In a Japanese cedar pollen-induced
allergic conjunctivitis model in guinea pigs, symptoms were aggravated by repeated pollen challenges. In addition, the number of mast cells in the conjunctiva was increased by multiple challenges. The amount of a mast cell mediator,
histamine in ophthalmic lavage fluid was also increased by multiple challenges. In the present study, we evaluated the effects of multiple
dexamethasone treatments to assess the relationship between the aggravation of symptoms and mast cell
hyperplasia. Sensitized guinea pigs were challenged by dropping a pollen
suspension onto their eye surface once a week until the 15th challenge.
Dexamethasone (10 mg/kg, p.o.) was administered once 3 h before the 15th challenge or 3 h before every 1st--15th challenge. Mast cells in the conjunctival tissue were detected by
toluidine blue staining.
Histamine was fluorometrically assayed by high-performance liquid chromatography. Serum Cry j 1-specific
IgE titer was measured by an
enzyme-linked
immunosorbent assay. The results indicated that a single treatment with
dexamethasone did not affect the 15th challenge-induced symptoms; however, multiple treatments with the
corticosteroid suppressed not only
conjunctivitis symptoms after every challenge but also the mast cell
hyperplasia and the increase in
histamine in the lavage fluid. Conversely, the increase in the
IgE titer in the serum was not affected by multiple treatments with
dexamethasone. In conclusion, increased numbers of mast cells in the conjunctival tissue may be associated with the aggravation of
allergic conjunctivitis symptoms.