J chain synthesis in lymphocytes from patients with selective IgA deficiency.

J chain synthesis was investigated by in vitro pokeweed mitogen (PWM) stimulated peripheral blood lymphocyte (PBL) cultures in eight patients with selective IgA deficiency and compared with that of normal persons. In normals, all IgM-containing cells always had the J chain but only in a portion of IgG- and IgA-containing cells was J chain detectable. The percentage of J chain-positive cells amongst IgG or IgA cells increased during culture, reached a peak at days 5-6 or 6-7, respectively, and then decreased. IgA-deficient patients had very few IgA-containing cells and an increased number and percentage of J chain-positive IgG cells, except for one patient, who had a significant number of IgA-containing cells without IgA secretion into the culture supernatants. Measurement of Ig in culture supernatants by radioimmunoassay revealed that lymphocytes from seven patients secreted significantly smaller amounts of IgG and IgM than did the normal controls, in addition to the defect in IgA production. These results suggested the presence of some ontogenetic relationship between J chain-positive IgG cells and the precursors of IgA-producing cells, and some functional immaturity of most IgG-producing clones seen in patients with selective IgA deficiency.