Proteolytically active allergens cause barrier breakdown

Two major allergens-the house dust mite Dermatophagoides pteronyssinus (Der p 1) and cockroach allergens-are proteolytically active and stimulate the protease-activated receptor 2 (PAR-2). Jeong et al. (2008, this issue) exposed mouse and human epidermis to both allergens and correlated the observed delay in permeability barrier recovery to PAR-2 activation/signaling. This article exposes the secretive boundaries between barrier homeostasis and immunity.