Impaired germinal center maturation in adenosine deaminase deficiency |
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Authors: | Aldrich Melissa B Chen Wilma Blackburn Michael R Martinez-Valdez Hector Datta Surjit K Kellems Rodney E |
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Institution: | Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston, TX 77030, USA. |
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Abstract: | Mice deficient in the enzyme adenosine deaminase (ADA) have small lymphoid organs that contain reduced numbers of peripheral lymphocytes, and they are immunodeficient. We investigated B cell deficiency in ADA-deficient mice and found that B cell development in the bone marrow was normal. However, spleens were markedly smaller, their architecture was dramatically altered, and splenic B lymphocytes showed defects in proliferation and activation. ADA-deficient B cells exhibited a higher propensity to undergo B cell receptor-mediated apoptosis than their wild-type counterparts, suggesting that ADA plays a role in the survival of cells during Ag-dependent responses. In keeping with this finding, IgM production by extrafollicular plasmablast cells was higher in ADA-deficient than in wild-type mice, thus indicating that activated B cells accumulate extrafollicularly as a result of a poor or nonexistent germinal center formation. This hypothesis was subsequently confirmed by the profound loss of germinal center architecture. A comparison of levels of the ADA substrates, adenosine and 2'-deoxyadenosine, as well resulting dATP levels and S-adenosylhomocysteine hydrolase inhibition in bone marrow and spleen suggested that dATP accumulation in ADA-deficient spleens may be responsible for impaired B cell development. The altered splenic environment and signaling abnormalities may concurrently contribute to a block in B cell Ag-dependent maturation in ADA-deficient mouse spleens. |
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