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Membrane isoforms of human immunoglobulins of the A1 and A2 isotypes: structural and functional study
Author(s) -
LEDUC I.,
DROUET M.,
BODINIER M.C.,
HELAL A.,
COGNE M.
Publication year - 1997
Publication title -
immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.297
H-Index - 133
eISSN - 1365-2567
pISSN - 0019-2805
DOI - 10.1111/j.1365-2567.1997.00330.x
Subject(s) - isotype , breakpoint cluster region , immunoglobulin class switching , biology , antibody , cd19 , alpha chain , microbiology and biotechnology , antigen , b cell receptor , alternative splicing , signal transduction , receptor , b cell , monoclonal antibody , gene isoform , immunology , gene , biochemistry
SUMMARY As for IgM, human IgA occurs either as soluble molecules in plasma and various other body fluids, or as membrane‐bound molecules on differentiated B cells, where they are part of the B‐cell receptor for antigen (BCR). We studied the structure of transcripts encoding the membrane‐anchored α‐chain of the human BCRα, which may be present in two different forms resulting from alternate splicing of the α‐chain mRNA (type I or type II). The ratio of type I versus type II did not vary upon stimulation of a B‐cell line with various cytokines. Rather, it differed strikingly in cells expressing either the IgA1 or IgA2 isotype of the BCRα, with virtually no type II α‐chain in the latter. Co‐modulation experiments also yielded different results for both isotypes, since they demonstrated a physical association of both membrane (m)IgA1 and mIgA2 with CD79b, the β component of the BCR Igα/Igβ heterodimer, but only of mIgA1 with CD19. Whatever the isotype, the BCR of the IgA class was able to carry out signal transduction upon cross‐linking by specific monoclonal antibodies but, in contrast to mIgM, it relied mainly on the entry of extracellular Ca 2+ rather than on the release of intracellular stocks.