The germline immunoglobulin (Ig) variable heavy chain 4–34 (VH4-34) gene segment encodes in humans intrinsically self-reactive antibodies that recognize I/i carbohydrates expressed by erythrocytes with a specific motif in their framework region 1 (FWR1). VH4-34–expressing clones are common in the naive B cell repertoire but are rarely found in IgG memory B cells from healthy individuals. In contrast, CD27+IgG+ B cells from patients genetically deficient for IRAK4 or MYD88, which mediate the function of Toll-like receptors (TLRs) except TLR3, contained VH4-34–expressing clones and showed decreased somatic hypermutation frequencies. In addition, VH4-34–encoded IgGs from IRAK4- and MYD88-deficient patients often displayed an unmutated FWR1 motif, revealing that these antibodies still recognize I/i antigens, whereas their healthy donor counterparts harbored FWR1 mutations abolishing self-reactivity. However, this paradoxical self-reactivity correlated with these VH4-34–encoded IgG clones binding commensal bacteria antigens. Hence, B cells expressing germline-encoded self-reactive VH4-34 antibodies may represent an innate-like B cell population specialized in the containment of commensal bacteria when gut barriers are breached.
Self-reactive VH4-34–expressing IgG B cells recognize commensal bacteria
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Jean-Nicolas Schickel, Salomé Glauzy, Yen-Shing Ng, Nicolas Chamberlain, Christopher Massad, Isabelle Isnardi, Nathan Katz, Gulbu Uzel, Steven M. Holland, Capucine Picard, Anne Puel, Jean-Laurent Casanova, Eric Meffre; Self-reactive VH4-34–expressing IgG B cells recognize commensal bacteria. J Exp Med 3 July 2017; 214 (7): 1991–2003. doi: https://doi.org/10.1084/jem.20160201
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