| Abstract: |
Background: During differentiation, B cells receive signals by antigen through the B-cell receptor (BCR) and signals that induce isotype switching. Objective: We sought to investigate the effects of BCR ligation on isotype switching. Methods: Naive B cells from BALB/c mice were stimulated with LPS plus IL-4 alone or plus anti-IgM (0.1-10 μg/mL). IgE and IgG1 levels in supernatants were measured by means of ELISA on day 6. Cμ or Cε germline transcripts, activation-induced cytidine deaminase (AID), and Iμ-Cε postswitch transcripts were measured by means of RT-PCR. Deletional switch recombination was assessed by means of digestion circularization PCR of Sμ-Sε products. Results: BCR cross-linking inhibited IgE and IgG1 switching in a dose-dependent fashion. This was not due to inhibition of proliferation, increased apoptosis, or cell death. BCR cross-linking had no effect on Cμ or Cε germline transcripts but suppressed the generation of Sμ-Sε switch products and Iμ-Cε postswitch transcripts and caused a delay in the expression of AID mRNA, with decreased expression on days 2 and 3 after stimulation. Concomitantly, the number of DNA repair foci at the IgH locus on day 3 was significantly decreased. AID expression and activity became normal on day 4, but isotype switching remained profoundly diminished 8 days after stimulation. Conclusion: BCR cross-linking delays AID expression. This might interfere with class-switch recombination by disrupting the temporal coordination of signals that lead to class-switch recombination. © 2008 American Academy of Allergy, Asthma & Immunology. |
| Keywords: |
protein expression; nonhuman; cell proliferation; animal cell; mouse; animals; mice; cell death; cells, cultured; dna repair; apoptosis; interleukin 4; enzyme linked immunosorbent assay; mice, inbred balb c; b lymphocyte; b-lymphocytes; immune response; cytidine deaminase; bagg albino mouse; immunoglobulin g; messenger rna; recombination, genetic; lipopolysaccharide; real time polymerase chain reaction; immunoglobulin g1; immunoglobulin class switching; enzyme induction; immunoglobulin m antibody; immunoglobulin e; receptors, antigen, b-cell; cross linking; b lymphocyte receptor; ige; activation-induced cytidine deaminase; b-cell receptor; isotype switching
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