The basic interest of my laboratory concerns proteins that promote the adhesion of keratinocytes to epidermal basement membrane. Our clinical interests focus on patients with autoimmune or genetic subepidermal blistering diseases, disorders characterized by impaired adhesion of keratinocytes to epidermal basement membrane. Several years ago we identified patients with a scarring and blistering disease of mucous membranes and skin who have IgG autoantibodies directed against a multiunit protein localized just beneath basal keratinocytes in epidermal basement membrane. Such patients have now been identified in North America, South America, Asia, and Europe and are distinguished by their disease-specific autoantibodies. Recently, we showed that the protein bound by these patients' autoantibodies is the alpha subunit of laminin 5, an adhesion molecule that is thought to directly promote the adhesion of keratinoyctes to epidermal basement membrane. To determine if anti-laminin 5 IgG can be pathogenic in vivo, we have developed a passive transfer animal model of this human blistering disease. These studies have shown that anti-laminin 5 IgG induces subepidermal blisters in the skin of neonatal and adult mice as well as human skin grafted onto immunodeficient mice. Interestingly, such blisters develop independent of the activation of complement or the degranulation of dermal mast cells. This model should prove useful in further defining the pathophysiology and treatment of the human blistering disease as well as providing insights about which domains of laminin 5 promote keratinocyte adhesion. In other studies, we have recently shown that BPAG2, a constituent of hemidesmosomes in basal keratinocytes, is not present in the skin of patients with a rare but distinctive inherited blistering disease. Moreover, using intron-specific primers, PCR, heteroduplex analysis, and nucleotide sequencing, we have identified three different mutations in the BPAG2 gene of five such families. Affected individuals in three of these families are homozygous for a 2 base pair deletion in the BPAG2 gene, while probands in two unrelated families carry one copy of the same mutation as well as a missense mutation on their alternate BPAG2 allele. Interestingly, all of these mutations result in premature termination codons. Northern blot and immunoprecipitation studies of these patients' keratinocytes have shown that these cells contain no detectable BPAG2 mRNA or protein, findings supporting the idea that nonsense-mediated mRNA decay is responsible for the total lack of BPAG2 protein in these patients' skin. These studies defining and characterizing defects in the skin of patients with autoimmune and genetic blistering diseases have furthered our understanding of keratinocyte adhesion and cutaneous biology.
