These studies deal with the mechanism of pemphigus IgG-induced epidermal acantholysis. When normal human skin was cultured with defined medium containing IgG from pemphigus serum, extensive epidermal acantholysis developed and heat-labile proteolytic enzyme(s) were recovered in the culture medium. The enzyme(s) displayed maximal activity at pH 6.5 when a ³H-amino acid-labeled, insoluble epidermal cell material was used as substrate. The enzyme activity increased during the first 3 days of culture and the appearance of maximal activity coincided with the time of onset of acantholysis. Acantholysis did not occur in control cultures incubated with normal IgG and the enzyme did not appear in the medium or in aqueous extracts of cultured tissues. The enzyme(s) is probably not of lysosomal origin because low pH-active proteases characteristic of these organelles remained within the cells. The effects of puromycin on appearance of enzyme activity, acantholysis and cell viability was studied. At cytotoxic concentrations, the appearance of the enzyme(s) and acantholysis were prevented, whereas at less toxic concentrations enzyme activity and acantholysis were not prevented. Because inhibition of protein synthetic rates by puromycin could not be dissociated from the cytotoxic effects, it is uncertain whether enzyme appearance and acantholysis were dependent upon living tissue or on specific protein synthesis. After pemphigus IgG was removed from the conditioned medium by DEAE cellulose and affinity column chromatography, the remaining material contained enzyme activity and caused acantholysis in fresh skin explants. Similar activities were not present in normal IgG-containing conditioned medium or unfractionated epidermal extracts from normal skin.

These data indicate that when the pemphigus IgG autoantibody interacts with epidermal cell surface antigens, the cell responds by synthesis or activation of a non-IgG “pemphigus acantholysis factor” (PAF) which may be a nonlysosomal proteolytic enzyme. It is suggested that PAF causes loss of adhesion between keratinocytes and utimately produces the characteristic acantholytic cell of pemphigus.