Molecular analysis of B-cell differentiation in selective or partial IgA deficiency.

Selective IgA deficiency is the most common form of primary immunodeficiency, the molecular basis of which is unknown. To investigate the cause of selective IgA deficiency, we examined what stage of B-cell differentiation was blocked. DNA and RNA were extracted from three Japanese patients with selective IgA deficiency and three with a partial IgA deficiency. In selective IgA deficiency patients, Ialpha germline transcript expression levels decreased and alpha circle transcripts were not detected. Stimulation with PMA and TGF-beta1 up-regulated Ialpha germline and alpha circle transcripts. In some patients, IgA secretion was induced by stimulation with anti-CD40, IL-4 and IL-10. In partial IgA deficiency patients, Ialpha germline, alpha circle transcripts and Calpha mature transcripts were detected in the absence of stimulation. Our findings suggest that the decreased expression level of Ialpha germline transcripts before a class switch might be critical for the pathogenesis of some patients with selective IgA deficiency. However, in patients with a partial IgA deficiency, B-cell differentiation might be disturbed after a class switch.