Mast cell
chymase is a
chymotrypsin-like
serine proteinase primarily stored in secretory mast cell granules. Mast cell
chymase has various effects on
angiotensin,
metalloproteases,
lipoproteins,
procollagen,
neuropeptides and
cytokines. Recent studies have demonstrated that
chymase inhibitors inhibit skin
inflammation. In this study we sought to determine the role of mast cell
chymase in
atopic dermatitis (AD) in comparison with its role in
psoriasis and normal skin. Skin biopsy specimens were obtained from non-lesional and lesional skin of patients with chronic AD and
psoriasis and from normal skin of non-atopic and non-psoriatic controls. The number of mast cells containing
chymase was determined by immunohistochemistry using a
chymase-specific
monoclonal antibody. A significantly (P < 0.05) enhanced number of
chymase-positive cells was found in lesional AD skin as compared to normal skin as well as to lesional and non-lesional skin of patients with
psoriasis. A significant (P < 0.05) increase in the number of
chymase-positive cells was also found in non-lesional AD skin in comparison to
psoriasis. An enhanced, albeit not statistically significant difference was noted in non-lesional AD skin as compared to normal skin. In conclusion, these results suggest that mast cell
chymase may play an integral part in eliciting and maintaining cutaneous
inflammation in AD but not in
psoriasis. The increased
proteinase activity of mast cell
chymase may also be involved in promoting a skin barrier defect in AD, which subsequently enhances the skin's permeability to
allergens and microbes and thereby aggravates the
eczema.