Induction and Down-Regulation of Conjunctival Type-I Hypersensitivity Reactions in Guinea Pigs Sensitized Topically with Fluoresceinyl Ovalbumin

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Abstract
Type-I hypersensitivity reactions were induced in guinea pigs by repeated topical/conjunctival application of fluoresceinyl ovalbumin (FL-OA). The ocular reactivity in early responding animals was maximal between 16 and 25 days and decreased exponentially. Desensitized eyes responded minimally to compound 48/80 [condensation product of 4-methoxy-N-methylbenzeneethanamine and formaldehyde] but maximally to histamine. Unilateral sensitization and challenge with FL-OA produced desensitization of the immunized eye, but the reactivity of the contralateral eye persisted. A significant reduction in conjunctival stained mast cells was found in repeatedly challenged eyes. The desensitization therefore was due to a loss of reactive mast cells. Systemic infection with Ascaris suum, after repeated topical challenge with FL-OA had led to desensitization, produced a reappearance of type-I hypersensitivity reactions toward both FL-OA and ascarid antigens.