High IgE secretion capacity of human plasma cells

A defined clathrin-mediated trafficking pathway regulates sFLT1/VEGFR1 secretion from endothelial cells

FLT1/VEGFR1 negatively regulates VEGF-A signaling and is required for proper vessel morphogenesis during vascular development and vessel homeostasis. Although a soluble isoform, sFLT1, is often mis-regulated in disease and aging, how sFLT1 is trafficked and secreted from endothelial cells is not well understood. Here we define requirements for constitutive sFLT1 trafficking and secretion in endothelial cells from the Golgi to the plasma membrane, and we show that sFLT1 secretion requires clathrin at or near the Golgi. Perturbations that affect sFLT1 trafficking blunted endothelial cell secretion and promoted intracellular mis-localization in cells and zebrafish embryos. siRNA-mediated depletion of specific trafficking components revealed requirements for RAB27A, VAMP3, and STX3 for post-Golgi vesicle trafficking and sFLT1 secretion, while STX6, ARF1, and AP1 were required at the Golgi. Live-imaging of temporally controlled sFLT1 release from the endoplasmic reticulum showed clathrin-dependent sFLT1 trafficking at the Golgi into secretory vesicles that then trafficked to the plasma membrane. Depletion of STX6 altered vessel sprouting in 3D, suggesting that endothelial cell sFLT1 secretion influences proper vessel sprouting. Thus, specific trafficking components provide a secretory path from the Golgi to the plasma membrane for sFLT1 in endothelial cells that utilizes a specialized clathrin-dependent intermediate, suggesting novel therapeutic targets.

A defined clathrin-mediated trafficking pathway regulates sFLT1/VEGFR1 secretion from endothelial cells

FLT1/VEGFR1 negatively regulates VEGF-A signaling and is required for proper vessel morphogenesis during vascular development and vessel homeostasis. Although a soluble isoform, sFLT1, is often mis-regulated in disease and aging, how sFLT1 is trafficked and secreted from endothelial cells is not well understood. Here we define requirements for constitutive sFLT1 trafficking and secretion in endothelial cells from the Golgi to the plasma membrane, and we show that sFLT1 secretion requires clathrin at or near the Golgi. Perturbations that affect sFLT1 trafficking blunted endothelial cell secretion and promoted intracellular mis-localization in cells and zebrafish embryos. siRNA-mediated depletion of specific trafficking components revealed requirements for RAB27A, VAMP3, and STX3 for post-Golgi vesicle trafficking and sFLT1 secretion, while STX6, ARF1, and AP1 were required at the Golgi. Depletion of STX6 altered vessel sprouting in a 3D angiogenesis model, indicating that endothelial cell sFLT1 secretion is important for proper vessel sprouting. Thus, specific trafficking components provide a secretory path from the Golgi to the plasma membrane for sFLT1 in endothelial cells that utilizes a specialized clathrin-dependent intermediate, suggesting novel therapeutic targets.

Effect of IL-15 on IgG versus IgE antibody-secreting cells in vitro

Immunoglobulin E (IgE) antibodies are major contributors to the pathology of atopic and allergic diseases as well as to immune response to helminth infections. Development of an adequate immunoglobulin G (IgG) immune response against infectious agents and vaccine antigens is considered in most cases as crucial for protection from disease. In vivo and in vitro production of IgE and IgG depends on cytokines and other soluble factors. Recently it has been shown that IgG antibody secreting cells (ASCs) can be generated by in vitro maturation of blood cells with Interleukin- (IL-)15 and CpG DNA or other stimulation cocktails, while IgE-ASCs develop upon cultivation with anti-CD40 and IL-4. In the present study we employed an enzyme linked immunospot assay (ELISPOT) to assess the capacity of individuals to develop into either IgE-ASCs or IgG-ASCs upon stimulation with different combinations of stimulation cocktails in order to investigate the influence of cytokines that are dysregulated in IgE-mediated immune reactions on ASC generation. Furthermore, we modified the method to assess IgG- and IgE-ASCs specific for two model antigens causing allergic rhinitis in humans. We demonstrate that IL-15, which is important for development of IgG-ASCs, decreases the number of IgE-ASCs when added to media commonly used for in vitro development of IgE-ASCs. We show that our method is suitable for the detection of specific and non-specific IgE-ASCs and IgG-ASCs and allows the investigation of the interplay between IgG-ASCs and IgE-ASCs in different populations.

The third dimension of ELISPOTs: quantifying antibody secretion from individual plasma cells

The enzyme-linked immunospot assay (ELISPOT) is a technique widely used to enumerate the number of immune cells secreting a specific protein, such as antibodies or cytokines. A limitation with the ELISPOT assay is that it can only be used to detect a single protein of interest. Recently, the ELISPOT technique has been modified to use fluorophores allowing multiple secreted proteins to be detected simultaneously. This technique has greatly enhanced the ability to identify cells secreting multiple proteins, but has not been used to its fullest potential. We wished to accurately quantify the expression of antigen-specific antibody from a single plasma cell and to determine whether plasma cells recovered from different locations had different secretion rates. To achieve this we analyzed fluorospot images quantitatively using Mira MX 7 UL Astronomy software, and coupled this data with a quantitative ELISA to determine secretion rates from individual cells. Using this technique we were able to determine that plasma cells recovered from the peripheral blood secreted the most antibody (1.667 ng/cell/12 h) while splenic antibody secreting cells the least (0.399 ng/cell/12 h). We were able to quantify a 150 fold difference in antibody secretion between cells, with most plasma cells divided into two groups, low secretors (<0.1 ng/cell) or high secretors (>2 ng/cell). We believe this technique will be particularly useful for examining the secretion ratio of two proteins secreted from an individual cell, allowing us to determine if secretion is fixed or variable.

Migration of antibody secreting cells towards CXCL12 depends on the isotype that forms the BCR

Truncation of the cytoplasmic tail of membrane-bound IgE in vivo results in lower serum IgE levels, decreased numbers of IgE-secreting plasma cells and the abrogation of specific secondary immune responses. Here we present mouse strain KN1 that expresses a chimeric epsilon-gamma1 BCR, consisting of the extracellular domains of the epsilon gene and the transmembrane and cytoplasmic domains of the gamma1 gene. Thus, differences in the IgE immune response of KN1 mice reflect the influence of the "gamma1-mediated signalling" of mIgE bearing B cells. KN1 mice show an increased serum IgE level, resulting from an elevated number of IgE-secreting cells. Although the primary IgE immune response in KN1 mice is inconspicuous, the secondary response is far more robust. Most strikingly, IgE-antibody secreting cells with "gamma1-signalling history" migrate more efficiently towards the chemokine CXCL12, which guides plasmablasts to plasma cell niches, than IgE-antibody secreting cells with WT "epsilon-signalling history". We conclude that IgE plasmablasts have an intrinsic, lower chance to contribute to the long-lived plasma cell pool than IgG1 plasmablasts.

Hydrocortisone enhances allergen-specific IgE production by peripheral blood mononuclear cells from atopic patients with high serum allergen-specific IgE levels

BACKGROUND

Although there is convincing evidence that human B cells can be induced to produce IgE by a combination of interleukin 4 (IL-4) and hydrocortisone (HC) in atopic subjects, it is still uncertain if this performs the same functions in allergen-specific IgE synthesis.

OBJECTIVE

This study was designed to investigate the differences of IgE regulation between atopics and nonatopics, interactions of HC with IL-4, and the correlation between in vitro total IgE, allergen-specific IgE synthesis and serum IgE levels.

METHODS

Peripheral blood mononuclear cells (PBMCs) from 16 atopic asthma patients sensitive to Dermatophagoides farinae and seven nonatopic controls were cultured with IL-4 and/or HC. Total IgE and D. farinae-specific IgE in culture supernatant were measured by ELISA and FAST.

RESULTS

IL-4 increased total IgE synthesis in PBMCs from both atopics and nonatopics, whereas, HC had this effect only in some atopics who showed spontaneous IgE production in vitro. HC acted synergistically with IL-4 in total IgE synthesis. Their effects were more remarkable in cases with lower total serum IgE levels. PBMCs from eight of 16 atopics produced D. farinae-specific IgE in vitro either spontaneously or by IL-4 and/or HC. HC had more profound effects than IL-4 in these patients. They also showed higher total IgE synthesis by HC, and higher specific serum IgE levels than the others. IL-4 and/or HC did not induce any D. farinae-specific IgE synthesis by PBMCs from nonatopics.

CONCLUSION

HC had a more profound effect than IL-4 on the induction of D. farinae-specific IgE synthesis in atopic patients with high serum allergen specific IgE levels. Further studies to determine the causes of these effects, such as the presence of long lived allergen specific B cells as the result of the priming effect of IL-4 in vivo, may be needed.

Serum interleukin-10 in plasma-cell dyscrasias

Serum levels of interleukin-10 (IL-10) were measured by enzyme-linked immunosorbent assay in 115 patients with multiple myeloma (MM) in various phases of the disease (68 at diagnosis, 22 in plateau phase, 22 in relapse), in 71 individuals with monoclonal gammopathy of undetermined significance (MGUS), and in 53 normal volunteers. Detectable levels of serum IL-10 were found in 24 myelomas (20.9%), in 7 cases of MGUS (9.9%), and in 4 normal subjects (7.5%) (P = NS, chi2 test). In patients with MM, cytokine was detected with a comparable frequency in all pathologic stages and phases of the disease: 4/19 in stage I, 6/26 in stage II, 5/23 in stage III, 4/22 in plateau phase, and 5/25 in progressing or relapsed disease. IL-10 concentrations did not differ significantly between controls and patients with plasma-cell dyscrasia, between patients with MGUS and those with MM, between early vs. advanced MM, or between patients in different phases of the disease. In 36 patients with MM in whom IL-10 was measured serially, no significant changes were observed over the course of the disease. Also, when comparing the outcomes of individuals with detectable or undetectable IL-10 in single stages or in the whole myeloma group, no differences were revealed. Our results do not support an apparent involvement of IL-10 in the pathogenesis of MM in vivo. However, further studies are required to define the exact role of this cytokine within the complex cytokine network of this neoplastic disorder.

Cytokine expression and regulation of human plasma cells: disappearance of interleukin-10 and persistence of transforming growth factor-beta 1

Less is known about the cytokine expression and regulation of normal plasma cells compared to that of activated B cells or myeloma cells. This study shows that nonproliferating (hydroxyurea-treated), immunoglobulin (Ig)-secreting cells generated from human B cells in the EL-4 culture system no longer express interleukin (IL)-6 mRNA, progressively lose IL-10 mRNA, but continue to express transforming growth factor (TGF)-beta 1 mRNA. Secretion of TGF-beta 1 protein was demonstrated. On the other hand, and in contrast to the suppression of B cell proliferation and Ig secretion, the basal or the IL-6/IL-10 stimulated Ig secretion of nonproliferating cells was not inhibited by recombinant TGF-beta 1. Plasma cells isolated from human bone marrow expressed neither IL-6 nor IL-10 mRNA; only TGF-beta 1 mRNA was detected by reverse transcription-polymerase chain reaction analysis. Such plasma cells may be on average more "aged" cells than those generated in vitro. Thus, plasma cells persistently express TGF-beta 1, a known suppressor of various lymphoid and hemopoietic cell activities, but do not limit their own Ig secretion via this cytokine.