Secretory component deficiency. A disorder of the IgA immune system.

We studied a 15-year-old boy with chronic intestinal candidiasis who had normal serum IgA levels without IgA in his secretions. There was an elevated number of peripheral blood lymphocytes bearing surface IgA. In addition, the lymphocytes cultured in vitro with pokeweed mitogen produced IgA as well as other immunoglubulins. Despite this evidence of normal IgA synthetic capacity, the patient had greatly diminished levels of IgA in the saliva and jejunal fluid, and, as estimated by 14C-L-leucine incorporation, could not synthesize IgA locally at intestinal-mucosal sites. Finally, the patient had no detectable free secretory component in saliva or jejunal fluid in contrast to normal persons and to patients with IgA deficiency. The basis of this disorder is probably a defect in the homing of IgA precursor cells to secretory sites or in the selective proliferation/differentiation of IgA cells at such sites.