Histological Study on Mast Cells in Conjunctiva of NC/Nga Mice

Purpose: To investigate the pathological findings in conjunctiva of NC/Nga mice, which develop atopic dermatitis spontaneously, we focused our study on the density of mast cells as determined by histological methods.

Methods: NC/Nga mice were divided into five groups; the 4W-group comprised four 4-week-old mice without treatment, the 10W-group comprised four 10-week-old mice without treatment, the 16W-group comprised four 16-week-old mice without treatment, the Dx group comprised three 16-week-old mice undergoing topical 0.1% dexamethasone (Dx) ointment treatment, and the FK506 group comprised three 16-week-old mice undergoing topical 0.1% FK506 ointment treatment. For the histological examination, the lids and eyeballs of the mice were removed and fixed with Carnoy's solution and thin sections were made. The Carnoy-fixed specimens were stained with toluidine blue or H&E and examined histologically. Toluidine blue-stained tissue sections were examined for the density per square millimeter of mast cells, which were identified as metachromatic cells in the conjunctival tissue and lid cutaneous tissue by light microscopy.

Results: Mast cell density in the conjunctiva was 8.6 +/- 8.2 cells/mm(2) in the 4W-group, 29.2 +/- 22.0 cells/mm(2) in the 10W-group, 41.0 +/- 21.1 cells/mm(2) in the 16W-group, 22.7 +/- 17.1 cells/mm(2) in the Dx group, and 33.6 +/- 27.7 cells/mm(2) in the FK506 group. Mast cell density increased significantly with age among the 4W-, 10W-, and 16W-groups ( P < 0.001). The mast cell density of lid cutaneous tissue was higher than the conjunctival mast cell density. Mast cell density was significantly higher in the 16W-group than in the Dx group, but not significantly higher than in the FK506 group.

Conclusions: An increase in mast cell density with age indicates that NC/Nga mice develop atopic keratoconjunctivitis-like signs. Dexamethasone ointment has a suppressive effect on the increase in mast cell density.