A p53 axis regulates B cell receptor-triggered, innate immune system-driven B cell clonal expansion

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Resting mature human B cells proliferate and contract during in vitro immune responses.
• Understanding the mechanisms of B cell clonal contraction, specifically activation-induced cell death (AICD), is crucial for immune regulation.

Purpose of the Study:

• To investigate the molecular mechanisms underlying clonal contraction in human B cells.
• To identify the role of apoptosis-regulating proteins and DNA damage in AICD of activated B cells.

Main Methods:

• CFSE-labeling to track cell division and proliferation.
• Analysis of pro- and anti-apoptotic protein expression (p53, Bax, Bad, Puma, Bid, Bcl-2, Bim).
• Assessment of DNA damage markers (phosphorylated ATM and H2AX).
• Intervention using p53 small interfering RNA, p53 genetic deletion, and Bcl-2 overexpression in mouse and human B cells.

Main Results:

• Activated B cells show elevated p53, pro-apoptotic proteins (Bax, Bad, Puma, Bid, procaspase 6), and reduced Bcl-2.
• Bid cleavage to truncated Bid was observed in AICD-susceptible cells.
• p53 inhibition or Bcl-2 overexpression diminished AICD.
• Elevated DNA damage markers (p-ATM, p-H2AX) indicate DNA damage as a trigger for p53-dependent AICD.
• Activation-induced deaminase deficiency partially reduced AICD in murine B cells.

Conclusions:

• A p53-dependent mitochondrial apoptotic pathway contributes significantly to AICD in activated human B cells.
• DNA damage, partly mediated by activation-induced deaminase, triggers this p53-dependent AICD.
• The findings suggest a potential mechanism for positive selection of B cells with p53 mutations in inflammatory environments.