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Generation of Human CD40-activated B cells
13:27

Generation of Human CD40-activated B cells

Published on: October 17, 2009

C4b-binding protein (C4BP) activates B cells through the CD40 receptor

Scott R Brodeur1, Federica Angelini, Leonard B Bacharier

  • 1Division of Immunology, Children's Hospital and Department of Pediatrics, Harvard Medical School, Boston, MA, USA.

Immunity
|June 24, 2003
PubMed

Insights

Human complement protein C4b-binding protein (C4BP) activates B cells by binding to CD40. This discovery reveals a new link between complement and B cell immune responses.

Area of Science:

  • Immunology
  • Complement System
  • B cell Biology

Background:

  • CD40 is a critical receptor on B cells involved in immune responses.
  • The complement system plays a role in adaptive immunity.
  • The interaction between complement proteins and B cell surface receptors is not fully understood.

Purpose of the Study:

  • To investigate the interaction between C4b-binding protein (C4BP) and CD40 on human B cells.
  • To determine the functional consequences of C4BP binding to CD40.
  • To explore the role of C4BP in B cell activation and germinal center reactions.

Main Methods:

  • Surface plasmon resonance to assess C4BP binding to CD40.
  • Flow cytometry to analyze B cell proliferation and marker expression (CD54, CD86).
  • Cytokine measurements (IL-4) and IgE isotype switching assays.
  • Immunohistochemistry to visualize C4BP and B cell colocalization in human tonsil tissues.

Main Results:

  • The alpha chain of C4BP directly binds to CD40 on human B cells at a distinct site from the CD40 ligand.
  • C4BP induces B cell proliferation, upregulates CD54 and CD86 expression, and promotes IL-4-dependent IgE isotype switching.
  • These effects are dependent on functional CD40 and IKKgamma/NEMO signaling pathways.
  • C4BP was observed to colocalize with B cells within the germinal centers of human tonsils.

Conclusions:

  • C4BP acts as a novel activating ligand for CD40 on human B cells.
  • This finding establishes a previously unrecognized interface between the complement system and B cell activation.
  • C4BP may play a significant role in regulating B cell responses within lymphoid tissues.

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