Conjunctival provocation test as a model for the study of allergy and inflammation in humans

The clinical response after allergen challenge and immunologic mechanisms leading to tissue inflammation have been extensively studied in the skin, nose and lung of allergic subjects. The present paper reviews personal studies aimed at evaluating clinical, cellular and humoral events after administration of specific allergen to the eye. Specific conjunctival provocation tests performed in grass-sensitive patients caused persisting inflammatory changes in conjunctival scrapings and tear fluid with a significant accumulation of different inflammatory cells depending on the time of observation (neutrophils, 20 min; eosinophils, 6 h; neutrophils, eosinophils and lymphocytes, 12-24 h after provocation). Increasing the dose of allergen resulted in a dose-dependent increase in the number of inflammatory cells recruited. When high doses of allergen were used, the challenge not only induced late-phase histological changes, but also clinical symptoms 6-10 h after provocation. Several mediators of allergic inflammation, such as histamine, C3a des-Arg, leukotrienes B4 and C4, were also present and could be measured in tears after allergen challenge. Our studies represent the first evidence in humans that a late phase of allergic reaction occurs in the eye. They also suggest that the conjunctival provocation test may represent a model for the study of cells and mediators involved in the pathophysiology of allergic inflammation as well as of its pharmacologic modulation.