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Induction and Assessment of Class Switch Recombination in Purified Murine B Cells
09:49

Induction and Assessment of Class Switch Recombination in Purified Murine B Cells

Published on: August 14, 2010

The different process of class switching and somatic hypermutation; a novel analysis by CD27(-) naive B cells

Haruo Nagumo1, Kazunaga Agematsu, Norimoto Kobayashi

  • 1Shinshu University, Graduate School of Medicine, Department of Infectious Immunology and Pediatrics, Matsumoto, Japan.

Blood
|January 10, 2002
PubMed

Insights

Class switch recombination (CSR) can occur in naive B cells without significant somatic hypermutation, indicating these processes may function independently. This study reveals insights into immunoglobulin production pathways.

Area of Science:

  • Immunology
  • Molecular Biology

Background:

  • The interplay between class switch recombination (CSR) and somatic hypermutation (SHM) in B cell development is not fully understood.
  • Human CD27(-) naive B cells are critical for initiating adaptive immune responses but their capacity for CSR and SHM post-activation requires clarification.

Purpose of the Study:

  • To investigate the induction of somatic hypermutation and immunoglobulin production in human CD27(-) naive B cells following class switch recombination.
  • To determine if CSR and SHM occur concurrently or independently in naive B cells.

Main Methods:

  • Human CD27(-) naive B cells were stimulated with a combination of Staphylococcus aureus Cowan strain (SAC), IL-2, IL-10, anti-CD40 mAb, CD32 transfectants (CD40/CD32T), and IL-4.
  • Immunoglobulin production (IgG, IgM, IgA, IgE) and the expression of gamma1 and gamma2 transcripts were analyzed.
  • Somatic hypermutation levels in Ig V-region genes and activation-induced cytidine deaminase (AID) mRNA expression were assessed in naive B cells and compared to CD27(+) memory B cells.

Main Results:

  • Naive B cells stimulated with SAC + IL-2 + IL-10 + CD40/CD32T produced IgG and IgM, while IL-4 + CD40/CD32T induced IgE production.
  • Mature gamma1 and gamma2 transcripts were induced, indicating CSR, but significant SHM was not observed in the Ig V-region genes of plasma cells derived from naive B cells.
  • CD27 expression was induced on naive B cells, but AID mRNA expression was delayed compared to CD27(+) memory B cells.

Conclusions:

  • Class switch recombination can be induced in human CD27(-) naive B cells through B-cell receptor engagement and CD40 signaling, independent of significant somatic hypermutation.
  • These findings suggest that CSR and SHM are distinct processes that can occur separately during B cell activation.
  • The antibodies generated in this in vitro system are likely of low affinity due to the limited SHM.

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