Phenotypic and Ig Repertoire Analyses Indicate a Common Origin of IgD - CD27 - Double Negative B Cells in Healthy Individuals and Multiple Sclerosis Patients.

IgD ^- CD27 ^- double negative (DN) B cells with proinflammatory characteristics are abnormally elevated in a proportion of multiple sclerosis (MS) patients. In this study, the origin and selection characteristics of DN B cells were studied in MS patients and healthy controls (HC). Expression of developmental markers on peripheral blood DN, IgD ^- CD27 ⁺ class-switched memory (CSM) and IgD ⁺ CD27 ^- naive B cells of HC ( n = 48) and MS patients ( n = 96) was determined by flow cytometry. High-throughput adaptive immune receptor repertoire sequencing was performed on peripheral blood DN and CSM B cells of HC and MS patients ( n = 3 each). DN B cells from HC and MS patients showed similar phenotypic and Ig repertoire characteristics. Phenotypic analysis indicated a mature state of DN B cells by low CD5, CD10, and CD38 expression. However, the frequency of CD95 ⁺ and IgA ⁺ cells was lower in DN versus CSM B cells. DN B cells are Ag experienced, as shown by somatic hypermutation of their Ig genes in adaptive immune receptor repertoire sequencing, although they showed a lower mutation load than CSM B cells. Shared clones were found between DN and CSM B cells, although >95% of the clones were unique to each population, and differences in V(D)J usage and CDR3 physicochemical properties were found. Thus, DN B cells arise in HC and MS patients via a common developmental pathway that is probably linked to immune aging. However, DN and CSM B cells develop through unique differentiation pathways, with most DN B cells representing an earlier maturation state.
(Copyright © 2019 by The American Association of Immunologists, Inc.)