Dermatitis herpetiformis: 'pH optimum' for the release of potentially antigen-binding IgA fragments from papillary dermis of uninvolved skin by peptic digestion.

In preparations of papillary dermis taken from clinically normal skin of patients with dermatitis herpetiformis (DH), the disappearance of granular IgA deposits induced by peptic digestion was partial at pH 4.5 and total at pH 4.1, as visualized by immunofluorescence microscopy. In a model system in which human monomeric IgA was digested by pepsin using a pepsin-IgA ratio of 100:0.3, an IgA concentration of 3 lambda g/ml and a pH range of 5.1-4.1, the degradation of IgA molecules did not appear to proceed beyond the formation of fragments corresponding to F (ab)'. When supernatants after peptic digestion of papillary dermis at pH 4.1 were analysed by sodium-dodecylsulphate (SDS)-polyacrylamide gel electrophoresis after reduction and alkylation followed by electrophoretic transfer to nitrocellulose membranes and subsequent immunochemical detection, IgA-like material corresponding to the alpha-chain part of F (ab)' fragments was found in preparations from DH patients but not in those from controls.