A case of episodic angioedema associated with blood eosinophilia: upregulated C5a receptor expression on eosinophils

A 47-year-old woman was admitted to hospital complaining of swelling and pain of the extremities, accompanied by high fever and generalized erythema. Laboratory examination showed marked blood eosinophilia with elevation of IgM, IgE, and C-reactive protein. All autoantibodies examined were negative. The heart and lungs showed no untoward findings. Biopsies of the skin and muscle revealed cellular infiltration of eosinophils around small blood vessels. Quantitation of C5a receptor (C5aR) expression by flow cytometry using anti-C5aR antibody showed upregulated expression of C5aR on blood eosinophils but downregulated expression on neutrophils. The abnormal C5aR expression on eosinophils and neutrophils became normal after spontaneous resolution of symptoms and blood eosinophilia. The possibility that C5aR expression on granulocytes is related to the pathogenesis of this syndrome may be considered.