Extracellular binding sites of IgA anti-jejunal antibodies on normal small bowel detected by indirect immunoelectronmicroscopy.

Patients with dermatitis herpetiformis (DH) have IgA deposition in the papillary dermis and in the lamina propria of the small bowel. In addition, most of DH patients' sera contain IgA class anti-reticulin antibodies, anti-endomysium antibodies (EMA), and anti-jejunal antibodies (JAB) during times of gluten intake. In previous studies, JAB and EMA seemed to be identical and related to the group of anti-reticulin antibodies. In the present study, pre-embedding en bloc immunoelectronmicroscopic methods were applied for analysis of the ultrastructural binding sites of JAB on monkey and rabbit small bowels. These substrates were incubated with sera from DH patients strongly positive for JAB. Simultaneous investigations with the PAP technique and with 5 nm gold-labeled protein A or second antibodies visualized the bound IgA identically: it was associated with collagen fibrils underlying the epithelial and cryptal basement membranes and with collagen fibrils around capillaries. Staining was also detected along the endomysial collagen fibrils of smooth muscle layers, around elastica and smooth muscle cells of blood vessel walls, and along collagen fibrils near smooth muscle cells in the lamina propria. Neither the peroxidase product nor gold deposition was detected directly on the fibers, but was associated with amorphous material surrounding collagen fibers of different diameters. The distribution of JAB-stained structures corresponded to the localization of reticulin network of the small bowel. Our data indicate that JAB recognize an antigen or antigens associated with an amorphous component of the reticulin-collagen structure of jejunum and may have identical binding sites, as anti-reticulin antibodies and EMA.