granules: Absent specific granules + Absent Lactoferrin and ALP (primary granules) but normal MPO.

3. NADPH oxidase deficiency: Chronic Granulomatous Disease (CGD)

  • Mostly X-linked recessive trait; 30% autosomal recessive
  • Infections due to catalse positive organisms (organisms that destroy their own hydrogen peroxide) – extensive inflammatory reactions, and lymph node suppuration is common despite administration of appropriate antibiotics.

Platelet Granules

platelet granules

Alpha granules

Mnemonic: Alpha granules are bigger like Alpha males. These are bigger molecules like proteins and peptides. The granules can be remembered using mnemonic Platelet Function Test (PFT).

  1. P-selectin
  2. Platelet factor 4
  3. Platelet Derived Growth Factor (PDGF) and othr growth factors
  4. Fibronectin
  5. Fibrinogen and other factors (factor V, VIII and vWF)
  6. Transforming Growth Factor – beta (TGF-beta)

Delta (Dense) granules

Mnemonic: Delta granules are smaller and weakers like Delta males. These are smaller molecules. It can be remembered using mnemonic – CAN.

  1. Cations (Ca++, Mg++)
  2. Amines (Serotonin, Histamine)
  3. Nucleotides (ADP, ATP, PPi)

Lysosomes

Defect in Platelet Granules

Alpha granule defect:

  • Gray platelet syndrome (Alpha storage pool defect) – characterized by thrombocytopenia and abnormal enlarged gray-blue platelets with a washed-out appearance due to deficeint alpha granules.
  • Quebec platelet disorder – an autosomal dominant trait caused by deficient platelet alpha granule factor V (due to increased expression of alpha granule urokinase-type plasminogen activator that generates plasmin and cleaves factor V) but normal plasma factor V.

Delta granule defect:

  • Delta storage pool defect – Normal number and normal appearing platelets in peripheral smear, absence of dense granules in electron microscopy and impaired second wave of platelet aggregation (prolonged bleeding time).
  • Hermansky-Pudlak syndrome and Chediak-Higasghi syndrome – Rare autosomal disorders that have in common platelet dense granule deficiency, albinism and lysosomal granule defects.

 

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