Systemic Lupus Erythematosus (SLE) is characterized by B cells lacking IgD and CD27 (double negative; DN). We show that DN cell expansions reflected a subset of CXCR5- CD11c+ cells (DN2) representing pre-plasma cells (PC). DN2 cells predominated in African-American patients with active disease and nephritis, anti-Smith and anti-RNA autoantibodies. They expressed a T-bet transcriptional network; increased Toll-like receptor-7 (TLR7); lacked the negative TLR regulator TRAF5; and were hyper-responsive to TLR7. DN2 cells shared with activated naive cells (aNAV), phenotypic and functional features, and similar transcriptomes. Their PC differentiation and autoantibody production was driven by TLR7 in an interleukin-21 (IL-21)-mediated fashion. An in vivo developmental link between aNAV, DN2 cells, and PC was demonstrated by clonal sharing. This study defines a distinct differentiation fate of autoreactive naive B cells into PC precursors with hyper-responsiveness to innate stimuli, as well as establishes prominence of extra-follicular B cell activation in SLE, and identifies therapeutic targets.
Copyright © 2018 Elsevier Inc. All rights reserved.

B-cell differentiation and B-cell tolerance checkpoints may be different in antiphospholipid syndrome (APS) from systemic lupus erythematosus (SLE) and can help to understand differences between them. Our aim was to define alterations of B-cell subsets in patients with primary APS (pAPS) and to compare them with SLE patients and healthy controls (HC).
Cross-sectional study including three study groups: 37 patients with pAPS, 11 SLE patients, and 21 age- and gender-matched HC. We determined the frequencies of different B-cell subsets in peripheral blood naïve and memory compartments. In addition, we measured serum B cell-activating factor (BAFF) levels and circulating pro-inflammatory cytokines, such as IL-6, by commercial ELISA and CBA, respectively.
Patients with pAPS showed a lower percentage of immature and naïve B cells than patients with SLE (p = 0.013 and p = 0.010, respectively) and a higher percentage of non-switched memory B cells than patients with SLE (p = 0.001). No differences either in the percentage of switched memory cells or plasma cells were found among the different groups. Serum BAFF levels were higher in SLE patients than in healthy controls and pAPS patients (p = 0.001 and p = 0.017, respectively). A significant increase in the serum BAFF levels was also observed in pAPS patients compared to HC (p = 0.047). Circulating IL-6 levels were higher in SLE and pAPS patients than HC (p = 0.036 and p = 0.048, respectively). A positive correlation was found between serum BAFF and IL-6 levels in patients with SLE but not in pAPS (p = 0.011).
Our characterization of peripheral blood B-cell phenotypes in pAPS demonstrates different frequencies of circulating B cells at different stages of differentiation. These differences in the naïve B-cell repertoire could explain the higher number and variety of autoantibodies in SLE patients in comparison to pAPS patients, especially in those with obstetric complications.

Using flow cytometry, the present study aimed to investigate the immunophenotypic characteristics of malignant plasma cells (PCs) in the bone marrow of patients with primary systemic light chain amyloidosis (AL) compared with the characteristics of patients with multiple myeloma (MM). Flow cytometric results of 51 patients with AL and 150 patients with MM were reviewed. The proportion of total bone marrow PCs in the patients with AL was significantly lower than that in the patients with MM, 1.35% (0.3-9.5%) vs. 9.7% (0.4-75.7%); (P<0.001). The cells in 24/51 patients with AL comprised two distinct populations: Normal PCs and malignant PCs, whereas only 11/150 patients with MM exhibited two populations. Patients with AL exhibited an increased cluster of differentiation (CD)19 expression compared with patients with MM, 4.5% (0.1-80.9%) vs. 1.6% (0.1-33.6%; P<0.001) and reduced CD138, with 90.8% (30.4-99.9%) vs. 95.0% (40.7-100%; P=0.006) and CD56, with 61.0% (1.5-99.2%) vs. 98.3% (0.1-100%; P<0.001) expression in malignant PCs. Light chain restriction was identified in all patients with AL, and the proportion of λ light chain restriction was 72.5%. The immunophenotypic characteristics of patients with AL demonstrated by flow cytometry were different compared with the characteristics of patients with MM in the number and composition of plasma cells, and the intracellular and extracellular expression of antigens. These differences may be associated with a less malignant phenotype of clonal PCs in AL than MM.

Flow cytometry has increasing relevance for prognosis in myeloma and precursor disease (monoclonal gammopathy of unknown significance/smoldering myeloma), yet it has been reported that plasma cell enumeration by flow varies depending on the quality of marrow aspirate and field biopsied in patchy disease. We demonstrated increased sensitivity of flow over immunohistochemistry in abnormal-plasma cell detection in monoclonal gammopathy (n = 59)/smoldering myeloma (n = 87). We prospectively evaluated treatment-na ve smoldering myeloma (n = 9)/myeloma (n = 11) patients for the percentage of abnormal plasma cells/total plasma cell compartment, plasma cell viability/infiltration and flow immunophenotype depending on anticoagulant use, biopsy site and pull sequence in uni-and-bilateral bone marrow biopsies and aspirates. We found no statistical difference regarding the percentage of abnormal plasma cells, their immunophenotype or number/distribution in marrow samples even when obtained by different sequence in aspirates, or anticoagulants (p > 0.05). Our results show that plasma cell enumeration and immunophenotyping by flow cytometry is consistent under different conditions in these populations.