Degranulation is a cellular process that releases
antimicrobialAn antimicrobial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, or protozoans, as well as destroying viruses. Antimicrobial drugs either kill microbes or prevent the growth of microbes...
cytotoxic molecules from
secretorySecretion is the process of elaborating, releasing, and oozing chemicals from a cell, a secreted chemical substance or amount of substance. In contrast to excretion, the substance may have a certain function, rather than being a waste product....
vesicleA vesicle is a bubble of liquid within a cell. More technically, a vesicle is a small, intracellular, membrane-enclosed sac that stores or transports substances within a cell. Vesicles form naturally because of the properties of lipid membranes ...
s called
granulesIn cell biology, a granule can be any structure barely visible by light microscopy. The term is most often used to describe a secretory vesicle.-Leukocytes:...
found inside some cells. It is used by several different cells involved in the
immune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
, including granulocytes (neutrophils, basophils and eosinophils) and
Mast cellA mast cell is a resident cell of several types of tissues and contains many granules rich in histamine and heparin. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing and defense against...
s, and certain
lymphocyteA lymphocyte is a type of white blood cell in the vertebrate immune system.By their appearance under the light microscope, there are two broad categories of lymphocytes, namely the large granular lymphocytes and the small lymphocytes. Functionally distinct subsets of lymphocytes correlate with...
s such as
natural killer (NK) cellsNatural killer cells are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses...
and
cytotoxic T cellA cytotoxic T cell belongs to a sub-group of T lymphocytes that are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses , or are otherwise damaged or dysfunctional...
s, whose main purpose is to destroy invading microorganisms.
Cytotoxic T cells and NK cells release molecules like
perforinPerforin-1 is a protein that in humans is encoded by the PRF1 gene.Perforin is a cytolytic protein found in the granules of CD8 T-cells and NK cells. Upon degranulation, perforin inserts itself into the target cell's plasma membrane, forming a pore. The lytic membrane inserting part of perforin...
and
granzymeGranzymes are serine proteases that are released by cytoplasmic granules within cytotoxic T cells and natural killer cells. Their purpose is to induce apoptosis within virus-infected cells, thus destroying them....
s by
a process of directed
exocytosisExocytosis is the durable process by which a cell directs the contents of secretory vesicles out of the cell membrane...
to kill infected target cells.
Four kinds of granules exist in neutrophils that display differences in content and regulation.
Degranulation is a cellular process that releases
antimicrobialAn antimicrobial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, or protozoans, as well as destroying viruses. Antimicrobial drugs either kill microbes or prevent the growth of microbes...
cytotoxic molecules from
secretorySecretion is the process of elaborating, releasing, and oozing chemicals from a cell, a secreted chemical substance or amount of substance. In contrast to excretion, the substance may have a certain function, rather than being a waste product....
vesicleA vesicle is a bubble of liquid within a cell. More technically, a vesicle is a small, intracellular, membrane-enclosed sac that stores or transports substances within a cell. Vesicles form naturally because of the properties of lipid membranes ...
s called
granulesIn cell biology, a granule can be any structure barely visible by light microscopy. The term is most often used to describe a secretory vesicle.-Leukocytes:...
found inside some cells. It is used by several different cells involved in the
immune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
, including granulocytes (neutrophils, basophils and eosinophils) and
Mast cellA mast cell is a resident cell of several types of tissues and contains many granules rich in histamine and heparin. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing and defense against...
s, and certain
lymphocyteA lymphocyte is a type of white blood cell in the vertebrate immune system.By their appearance under the light microscope, there are two broad categories of lymphocytes, namely the large granular lymphocytes and the small lymphocytes. Functionally distinct subsets of lymphocytes correlate with...
s such as
natural killer (NK) cellsNatural killer cells are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses...
and
cytotoxic T cellA cytotoxic T cell belongs to a sub-group of T lymphocytes that are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses , or are otherwise damaged or dysfunctional...
s, whose main purpose is to destroy invading microorganisms.
Cytotoxic T cells and NK cells
Cytotoxic T cells and NK cells release molecules like
perforinPerforin-1 is a protein that in humans is encoded by the PRF1 gene.Perforin is a cytolytic protein found in the granules of CD8 T-cells and NK cells. Upon degranulation, perforin inserts itself into the target cell's plasma membrane, forming a pore. The lytic membrane inserting part of perforin...
and
granzymeGranzymes are serine proteases that are released by cytoplasmic granules within cytotoxic T cells and natural killer cells. Their purpose is to induce apoptosis within virus-infected cells, thus destroying them....
s by
a process of directed
exocytosisExocytosis is the durable process by which a cell directs the contents of secretory vesicles out of the cell membrane...
to kill infected target cells.
Neutrophils
Four kinds of granules exist in neutrophils that display differences in content and regulation. Secretory vesicles are the most likely to release their contents by degranulation, followed by
gelatinaseIn biology and chemistry, gelatinase is a proteolytic enzyme that allows a living organism to hydrolyse gelatin into its sub-compounds that can cross the cell membrane and be used by the organism...
granules, specific granules, and
azurophilAzurophil is the term used to refer to objects that are readily staining with an azure dye. The term is used especially in reference to certain cytoplasmic granules in white blood cells, particularly hyperchromatin and reddish purple granules of certain blood cells.As another example, neutrophils...
granules.
Mast cells
Antigens interact with
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molecules already bound to high affinity
Fc receptorAn Fc receptor is a protein found on the surface of certain cells - including natural killer cells, macrophages, neutrophils, and mast cells - that contribute to the protective functions of the immune system....
s on the surface of
mast cellA mast cell is a resident cell of several types of tissues and contains many granules rich in histamine and heparin. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing and defense against...
s to induce degranulation. The mast cell releases a mixture of compounds, including
histamineHistamine is a biogenic amine involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by basophils and by...
,
proteoglycanProteoglycans are glycoproteins that are heavily glycosylated. They have a core protein with one or more covalently attached glycosaminoglycan chain. The chains are long, linear carbohydrate polymers that are negatively charged under physiological conditions, due to the occurrence of sulfate and...
s and
serine proteaseSerine proteases or serine endopeptidases are proteases in which one of the amino acids at the active site is serine....
s, from its cytoplasmic granules.
Eosinophils
In a similar mechanism, activated eosinophils release preformed mediators such as
major basic proteinProteoglycan 2, bone marrow , also known as PRG2, is a protein which in humans is encoded by the PRG2 gene.- Function :...
, and
enzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at...
s such as
peroxidasePeroxidases are a large family of enzymes that typically catalyze a reaction of the form:For many of these enzymes the optimal substrate is hydrogen peroxide, but others are more active with organic hydroperoxides such as lipid peroxides...
, following interaction between their Fc receptors and IgE molecules that are bound to large parasites like helminths.