Germinal Center Founder Cells Research Articles

Altered B Cell Homeostasis in Patients with Major Depressive Disorder and Normalization of CD5 Surface Expression on Regulatory B Cells in Treatment Responders.

Pro-inflammatory activity and cell-mediated immune responses have been widely observed in patients with major depressive disorder (MDD). Besides their well-known function as antibody-producers, B cells play a key role in inflammatory responses by secreting pro- and anti-inflammatory factors. However, homeostasis of specific B cell subsets has not been comprehensively investigated in MDD. In this study, we characterized circulating B cells of distinct developmental steps including transitional, naïve-mature, antigen-experienced switched, and non-switched memory cells, plasmablasts and regulatory B cells by multi-parameter flow cytometry. In a 6-weeks follow-up, circulating B cells were monitored in a small group of therapy responders and non-responders. Frequencies of naïve lgD+CD27- B cells, but not lgD+CD27+ memory B cells, were reduced in severely depressed patients as compared to healthy donors (HD) or mildly to moderately depressed patients. Specifically, B cells with immune-regulatory capacities such as CD1d+CD5+ B cells and CD24+CD38hi transitional B cells were reduced in MDD. Also Bm1-Bm5 classification in MDD revealed reduced Bm2' cells comprising germinal center founder cells as well as transitional B cells. We further found that reduced CD5 surface expression on transitional B cells was associated with severe depression and normalized exclusively in clinical responders. This study demonstrates a compromised peripheral B cell compartment in MDD with a reduction in B cells exhibiting a regulatory phenotype. Recovery of CD5 surface expression on transitional B cells in clinical response, a molecule involved in activation and down-regulation of B cell responses, further points towards a B cell-dependent process in the pathogenesis of MDD.

Analysis of B-cell subpopulations in monoclonal gammopathies.

Multiple myeloma (MM) is characterized by accumulation of pathological plasma cells (PCs) in bone marrow (BM) as a result of deregulation of B-cell development. To clarify its pathophysiology it is necessary to investigate in detail the developmental stages of B-cells. Enumeration of total CD19-positive (CD19(+)) cells and their subpopulations together with PCs was done in peripheral blood (PB) and BM of newly diagnosed monoclonal gammopathy patients and control subjects. Representation of subsets was compared among groups and relationships between subset percentage and cytogenetic/biochemical findings were analyzed. A lower number of total CD19(+) cells was found in MM, particularly in advanced stages of disease. Reduction of naive (P < .01) and transitional B-cells (P < .05) and increase of switched memory and switched CD27(-) B-cells and germinal center founder cells were detected in PB of MM compared with controls (P < .01). Similar results were found in BM. β2 microglobulin level in MM positively correlated with the number of PCs and negatively with percentage of naive B-cells (P < .05). Our results provided a detailed phenotypic profile and enumeration of B and PC subpopulations in monoclonal gammopathy patients. A reduced number of B-cells and particularly a differentiation shift to more numerous antigen-stimulated forms was observed in MM. This might indicate a potential source of myeloma-initiating cells in one of these subpopulations.

Dynamic Analysis of B-Cell Subsets in De Novo Living Related Kidney Transplantation With Induction Therapy of Basiliximab

BackgroundAccumulative evidence has suggested B-cell–mediated alloimmune response plays an important role in kidney transplantation. Monitoring the dynamics of B-cell subsets could enhance understanding of B-cell immunology in clinical transplantation, and may facilitate optimization of current immunosuppressive regimens. Patients and MethodsBetween June 2011 and June 2012, 16 de novo living related kidney transplant recipients were enrolled in this study. All patients were given basiliximab as induction therapy. The maintenance therapy consisted of tacrolimus, mycophenolate mofetil (MMF), and steroids. Phenotype of B-cell subsets in peripheral blood was examined at day 0, day 1, day 3, day 7, day 14, month 1, month 3, and month 6. ResultsCD19+ B cells in peripheral lymphocytes significantly increased by 1.8–2.1 times within 1 month after transplantation, and recovered to the baseline level at month 3. Notably in B cells, CD5+CD19+B cells dramatically decreased by 45% at month 6. CD19+CD27+ memory B cells increased by 127% at month 6. B-cell activating factor receptor (BAFF-R) expression on the B-cell population was maintained at a high level of 91.7%–97.9%. Within 7 days after transplantation, Bm1 (IgD+CD38−) did not change apparently, Bm2 (IgD+CD38int) significantly increased, whereas Bm2' (IgD+CD38high, germinal center founder cells), Bm3+Bm4 (IgD−CD38high, germinal center B cells), early Bm5 (IgD−CD38int), and late Bm5 (IgD−CD38−) significantly decreased. After day 7, Bm1 stayed stable, Bm2 decreased to the baseline level (day 0), and Bm2' and Bm3+Bm4 kept decreasing, whereas early Bm5 and late Bm5 increased to baseline level. At month 6, Bm1 significantly increased, Bm2 was maintained at the baseline level, Bm2' constantly decreased to the lowest, and Bm3+Bm4 was slightly lower than the baseline, whereas early and late Bm5 increased to the baseline level. ConclusionsThe proportion of B cells in peripheral lymphocytes significantly increased at the early stage, whereas CD5+CD19+B cells consistently decreased after transplantation. Mature circulating B-cell subsets dynamically changed, especially at the early stage after transplantation, which might be attributed to the induction therapy.

Molecular Single-Cell Analysis of Hodgkin- and Reed-Sternberg Cells Harboring Unmutated Immunoglobulin Variable Region Genes

Hodgkin- and Reed-Sternberg (H/RS) cells in classical Hodgkin's disease of the B lineage are the clonal progeny of antigen-experienced B cells harboring highly mutated immunoglobulin variable (V) region genes. Based on the detection of obviously destructive somatic mutations in a fraction of cases, we speculated that H/RS cells may be derived from a pre-apoptotic germinal center B cell. Seemingly contradicting this speculation, we present here the first case of classical Hodgkin's disease with H/RS cells harboring unmutated, potentially functional V region genes, which may indicate the derivation of the H/RS clone from a naive B cell. However, germinal center founder cells, which have not yet acquired somatic mutations, already have the intrinsic propensity to die by apoptosis. Thus, the rare occurrence of H/RS cells with unmutated V genes is expected if the H/RS cells are derived from the pool of pre-apoptotic germinal center B cells.

Follicular dendritic cells in vitro modulate the expression of Fas and Bcl-2 on germinal center B cells.

Germinal center (GC) B cells are highly susceptible to apoptosis. The cellular mechanism regulating this sensitivity, however, has not yet been fully delineated. To investigate whether follicular dendritic cells (FDC) are capable of regulating the susceptibility to apoptosis of GC B cells, we constructed a GC model in vitro: emperipolesis of tonsillar B cells by FDC. We then analyzed the expressions of apoptosis-related proteins (Bcl-2 and Fas) on the cells by three-color flow cytometry. B cells nonentrapped by FDC decreased rapidly in number owing to early apoptosis in vitro, whereas entrapped B cells were rescued for at least 18 h and showed peculiar regulation of Fas and Bcl-2. GC founder cells (CD38+, IgD+; GCFC) and GC B cells (CD38+, IgD-) showed approximately a twofold increased expression of Fas; in contrast, mantle zone B cells (CD38-, IgD+) and memory B cells (CD38-, IgD-) showed no changes. Bcl-2 expression in mantle zone and memory B cells was reduced by approximately one-half; however, GCFC and GC B cells continued to express little Bcl-2 and this did not change. Our findings strongly suggest that FDC play a part in the modulation of the susceptibility to apoptosis on B cells within GC.

Germinal center development.

Using a set of surface markers including IgD and CD38, human tonsillar B cells were classified into discrete subpopulations. Molecular and functional analysis allowed us to identify: i) two sets of naive B cells (Bm1 and Bm2); ii) germinal center founder cells (Bm2'); iii) an obscure population of germinal center B cells, displaying a high load of somatic mutations in IgV genes, C mu to C delta switch and preferential Ig lambda light chain usage: these cells may represent the precursors of normal and malignant IgD-secreting plasma cells; iv) the centroblasts (Bm3) in which somatic mutation machinery is activated; v) the centrocytes (Bm4) in which isotype switch occurs; vi) the memory B cells. The characterization of these subpopulations showed that: i) programmed cell death is set before somatic mutations, possibly providing an efficient way for affinity maturation; ii) only high affinity centrocytes are allowed to switch isotype; iii) CD40-ligation inhibits plasmacytic differentiation of mature B lymphocytes; iv) memory B cells preferentially differentiate into plasma cells; v) IgD isotype switch occurs in normal B cells; vi) receptor editing may be induced by somatic mutations in germinal centers. We also characterized two types of antigen-presenting cells in germinal centers: follicular dendritic cells that select high affinity B cells, and a new subset of germinal center dendritic cells that activate germinal center T cells.

Germinal center founder cells display propensity for apoptosis before onset of somatic mutation.

B lymphocytes undergo affinity maturation of their antigen receptors within germinal centers. These anatomical structures develop in secondary lymphoid organs from the clonal expansion of a few antigen-specific founder B cells, whose isolation and characterization are reported here. Human germinal center founder cells express the naive B cell markers surface IgM and IgD as well as the germinal center B cell markers CD10 and CD38. They express low levels of Bcl-2, high levels of Fas, and undergo rapid apoptosis in culture. The smaller nonproliferating sIgM+IgD+CD38+ B cells displayed a lower level of somatic mutation in their immunoglobulin variable region genes compared with the large proliferating ones. Unmutated sIgM+IgD-CD38+ tonsillar B cells may thus represent germinal center founder cells in which the program for apoptotic cell death is triggered before the onset of somatic mutation, allowing the selection of the germline antibody repertoire at an early stage.

A Putative Chemokine Receptor, BLR1, Directs B Cell Migration to Defined Lymphoid Organs and Specific Anatomic Compartments of the Spleen

We describe the phenotype of gene-targeted mice lacking the putative chemokine receptor BLR1. In normal mice, this receptor is expressed on mature B cells and a subpopulation of T helper cells. Blr1 mutant mice lack inguinal lymph nodes and possess no or only a few phenotypically abnormal Peyer's patches. The migration of lymphocytes into splenic follicles is severely impaired, resulting in morphologically altered primary lymphoid follicles. Furthermore, activated B cells fail to migrate from the T cell–rich zone into B cell follicles of the spleen, and despite high numbers of germinal center founder cells, no functional germinal centers develop in this organ. Our results identify the putative chemokine receptor BLR1 as the first G protein–coupled receptor involved in B cell migration and localization of these cells within specific anatomic compartments.