Eosinophil cationic protein (ECP)

Eosinophil cationic protein (ECP), also known as ribonuclease 3 or RNase 3, is a highly basic single-chain polypeptide found predominantly within the granules of human eosinophils. Encoded by the *RNASE3* gene on chromosome 14q11.2–q13,[1] it belongs to the RNase A superfamily but has much lower ribonucleolytic activity than related enzymes.[2] The mature protein ranges from about 16–22 kDa depending on glycosylation state,[10] with an unusually high content of surface arginine residues conferring strong positive charge.[6] Upon activation and degranulation—such as during parasitic infection or allergic inflammation—eosinophils release ECP into tissues and bodily fluids. There it exerts potent cytotoxic effects against parasites (helminths), bacteria, viruses,[2] tumor cells,[1] and host epithelial cells through mechanisms including membrane disruption via pore formation.[6] Its ribonuclease function is not essential for cytotoxicity but may contribute to its antimicrobial properties. Beyond direct cytotoxic action, ECP modulates immune responses by regulating fibroblast proliferation/activity,[3] inducing airway mucus secretion,[3] influencing cytokine release from immune cells,[5], and participating broadly in tissue remodeling during chronic inflammation. Clinically, elevated levels of ECP serve as a biomarker for active eosinophilic inflammation—most notably in asthma where they correlate with disease severity/exacerbations—as well as other atopic/allergic conditions.[4][5]. However, excessive local concentrations can contribute to tissue injury/remodeling—a key safety concern limiting therapeutic strategies aimed at enhancing its functions. No drugs currently act directly on ECP; instead therapies like corticosteroids reduce its production/release by suppressing overall eosinophil activation/degranulation.

Other names

Ribonuclease 3RNase 3ECP

Drugs that reduce eosinophil activation or degranulation can lower ECP release.