Granulocytes: Introduction, Types, Functions and Roles

Granulocytes are at the front lines of attack during an immune response and are considered part of the innate immune system.
Granulocytes are white blood cells (leukocytes) that are classified as neutrophils, basophils, mast cells, or eosinophils on the idea of differences in cellular morphologyand therefore the staining of their characteristic cytoplasmic granules.
All granulocytes have multilobed nuclei that make them visually distinctive and easily distinguishable from lymphocytes, whose nuclei are round.
The granulocytes cytoplasm is replete with some granules that are released in when it contact with pathogens.
These granules contains many of the proteins with different functions.
1. Some damage pathogens directly.
2. Some regulate trafficking and activity of other white blood cells, including lymphocytes.
3. Some contribute to the remodeling of tissues at the site of infection.

Neutrophils

Neutrophils constitute the majority (50% to 70%) of circulating leukocytes and are much more numerous than eosinophils (1%–3%), basophils (1%), or mast cells (1%).
After differentiation within the bone marrow, neutrophils are released into the peripheral blood and circulate for 7 to 10 hours before migrating into the tissues, where they have a life expectancy of a couple of days.
In response to many types of infections, the number of circulating neutrophils increases significantly and more are recruited to tissues, partially in response to cues the bone marrow receives to produce and release more myeloid cells.
The subsequent transient increase within the number of circulating neutrophils, called leukocytosis, is employed medically as a sign of infection.

Neutrophil

Neutrophils are present to the site of infection in response to inflammatory molecules (e.g., chemokines) generated by innate cells (including other neutrophils) that have bound a pathogen.
Bacteria were very effectively engulf by neutrophils once in the tissue, and secrete a wide range of proteins that have antimicrobial activity and tissue remodeling potential.
Neutrophils are the dominant first responders to infection and therefore the main cellular components of pus, where they accumulate at the last of their short lives.
Although once considered a simple and “disposable” effector cell, the neutrophil has recently inspired renewed interest from investigations indicating that it may also regulate the adaptive immune response.

Basophils are nonphagocytic granulocytes that contain large granules filled with basophilic proteins (i.e., they stain blue in standard H&E staining protocols).
Basophils are relatively rare in the circulation, but can be very potent. In response to binding of circulating antibodies, basophils release the contents of their granules.

Basophil

Histamine, one among the simplest proteins in basophilic granules, increases blood vessel permeability and smooth muscle activity.
Basophils (and eosinophils, below) are critical to our response to parasites, particularly helminths (worms), but in areas where worm infection is less prevalent, histamines are best appreciated as the cause of allergy symptoms. Like neutrophils, basophils may also secrete cytokines that modulate the adaptive immune response.

Mast cells are released From bone marrow mast cells are released into the blood as undifferentiated cells; after leaving the blood mast cell will mature.
Mast cells are often found in a wide assortment of tissues, including the skin, connective tissues of different organs, and mucosal epithelial tissue of the respiratory, genitourinary, and stomach related things.

Mast cell

The circulating basophils, these cells have huge amount of cytoplasmic granules that may contains histamine and other pharmacologically active substances.
Mast cells also play a crucial role within the development of allergies.
many features of basophils and mast cells are similar their relationship is not clearly understood. Some says that basophils are the blood-borne version of mast cells; others speculate that they have distinct origins and functions.

Eosinophils, like neutrophils, are motile phagocytic cells which will migrate from the blood into the tissue spaces.
Their phagocytic role is significantly lesser important than that of neutrophils, and it’s thought that they play their most vital role within the defense against multicellular parasitic organisms, including worms.
They can also do clustering around invading worms, whose membranes are damaged by the activity of proteins released from eosinophilic granules.
Their phagocytic role is significantly smaller than that of neutrophils, and it’s thought that they play their most vital role within the defense against multicellular parasitic organisms, including worms.
They can be found clustering around invading worms, whose membranes are damaged by the activity of proteins released from eosinophilic granules.

Eosinophil

Neutrophils, Basophils and eosinophils may also secrete cytokines that regulate B and T lymphocytes, thereby influencing the adaptive immune response.
In areas where parasites are less of a health problem, eosinophils are better appreciated as contributors to asthma and allergy symptoms.

Cell type	Molecule in granule	Function
Neutrophil	Proteases Antimicrobial proteins Protease inhibitors Histamine	Tissue remodeling Direct harm to pathogens Regulation of proteases Vasodilation, inflammation
Eosinophil	Cationic proteins Ribonucleases Cytokines Chemokines	Induces formation of ROS Vasodilation, basophil degranulation Antiviral activity Modulation of adaptive immune responses Attract leukocytes
Basophil/Mast Cell	Cytokines Lipid mediators Histamine	Modulation of adaptive immune response Regulation of inflammation Vasodilation, smooth muscle activation

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