The role of eosinophil cationic protein (ECP) and histamine in vernal keratoconjunctivitis

(1) to measure levels of tear eosinophil cationic protein (ECP) in patients with vernal keratoconjunctivitis (VKC); (2) to verify any correlation between ECP and the severity of the disease; (3) to verify the effect of different topical therapies on the levels of tear ECP; (4) to investigate the activity of histamine degrading enzymes in tears and plasma of VKC patients.

ECP was measured by RIA in tears from 23 VKC patients before and after therapy, and from seven controls. Tear cytology, ocular signs and symptoms were also evaluated before and after treatment. Histamine was measured by ELISA in both plasma and tears from 19 VKC patients and six age-matched controls, in both acid-treated (no enzyme activity) and untreated (enzyme activity) samples.

(1) tear ECP levels were significantly higher in VKC patients than in healthy controls; (2) tear ECP levels showed a significant correlation to signs (p <0.005) and symptoms (p <0.001) of the disease; (3) tear ECP was reduced by both 2% cyclosporine and 0.1% dexamethasone; (4) tear and plasma histaminase activity, measured by the ratio of histamine in treated to untreated samples, were significantly lower in VKC patients compared to controls (p <0.0001 and p <0.001, respectively).

Tear ECP levels reflect the clinical status of VKC patients. The measurement of ECP may prove to be a useful objective tool in evaluating allergic conjunctivitis and the effectiveness of specific treatments. Moreover, VKC patients show a significantly impaired histaminase capability, at both the local and systemic level. This dysfunction may exacerbate the effects of local histamine release in the course of the disease.