Key Points• Chronic graft-versus-host disease is associated with a global Breg defect.• This defect is particularly accentuated in the CD24 hi CD27 1 Breg compartment.Interleukin 10 (IL-10)-producing B cells (regulatory B cells [Bregs]) regulate autoimmunity in mice and humans, and a regulatory role of IL-10-producing plasma cells has been described in mice. Dysfunction of B cells that maintain homeostasis may play a role in the pathogenesis of chronic graft-versus-host disease (cGVHD) after allogeneic stem cell transplantation. Here, we found a relation between decreased Breg frequencies and cGVHD severity. An impaired ability of B cells to produce IL-10, possibly linked to poor signal transducer and activator of transcription 3 and extracellular signal-regulated kinase phosphorylation, was found in patients with active cGVHD. IL-10 production was not confined to a single B-cell subset, but enriched in both the CD24 hi CD27 1 and CD27 hi CD38 hi plasmablast B-cell compartments. In vitro plasmablast differentiation increased the frequency of IL-10-producing B cells. We confirmed that allogeneic transplant recipients had an impaired reconstitution of the memory B-cell pool. cGVHD patients had less CD24 hi CD27 1 B cells and IL-10-producing CD24 hi CD27 1 B cells. Patients with cGVHD had increased plasmablast frequencies but decreased IL-10-producing plasmablasts. These results suggest a role of CD24 hi CD27 1 B-cell and plasmablast-derived IL-10 in the regulation of human cGVHD. (Blood. 2015;125(11):1830-1839 IntroductionChronic graft-versus-host disease (cGVHD) is the leading cause of morbi-mortality after allogeneic hematopoietic stem cell transplantation (AHSCT). 1 GVHD prevention by means of adoptive transfer of regulatory T cells (Tregs) 2,3 and cGVHD treatment by in vivo induction of Tregs by low-dose interleukin 2 (IL-2) 4,5 may be effective. The exact role of IL-10-producing regulatory B cells (Bregs) in cGVHD is yet to be understood. Bregs have been shown to downmodulate adaptive 6 or innate immune responses 7 in mice and humans. In cGVHD, B cells are essentially recognized as positive regulators of inflammation. 1,8,9 Increased B-cell receptor responsiveness was found in cGVHD patients. 10 B-cell homeostatic defects were described in cGVHD, including elevated B-cell activating factor of the tumor necrosis factor (TNF) family (BAFF)/B-cell ratios, 11-15 expansion of CD21 lo B cells, 16 reduced CD5 1 B1-like cell numbers, 17 decreased CD27 1 memory B cells, and hypogammaglobulinemia. 18 BAFF concentrations correlated with increased circulating pre-germinal center (GC) B-cell and post-GC plasmablast cell counts in patients with cGVHD. 11 B-cell depletion with rituximab prevented cGVHD in humans. 19 Patients with cGVHD frequently have circulating antibodies reactive to recipient cells. 1,9,20 Besides their functions in antibody secretion, cytokine and chemokine production, and antigen presentation, B cells exhibit regulatory properties in several human autoimmune diseases including systemic lupus erythemat...

Summary Background Acral lesions, mainly chilblains, are the most frequently reported cutaneous lesions associated with COVID‐19. In more than 80% of patients tested, nasopharyngeal swabs were negative on reverse transcription polymerase chain reaction (RT‐PCR) for SARS‐CoV‐2 when performed, and serology was generally not performed. Methods A national survey was launched on 30 March 2020 by the French Society of Dermatology asking physicians to report cases of skin manifestations in patients with suspected or confirmed COVID‐19 by using a standardized questionnaire. We report the results for acral manifestations. Results We collected 311 cases of acral manifestations [58.5% women, median age 25.7 years (range 18–39)]. The most frequent clinical presentation (65%) was typical chilblains. In total, 93 cases (30%) showed clinical suspicion of COVID‐19, 67 (22%) had only less specific infectious symptoms and 151 (49%) had no clinical signs preceding or during the course of acral lesions. Histology of skin biopsies was consistent with chilblains. Overall, 12 patients showed significant immunological abnormalities. Of the 150 (48%) patients who were tested, 10 patients were positive. Seven of 121 (6%) RT‐PCR‐tested patients were positive for SARS‐CoV‐2, and five of 75 (7%) serology‐tested patients had IgG anti‐SARS‐CoV‐2. Tested/untested patients or those with/without confirmed COVID‐19 did not differ in age, sex, history or acral lesion clinical characteristics. Conclusions The results of this survey do not rule out that SARS‐CoV‐2 could be directly responsible for some cases of chilblains, but we found no evidence of SARS‐CoV‐2 infection in the large majority of patients with acral lesions during the COVID‐19 lockdown period in France. What is already known about this topic? About 1000 cases of acral lesions, mainly chilblains, were reported during the COVID‐19 outbreak. Chilblains were reported to occur in young people within 2 weeks of infectious signs, which were mild when present. Most cases did not have COVID‐19 confirmed by reverse transcription polymerase chain reaction (RT‐PCR), and few serology results were available. What does this study add? Among 311 patients with acral lesions, mainly chilblains, during the COVID‐19 lockdown period in France, the majority of patients tested had no evidence of SARS‐CoV‐2 infection. Overall, 70 of 75 patients were seronegative for SARS‐Cov‐2 serology and 114 of 121 patients were negative for SARS‐CoV‐2 RT‐PCR.