HISTAMINASE ACTIVITY IN PATIENTS WITH VERNAL KERATOCONJUNCTIVITIS

Purpose: To investigate the activity of histamine-degradating enzymes in tears and plasma of patients with vernal keratoconjunctivitis (VKC) . Method: Tear and plasma samples were collected from patients with VK C and from age-matched control subjects. Histamine was measured by enz yme-linked immunosorbent assay in acid samples treated with perchloric to deactivate histaminase and in untreated samples. Tear cytology, sk in test reactivity to histamine, and the sum clinical score of allergi c signs and symptoms in patients with VKC also were evaluated, Ninetee n patients with active VKC and six age-matched control subjects partic ipated in this study. Results: In untreated samples, tear histamine (m ean +/- standard error of the mean) was 11.15 +/- 2.16 ng/ml in patien ts with VKC and 0.855 +/- 0.225 ng/ml in control tears (P < 0.001). In treated samples, mean tear histamine was 22.25 +/- 4.17 ng/ml in pati ents with VKC versus 10.64 +/- 2.85 ng/ml in control subjects (not sta tistically different). The ratio of histamine in treated to untreated samples (indicating histaminase activity) was significantly lower in p atients with VKC (2.30 +/- 0.263) than in control subjects (17.57 +/- 5.97; P = 0.0001). Plasma histamine levels in untreated and treated sa mples were significantly higher in patients with VKC (untreated, 2.23 +/- 0.334 ng/ml; treated, 4.37 +/- 0.357 ng/ml) than in control subjec ts (untreated, 0.254 +/- 0.068, P = 0.0002; treated, 2.96 +/- 0.171 ng /ml, P = 0.0082), The enzymatic breakdown of histamine (treated/ untre ated) in plasma was significantly decreased in patients with VKC (2.54 +/- 0.447) compared with control subjects (14.78 +/- 4.86; P = 0.0012 ). Skin reactivity to histamine was not increased in VKC. Tear histami ne levels were significantly correlated to tear lymphocyte content in the general population and to tear basophils in the patients with tars al-vernal VKC only. An increased number of tear eosinophils were corre lated with elevated enzyme activity only in patients with tarsal-verna l VKC and to the clinical score only in limbal-vernal patients. Conclu sion: The enzymatic degradation of histamine was significantly decreas ed in patients with VKC compared with control subjects in both tears a nd plasma, suggesting that this dysfunction may be a primary factor in the pathophysiology of VKC.