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Defective assembly of the B-cell receptor chains accounts for its low expression in B-chronic lymphocytic leukaemia

Béatrice Payelle-Brogard1, Christian Magnac, Andres Alcover

  • 1Unité d'Immuno-Hématologie et d'Immunopathologie, CNRS URA 1960, Paris, France. bbrogard@pasteur.fr

British Journal of Haematology
|August 30, 2002
PubMed

Insights

Low B-cell receptor (BCR) expression in B-cell chronic lymphocytic leukaemia (B-CLL) is due to intracellular assembly and transport defects, not gene transcription issues. Nascent IgM chains fail to mature, impacting BCR surface expression.

Area of Science:

  • Immunology
  • Molecular Biology
  • Hematology

Background:

  • B-cell chronic lymphocytic leukaemia (B-CLL) is characterized by reduced B-cell receptor (BCR) expression on the cell surface.
  • The BCR complex, crucial for B-cell signaling, comprises surface immunoglobulin (SIg) non-covalently bound to the CD79a/CD79b heterodimer.

Purpose of the Study:

  • To investigate the mechanisms underlying low BCR surface expression in B-CLL.
  • To examine transcription, protein synthesis, assembly, and transport of BCR components in B-CLL cells.

Main Methods:

  • Analysis of B29 (CD79b) gene transcriptional expression.
  • Detection of intracellular BCR components (synthesis).
  • Investigation of genetic defects in SIg, CD79a/CD79b, and calnexin.
  • Assessment of IgM and CD79b chain assembly and intracellular accumulation.
  • Evaluation of nascent IgM processing and transport.

Main Results:

  • No significant defects were found in B29 gene transcription or synthesis of BCR components.
  • Genetic analysis ruled out abnormalities in SIg, CD79a/CD79b, or calnexin.
  • A consistent defect in IgM and CD79b chain assembly was observed, leading to intracellular accumulation.
  • Nascent IgM chains frequently failed to mature and were unsuitable for transport to the cell surface.

Conclusions:

  • Low BCR surface expression in B-CLL is primarily caused by post-transcriptional defects.
  • These defects involve aberrant intracellular assembly and/or trafficking of BCR components.
  • The findings highlight intracellular processing as a critical factor in BCR expression regulation in B-CLL.

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