Types of Neutrophil Granules

Neutrophil Granules

• There are three main types of neutrophil granules: primary (azurophilic) granules, secondary (specific) granules, and tertiary granules.
• Primary granules contain peroxidase, antimicrobial compounds, elastase, cationic proteins, defensins, cathepsin G, lysozyme, and bacterial permeability increasing protein (BPI).
• Primary granules are found in young cells and are surrounded by a phospholipid membrane.
• Secondary granules contain plasma proteins, including albumin, and are formed by endocytosis in the later stages of neutrophil maturation.

Neutrophil Functions

• Neutrophils have various functions, including phagocytosis of Escherichia coli, promotion of complement activation, regulation of inflammation, and control of blood pressure.
• Neutrophils also contribute to the degradation of extracellular matrices, aiding tissue penetration and facilitating the immune response.
• Lysozyme breaks down bacterial cell walls, while BPI has both bactericidal and lipopolysaccharide-neutralizing activities.

Cytochemical Stains

• Myeloperoxidase (MPO) is used to stain neutrophils and is an important component of the respiratory burst.
• Sudan black B (SBB) is used to stain lipids and differentiate myeloid precursors from lymphoid precursors.
• Esterase is an enzyme released by activated neutrophils after they have been recruited to sites of infection.
• Periodic Acid Schiff (PAS) is used to detect glycogen in cells.
• Toluidine blue (TB) is used to stain acidic tissue components and has an affinity for nucleic acids.

Neutrophil Granulopoiesis and Recruitment

• Granulopoiesis is characterized by the sequential formation of neutrophil granules.
• The process includes the formation of azurophilic or primary granules, specific or secondary granules, and finally, secretory vesicles (SVs).
• Mature neutrophils egress from the bone marrow into circulation and then migrate to the site of infection or injury in a process called extravasation.
• There are three populations of neutrophils: stem cell pool, circulating pool, and marginating pool.

Leukocyte Extravasation

• Leukocyte extravasation is the movement of leukocytes out of the circulatory system and towards the site of tissue damage or infection.
• The process involves the activation of vascular endothelial cells (VECs), the rolling of neutrophils on the VEC surface, and the activation of neutrophils by chemokines or other chemoattractants.
• The activated neutrophils then express adhesion receptors, including β2 integrin molecules, and migrate through the endothelium and basement membrane to the site of infection.

This quiz covers the three main types of granules found in neutrophils, including primary and secondary granules, and their functions.