Specific granules
Encyclopedia
Specific granules are secretory vesicles
found exclusively in cells of the immune system
called granulocyte
s. They are also known as secondary granules.
It is sometimes described as applying specifically to neutrophils,, and sometimes the term is applied to other types of cells.
These granule
s store a mixture of cytotoxic molecules, including many enzyme
s and antimicrobial peptides, that are released by a process called degranulation
following activation of the granulocyte by an immune stimulus.
Specific granules are also known as "secondary granules".
Vesicle (biology)
A vesicle is a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes , or...
found exclusively in cells of the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
called granulocyte
Granulocyte
Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes because of the varying shapes of the nucleus, which is usually lobed into three segments...
s. They are also known as secondary granules.
It is sometimes described as applying specifically to neutrophils,, and sometimes the term is applied to other types of cells.
These granule
Granule
Granule is a generic term used for a small particle or grain. The generic term is employed in a variety of specific contexts.* Granule , visible structures in the photosphere of the Sun arising from activity in the Sun's convective zone...
s store a mixture of cytotoxic molecules, including many enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s and antimicrobial peptides, that are released by a process called degranulation
Degranulation
Degranulation is a cellular process that releases antimicrobial cytotoxic molecules from secretory vesicles called granules found inside some cells...
following activation of the granulocyte by an immune stimulus.
Specific granules are also known as "secondary granules".
Contents
Examples of cytotoxic molecule stored by specific granules in different granulocytes include:- Neutrophil: alkaline phosphataseAlkaline phosphataseAlkaline phosphatase is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids. The process of removing the phosphate group is called dephosphorylation...
, lactoferrinLactoferrinLactoferrin , also known as lactotransferrin , is a multifunctional protein of the transferrin family. Lactoferrin is a globular glycoprotein with a molecular mass of about 80 kDa that is widely represented in various secretory fluids, such as milk, saliva, tears, and nasal secretions...
, lysozymeLysozymeLysozyme, also known as muramidase or N-acetylmuramide glycanhydrolase, are glycoside hydrolases, enzymes that damage bacterial cell walls by catalyzing hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan and between...
, myeloperoxidaseMyeloperoxidaseMyeloperoxidase is a peroxidase enzyme that in humans is encoded by the MPO gene. Myeloperoxidase is most abundantly expressed in neutrophil granulocytes . It is a lysosomal protein stored in azurophilic granules of the neutrophil...
, NADPH oxidaseNADPH oxidaseThe NADPH oxidase is a membrane-bound enzyme complex. It can be found in the plasma membrane as well as in the membrane of phagosome.-Subunits:It is made up of six subunits...
- Eosinophil: cathepsinCathepsinCathepsins are proteases: proteins that break apart other proteins, found in many types of cells including those in all animals. There are approximately a dozen members of this family, which are distinguished by their structure, catalytic mechanism, and which proteins they cleave...
, major basic proteinMajor Basic ProteinProteoglycan 2, bone marrow , also known as PRG2, is a protein which in humans is encoded by the PRG2 gene.- Function :...
- Basophil: heparinHeparinHeparin , also known as unfractionated heparin, a highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule...
, histamineHistamineHistamine is an organic nitrogen compound 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...
(not directly cytotoxic)