The role of eosinophils in chronic spontaneous urticaria

Chronic spontaneous urticaria is a mast-cell driven skin disease characterized by the recurrence of transient wheals, angioedema or both for more than 6 weeks. Recent studies have suggested that eosinophils may also have a major role in symptomatology. In urticaria, it is usually observed a peripheral blood eosinopenia, opposed to other allergic and inflammatory conditions. Histological studies have shown the presence of eosinophils and eosinophil granules in urticaria lesions. They may enhance urticaria in three ways: first, eosinophil-derived stem cell factor (SCF) promotes the recruitment and local maturation of mast cells in the tissues. Second, eosinophil proteins, such as major basic protein, eosinophil cationic protein and eosinophil peroxidase can provoke mast cell degranulation. And third, activated eosinophils also express tissue factor, the main initiator of the coagulation cascade leading to thrombin formation. Eosinophil infiltration may contribute to tissue edema of skin in urticaria but can also, together with increased mast cells, prime the skin for further healing.

Treatments aimed at reducing eosinophil accumulation and activation, such as the anti-IL5 humanized antibodies mepolizumab, reslizumab and benralizumab, have shown to reduce chronic spontaneous urticaria.