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 Carnoys 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/mm² in the 4W-group, 29.2 ± 22.0 cells/mm² in the 10W-group, 41.0 ± 21.1 cells/mm² in the 16W-group, 22.7 ± 17.1 cells/mm² in the Dx group, and 33.6 ± 27.7 cells/mm² 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. Jpn J Ophthalmol 2004;48:189–194 © Japanese Ophthalmological Society 2004