COX-2 inhibition enhances the TH2 immune response to epicutaneous sensitization.

Background: Mechanical injury to the skin by scratching is an important feature of atopic dermatitis (AD).

Objective: To investigate the role of COX-2 in allergic skin inflammation elicited by epicutaneous (EC) sensitization via introduction of ovalbumin through shaved tape-stripped skin.

Methods: COX-2 mRNA was measured by quantitative PCR, and COX-2 protein was measured by Western blotting. We investigated the effect of administration of the COX-2 selective inhibitor NS-398 during EC sensitization with ovalbumin in a mouse model of AD characterized by eosinophil skin infiltration, elevated total and antigen specific IgE, and a systemic TH2 response to antigen. We further examined the response of COX-2-deficient mice to EC immunization with ovalbumin.

Results: Tape stripping caused a transient increase in skin COX-2 mRNA. In contrast, COX-2 mRNA was not increased after ovalbumin sensitization. Infiltration by eosinophils and expression of IL-4 mRNA in ovalbumin-sensitized skin sites, ovalbumin specific IgE and IgG1 antibody responses, and IL-4 secretion by splenocytes after ovalbumin stimulation were all significantly increased in EC mice that received NS-398. In contrast, ovalbumin specific IgG 2a antibody response and IFN-gamma secretion by splenocytes after ovalbumin stimulation were significantly decreased in these mice. COX-2-deficient mice also exhibited an enhanced systemic TH2 response to EC sensitization.

Conclusions: These results demonstrate that COX-2 limits the TH2 response to EC sensitization and suggest that COX inhibitors may worsen allergic skin inflammation in patients with AD.