Characterization of the IgA immunocyte population and its product in a patient with excessive intestinal formation of IgA.

An 11-year-old Norwegian boy presented with clinico-pathological features indicative of coeliac or alpha-chain disease. However, his major serum component (about 50 mg/ml) was found to be a polyclonal, polymeric (about 80% dimeric) IgA consisting mainly of the subclass IgA1 and showing a kappa:lambda ratio of 67:33. Also the serum concentration of IgA monomers was increased (about 9 mg/ml). The polymers were heterogeneous with regard to J-chain content--varying on a molar basis from 1.9 for the more basic fraction to at least 2.4 for the more acidic one. Both fractions showed non-covalent affinity for secretory component (SC) in vitro. Most of the serum IgA seemed to originate from the small intestine, which contained a five-times-increased population of IgA immunocytes. These cells were heterogeneous with regard to production of polymeric IgA; many of them showed definitely more J-chain synthesis than normal intestinal IgA immunocytes. The cell population had apparently not spread to the bone marrow, but the polymeric IgA product permeated the connective tissue throughout the body and appeared also in the urine, partly associated with SC. The possibility that such an excessively proliferating intestinal B-cell population may bear some relation to alpha-chain disease is discussed.