Transport defect of IgM into luminal space in selective IgA deficiency

This study explored the pathogenesis of a transport defect of IgM into the lumen in a patient with selective IgA deficiency. In addition to the absence of IgM in the saliva, no IgM was localized on the luminal surface of colonic mucosa from the patient despite the presence of J chain-positive IgM cells. On tissue sections, IgM cells did not bind secretory component. The serum IgM also showed a negligible capacity to bind secretory component in vitro. Such abnormalities of IgM molecules as stated above seem to be clinicopathologically linked with IgA deficiency or its associated Sjögren's syndrome.