Promote B-cell Differentiation Research Articles

Tfh cell-derived small extracellular vesicles exacerbate the severity of collagen-induced arthritis by enhancing B-cell responses

Soluble components secreted by Tfh cells are critical for the germinal center responses. In this study, we investigated whether Tfh cells could regulate the B-cell response by releasing small extracellular vesicles (sEVs). Our results showed that Tfh cells promote B-cell differentiation and antibody production through sEVs and that CD40L plays a crucial role in Tfh-sEVs function. In addition, increased Tfh-sEVs were found in mice with collagen-induced arthritis (CIA). Adoptive transfer of Tfh cells significantly exacerbated the severity of CIA; however, the effect of Tfh cells on exacerbating the CIA process was significantly diminished after inhibiting sEVs secretion. Moreover, the levels of plasma Tfh-like-sEVs and CD40L expression on Tfh-like-sEVs in RA patients were significantly higher than those in healthy subjects. In summary, Tfh cell-derived sEVs can enhance the B-cell response, and exacerbate the procession of autoimmune arthritis.

Telitacicept for autoimmune nephropathy.

B cells and the humoral immunity are important players in the pathogenesis of autoimmune diseases. BAFF (also known as BLYS) and a proliferation-inducing ligand APRIL are required for the maintenance of the B-cell pool and humoral immunity. BAFF and APRIL can promote B-cell differentiation, maturation, and plasma cell antibody secretion. BAFF/APRIL overexpression has been identified in several autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, IgA nephropathy, etc. Telitacicept, a novel fully human TACI-Fc fusion protein that binds both BAFF and APRIL, was approved in China in March 2021 for the treatment of systemic lupus erythematosus at a recommended dose of 160 mg/w subcutaneously and is in clinical trials for the treatment of multiple indications in other autoimmune diseases. In this review, we explored telitacicept's mechanism of action and clinical data. In addition, the immune features of autoimmune nephropathy were discussed, emphasizing lupus nephritis, IgA nephropathy, and membranous nephropathy.

Aberrant expression of JMJD3 in SLE promotes B-cell differentiation

Systemic lupus erythematosus (SLE) is a typical autoimmune disease distinguished by multiple organ dysfunction, which is related to a variety of causative factors. B-cell overactivation is a key factor in SLE. However, the pathogenesis underlying anomalous B cells has not been well elucidated. B-cell fate is regulated in diverse epigenetic ways apart from traditional ways. As one of the mechanisms of epigenetics, histone modification mainly affects transcription and translation by changing the chemical groups on histones by histone modification enzymes. JMJD3, a histone demethylase, can promote T-cell proliferation in SLE patients, which exacerbates SLE. However, the mechanism of JMJD3 in B cells in SLE has not been studied. Here, we found that the mean fluorescence intensity (MFI) of JMJD3 in classical memory B cells (CMBs) was higher than that in naïve B cells (NBs) from human tonsil tissue; JMJD3 was overexpressed in B cells from the peripheral blood of SLE patients compared with healthy controls (HCs). In vitro, our experiment showed that JMJD3 could regulate B-cell differentiation by promoting naïve B-cell differentiation into CD27+ B cells, and Blimp-1 and Bcl-6 also decreased after inhibitor treatment. These findings provide a new direction for the pathogenesis of SLE and may supply a new idea for subsequent drug development.

AIM2 deficiency in B cells ameliorates systemic lupus erythematosus by regulating Blimp-1\u2013Bcl-6 axis-mediated B-cell differentiation

Absent in melanoma 2 (AIM2) has been reported to be a component of inflammasomes in innate immune cells. Surprisingly, AIM2 is expressed by B cells, and higher AIM2 expression is observed in the B cells from lupus patients. To date, the inflammasome-independent function of AIM2 in B cells remains unclear. Here, we report increased expression of AIM2 in human tonsil memory and germinal center (GC) B cells and in memory B cells and plasma cells from the circulation and skin lesions of lupus patients. Conditional knockout of AIM2 in B cells reduces the CD19+ B-cell frequency in lymph nodes and spleens, and dampens KLH-induced IgG1-antibody production. In a pristane-induced mouse model of lupus, AIM2 deficiency in B cells attenuates lupus symptoms and reduces the frequency of GC B cells, T follicular helper (Tfh) cells, plasmablast cells, and plasma cells. Furthermore, the loss of AIM2 in human B cells leads to the increased expression of Blimp-1 and reduces the expression of Bcl-6. However, the silencing of Blimp-1 and Bcl-6 has no significant effect on AIM2 expression, indicating that AIM2 might be the upstream regulator for Blimp-1 and Bcl-6. In addition, IL-10 is found to upregulate AIM2 expression via DNA demethylation. Together, our findings reveal that AIM2 is highly expressed in the B cells of lupus patients and promotes B-cell differentiation by modulating the Bcl-6–Blimp-1 axis, providing a novel target for SLE treatment.

Enhanced B-Cell Differentiation and Increased Production of Antibodies Targeting Surface Membrane Antigens in Patients with Chronic Graft-Versus-Host Disease

The mechanisms of chronic graft-versus-host disease (cGVHD) are complex and involve multiple elements of the immune system. Previous studies have indicated that donor B cells and the antibodies they produce play an important role in the development of cGVHD. T cells that facilitate B-cell differentiation, such as T Follicular Helper cells (Tfh), were also shown to exhibit enhanced function in patients with cGVHD. IL-21, a cytokine produced by Tfh cells plays an important role in the B-cell differentiation process. Activation of IL-21R expressed on B cells promotes B-cell differentiation into plasmablasts and plasma cells. To examine the responsiveness of B cells to this Tfh cytokine and antibody production in the setting of cGVHD, we analyzed B cells from 107 patients after allogeneic HSCT: 31 with no cGVHD, 44 with persistent stable cGVHD, and 22 patients with cGVHD receiving high-dose steroid therapy. Samples were collected from 9 months on after transplant. We also analyzed samples from 32 healthy donors as controls. The total CD19+CD20+ B-cell numbers in patients with stable cGVHD were comparable to those of healthy donors and slightly higher than normal in patients without cGVHD, suggesting normal recovery of B cells in these patients by the time the samples were collected. In patients with cGVHD, the number of IL-21R expressing B cells (CD19+CD20+IL21R+) was significantly increased compared to patients without cGVHD (p=0.046) or healthy donors (p=0.0036). The number of plasmablasts (CD19+CD20-CD38Hi) in patients with cGVHD was also significantly higher than in healthy donors (p=0.0079). Plasmablasts levels were higher in patients with cGVHD compared to those without cGVHD, but this difference was not statistically significant (p=0.3702). High-dose steroid therapy reduced both the number of IL-21R positive B cells and the number of plasmablasts, but neither reduction was statistically significant. We also examined IL-21 levels in plasma using multiplex cytokine bead arrays. Levels of circulating IL-21 were significantly higher in patients with cGVHD compared with healthy donors or patients without cGVHD. Increased levels of IL-21 and increased numbers of IL-21R+ B cells suggest that both homeostatic stimulation and inherent B-cell susceptibility promote B-cell differentiation in patients with cGVHD. Previous studies have shown that male transplant patients who received sex-mismatched grafts developed significantly higher levels of anti-H-Y IgG antibodies and the development of H-Y antibodies is highly correlated with development of cGVHD. To examine the impact of the observed enhanced B-cell differentiation on production of allo- and autoantibodies, we developed a fluorescent-linked immuno-assay to detect antibodies capable of targeting cell-surface proteins. Membrane protein extracts were prepared from a human skin fibroblast cell line (Detroit 551) and coated onto 96-well plates. Plasma samples from the above cohort of patients and healthy donors were incubated on the plate, and IgG antibodies reactive with plate-bound antigens were detected with fluorescence-conjugated anti-human IgG. Compared with patients who did not develop cGVHD and healthy donors, patients who developed cGVHD showed significantly higher levels of IgG reactive against cell-surface antigens (cGVHD vs HD, p=0.0124; cGVHD vs no GVHD, p=0.0027). High-dose steroid therapy significantly reduced the level of these antibodies (cGVHD vs cGVHD-T, p=0.0009). We also examined the presence of these antibodies at various times following HSCT. While patients who did not develop cGVHD had persistently low levels of these antibodies over a 3-year period, patients who developed cGVHD during this time had persistently high levels of these antibodies. These results indicate that in patients who developed cGVHD after transplant, B-cell differentiation and the production of antibodies that target living cells were enhanced. These data further support a role for B cells and antibodies in the development of cGVHD. Further characterization of the specificity of these antibodies will enhance our understanding of the role played by donor B cells in the development of cGVHD and provide new potential targets for therapy. Disclosures Koreth: prometheus labs inc: Research Funding; kadmon corp: Membership on an entity's Board of Directors or advisory committees; takeda pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; amgen inc: Consultancy; LLS: Research Funding; millennium pharmaceuticals: Research Funding. Armand:Roche: Research Funding; Pfizer: Research Funding; Infinity Pharmaceuticals: Consultancy; Sequenta Inc: Research Funding; Merck: Consultancy, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding. Soiffer:GentiumSpA/Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Ritz:Kiadis: Membership on an entity's Board of Directors or advisory committees.

Splenic TFH expansion participates in B-cell differentiation and antiplatelet-antibody production during immune thrombocytopenia

AbstractAntiplatelet-antibody-producing B cells play a key role in immune thrombocytopenia (ITP) pathogenesis; however, little is known about T-cell dysregulations that support B-cell differentiation. During the past decade, T follicular helper cells (TFHs) have been characterized as the main T-cell subset within secondary lymphoid organs that promotes B-cell differentiation leading to antibody class-switch recombination and secretion. Herein, we characterized TFHs within the spleen of 8 controls and 13 ITP patients. We show that human splenic TFHs are the main producers of interleukin (IL)-21, express CD40 ligand (CD154), and are located within the germinal center of secondary follicles. Compared with controls, splenic TFH frequency is higher in ITP patients and correlates with germinal center and plasma cell percentages that are also increased. In vitro, IL-21 stimulation combined with an anti-CD40 agonist antibody led to the differentiation of splenic B cells into plasma cells and to the secretion of antiplatelet antibodies in ITP patients. Overall, these results point out the involvement of TFH in ITP pathophysiology and the potential interest of IL-21 and CD40 as therapeutic targets in ITP.

IL‐21 promotes the production of anti‐DNA IgG but is dispensable for kidney damage in lyn−/− mice

The autoimmune disease systemic lupus erythematosus is characterized by loss of tolerance to nuclear Ags and a heightened inflammatory environment, which together result in end organ damage. Lyn-deficient mice, a model of systemic lupus erythematosus, lack an inhibitor of B-cell and myeloid cell activation. This results in B-cell hyper-responsiveness, plasma cell accumulation, autoantibodies, and glomerulonephritis (GN). IL-21 is associated with autoimmunity in mice and humans and promotes B-cell differentiation and class switching. Here, we explore the role of IL-21 in the autoimmune phenotypes of lyn(-/-) mice. We find that IL-21 mRNA is reduced in the spleens of lyn(-/-) IL-6(-/-) and lyn(-/-) Btk(lo) mice, neither of which produce pathogenic autoantibodies or develop significant GN. While IL-21 is dispensable for plasma cell accumulation and IgM autoantibodies in lyn(-/-) mice, it is required for anti-DNA IgG antibodies and some aspects of T-cell activation. Surprisingly, GN still develops in lyn(-/-) IL-21(-/-) mice. This likely results from the presence of IgG autoantibodies against a limited set of non-DNA Ags. These studies identify a specific role for IL-21 in the class switching of anti-DNA B cells and demonstrate that neither IL-21 nor anti-DNA IgG is required for kidney damage in lyn(-/-) mice.

Context-specific roles for paracrine IL-6 in lymphomagenesis

A basic requirement for the development of complex organ systems is that the cellular response to identical environmental cues can vary significantly between distinct cell types and developmental stages. While it is well established that paracrine signaling can similarly elicit diverse responses in distinct tumor types, the relevance of developmental stage-specific signaling responses to tumor development remains unclear. Here, we show that the same microenvironmental factor, IL-6, can both promote and prevent lymphoma development by acting on cells at distinct stages of hematopoietic development. Specifically, paracrine IL-6 signaling promotes the survival of transplanted hematopoietic stem cells following lethal irradiation, allowing for the persistence and expansion of progenitor cells bearing a cancer-promoting alteration. Conversely, IL-6 signaling also initiates a paracrine secretory program in the bone marrow that promotes B-cell differentiation and inhibits the development of B-cell malignancies. Thus, stage-specific responses to cytokines may promote progenitor cell expansion while also inhibiting neoplastic development within a single developmental lineage. Once transformed, the resulting B-cell lymphomas again use paracrine IL-6 signaling as a survival signal, highlighting the ability of tumor cells to co-opt pathways used for stem cell protection. These data not only suggest a complex regulation of tumor development by the preneoplastic microenvironment, but also that this regulation can decisively impact the outcome of well-established tumor modeling approaches.

Impact of interleukin-21 in the pathogenesis of primary Sjogren's syndrome: increased serum levels of interleukin-21 and its expression in the labial salivary glands

IntroductionInterleukin (IL)-21 is a cytokine that controls the functional activity of effector T helper cells and the differentiation of Th17 cells, and promotes B-cell differentiation. To test whether IL-21 participates in the pathogenesis of primary Sjögren's syndrome (SS), serum IL-21 level was measured and IL-21 expression in the labial salivary glands (LSG) was examined.MethodsSerum IL-21 levels in 40 primary SS, 40 rheumatoid arthritis (RA), and 38 systemic lupus erythematosus (SLE) patients and 20 healthy controls were measured. Serum IL-21 levels of SS patients were assessed for correlations with laboratory data, including anti-nuclear antibody, anti-Ro/La antibodies, globulin, immunoglobulin (Ig) class, and IgG subclass. LSGs from 16 primary SS and 4 controls with sicca symptoms were evaluated for IL-21 and IL-21 receptor (IL-21R) expression by immunohistochemistry. Confocal microscopy was performed to further characterize the IL-21 positive cells.ResultsPrimary SS patients had significantly higher serum IL-21 levels than controls, and these increments correlated positively with levels of IgG, IgG1. Serum IgG1 levels correlated with anti-Ro antibody titers. Immunohistochemical analyses showed that lymphocytic foci and the periductal area of the LSGs from SS patients expressed high levels of IL-21 and lower levels of IL-21R, whereas the control LSGs showed minimal expression of both antigens. The more the lymphocyte infiltrated, IL-21expression in LSGs showed a tendency to increase. Confocal microscopic analyses revealed that IL-21 expressing infiltrating lymphocytes in the LSGs of SS patients also expressed CXCR5.ConclusionsPrimary SS is associated with high serum IL-21 levels that correlate positively with serum IgG, especially IgG1, levels. The expression of IL-21 is increased as more lymphocytes infiltrated in LSGs. These observations suggest that IL-21 may play an important role in primary SS pathogenesis.

Purpura thrombopénique immunologique : étude rétrospective descriptive de 40 patients et réponse aux traitements

Antiplatelet-antibody-producing B cells play a key role in immune thrombocytopenia (ITP) pathogenesis; however, little is known about T-cell dysregulations that support B-cell differentiation. During the past decade, T follicular helper cells (TFHs) have been characterized as the main T-cell subset within secondary lymphoid organs that promotes B-cell differentiation leading to antibody class-switch recombination and secretion. Herein, we characterized TFHs within the spleen of 8 controls and 13 ITP patients. We show that human splenic TFHs are the main producers of interleukin (IL)-21, express CD40 ligand (CD154), and are located within the germinal center of secondary follicles. Compared with controls, splenic TFH frequency is higher in ITP patients and correlates with germinal center and plasma cell percentages that are also increased. In vitro, IL-21 stimulation combined with an anti-CD40 agonist antibody led to the differentiation of splenic B cells into plasma cells and to the secretion of antiplatelet antibodies in ITP patients. Overall, these results point out the involvement of TFH in ITP pathophysiology and the potential interest of IL-21 and CD40 as therapeutic targets in ITP.

B-cell activation in cats with feline infectious peritonitis (FIP) by FIP-virus-induced B-cell differentiation/survival factors

It has been suggested that antibody overproduction plays a role in the pathogenesis of feline infectious peritonitis (FIP). However, only a few studies on the B-cell activation mechanism after FIP virus (FIPV) infection have been reported. The present study shows that: (1) the ratio of peripheral blood sIg+ CD21− B-cells was higher in cats with FIP than in SPF cats, (2) the albumin-to-globulin ratio has negative correlation with the ratio of peripheral blood sIg+ CD21− B-cell, (3) cells strongly expressing mRNA of the plasma cell master gene, B-lymphocyte-induced maturation protein 1 (Blimp-1), were increased in peripheral blood in cats with FIP, (4) mRNA expression of B-cell differentiation/survival factors, IL-6, CD40 ligand, and B-cell-activating factor belonging to the tumor necrosis factor family (BAFF), was enhanced in macrophages in cats with FIP, and (5) mRNAs of these B-cell differentiation/survival factors were overexpressed in antibody-dependent enhancement (ADE)-induced macrophages. These data suggest that virus-infected macrophages overproduce B-cell differentiation/survival factors, and these factors act on B-cells and promote B-cell differentiation into plasma cells in FIPV-infected cats.

Identification Genetic Variations (GVs) Causing Splicing of TNF Family Members and Adaptor Proteins That Modulate NFkB Pathways in Waldenstrom's Maroglobulinemia (WM).

The TNF ligand-receptor superfamily and their adaptor proteins regulate important B-cell signaling pathways, including CD40L-CD40 and APRIL/BLYS-TACI through adaptor protein TRAF2. These pathways promote B-cell differentiation and immunoglobulin heavy chain class switching. Defects in immunoglobulin heavy chain class switching and presence of constitutive IgA and IgG hypogammaglobulinemia in patients with WM have previously been reported by us (Hunter et al, ASH2006). In WM patients we identified several novel splice variants of TNF-family members CD40 and BLYS, and their adaptor protein TRAF2. Cloning, sequencing and alignment analysis document that aberrant splice transcripts of CD40, CD40-Va, Vb and Vc, and BLYS, BLYS-Va and Vb, result from partial exon skipping (CD40Va and Vc) and entire or partial intron retention (CD40-Vb, BLYS-Va and Vb), while the TRAF2 variant is a result of exon skipping only. Using RT-PCR DNA fragment analysis, malignant and normal B-cells from the bone marrow of 25 WM patients and 6 healthy donors (HDs) were screened for the expression of CD40, BLYS and TRAF2 splice transcripts. This analysis identified overexpression of CD40-Vb (15/25WM vs. 0/6HD; P=0.01), CD40-Vc (21/25WM vs. 0/6HD; P=0.0003), BLYS-Vb (18/25WM vs. 0/6HD; P=0.002) and TRAF2-V (21/25WM vs. 1/6HD; P=0.004) in WM patients. The expression of other splice variants CD40-Va (18/25WM vs.2/4HD; P=0.09) and BLYS-Va (23/25WM vs. 4/6HD P=0.2) in the same group of WM patients were not significant. We hypothesized that these aberrations are consequences of genetic variations (GVs) distributed in the vicinity of splicing elements of these genes, as well as, alterations may have occurred in the repertoire of splicing factors (SFs) with respect of their expression levels. To address these issues, we started sequencing CD40, BLYS, and TRAF2 gene segments that are subjected to aberrant splicing. Sequencing analysis of the CD40 gene from WM B cells revealed 6 recurrent genetic variations (GVs-defined as mutations occurring more than one patients) that include 2 missense (on exon 3) and 3 silent substitutions (on exons 3-4-5), and 1 frame-shift deletion on exon 5. These substitutions lead to amino acid changes on CD40 gene, while the frame-shift deletion may cause truncation of wild-type CD40 protein. We also identified recurrent GVs on introns 4 and 5. All these GVs detected on exons and introns are distributed in the vicinity of key splicing elements that create and/or activate a new splice site in precisely the position required for the splicing events to create CD40 variants. Also, using TaqMan low density array (TaqMan-LDA) we evaluated levels of major SFs and other TNF family members involved in CD40 and BLYS signaling. These analyses showed that patients expressing aberrant splice variants of CD40 and BLYS overexpress not only other members of TNF family but also major SFs: SF2/ASF (a proto-oncogene), U2, hNRPA1 and SRP55. TaqMan-LDA analysis suggests that these SFs may play a significant role in CD40, BLYS and TRAF2 splicing in WM patients since these transcripts were upregulated (1.2-2.2 fold higher) only in those patients which expressed CD40, BLYS and TRAF2 variants. In conclusion, presence of GVs in the vicinity of splicing elements and upregulation of SFs collectively may promote aberrant CD40, BLYS and TRAF2 splicing and thus modulate TNF family pathways supportive of B-cell differentiation and immunoglobulin heavy chain class switching in patients with WM.

Transmembrane activator and calcium modulator and cyclophilin ligand interactor enhances CD40-driven plasma cell differentiation

Transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) is a receptor used by B cell-activating factor of the TNF family and a proliferation-inducing ligand (APRIL) to induce isotype switching independently of CD40 and is mutated in patients with common variable immunodeficiency. We sought to determine whether TACI and CD40 cooperate in inducing class switch recombination and immunoglobulin production. Naive mouse B cells were stimulated with suboptimal concentrations of anti-CD40 plus IL-4 in the presence or absence of APRIL or anti-TACI. IgG(1) and IgE production was measured by means of ELISA. mRNA for Cgamma(1) and Cepsilon germ-line transcripts, activation-induced cytidine deaminase, and mature gamma(1) and epsilon transcripts were measured by means of RT-PCR. Plasmablasts were enumerated by using syndecan-1/CD138 staining. Interferon regulatory factor 4, B lymphocyte-induced maturation protein 1, and IL6 mRNA expression was measured by using quantitative PCR. TACI ligation enhanced IgG(1) and IgE secretion by naive murine B cells stimulated by anti-CD40 plus IL-4, with little effect on B-cell proliferation or class switch recombination. In contrast, TACI ligation of anti-CD40 plus IL-4-stimulated B cells induced a significant increase in syndecans-1/CD138-positive cells. TACI ligation caused a modest but significant increase in the expression of interferon regulatory factor 4, with no detectable change in B lymphocyte-induced maturation protein 1 expression. TACI and CD40 signaling converge to promote B-cell differentiation into plasmablasts. Our data suggest that TACI dysfunction could contribute to the impaired antibody response to T-dependent antigens in common variable immunodeficiency.

Multidirectional interactions are bridging human NK cells with plasmacytoid and monocyte-derived dendritic cells during innate immune responses

AbstractDuring innate immune responses, natural killer (NK) cells may interact with both plasmacytoid dendritic cells (pDCs) and monocyte-derived dendritic cells (MDDCs). We show that freshly isolated NK cells promote the release by pDCs of IFN-α, in a CpG-dependent manner, whereas they induce IL-6 production in a CpG-independent manner. In turn pDC-derived IFN-α up-regulates NK-mediated killing, whereas IL-6 could promote B-cell differentiation. We also show that exposure to exogenous IL-12 or coculture with maturing MDDCs up-regulates the NK-cell–dependent IFN-α production by pDCs. On the other hand, NK cells cocultured with pDCs acquire the ability to kill immature MDDCs, thus favoring their editing process. Finally, we show that activated NK cells are unable to lyse pDCs because these cells display an intrinsic resistance to lysis. The exposure of pDCs to IL-3 increased their susceptibility to NK-cell cytotoxicity resulting from a de novo expression of ligands for activating NK-cell receptors, such as the DNAM-1 ligand nectin-2. Thus, different cell-to-cell interactions and various cytokines appear to control a multidirectional network between NK cells, MDDCs, and pDCs that is likely to play an important role during the early phase of innate immune responses to viral infections and to tumors.

MicroRNAs as regulators of mammalian hematopoiesis

MicroRNAs (miRNAs) are an abundant class of ∼22 nucleotide non-coding RNAs and play important regulatory roles in animal and plant development at the post-transcriptional level. Many miRNAs cloned from mouse bone marrow cells are differentially regulated in various hematopoietic lineages, suggesting that they might influence hematopoietic lineage differentiation. miR-181, a miRNA specifically expressed in B cells within mouse bone marrow, promotes B-cell differentiation when expressed in hematopoietic stem/progenitor cells. Some human miRNAs are linked to leukemias: the miR-15a/miR-16 locus is frequently deleted or down-regulated in patients with B-cell chronic lymphocytic leukemia and miR-142 is at a translocation site found in a case of aggressive B-cell leukemia. Collectively, these results indicate that miRNAs may be important regulators of mammalian hematopoiesis. Here, we provide background on the biogenesis and function of miRNAs and discuss how miRNA-mediated post-transcriptional regulation may influence the development and function of blood cells.

Plasmacytoid dendritic cells, antigen, and CpG-C license human B cells for plasma cell differentiation and immunoglobulin production in the absence of T-cell help

AbstractIt has been reported that interferon α (IFN-α) enhances humoral immunity and that dendritic cells of the myeloid lineage promote B-cell differentiation. Here we studied whether the plasmacytoid dendritic cell (PDC), a subset of dendritic cells specialized for the production of IFN-α, is involved in regulating B-cell differentiation and immunoglobulin production. The recently identified class of CpG oligonucleotides (CpG-C) was used to activate both B cells and PDCs via Toll-like receptor 9 (TLR9). The presence of PDCs synergistically enhanced CD86 expression, cytokine production (interleukin 6 [IL-6], tumor necrosis factor α, and IL-10) and plasma cell differentiation of isolated human peripheral blood B cells stimulated through CpG-C and B-cell antigen receptor (BCR) ligation. This stimulation protocol was sufficient to drive purified naive B cells into IgM-producing plasma cells and to trigger IgG synthesis in memory B cells. PDCs contributed to B-cell activation via IFN-α secretion. Up-regulation of TLR9 on B cells was not involved. These results demonstrate that CpG-stimulated PDCs induce plasma cell differentiation in naive and memory B cells in the absence of T-cell help, providing an explanation for the excellent activity of CpG oligonucleotides as a humoral vaccine adjuvant. (Blood. 2004;103:3058-3064)

PPAR‐γ‐Mediated Regulation of Normal and Malignant B Lineage Cells

Prostaglandins of the E-series stimulate B lymphocytes by enhancing immunoglobulin-class switching and antibody production. Little is known about whether or not other prostaglandins affect B lineage cells and perhaps counterbalance the stimulatory effects of PGE2. PGD2 is a major product of cyclooxygenase in bone marrow and in macrophages, suggesting a role for this lipid product in immunological responses. PGD2 undergoes dehydration to the biologically active prostaglandin 15-deoxy-delta 12,14-PGJ2 (15d-PGJ2) that binds to the nuclear receptor known as peroxisome proliferator-activated receptor gamma (PPAR-gamma). We found that normal mouse B cells and a variety of B lymphoma cells (e.g., 70Z/3, WEHI-231, CH12, and J558) express PPAR-gamma mRNA and the 67-kDa PPAR-gamma protein. 15d-PGJ2 had a dose-dependent antiproliferative/cytotoxic effect on normal and malignant B cells, as shown by 3H-thymidine and MTT assays. Only PPAR-gamma agonists (i.e., thiazolidinediones) mimicked the effect of 15d-PGJ2 on B lineage cells, indicating that the mechanism by which 15d-PGJ2 negatively affects B lineage cells involves PPAR-gamma. The mechanism whereby PPAR-gamma agonists induced cytotoxicity is via apoptosis, as shown by Annexin V assay. PPAR-gamma agonists may serve as a counterbalance to the stimulating effects of PGE2, which promotes B-cell differentiation. The use of prostaglandins, such as 15d-PGJ2, and synthetic PPAR-gamma agonists to induce apoptosis in B lineage cells may lead to the development of therapies for fatal PGE2-resistant B lymphomas.

Interleukin 2-dependent and interleukin 2-independent pathways of regulation of thymocyte function by interleukin 6.

Recombinant human interleukin 6 (IL-6), also termed B-cell-stimulatory factor 2 (BSF-2) or interferon-beta 2, was found to stimulate the proliferation of mouse thymocytes costimulated with phytohemagglutinin (PHA). In addition, IL-6 synergistically enhanced the stimulation of thymocyte proliferation by recombinant human interleukin 1 (IL-1) or interleukin 2 (IL-2). Mature thymocytes lacking peanut agglutinin receptor are the main target of IL-6 action. Incubation of thymocytes with IL-6 in the presence of PHA resulted in an increased expression of the IL-2 receptor (IL-2R) as demonstrated by flow cytometry. Monoclonal antibody specific for the p55 chain of the murine IL-2R significantly reduced IL-6-stimulated thymocyte proliferation in the presence of the optimal concentration of PHA. However, the same monoclonal antibody failed to reduce IL-6-driven thymocyte proliferation in the presence of a suboptimal PHA concentration, suggesting that IL-6 stimulates thymocyte proliferation by way of IL-2-dependent and IL-2-independent pathways. These results indicate that, in addition to its earlier demonstrated ability to promote B-cell differentiation and growth, IL-6 also acts as a growth regulator in cells of the T-lymphocyte lineage. IL-6 is emerging as an important regulatory cytokine with multiple actions on immune functions.

T-cell factors that promote B-cell proliferation and differentiation.

The goal of this chapter is to summarize and discuss the studies that have sought to understand just how helper T cells help B cells to proliferate and differeniate into antibody-secreting cells by the production of T-cell factors. The studies of Mitchison and others (Mitchison, 1969) showed that effective T-cell help was only delivered to B cells when both T cell and B cell recognized determinants on the same antigen molecule. This observation led to the hypothesis that T-cell help was delivered via an obligatory cell-cell interaction, and it was later shown that such interactions were major histocompatibility complex (MHC) restricted. Our own studies (Dutton et al, 1971) and those of others (Schimpl and Wecker, 1972) showed that in certain experimental models T cells could be replaced by factors contained in culture supernatants of activated T cells. For awhile, there were those who suggested that the latter mechanism represented a special case seen only with erythrocyte antigens or with previously activated B cell. It is now clear that both mechanisms of T-cell help exist. It is thought that some B cells become activated only via direct cell-cell interaction and that others can be affected directly by T-cell factors (Singer et al., 1982). It has been shown that a major fraction of all resting B cells can be driven through activation, proliferation, and differentiation to immunoglobulin secretion solely with the aid of the appropriate soluble agents—antiimmunoglobulin and T-cell culture supernatants (Howard and Paul, 1983). All B cells can be made to respond to the B-cell mitogens, dextran sulfate, and lipopolysaccharide (LPS), in the presence of macrophage-derived factors (Wetzel and Kettman, 1981).

Humoral Helper Activity for B-Cell Differentiation Released From Non-Hodgkin’s Lymphoma Cells Having Both SRBC and Complement Receptors in the Pokeweed Mitogen System

AbstractThe majority of lymphoid cells from a patient with non-Hodgkin’s lymphoma with leukemic transformation were demonstrated to carry receptors for both sheep erythrocytes and complements by the combined rosette assay using neuraminidase-treated sheep erythrocytes and complement-coated zymosan beads. Most of them were considered morphologically lymphoblasts and were positive for acid phosphatase staining. Terminal deoxynucleotidyl transferase activity was not detected in these cells. Lymphoid cells from this patient did not respond to the stimulation with phytohemagglutinin-P, concanavalin-A, and pokeweed mitogen (PWM). When these cells were cultured with PWM for 7 days, no plasma cell was generated. Although only few plasma cells were generated in the PWM-stimulated culture of normal purified B cells alone, the addition of the patient’s cells to purified normal B cells resulted in a markedly enhanced generation of plasma cells in response to PWM, as was the case with normal T cells. But leukemic cells either from a patient with T-cell leukemia not having complement receptors or from a patient with null-cell leukemia showed no enhancing ability in B-cell differentiation. In addition, the culture supernates of the patient’s cells obtained after 24-hr PWM stimulation had an ability to promote B-cell differentiation comparable in activity to those from the PWM-stimulated normal T cells.