NGFR regulates stromal cell activation in germinal centers

Nerve growth factor receptor (NGFR) is expressed by follicular dendritic cells (FDCs). However, the role of NGFR in the humoral response is not well defined. Here, we study the effect of Ngfr loss on lymph node organization and function, demonstrating that Ngfr depletion leads to spontaneous germinal center (GC) formation and an expansion of the GC B cell compartment. In accordance with this effect, stromal cells are altered in Ngfr-/- mice with a higher frequency of FDCs, characterized by CD21/35, MAdCAM-1, and VCAM-1 overexpression. GCs are located ectopically in Ngfr-/- mice, with lost polarization together with impaired high-affinity antibody production and an increase in circulating autoantibodies. We observe higher levels of autoantibodies in Bcl2 Tg/Ngfr-/- mice, concomitant with a higher incidence of autoimmunity and lower overall survival. Our work shows that NGFR is involved in maintaining GC structure and function, participating in GC activation, antibody production, and immune tolerance.

CD95L concatemers highlight different stoichiometries of CD95-mediated apoptotic and nonapoptotic pathways

To better understand the stoichiometry of CD95L required to trigger apoptotic and nonapoptotic signals, we generated several CD95L concatemers from dimer to hexamer conjugated via a flexible link (GGGGS)2 . These ligands reveal that although the hexameric structure is the best stoichiometry to trigger cell death, a dimer is sufficient to induce the apoptotic response in CD95-sensitive Jurkat cells. Interestingly, only trimeric and hexameric forms can implement a potent Ca2+ response, suggesting that while CD95 aggregation controls the implementation of the apoptotic signal, both aggregation and conformation are required to implement the Ca2+ pathway.

Attempts to evaluate locus suicide recombination and its potential role in B cell negative selection in the mouse

Introduction

In mature B cells, activation-induced deaminase reshapes Ig genes through somatic hypermutation and class switch recombination of the Ig heavy chain (IgH) locus under control of its 3' cis-regulatory region (3'RR). The 3'RR is itself transcribed and can undergo "locus suicide recombination" (LSR), then deleting the constant gene cluster and terminating IgH expression. The relative contribution of LSR to B cell negative selection remains to be determined.

Methods

Here, we set up a knock-in mouse reporter model for LSR events with the aim to get clearer insights into the circumstances triggering LSR. In order to explore the consequences of LSR defects, we reciprocally explored the presence of autoantibodies in various mutant mouse lines in which LSR was perturbed by the lack of Sµ or of the 3'RR.

Results

Evaluation of LSR events in a dedicated reporter mouse model showed their occurrence in various conditions of B cell activation, notably in antigen-experienced B cells Studies of mice with LSR defects evidenced increased amounts of self-reactive antibodies.

Discussion

While the activation pathways associated with LSR are diverse, in vivo as well as in vitro, this study suggests that LSR may contribute to the elimination of self-reactive B cells.

Distinct B-Cell Specific Transcriptional Contexts of the BCL2 Oncogene Impact Pre-Malignant Development in Mouse Models

Simple Summary

Beyond the classical t(14;18) translocation associated with follicular lymphoma, BCL2 is deregulated in multiple B-cell malignancies, including some cases of myeloma, and through diverse genetic anomalies. It is currently unclear how the various deregulation patterns mechanistically impact the phenotype of theses malignancies. We designed two different BCL2 deregulation models in transgenic mice, whereby the oncogene was either associated with the IgH3′RR superenhancer, as in t(14;18), or inserted into the kappa light chain locus. We compared the impact of these models on B-cell fate and lymphoid tissues. Linkage to the IgH superenhancer showed a quite specific impact on germinal center B cell populations. The Ig kappa model was much less specific and strongly boosted the plasma cell in-flow and the accumulation of long-lived plasma cells.

Abstract

Upregulated expression of the anti-apoptotic BCL2 oncogene is a common feature of various types of B-cell malignancies, from lymphoma to leukemia or myeloma. It is currently unclear how the various patterns of deregulation observed in pathology eventually impact the phenotype of malignant B cells and their microenvironment. Follicular lymphoma (FL) is the most common non-Hodgkin lymphoma arising from malignant germinal center (GC) B-cells, and its major hallmark is the t(14:18) translocation occurring in B cell progenitors and placing the BCL2 gene under the control of the immunoglobulin heavy chain locus regulatory region (IgH 3′RR), thus exposing it to constitutive expression and hypermutation. Translocation of BCL2 onto Ig light chain genes, BCL2 gene amplification, and other mechanisms yielding BCL2 over-expression are, in contrast, rare in FL and rather promote other types of B-cell lymphoma, leukemia, or multiple myeloma. In order to assess the impact of distinct BCL2 deregulation patterns on B-cell fate, two mouse models were designed that associated BCL2 and its full P1-P2 promoter region to either the IgH 3′RR, within a “3′RR-BCL2” transgene mimicking the situation seen in FL, or an Ig light chain locus context, through knock-in insertion at the Igκ locus (“Igκ-BCL2” model). While linkage to the IgH 3′ RR mostly yielded expression in GC B-cells, the Igκ-driven up-regulation culminated in plasmablasts and plasma cells, boosting the plasma cell in-flow and the accumulation of long-lived plasma cells. These data demonstrate that the timing and level of BCL2 deregulation are crucial for the behavior of B cells inside GC, an observation that could strongly impact the lymphomagenesis process triggered by secondary genetic hits.

Targeting IgE polyadenylation signal with antisense oligonucleotides decreases IgE secretion and plasma cell viability

BACKGROUND

Allergy regroups numerous complex and various diseases classified as IgE-dependent or non-IgE-dependent hypersensitivities. IgEs are expressed as membrane and secreted forms by B cells and plasma cells, respectively. In IgE-mediated hypersensitivity, IgE secretion and binding to the high-affinity IgE receptor FcεRI on effector cells are responsible for the onset of allergic symptoms; in contrast, surface IgE expression as a B-cell receptor is barely detectable.

OBJECTIVE

Our aim was to test an innovative antisense approach to reducing IgE secretion.

METHODS

We designed an antisense oligonucleotide (ASO) targeting the polyadenylation signal of human secreted IgE to redirect IgE transcript polyadenylation from the secreted form to the membrane form. ASO treatments were performed on B cells from transgenic mice expressing humanized IgE (InEps mice), as well as on human primary B cells and myeloma cells. In vivo ASO delivery was tested by using an InEps mouse model.

RESULTS

We demonstrated that treatment with a morpholino ASO targeting the secreted IgE polyadenylation signal drastically decreased IgE secretion and inversely increased membrane IgE mRNA expression. In addition, ASO treatment induced apoptosis of IgE-expressing U266 myeloma cells, and RNA sequencing revealed attenuation of their plasma cell phenotype. Remarkably, systemic administration of an ASO coupled with Pip6a as an arginine-rich cell-penetrating peptide decreased IgE secretion in vivo.

CONCLUSION

Altogether, this ASO strategy could be an effective way to decrease IgE secretion and allergic symptoms in patients with IgE-dependent allergies, and it could also promote allergen tolerance through apoptosis of IgE⁺ antibody-secreting cells.

Continuous MYD88 Activation Is Associated With Expansion and Then Transformation of IgM Differentiating Plasma Cells

Activating mutations of MYD88 (MYD88^L265P being the far most frequent) are found in most cases of Waldenström macroglobulinemia (WM) as well as in various aggressive B-cell lymphoma entities with features of plasma cell (PC) differentiation, such as activated B-cell type diffuse large B-cell lymphoma (DLBCL). To understand how MYD88 activation exerts its transformation potential, we developed a new mouse model in which the MYD88^L252P protein, the murine ortholog of human MYD88^L265P, is continuously expressed in CD19 positive B-cells together with the Yellow Fluorescent Protein (Myd88^L252P mice). In bone marrow, IgM B and plasma cells were expanded with a CD138 expression continuum from IgM^high CD138^low to IgM^low CD138^high cells and the progressive loss of the B220 marker. Serum protein electrophoresis (SPE) longitudinal analysis of 40 Myd88^L252P mice (16 to 56 weeks old) demonstrated that ageing was first associated with serum polyclonal hyper gammaglobulinemia (hyper Ig) and followed by a monoclonal immunoglobulin (Ig) peak related to a progressive increase in IgM serum levels. All Myd88^L252P mice exhibited spleen enlargement which was directly correlated with the SPE profile and was maximal for monoclonal Ig peaks. Myd88^L252P mice exhibited very early increased IgM PC differentiation. Most likely due to an early increase in the Ki67 proliferation index, IgM lymphoplasmacytic (LP) and plasma cells continuously expanded with age being first associated with hyper Ig and then with monoclonal Ig peak. This peak was consistently associated with a spleen LP-like B-cell lymphoma. Clonal expression of both membrane and secreted µ chain isoforms was demonstrated at the mRNA level by high throughput sequencing. The Myd88^L252P tumor transcriptomic signature identified both proliferation and canonical NF-κB p65/RelA activation. Comparison with MYD88^L265P WM showed that Myd88^L252P tumors also shared the typical lymphoplasmacytic transcriptomic signature of WM bone marrow purified tumor B-cells. Altogether these results demonstrate for the first time that continuous MYD88 activation is specifically associated with clonal transformation of differentiating IgM B-cells. Since MYD88^L252P targets the IgM PC differentiation continuum, it provides an interesting preclinical model for development of new therapeutic approaches to both WM and aggressive MYD88 associated DLBCLs.

Mesangial Deposition Can Strongly Involve Innate-Like IgA Molecules Lacking Affinity Maturation

BACKGROUND

IgA nephropathy (IgAN) often follows infections and features IgA mesangial deposition. Polymeric IgA deposits in the mesangium seem to have varied pathogenic potential, but understanding their pathogenicity remains a challenge. Most mesangial IgA1 in human IgAN has a hypogalactosylated hinge region, but it is unclear whether this is required for IgA deposition. Another important question is the role of adaptive IgA responses and high-affinity mature IgA antibodies and whether low-affinity IgA produced by innate-like B cells might also yield mesangial deposits.

METHODS

To explore the effects of specific qualitative variations in IgA and whether altered affinity maturation can influence IgA mesangial deposition and activate complement, we used several transgenic human IgA1-producing models with IgA deposition, including one lacking the DNA-editing enzyme activation-induced cytidine deaminase (AID), which is required in affinity maturation. Also, to explore the potential role of the IgA receptor CD89 in glomerular inflammation, we used a model that expresses CD89 in a pattern observed in humans.

RESULTS

We found that human IgA induced glomerular damage independent of CD89. When comparing mice able to produce high-affinity IgA antibodies with mice lacking AID-enabled Ig affinity maturation, we found that IgA deposition and complement activation significantly increased and led to IgAN pathogenesis, although without significant proteinuria or hematuria. We also observed that hinge hypoglycosylation was not mandatory for IgA deposition.

CONCLUSIONS

In a mouse model of IgAN, compared with high-affinity IgA, low-affinity innate-like IgA, formed in the absence of normal antigen-driven maturation, was more readily involved in IgA glomerular deposition with pathogenic effects.

The IgH 3' regulatory region governs μ chain transcription in mature B lymphocytes and the B cell fate

We report that the IgH 3' regulatory region (3'RR) has no role on μ chain transcription and pre-BCR expression in B cell progenitors. In contrast, analysis of heterozygous IgH aΔ3'RR/bwt mice indicated that the 3'RR controls μ chain transcripts in mature splenocytes and impacts membrane IgM density without obvious effect on BCR signals (colocalisation with lipid rafts and phosphorylation of Erk and Akt after BCR crosslinking). Deletion of the 3'RR modulates the B cell fate to less marginal zone B cells. In conclusion, the 3'RR is dispensable for pre-BCR expression and necessary for optimal commitments toward the marginal zone B cell fate. These results reinforce the concept of a dual regulation of the IgH locus transcription and accessibility by 5' elements at immature B cell stages, and by the 3'RR as early as the resting mature B cell stage and then along further activation and differentiation.

IgA Structure Variations Associate with Immune Stimulations and IgA Mesangial Deposition

IgA1 mesangial deposition is the hallmark of IgA nephropathy and Henoch-Schönlein purpura, the onset of which often follows infections. Deposited IgA has been reported as polymeric, J chain associated, and often, hypogalactosylated but with no information concerning the influence of the IgA repertoire or the link between immune stimuli and IgA structure. We explored these issues in the α1KI mouse model, which produces polyclonal human IgA1 prone to mesangial deposition. Compared with mice challenged by a conventional environment, mice in a specific pathogen-free environment had less IgA deposition. However, serum IgA of specific pathogen-free mice showed more galactosylation and much lower polymerization. Notably, wild-type, α1KI, and even J chain-deficient mice showed increased polymeric serum IgA on exposure to pathogens. Strict germfree conditions delayed but did not completely prevent deposition; mice housed in these conditions had very low serum IgA levels and produced essentially monomeric IgA. Finally, comparing monoclonal IgA1 that had different variable regions and mesangial deposition patterns indicated that, independently of glycosylation and polymerization, deposition might also depend on IgA carrying specific variable domains. Together with IgA quantities and constant region post-translational modifications, repertoire changes during immune responses might, thus, modulate IgA propensity to deposition. These IgA features are not associated with circulating immune complexes and C3 deposition and are more pertinent to an initial IgA deposition step preceding overt clinical symptoms in patients.

The class-specific BCR tonic signal modulates lymphomagenesis in a c-myc deregulation transgenic model

Deregulation of c-myc by translocation onto immunoglobulin (Ig) loci can promote B cell malignant proliferations with phenotypes as diverse as acute lymphoid leukemia, Burkitt lymphoma, diffuse large B cell lymphoma, myeloma… The B cell receptor (BCR) normally providing tonic signals for cell survival and mitogenic responses to antigens, can also contribute to lymphomagenesis upon sustained ligand binding or activating mutations. BCR signaling varies among cell compartments and BCR classes. For unknown reasons, some malignancies associate with expression of either IgM or class-switched Ig. We explored whether an IgA BCR, with strong tonic signaling, would affect lymphomagenesis in c-myc IgH 3′RR transgenic mice prone to lymphoproliferations. Breeding c-myc transgenics in a background where IgM expression was replaced with IgA delayed lymphomagenesis. By comparison to single c-myc transgenics, lymphomas from double mutant animals were more differentiated and less aggressive, with an altered transcriptional program. Larger tumor cells more often expressed CD43 and CD138, which culminated in a plasma cell phenotype in 10% of cases. BCR class-specific signals thus appear to modulate lymphomagenesis and may partly explain the observed association of specific Ig classes with human B cell malignancies of differential phenotype, progression and prognosis.

Specific impairment of proximal tubular cell proliferation by a monoclonal κ light chain responsible for Fanconi syndrome

BACKGROUND

Fanconi syndrome (FS) is a rare renal disorder featuring proximal tubule dysfunction that may occur following tubular reabsorption of a monoclonal light chain (LC), in patients with multiple myeloma. FS may precede the recognition of multiple myeloma by several years. In most cases, crystalline inclusions of monoclonal κ LCs are observed within the lysosomes of proximal tubular cells (PTCs) and probably participate in their functional alteration.

METHODS

To investigate the mechanism implicated in proximal tubule dysfunction, we compared the effects of κ LC-CHEB obtained from a patient with myeloma-associated FS to those of control κ LC-BON obtained from a patient without evidence of FS, on the viability and proliferation of two different PTC lines.

RESULTS

Our data suggest that the tubular atrophy in myeloma-associated FS does not result from increased apoptosis of PTCs, but from their impaired capacity to proliferate and renew. Indeed, in vitro incubation of cultured PTCs with physiological amounts of the nephrotoxic κ LC-CHEB was sufficient to cause a depression in DNA synthesis and in cell proliferation. This effect was observed neither with control κ LC-BON nor in the absence of κ LC.

CONCLUSIONS

The reduced turnover of PTCs may affect tubular repair and regeneration. In addition, the reduced proliferation of myeloma cells producing the same monoclonal κ LC might explain the frequent association of FS with smoldering multiple myeloma.

IL-22 participates in an innate anti-HIV-1 host-resistance network through acute-phase protein induction

Certain individuals are resistant to HIV-1 infection, despite repeated exposure to the virus. Although protection against HIV-1 infection in a small proportion of Caucasian individuals is associated with mutant alleles of the CCR5 HIV-1 coreceptor, the molecular mechanism underlying resistance in repeatedly HIV-1-exposed, uninfected individuals (EU) is unclear. In this study, we performed complementary transcriptome and proteome analyses on peripheral blood T cells, and plasma or serum from EU, their HIV-1-infected sexual partners, and healthy controls, all expressing wild-type CCR5. We report that activated T cells from EU overproduce several proteins involved in the innate immunity response, principally those including high levels of peroxiredoxin II, a NK-enhancing factor possessing strong anti-HIV activity, and IL-22, a cytokine involved in the production of acute-phase proteins such as the acute-phase serum amyloid A (A-SAA). Cell supernatants and serum levels of these proteins were up-regulated in EU. Moreover, a specific biomarker for EU detected in plasma was identified as an 8.6-kDa A-SAA cleavage product. Incubation of in vitro-generated myeloid immature dendritic cells with A-SAA resulted in CCR5 phosphorylation, down-regulation of CCR5 expression, and strongly decreased susceptibility of these cells to in vitro infection with a primary HIV-1 isolate. Taken together, these results suggest new correlates of EU protection and identify a cascade involving IL-22 and the acute phase protein pathway that is associated with innate host resistance to HIV infection.

Soluble HIV-1 gp120 enhances HIV-1 replication in non-dividing CD4+ T cells, mediated via cell signaling and Tat cofactor overexpression

OBJECTIVES

The soluble HIV-1 gp120 envelope glycoprotein, after being shed from infected cells, can cross-link its receptors on both HIV-1 infected and non-infected target cells, leading to their activation. We have assessed the impact of soluble gp120 on viral replication in CD4+/CXCR4+ T cells, via its effects on Tat-mediated transactivation of the HIV-1/LTR.

MATERIALS AND METHODS

Primary cord blood-derived CD4+/CXCR4+ T cells were stimulated with soluble recombinant gp120 (rgp120) from the HIV-1/HXB2 clone. The level of gene or protein expression was assessed by serial analysis gene expression (SAGE), reverse transcriptase-polymerase chain reaction, western blotting or flow-cytometry analysis. Cellular division of rgp120-stimulated T cells was assessed by CFDA-SE labeling. Long terminal repeat (LTR) activity and HIV infection level were respectively measured by a chemiluminescent beta-gal Reporter Gene Assay and by p24 determination.

RESULTS

We have demonstrated that rgp120 activates both PKCepsilon and its upstream effector PI3K/Akt, involved in the HIV-1 replication process. Moreover, rgp120 enhances the gene, as well as protein expression of the cellular Tat cofactors Tat-Sf1 and SPT5 in primary CD4+/CXCR4+ T cells. Finally, stimulation of HIV-1 infected T cells with rgp120 was found to result in both a higher LTR-activity and an increased production of viral particles.

CONCLUSION

Taken together, these results show that soluble gp120 contributes to HIV-1 replication and dissemination, via the activation of multiple cell signaling pathways and the induction of Tat-cofactor expression, underscoring its potential as a therapeutic target in HIV-1-mediated pathogenesis.