026 – IgD-CD27- double negative B cells of multiple sclerosis patients are mature memory cells that can migrate towards pro-inflammatory chemokines
Beckers Lien (1) – Montes Diaz Gwendoline (1) – Villar Luisa M (2) – Van Wijmeersch Bart (1, 3) – Fraussen Judith (1) – Somers Veerle (1)
Hasselt University, Biomedical Research Institute and Transnationale Universiteit Limburg, School of Life Sciences, Hasselt, Belgium (1) – Department of Immunology, Hospital Universitario Ramn y Cajal, Madrid, Spain (2) – Rehabilitation & MS-Center, Pelt, Belgium (3)
Previously, we reported abnormal elevations of age-associated IgD-CD27- double negative (DN) B cells with pro-inflammatory characteristics in the peripheral blood of a proportion of multiple sclerosis (MS) patients (Claes N. et al. J Immunol 2016). This study aimed to further investigate the phenotype and pro-inflammatory function of DN B cells in MS.
The distribution of immunoglobulin (Ig) isotypes, developmental markers (CD5, CD10, CD38, CD95) and chemokine receptors C-X-C chemokine receptor (CXCR3, CXCR5) was measured on peripheral blood DN, IgD-CD27+ class-switched memory (CSM) and IgD+CD27- naive B cells of healthy controls (HC, n = 48) and MS patients (n = 96) by flow cytometry. Expression of the transcription factor T-bet was measured in DN B cells of MS patients (n = 58). Using an in vitro chemotaxis assay, migration of peripheral blood CD27- or CD27+ B cells of MS patients (n = 8) towards chemokines CXCL10 or CXCL13 was measured.
Most DN B cells were class-switched although IgA+ cells were less frequent in the DN versus CSM B cell population for HC and MS patients (p < 0.0001). DN B cells resembled CSM B cells in developmental marker expression, although the DN B cell population had a higher frequency of immature CD5+ (p = 0.007 HC, p = 0.0003 MS) and CD38+ (p = 0.0001 HC, p = 0.01 MS) cells and a lower frequency of activated CD95+ (p < 0.0001) cells. T-bet expression was found in 21.6 [3.3, 52.0] % of MS DN B cells. The pro-inflammatory chemokine receptors CXCR3 and CXCR5 were expressed in 14.0% and 69.0% of DN B cells, respectively. In addition, MS DN B cells showed high migration capacity towards CXCL10 and CXCL13 (CXCR3 and CXCR5 receptor, respectively) that was comparable to that of CSM B cells.
Thus, DN B cells resemble CSM B cells but are at an earlier maturation state. The potential importance of DN B cells in MS pathology was further underlined by their high migration capacity towards pro-inflammatory chemokines.