Abstract
In humans, IgA has two subclasses, IgA1 and IgA2, which contain, respectively, a1 and a2 heavy chains, respectively. For both subclasses, there are also membrane-bound forms, mIgA1, and mIgA2, containing ma1 and ma2 heavy chains. Ma1 and ma2 differ from a1 and a2 by having a “membrane-anchor” peptide segment extending from the C-termini of a1 and a2. The membrane-anchor segment has three parts: an extracellular, a trans-membrane, and an intracellular segments. It was found previously that ma1 exists in a short and a long isoforms, referred to as ma1(S) and ma1(L), with the later containing extra 6 amino acid residues, GSCSVA (numbered 453-458), at the N-terminal of the extracellular segment. By studying the genomic and mRNA sequences of 20 Taiwanese individuals, we have found that, in addition to ma1(456S), ma1 has a previously unknown allele, referred to as ma1(456C). Moreover, with m□1(456S) allele, both the long and short forms are produced, while the former is more abundant. However, ma1(456C) allele exists predominantly or entirely in long form. Furthermore, we have clarified that ma2 exist as short isoform only. Future studies will examine the variations in mIgA1 in other races and the possible association of such variations with the regulation of IgA synthesis.