An azurophilic granule is a cellular object readily
stainable with a
Romanowsky stain
Romanowsky staining, also known as Romanowsky–Giemsa staining, is a prototypical staining technique that was the forerunner of several distinct but similar stains widely used in hematology (the study of blood) and cytopathology (the study of ...
. In
white blood cells and
hyperchromatin, staining imparts a
burgundy or
merlot coloration.
Neutrophil
Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying ...
s in particular are known for containing azurophils loaded with a wide variety of anti-microbial
defensins that fuse with
phagocytic
Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is c ...
vacuole
A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic m ...
s. Azurophils may contain
myeloperoxidase
Myeloperoxidase (MPO) is a peroxidase enzyme that in humans is encoded by the ''MPO'' gene on chromosome 17. MPO is most abundantly expressed in neutrophil granulocytes (a subtype of white blood cells), and produces hypohalous acids to carry ...
,
phospholipase A2,
acid hydrolase
An acid hydrolase is an enzyme that works best at acidic pHs. It is commonly located in lysosomes, which are acidic on the inside. Acid hydrolases may be nucleases, proteases, glycosidases, lipases, phosphatases, sulfatases and phospholipases ...
s,
elastase
In molecular biology, elastase is an enzyme from the class of ''proteases (peptidases)'' that break down proteins. In particular, it is a serine protease.
Forms and classification
Eight human genes exist for elastase:
Some bacteria (includin ...
, defensins, neutral
serine protease
Serine proteases (or serine endopeptidases) are enzymes that cleave peptide bonds in proteins. Serine serves as the nucleophilic amino acid at the (enzyme's) active site.
They are found ubiquitously in both eukaryotes and prokaryotes. Seri ...
s,
bactericidal/permeability-increasing protein
Bactericidal/permeability-increasing protein (BPI) is a 456-residue (~50k Da) protein that is part of the innate immune system. It belongs to family of lipid-binding serum glycoproteins.
Distribution and function
BPI was initially identified in ...
,
lysozyme
Lysozyme (EC 3.2.1.17, muramidase, ''N''-acetylmuramide glycanhydrolase; systematic name peptidoglycan ''N''-acetylmuramoylhydrolase) is an antimicrobial enzyme produced by animals that forms part of the innate immune system. It is a glycoside ...
,
cathepsin G
Cathepsin G is a protein that in humans is encoded by the ''CTSG'' gene. It is one of the three serine proteases of the chymotrypsin family that are stored in the azurophil granules, and also a member of the peptidase S1 protein family. Cathepsin ...
,
proteinase 3, and
proteoglycans.
Azurophil granules are also known as "primary granules".
Furthermore, the term "azurophils" may refer to a unique type of cells, identified only in
reptiles. These cells are similar in size to so-called
heterophil
Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying in ...
s with abundant
cytoplasm
In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...
that is finely to coarsely granular and may sometimes contain vacuoles. Granules may impart a purplish hue to the cytoplasm, particularly to the outer region. Occasionally, azurophils are observed with vacuolated cytoplasm.
See also
*
Azure A
Azure A is an organic compound with the chemical formula C14H14ClN3S. It is a light blue to dark blue dye. It is used as a screening test for mucopolysaccharides. It can also be used to stain lysosome in blood smears, and is often used in Giemsa ...
*
Azure (color)
Azure ( , ) is the color between cyan and blue on the spectrum of visible light. It is often described as the color of the sky on a clear day.
On the RGB color wheel, "azure" ( hexadecimal #0080FF) is defined as the color at 210 degree ...
*
Granule
*
Lysosome
A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane pr ...
*
Specific granules Specific granules are secretory vesicles found exclusively in cells of the immune system called granulocytes.
It is sometimes described as applying specifically to neutrophils, and sometimes the term is applied to other types of cells.
These gran ...
*
Neutrophil degranulation
References
Hematology
Staining
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