B cell receptor stimulation inhibits class switch recombination through elevated DNA repair

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Antibody diversity in B cells is crucial for adaptive immunity.
• Activation-induced deaminase (AID) introduces uracils into immunoglobulin DNA, initiating somatic hypermutation and class switch recombination (CSR).
• Uracil DNA glycosylase (UNG) removes uracils, leading to DNA breaks essential for CSR.

Purpose of the Study:

• To investigate the mechanism behind anti-IgM inhibition of CSR.
• To determine the roles of AID and UNG in anti-IgM-mediated CSR regulation.

Main Methods:

• Stimulation of B cells ex vivo with anti-IgM and lipopolysaccharide (LPS).
• Analysis of AID expression and recruitment to immunoglobulin loci.
• Measurement of UNG levels and uracil accumulation.
• Assessment of cell-cycle progression.

Main Results:

• Anti-IgM and LPS stimulation led to increased AID expression and recruitment.
• UNG levels were upregulated, preventing uracil accumulation.
• Anti-IgM accelerated B cell entry into S-phase.
• Early S-phase entry resulted in reduced uracil accumulation and less CSR.

Conclusions:

• Efficient CSR requires sufficient accumulation of AID-induced uracils before S-phase entry.
• Anti-IgM stimulation promotes early S-phase entry, upregulating UNG and limiting uracil availability for CSR.
• This mechanism explains the inhibitory effect of anti-IgM on CSR.