MAST-CELL DISTRIBUTION AND NEUTRAL PROTEASE EXPRESSION IN ACUTE AND CHRONIC ALLERGIC CONJUNCTIVITIS

Allergic eye disease has a variety of clinical manifestations includin g seasonal atopic conjunctivitis (SAG), perennial atopic conjunctiviti s (PAC), atopic keratoconjunctivitis (AKC), and atopic blepharoconjunc tivitis (ABC). We have investigated the number, distribution and prote ase expression of mast cells in normal and diseased conjunctiva with t he use of immunohistochemistry in water-miscible resin sections. The m edian mast cell densities in normal subjects were 17 mm(-2) in the bul bar substantia propria and 9 mm(-2) in tarsal substantia propria. Mast cells were absent from the normal conjunctival epithelium at both sit es. Mast cell densities were increased in the bulbar substantia propri a in SAG, AKC and ABC. Tarsal substantia propria showed a significant increase in mast cells in ABC and AKC disease states. Mast cells expre ss a range of proteases which varies according to their anatomic site. Mast cells in connective tissue are described to contain tryptase, ch ymase, cathepsin-G and carboxypeptidase-A whereas mucosal mast cells c ontain only tryptase. In the diseased conjunctiva there was a marked r eduction in proteases other than tryptase in the intraepithelial mast cells. There were also significant reductions in protease expression o ther than tryptase in the bulbar substantia propria in AKC and ABC. Th ere appear to be specific alterations in the distribution of mast cell s in the sub-categories of allergic eye disease. The distinction betwe en mucosal and connective tissue mast cell phenotypes is not clear-cut and may depend on the functional state of the mast cells in relation to the microenvironment.