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Cutting Edge: A Hypomorphic Mutation in Ig (CD79b) in a Patient with Immunodeficiency and a Leaky Defect in B Cell Development¹

A. Kerry Dobbs^*, Tianyu Yang^*, Dana Farmer^*, Leo Kager, Ornella Parolini and Mary Ellen Conley^2,*,

^* Department of Immunology, St. Jude Children’s Research Hospital, Memphis, TN 38105; Department of Hematology/Oncology, St. Anna Children’s Hospital, Vienna, Austria; Centro di Ricerca E. Menni, Fondazione Poliambulanza, Brescia, Italy; and Department of Pediatrics, University of Tennessee, Memphis, TN 38163

Although null mutations in Ig have been identified in patients with defects in B cell development, no mutations in Ig have been reported. We recently identified a patient with a homozygous amino acid substitution in Ig, a glycine to serine at codon 137, adjacent to the cysteine required for the disulfide bond between Ig and Ig. This patient has a small percentage of surface IgM^dim B cells in the peripheral circulation (0.08% compared with 5–20% in healthy controls). Using expression vectors in 293T cells or Jurkat T cells, we show that the mutant Ig can form disulfide-linked complexes and bring the µ H chain to the cell surface as part of the BCR but is inefficient at both tasks. The results show that minor changes in the ability of the Ig/Ig complex to bring the BCR to the cell surface have profound effects on B cell development.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ These studies were supported in part by National Institutes of Health Grant AI25129, National Cancer Institute Grant P30 CA21765, American Lebanese Syrian Associated Charities, and funds from the Federal Express Chair of Excellence.

² Address correspondence and reprint requests to Dr. Mary Ellen Conley, University of Tennessee College of Medicine, St. Jude Children’s Research Hospital, 332 North Lauderdale, Memphis, TN 38105. E-mail address: maryellen.conley{at}stjude.org

³ Abbreviations used in this paper: SSCP, single-stranded conformational polymorphism; MSCV, mouse stem cell virus; YFP, yellow fluorescent protein.