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The tetraspanin CD81 regulates the expression of CD19 during B cell development in a postendoplasmic reticulum

Tsipi Shoham1, Ranjani Rajapaksa, Claude Boucheix

  • 1Department of Medicine, Division of Oncology, Stanford University Medical Center, CA 94305-5151, USA.

Journal of Immunology (Baltimore, Md. : 1950)
|October 8, 2003
PubMed

Insights

CD81 tetraspanin is essential for normal CD19 expression in B cells. Its absence affects CD19 protein trafficking and surface stability, not its mRNA levels.

Area of Science:

  • Immunology
  • Cell Biology
  • Molecular Biology

Background:

  • CD81 is a tetraspanin protein found on B cells.
  • CD81 forms a complex with CD19, crucial for B cell signaling.
  • CD19 expression is known to be regulated, but the precise mechanisms are not fully understood.

Purpose of the Study:

  • To investigate the role of CD81 in regulating CD19 expression and surface presentation in B cells.
  • To determine if CD81 affects CD19 at the mRNA or protein level.
  • To elucidate the cellular compartment where CD81 influences CD19.

Main Methods:

  • Comparative analysis of CD19 expression in wild-type and CD81-deficient (cd81(-/-)) B cells.
  • Quantitative analysis of CD19 mRNA levels.
  • Protein analysis of CD19 glycoforms using Western blotting and endoglycosidase H (endo-H) treatment.
  • Expression of human CD81 in mouse cd81(-/-) B cells to assess functional rescue.

Main Results:

  • CD81-deficient B cells exhibit significantly reduced surface levels of CD19, particularly in small pre-BII cells.
  • CD19 mRNA levels are normal in CD81-deficient B cells, indicating post-transcriptional regulation.
  • Two CD19 glycoforms were identified; the endo-H resistant, higher molecular weight form is reduced in cd81(-/-) cells.
  • endo-H sensitive, lower molecular weight CD19 glycoform is unaffected by CD81 deficiency.

Conclusions:

  • CD81 is specifically required for the proper expression and trafficking of CD19, independent of CD19 mRNA levels.
  • The dependence of CD19 expression on CD81 occurs post-endoplasmic reticulum.
  • CD81 likely facilitates CD19 trafficking or stabilizes its presence at the cell surface.

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