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PLoS One. 2015 Jun 12;10(6):e0129879. doi: 10.1371/journal.pone.0129879. eCollection 2015.

Innate Response Activator (IRA) B Cells Reside in Human Tonsils and Internalize Bacteria In Vitro.

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Novartis Vaccines and Diagnostics (a GSK company), Research Center, Via Fiorentina 1, Siena, Italy.
Otorhinolaryngology Department, University Hospital Le Scotte, Strada delle Scotte 14, Siena, Italy.
Department of Medical Biotechnologies, Infectious Unit, University Hospital Le Scotte, Strada delle Scotte 14, Siena, Italy.


Innate response activator (IRA) B cells have been described in mice as a subset of B-1a B cells that produce granulocyte/macrophage colony-stimulating factor (GM-CSF) and have been found in the spleen upon activation. In humans, identification, tissue localization and functionality of these lymphocytes are poorly understood. We hypothesized that IRA B cells could reside in human palatine tonsils, which are a first line of defense from infection of the upper respiratory tract. In the present work, we used flow cytometry and confocal microscopy to identify and characterize human IRA (hIRA) B cells in tonsils. We show that CD19⁺CD20⁺GM-CSF⁺ B cells are present in the tonsils of all the subjects studied at a frequency ranging between ~0.2% and ~0.4% of the conventional CD19⁺CD20⁺GM-CSF⁻ B cells. These cells reside within the B cell follicles, are mostly IgM⁺IgD⁺, express CD5 and show phagocytic activity. Our results support a role for hIRA B cells in the effector immune response to infections in tonsils.

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