Figure 2.

Induction of pemphigus in neonatal mice lacking Dsg 3 by passive transfer of IgGs from sera of PV patients that lack Dsg 1 antibody. Neonatal knockout Dsg3^null mice homozygous for a targeted mutation of the Dsg3 gene (a–d) and “balding” Dsg3^bal/Dsg3^bal mice homozygous for a spontaneous null mutation in the Dsg3 gene (e–h) were injected intraperitoneally with 20 mg/g body weight of IgGs from the PV1 serum that lacked Dsg 1 antibody. Approximately 18–24 hours after injection, large, flaccid blisters filled with serous fluid were seen on the skin of both Dsg3^null (a) and Dsg3^bal/Dsg3^bal (e) mice. At this time, the Nikolsky sign could be elicited on the skin of Dsg3^null (b) and Dsg3^bal/Dsg3^bal (f) mice by mechanical extension of a large erosion after spontaneous rupture of the blister. The blisters developed due to intraepidermal separation showing suprabasilar acantholysis and prominent tombstone appearance of the basal cell layer (c and g; hematoxylin and eosin [H&E]). DIF with FITC-conjugated anti-human IgG antibody revealed intercellular staining of epidermis due to deposition of injected PV IgGs (d and h). All neonates of the progeny from mating of homozygous Dsg3^null mice showed the PCR product of 280 bp, representing the sequence of the neomycin resistance gene used for the targeted disruption of the Dsg3 gene (17), and no 500-bp product, representing normal Dsg3 gene amplified from DNA extracted from a normal, Dsg 3–positive mouse (positive control). Likewise, all pups in the progeny from mating homozygous Dsg3^bal/Dsg3^bal mice lacked Dsg 3, as illustrated by finding a nonfunctional homozygous mutational insertion, 2275insT, upon direct nucleotide sequencing of the PCR product representing a portion of exon 14 of the mouse Dsg3 gene (data not shown). Scale bars = 50 μm.