Eosinophil cationic protein (ECP) also known as ribonuclease 3 is a basic protein located in the eosinophil primary matrix. [3] In humans, the eosinophil cationic protein is encoded by the RNASE3 gene. [4]
ECP is released during degranulation of eosinophils. This protein is related to inflammation and asthma because in these cases, there are increased levels of ECP in the body. There are three glycosylated forms of ECP and consequently ECP has a range of molecular weights from 18-22 kDa. [5]
Eosinophil cationic protein and the sequence related eosinophil-derived neurotoxin (RNASE2) are both members of the Ribonuclease A superfamily. Both proteins possess neurotoxic, helmintho-toxic, and ribonucleo-lytic activities. Eosinophil cationic protein is localized to the granule matrix of the eosinophil. [6]
The ribonuclease activity of ECP is not essential for cytotoxicity. [7]
When the two known ribonuclease active-site residues are modified to non-functional counterparts (Lysine at position 38 to Arginine and Histidine at position 128 to Aspartate) [8] and compared to the wild-type ECP, the mutated ECP retains its cytotoxicity but no longer has its ribonuclease activity. The experiment confirmed that converting the two amino acids to non-functional counterparts did inhibit ECP’s ribonuclease activity. However, ECP retained its anti-parasitic activity. Also, it did not change the production and transportation of ECP in bacteria.
ECP is a potent cytotoxic protein capable of killing cells of guinea pig tracheal epithelium, [9] mammalian leukemia, [10] epidermis carcinoma, [9] and breast carcinoma, [11] as well as non-mammalian cells such as parasites, bacteria, and viruses. [12]
Mature ECP is cytotoxic to human bronchial epithelial (BEAS-2B) cells by specific binding to cell surface heparan sulfate proteoglycans (HSPGs) followed by endocytosis. [13]
Studies show that ECP, along with other RNases including EDN, had been reported to induce apoptosis in cells. A latest study indicated that ECP caused cytotoxicity in HL-60 and HeLa cells via caspase-3 like activity. [15] Accordingly, cytotoxic RNases play an important role in cell death. However, the mechanism of ECP-induced apoptosis is still not fully verified. Recent studies have shown that eosinophils can induce epithelial cell death via apoptosis and necrosis. [16]
ECP triggers apoptosis by caspase-8 activation through mitochondria-independent pathway. [14] Increases in chromatin condensation, sub-G1 population, PARP cleavage, and DNA fragmentation indicate that ECP induces apoptosis in human bronchial epithelial (BEAS-2B) cells. [14]
Eosinophil granulocytes appear in large numbers in inflammation sites and in response to certain parasitic infections. These cytoplasmic granules contain positively charged proteins that characterize the cells. ECP is one of the four highly basic proteins that enter the surrounding tissues when activated eosinophils degranulate. Although circulating ECP levels can vary widely among patients, some studies show that serum ECP measurements are useful in monitoring many active inflammatory diseases. [17] ECP concentrations in plasma and other body fluids increase during inflammatory reactions marked by activated eosinophils. [18]
Serum ECP levels are also a useful, objective measurement for asthma severity. Increased ECP levels correspond to symptom onset. In seasonal asthmatic patients, ECP measurement reflected changes in disease activity throughout the year. [19]
There are several mechanisms that can be combined to generate an asthma attack, including specific IgE antibodies, activated inflammatory cells, neurogenic mechanisms, hyperresponsiveness and individual hormonal imbalances. Allergic reactions in the lung typically have two phases. The late phase typically occurs several hours after exposure, upon which eosinophils accumulate in the bronchus and release granule proteins that cause bronchial irritability. ECP is also toxic to neurons, some epithelial cell lines, and isolated myocardial cells. [20] This could be a reason for itching disorders of the skin.
Serum ECP concentrations have also been linked to atopic dermatitis (AD) activity. ECP correlates with the symptoms (lichenification, sleep deprivation, erythema, papules, pruritus and excoriations) for AD and also correlates with the total clinical score. [20]
Serum ECP measurement for assessing asthma severity, monitoring therapy, and indicating severity of certain inflammatory skin conditions present an advantage over subjective clinical measures that are prone to inconsistencies due to broad variability of individual investigator and patient assessments, especially in young children.
The normal reference range for blood tests for eosinophil cationic protein is between 2.3 and 16 μg/L. [21]
Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. Along with mast cells and basophils, they also control mechanisms associated with allergy and asthma. They are granulocytes that develop during hematopoiesis in the bone marrow before migrating into blood, after which they are terminally differentiated and do not multiply.
Eosinophilia is a condition in which the eosinophil count in the peripheral blood exceeds 5×108/L (500/μL). Hypereosinophilia is an elevation in an individual's circulating blood eosinophil count above 1.5 × 109/L (i.e. 1,500/μL). The hypereosinophilic syndrome is a sustained elevation in this count above 1.5 × 109/L (i.e. 1,500/μL) that is also associated with evidence of eosinophil-based tissue injury.
Basophils are a type of white blood cell. Basophils are the least common type of granulocyte, representing about 0.5% to 1% of circulating white blood cells. However, they are the largest type of granulocyte and how they work is not fully understood. They are responsible for inflammatory reactions during immune response, as well as in the formation of acute and chronic allergic diseases, including anaphylaxis, asthma, atopic dermatitis and hay fever. They also produce compounds that coordinate immune responses, including histamine and serotonin that induce inflammation, and heparin that prevents blood clotting, although there are less than that found in mast cell granules. Mast cells were once thought to be basophils that migrated from the blood into their resident tissues, but they are now known to be different types of cells.
Immunoglobulin E (IgE) is a type of antibody that has been found only in mammals. IgE is synthesised by plasma cells. Monomers of IgE consist of two heavy chains and two light chains, with the ε chain containing four Ig-like constant domains (Cε1–Cε4). IgE is thought to be an important part of the immune response against infection by certain parasitic worms, including Schistosoma mansoni, Trichinella spiralis, and Fasciola hepatica. IgE is also utilized during immune defense against certain protozoan parasites such as Plasmodium falciparum. IgE may have evolved as a defense to protect against venoms.
Granulocytes are cells in the innate immune system characterized by the presence of specific granules in their cytoplasm. Such granules distinguish them from the various agranulocytes. All myeloblastic granulocytes are polymorphonuclear, that is, they have varying shapes (morphology) of the nucleus ; and are referred to as polymorphonuclear leukocytes. In common terms, polymorphonuclear granulocyte refers specifically to "neutrophil granulocytes", the most abundant of the granulocytes; the other types have varying morphology. Granulocytes are produced via granulopoiesis in the bone marrow.
The interleukin 4 is a cytokine that induces differentiation of naive helper T cells (Th0 cells) to Th2 cells. Upon activation by IL-4, Th2 cells subsequently produce additional IL-4 in a positive feedback loop. IL-4 is produced primarily by mast cells, Th2 cells, eosinophils and basophils. It is closely related and has functions similar to IL-13.
Interleukin 5 (IL-5) is an interleukin produced by type-2 T helper cells and mast cells.
Degranulation is a cellular process that releases antimicrobial cytotoxic or other molecules from secretory vesicles called granules found inside some cells. It is used by several different cells involved in the immune system, including granulocytes. It is also used by certain lymphocytes such as natural killer (NK) cells and cytotoxic T cells, whose main purpose is to destroy invading microorganisms.
The prostaglandin D2 receptor 1 (DP1), a G protein-coupled receptor encoded by the PTGDR1 gene (also termed PTGDR), is primarily a receptor for prostaglandin D2 (PGD2). The receptor is a member of the prostaglandin receptors belonging to the subfamily A14 of rhodopsin-like receptors. Activation of DP1 by PGD2 or other cognate receptor ligands is associated with a variety of physiological and pathological responses in animal models.
Pancreatic ribonuclease family is a superfamily of pyrimidine-specific endonucleases found in high quantity in the pancreas of certain mammals and of some reptiles.
Eosinophil-derived neurotoxin is an enzyme that in humans is encoded by the RNASE2 gene.
Creola bodies are a histopathologic finding indicative of asthma. Found in a patient's sputum, they are ciliated columnar cells sloughed from the bronchial mucosa of a patient with asthma. Other common findings in the sputum of asthma patients include Charcot-Leyden crystals, Curschmann's Spirals, and eosinophils.
Cysteinyl leukotriene receptor 1, also termed CYSLTR1, is a receptor for cysteinyl leukotrienes (LT). CYSLTR1, by binding these cysteinyl LTs contributes to mediating various allergic and hypersensitivity reactions in humans as well as models of the reactions in other animals.
Prostaglandin D2 receptor 2 (DP2 or CRTH2) is a human protein encoded by the PTGDR2 gene and GPR44. DP2 has also been designated as CD294 (cluster of differentiation 294). It is a member of the class of prostaglandin receptors which bind with and respond to various prostaglandins. DP2 along with Prostaglandin DP1 receptor are receptors for prostaglandin D2 (PGD2). Activation of DP2 by PGD2 or other cognate receptor ligands has been associated with certain physiological and pathological responses, particularly those associated with allergy and inflammation, in animal models and certain human diseases.
Cysteinyl leukotriene receptor 2, also termed CYSLTR2, is a receptor for cysteinyl leukotrienes (LT). CYSLTR2, by binding these cysteinyl LTs contributes to mediating various allergic and hypersensitivity reactions in humans. However, the first discovered receptor for these CsLTs, cysteinyl leukotriene receptor 1 (CysLTR1), appears to play the major role in mediating these reactions.
Granulysin (GNLY) is a protein expressed in most mammals which functions as an antimicrobial peptide released by killer lymphocytes in cytotoxic granules. It is a pore-forming peptide, as it can puncture a microbial cell wall, allowing for other death-inducing enzymes to enter the microbe and cause microptosis. GNLY is inhibited by cholesterol, and is most effective in helping to kill cholesterol-deficient microbes.
Peptidoglycan recognition protein 1, PGLYRP1, also known as TAG7, is an antibacterial and pro-inflammatory innate immunity protein that in humans is encoded by the PGLYRP1 gene.
Sialic acid-binding Ig-like lectin 8 is a protein that in humans is encoded by the SIGLEC8 gene. This gene is located on chromosome 19q13.4, about 330 kb downstream of the SIGLEC9 gene. Within the siglec family of transmembrane proteins, Siglec-8 belongs to the CD33-related siglec subfamily, a subfamily that has undergone rapid evolution.
5-Oxo-eicosatetraenoic acid is a nonclassic eicosanoid metabolite of arachidonic acid and the most potent naturally occurring member of the 5-HETE family of cell signaling agents. Like other cell signaling agents, 5-oxo-ETE is made by a cell and then feeds back to stimulate its parent cell and/or exits this cell to stimulate nearby cells. 5-Oxo-ETE can stimulate various cell types particularly human leukocytes but possesses its highest potency and power in stimulating the human eosinophil type of leukocyte. It is therefore suggested to be formed during and to be an important contributor to the formation and progression of eosinophil-based allergic reactions; it is also suggested that 5-oxo-ETE contributes to the development of inflammation, cancer cell growth, and other pathological and physiological events.
Lirentelimab is a humanized nonfucosylated monoclonal antibody that targets sialic acid-binding Ig-like lectin 8 (SIGLEC8). In a randomized clinical trial, lirentelimab was found to improve eosinophil counts and symptoms in individuals with eosinophilic gastritis and duodenitis. Adverse reactions include infusion reactions, which are mild to moderate and typically occur following the first infusion.
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