CD203c, also known as ENPP-3, is integral membrane ectoenzyme (ectonucleotide pyrophosphatase/phosphodiesterase 3), that hydrolyses nucleotide triphosphates and thus modulates purinergic signaling. CD203c is expressed mainly on activated basophils and mast cells. CD203c is upregulated in response to IgE-receptor cross-linking and is overexpressed on neoplastic mast cells in patients with systemic mastocytosis. Measurement of its induced enhancement on the plasma membrane is useful for diagnostics of allergies.