Immunoglobulin A deficiency (IgAD) is the most common immunodeficiency, but the pathogenesis of most cases of IgAD is poorly understood. The gene and protein expression levels of members of the IgA subclasses in IgAD patients were analyzed by a reverse transcriptase (RT)-PCR method that could differentiate between α1 and α2 gene expression. Three selective, 5 partial and 2 secondary IgAD patients were examined. Peripheral blood mononuclear cells which were unstimulated or stimulated with TGF-β1 and PMA for 24 h were cultured. The IgA1/IgA2 expression ratios were measured by zone densitometry. Three bands appeared (the α1 and α2 genes and a hetero-duplex formation), owing to the difference of 39 bases between α1 and α2 mRNAs. In the controls, there were no significant differences in the IgA1/IgA2 ratios between unstimulated and stimulated cells. In selective IgAD patients, both α1 and α2 gene expression was induced following stimulation, and α1 gene expression was induced more dominantly than in the other IgAD patients following stimulation. Based on our results, suppression of α1 gene expression may be related to the pathogenesis of IgAD.

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