Background CD19+CD24^highCD38^high B cells have been described to have a regulatory capacity and their frequency is altered in the peripheral blood of patients with various autoimmune diseases. The pathogenesis of AS is not well understood, and evidence suggesting the implication of either autoinflammatory or autoimmune mechanisms has been reported. In addition, increased frequencies of circulating B cells bearing a regulatory phenotype has recently been described in spondyloartrhitis (1).

Objectives To study the frequency of circulating CD19+CD24^high CD38^high B cells (Breg) in patients with Ankylosing Spondylitis (AS), and test the regulatory capacity of this B cell subset.

Methods Peripheral blood was drawn from AS patients naïve for TNF blockers (AS/nb) (n=37) and healthy controls (HC) (n=37), that were matched with patients for age and gender. After isolation by Ficoll-Hypaque gradient, PBMCs were stained with antibodies to CD3, CD4, CD19, CD24, and CD38, and examined by flow 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 total CD19+ B cells were depleted of CD19+CD24^highCD38^high B cells by cytometry in a FacsVantage sorter (Beckton Dickinson). 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.

Results When compared with healthy controls, AS/nb patients demonstrated a significantly increased frequency of CD19+CD24^highCD38^high B cells (Breg). The frequency of circulating Breg was increased not only in AS/nb patients with high or very high disease activity (ASDAS-CRP) >2.1 but also in AS patients with low activity or no activity (ASDAS-CRP<2.1). The frequency of circulating Breg cells did not correlate significantly with ASDAS-CRP, ASDAS-ESR, BASDAI, CRP or ESR values. Functional in vitro studies showed that the secretion of IFNγ was significantly higher in Breg-depleted CD19+ as compared with total CD19+ B cells, indicating that Breg have the capacity to downmodulate B cell pro-inflammatory cytokine secretion.

Conclusions An increased frequency of circulating CD19+CD24^highCD38^high B cells is observed in AS/nb patients, that is not related with disease activity. Functional in vitro studies confirmed that CD19+CD24^highCD38^high B cells are able to downmodulate B cell pro-inflammatory cytokine secretion.

1. Cantaert T, Doorenspleet ME, Francosalinas G, Paramarta JE, Klarenbeek PL, Tiersma Y, van der Loos CM, De Vries N, Tak PP, Baeten DL. Increased numbers of CD5+ B lymphocytes with a regulatory phenotype in spondylarthritis. Arthritis Rheum. 2012;64:1859–68.

Disclosure of Interest None declared