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Genomic Instability Resulting from Blm Deficiency Compromises Development, Maintenance, and Function of the B Cell Lineage

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Hobeika,  Elias
Research Group and Chair of Molecular Immunology of the University of Freiburg, Max Planck Institute of Immunobiology and Epigenetics, Max Planck Society;

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Reth,  Michael
Research Group and Chair of Molecular Immunology of the University of Freiburg, Max Planck Institute of Immunobiology and Epigenetics, Max Planck Society;

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Citation

Babbe, H., McMenamin, J., Hobeika, E., Wang, J., Rodig, S. J., Reth, M., et al. (2009). Genomic Instability Resulting from Blm Deficiency Compromises Development, Maintenance, and Function of the B Cell Lineage. The Journal of Immunology, 182, 347-360.


Cite as: http://hdl.handle.net/11858/00-001M-0000-002B-8F3C-A
Abstract
The RecQ family helicase BLM is critically involved in the maintenance of genomic stability, and BLM mutation causes the heritable disorder Bloom's syndrome. Affected individuals suffer from a predisposition to a multitude of cancer types and an ill-defined immunodeficiency involving low serum Ab titers. To investigate its role in B cell biology, we inactivated murine Blm specifically in B lymphocytes in vivo. Numbers of developing B lymphoid cells in the bone marrow and mature B cells in the periphery were drastically reduced upon Blm inactivation. Of the major peripheral B cell subsets, B1a cells were most prominently affected. In the sera of Blm-deficient naive mice, concentrations of all Ig isotypes were low, particularly IgG3. Specific IgG Ab responses upon immunization were poor and mutant B cells exhibited a generally reduced Ab class switch capacity in vitro. We did not find evidence for a crucial role of Blm in the mechanism of class switch recombination. However, a modest shift toward microhomology-mediated switch junction formation was observed in Blm-deficient B cells. Finally, a cohort of p53-deficient, conditional Blm knockout mice revealed an increased propensity for B cell lymphoma development. Impaired cell cycle progression and survival as well as high rates of chromosomal structural abnormalities in mutant B cell blasts were identified as the basis for the observed effects. Collectively, our data highlight the importance of BLM-dependent genome surveillance for B cell immunity by ensuring proper development and function of the various B cell subsets while counteracting lymphomagenesis.