Date Published: July 6, 2017
Publisher: Public Library of Science
Author(s): María-Belén Bautista-Caro, Eugenio de Miguel, Diana Peiteado, Chamaida Plasencia-Rodríguez, Alejandro Villalba, Irene Monjo-Henry, Amaya Puig-Kröger, Paloma Sánchez-Mateos, Emilio Martín-Mola, María-Eugenia Miranda-Carús, Frederic Rieux-Laucat.
Our objective was to study the frequency of circulating CD19+CD24hiCD38hi B cells (Breg) in AS patients. To this end, peripheral blood was drawn from AS patients naïve for TNF blockers (AS/nb) (n = 42) and healthy controls (HC) (n = 42). Six patients donated blood for a second time, 6 months after initiating treatment with anti-TNFα drugs. After isolation by Ficoll-Hypaque, PBMCs were stained with antibodies to CD3, CD4, CD19, CD24, and CD38, and examined by cytometry. For functional studies, total CD19+ B cells were isolated from PBMCs of 3 HC by magnetical sorting. Breg-depleted CD19+ B cells were obtained after CD19+CD24hiCD38hi B cells were removed from total CD19+ cells by cytometry. Total CD19+ B cells or Breg-depleted CD19+ B cells were established in culture and stimulated through their BCR. Secretion of IFNγ was determined by ELISA in culture supernatants. When compared with HC, AS/nb patients demonstrated a significantly increased frequency of Breg cells, which was independent of disease activity. Anti-TNFα drugs induced a significant reduction of circulating Breg numbers, which were no longer elevated after six months of treatment. Functional in vitro studies showed that the secretion of IFNγ was significantly higher in Breg-depleted as compared with total CD19+ B cells, indicating that Breg can downmodulate B cell pro-inflammatory cytokine secretion. In summary, an increased frequency of circulating CD19+CD24hiCD38hi B cells is observed in AS/nb patients, that is not related with disease activity; anti-TNFα drugs are able to downmodulate circulating Breg numbers in AS.
The pathogenesis of Ankylosing spondylitis (AS), the prototype form of Spondyloarthritis (SpA), is not well understood, and evidence indicating a role for either autoinflammatory or autoimmune mechanisms has been described . An interesting report by Cantaert et al  has shown an increased number of IL-10 producing CD19+CD5+ B lymphocytes in SpA.
We have herein described an increased frequency and absolute number of CD19+CD24hiCD38hi B cells in AS patients naïve for biological agents, that is not related with disease activity measures. These results parallel data published by Cantaert el al, who reported on elevated numbers of CD19+CD5+ B cells with a regulatory phenotype in SpA, independent of disease activity . Assessment of clinical activity in SpA is difficult due to the lack of a universally accepted ‘gold standard’ , and because some of the currently used indices measure only one aspect of the disease or are mostly patient or physician oriented. Therefore we were interested in ascertaining whether the lack of correlation of Breg cell numbers with ASDAS-CRP was relevant. Serum calprotectin has recently emerged as a good biomarker for disease activity in SpA [17,18] and we observed that serum calprotectin concentrations were significantly correlated with CRP and ASDAS-CRP but not with the percentage of circulating Breg cells, thereby confirming that Breg cell numbers do not vary with disease activity in AS.
In summary, we have described increased numbers of circulating CD19+CD24hiCD38hi B cells (Breg) in AS/nb patients, that are not related with disease activity. Treatment with anti-TNFα drugs is able to downmodulate circulating Breg cell numbers in AS.