Background/Purpose: Regulatory B cells are active participants in down-regulating inflammation and autoimmunity, through the production of IL-10. Despite intensive studies in mice, there is only a paucity of data concerning the regulation of IL-10 production in human. The purpose of this study is to understand IL-10 production by human B cells and to explore the development of regulatory B cells either in healthy individuals or in patients with SLE.

Methods: Healthy controls (HC) (n=15) and SLE patients (n=20) fulfilling the American College of Rheumatology revised classification criteria were included in this study. Total B cells were purified with MACS-negative selection and different B cell subsets were obtained by sorting. IL-10 producing B cells were identified with intracellular staining, Elispot, and dual color Flurospot assay. Elisa was used to determine the level of IL-10 in B cell cultures.

Results: In vitro and ex vivo analysis determined for the first time, that human plasma cells (PC: CD19+CD27++CD38++CD138+) and plasmablasts (PB: CD19+CD27++CD38⁺⁺CD138^–) are major sources of IL-10.  This cytokine was secreted from PB and PC generated in vitro from cultured memory cells using Elispot assay and intracellular flow cytometry. Both assay identified 1-2% of IL-10 positive PB/PC. Similarly, ex vivo analysis of unstimulated B cell subsets sorted 7 days after flu vaccination of HC identified PB and PC as the only source of IL-10 and up to 1% of PC and PB are able to produce IL-10. In contrast, circulating PB and PC spontaneously expanded in the circulation of active SLE patients failed to produce IL-10 ex vivo.  In vitro stimulation of purified B cell subsets with CpGDNA and IL-2 coupled with CFSE labeling identified the IgD(+)CD27(+) non-switched memory B-cell subpopulation as the main IL-10-producing precursor B cell in a division-linked fashion.  Of interest, IL-10 production from stimulated B cells was significantly lower in SLE patient (380.1±60.94 pg/ml) than in HC (857.6±97.06 pg/ml) (p<0.001), in direct correlation with the reduction in non-switched memory cells typical of this disease.  In contrast, SLE patients with normal distribution of B cell subsets had normal IL-10 secretion.

Conclusion: We provide the first description of spontaneous IL-10 production by human PB and PC in HC and its deficiency in SLE.  These findings suggest that IL-10 could negatively regulate antibody secreting cells in an autocrine fashion that would be deficient in SLE thereby enhancing autoantibody production. Our data also identify non-switched memory B cells as an important source of potent regulatory B cells and indicate that the decrease of this population typically observed in SLE may be a major contributor to the deficiency of regulatory IL-10 in this autoimmune disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/identification-of-il-10-producing-plasma-cells-in-human-and-its-deficiency-in-systemic-lupus-erythematosus-patients/