Immunoelectron-microscopic localization of immunoglobulin A and secretory component in jejunal mucosa from children with coeliac disease.

Using peroxidase-labelled antibodies, the ultrastructural localization of IgA and secretory component (SC) was investigated in duodeno-jejunal biopsies from six children with coeliac disease and compared with that observed in non-coelic mucosa. In normal intestinal mucosa this study confirmed the presence of IgA in the rough endoplasmic reticulum and the perinuclear space of numerous subepithelial plasma cells and one the lateral cell membranes of villous and especially crypt epithelial cells. SC was only detected in the epithelium and principally in crypt epithelium where it was identified in endoplasmic reticulum, Golgi saccules, perinuclear spaces and on lateral cell membranes. These findings support the suggestion that SC is synthesized mainly in crypt epithelium and acts as a receptor on epithelial cell membranes for dimeric IgA. In untreated coeliac patients, SC was observed at the same sites, but SC staining was reduced in damaged surface epithelial cells. The number of IgA immunocytes was increased and heavy deposits of IgA were found on basement membranes. In post-treatment biopsies, no abnormality was apparent. After re-exposure to gluten, depositions of IgA on basement membranes were the only early change. The unaltered distribution of SC and IgA in crypt epithelium strongly suggests that the epithelial transport mechanism of secretory IgA is normal in coeliac disease.