Eosinophil Cationic Protein (ECP)

Eosinophils are effector cells that play a role in allergic and nonallergic inflammation and mediate host immune response to parasites, bacteria and viruses.^1-3 The most prominent feature of these cells is large cytoplasmic granules, each containing four basic proteins, the most plentiful of which is eosinophil cationic protein (ECP).⁴ ECP is a protein with ribonuclease activity that is released during eosinophil activation. While the full physiologic role of ECP has not been completely defined, this protein has been attributed with cytotoxic, neurotoxic, fibrosis-promoting and immune-regulatory functions.^2,4,5 Studies suggest that ECP may play a role in regulating mucosal and immune cells and may directly fight parasitic, bacterial and viral infections.⁴

ECP is often elevated in diseases in which an eosinophil-mediated tissue inflammation plays a role.^2,4-8 Levels can be increased in patients with eosinophilic esophagitis.^9-13 Measuring ECP levels has been used to evaluate eosinophil-mediated allergic inflammation, asthma and rhinitis.² Levels can be increased during both seasonal and perennial rhinitis and may reflect current allergen exposure.^2,14 In atopic dermatitis, ECP has been shown to correlate with the symptoms and total clinical score.¹⁵

Eosinophilic inflammation is a relatively common feature of asthma.^14,16-19 Although not diagnostic for asthma, elevated ECP levels are thought to reflect the degree of asthma-related bronchial eosinophilic inflammation.^14,20 Increased ECP levels correspond to symptom onset and can precede bronchial hyper-reactivity.^2,16 ECP has been used to assess asthma severity and support the management of anti-inflammatory therapy.^5,20 It should be noted, however, that ECP is better correlated to symptom score than to lung function parameters, especially in children with mild and moderate asthma.¹⁴

ECP levels can be increased in a number of gastrointestinal disorders, including eosinophil intestinal diseases (esophagitis, gastroenteritis and colitis), gastrointestinal food allergy and intestinal parasitic infections.² ECP levels can also be increased in non−IgE-mediated conditions, including nonallergic asthma with aspirin intolerance, respiratory infections, sinonasal polyposis and idiopathic hypereosinophilia (HES) syndrome.^2,4 ECP has also been used as a disease activity marker in Churg-Strauss syndrome (CSS), a condition that is also known as allergic granulomatosis or allergic angiitis.²¹ CSS is a disorder marked by blood vessel inflammation that can restrict blood flow to vital organs and tissues, sometimes permanently damaging them.²