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Healthy B-cells are CXCL-8 negative.

Tumor-infiltrating neutrophils have been implicated in malignant development and progression, but mechanisms are ill defined. Neutrophils produce a proliferation-inducing ligand APRIL/TNFSF13, a factor that promotes development of tumors from diverse origins, including diffuse large B-cell lymphoma (DLBCL). High APRIL expression in DLBCL correlates with reduced patient survival, but the pathway(s) dictating APRIL expression are not known. Here, we show that all blood neutrophils constitutively secrete APRIL, and inflammation-associated stimuli, such as TNF, further upregulate APRIL. In a significant fraction of DLBCL patients, tumor cells constitutively produced the ELC-CXC chemokine CXCL-8 (IL8), enabling them to recruit APRIL-producing blood neutrophils. CXCL-8 production in DLBCL was unrelated to the cell of origin, as APRIL-producing neutrophils infiltrated CXCL-8+ DLBCL from both germinal center (GC) and non-GC subtypes. Rather, CXCL-8 production implied events affecting DNA methylation and acetylation. Overall, our results showed that chemokine-mediated recruitment of neutrophils secreting the tumor-promoting factor APRIL mediates DLBCL progression. Cancer Res; 77(5); 1097–107. ©2016 AACR.

Key Points CCL5 is differentially expressed by DLBCL cells and efficiently recruits TAMs through their expression of CCR1/CCR5.Most DLBCL TAMs have a noncanonical gene signature., Visual Abstract, Tissue invasion by tumor cells induces a host inflammatory response that variably impacts tumorigenesis. This has been well documented for tumor-associated macrophages (TAMs) that could play a pro/M2- or an anti/M1-tumoral function. TAMs frequently infiltrate diffuse large B-cell lymphoma (DLBCL), an aggressive neoplasm arising from germinal center–experienced B cells. However, the pathway leading to the presence of TAMs in DLBCL remains unknown, and their impact is unclear. Here, we show that some DLBCL tumor cells expressed the chemokine CCL5, enabling the differential recruitment of blood monocytes through their expression of CCR1 and CCR5. CCL5 expression by DLBCL was not related to molecular subtypes, and healthy tonsillar B cells did not produce this chemokine, implying a posttransformation event. A single-cell analysis revealed that most DLBCL TAMs had a noncanonical gene signature with the concomitant expression of M1 and M2 genes. The presence of noncanonical TAMs may explain the lack of impact of macrophages on DLBCL development reported in some survival studies.

The TNF superfamily member a proliferation inducing ligand (APRIL, TNFSF13) plays a late role in humoral immunity at the level of antibody-producing plasmocytes. The recent characterization of the first immunodeficient patient with an inactivating mutation in the APRIL gene provided the last piece of functional data lacking in the human system. Based on this function, APRIL has been considered as a valuable target to dampen unwanted antibody production. After reviewing the late data acquired on the physiological function of APRIL in humoral immunity, we will here review the state of the art regarding APRIL targeting in autoimmune diseases.

B lymphocytes have a central role in autoimmune diseases, which are often defined by specific autoantibody patterns and feature a loss of B cell tolerance. A prototypic disease associated with B cell hyperactivity is systemic lupus erythematosus (SLE). In patients with SLE, the loss of B cell tolerance to autoantigens is controlled in a cell-intrinsic manner by Toll-like receptors (TLRs), which sense nucleic acids in endosomes. TLR7 drives the extrafollicular B cell response and the germinal centre reaction that are involved in autoantibody production and disease pathogenesis. Surprisingly, TLR9 seems to protect against SLE, even though it is required for the production of autoantibodies recognizing double-stranded DNA-associated antigens, which are abundant in SLE and are a hallmark of this disease. The protective function of TLR9 is at least partly mediated by its capacity to limit the stimulatory activity of TLR7. The roles of TLR7 and TLR9 in the effector function of B cells in lupus-like disease and in patients with SLE, and the unique features of TLR signalling in B cells, suggest that targeting TLR signalling in SLE might be therapeutically beneficial., Loss of B cell tolerance to autoantigens in systemic lupus erythematosus (SLE) is driven by TLR7, whereas TLR9 appears to protect against SLE by limiting the stimulatory activity of TLR7. The unique features of Toll-like receptor signalling in B cells implicate it as a therapeutic target in SLE., Key points Intrinsic TLR7 and TLR9 signalling in B cells plays an important role in the development and pathogenesis of systemic lupus erythematosus (SLE).In patients with SLE, effector plasma cells are generated via the extrafollicular response and via the formation of spontaneous germinal centres.TLR7 plays key roles in the extrafollicular response and the response mediated by germinal centres.Some plasma cells produce IL-10 and can have protective roles in lupus-like disease.

Tumor-infiltrating neutrophils have been implicated in malignant development and progression, but mechanisms are ill defined. Neutrophils produce a proliferation-inducing ligand APRIL/TNFSF13, a factor that promotes development of tumors from diverse origins, including diffuse large B-cell lymphoma (DLBCL). High APRIL expression in DLBCL correlates with reduced patient survival, but the pathway(s) dictating APRIL expression are not known. Here, we show that all blood neutrophils constitutively secrete APRIL, and inflammation-associated stimuli, such as TNF, further upregulate APRIL. In a significant fraction of DLBCL patients, tumor cells constitutively produced the ELC-CXC chemokine CXCL-8 (IL8), enabling them to recruit APRIL-producing blood neutrophils. CXCL-8 production in DLBCL was unrelated to the cell of origin, as APRIL-producing neutrophils infiltrated CXCL-8+ DLBCL from both germinal center (GC) and non-GC subtypes. Rather, CXCL-8 production implied events affecting DNA methylation and acetylation. Overall, our results showed that chemokine-mediated recruitment of neutrophils secreting the tumor-promoting factor APRIL mediates DLBCL progression. Cancer Res; 77(5); 1097–107. ©2016 AACR.

The TNF family member a proliferation-inducing ligand (APRIL; also known as TNFSF13), produced by myeloid cells, participates in the generation and survival of antibody-producing plasma cells. We studied the potential role of APRIL in the pathogenesis of IgA nephropathy (IgAN). We found that a significant proportion of germinal centers (GCs) in tonsils of patients with IgAN contained cells aberrantly producing APRIL, contributing to an overall upregulation of tonsillar APRIL expression compared with that in tonsils of control patients with tonsillitis. In IgAN GC, antigen-experienced IgD-CD38+/-CD19+ B cells expressing a switched IgG/IgA B cell receptor produced APRIL. Notably, these GC B cells expressed mRNA encoding the common cleavable APRIL-α but also, the less frequent APRIL-δ/ζ mRNA, which encodes a protein that lacks a furin cleavage site and is, thus, the uncleavable membrane-bound form. Significant correlation between TLR9 and APRIL expression levels existed in tonsils from patients with IgAN. In vitro, repeated TLR9 stimulation induced APRIL expression in tonsillar B cells from control patients with tonsillitis. Clinically, aberrant APRIL expression in tonsillar GC correlated with greater proteinuria, and patients with IgAN and aberrant APRIL overexpression in tonsillar GC responded well to tonsillectomy, with parallel decreases in serum levels of galactose-deficient IgA1. Taken together, our data indicate that antibody disorders in IgAN associate with TLR9-induced aberrant expression of APRIL in tonsillar GC B cells.

It has long been assumed that the functions of B cells reflected the roles of antibodies. However, B cells also decisively influence immunity via antibody-independent mechanisms including the presentation of antigen to T cells and the secretion of cytokines. In fact, B cell depletion therapy improves the course of autoimmune diseases such as multiple sclerosis by removing pro-inflammatory cytokine-producing B cells rather than by reducing autoantibody levels. Remarkably, B cells can also produce anti-inflammatory cytokines, and subsequently suppress immunity, providing protection from autoimmune diseases while interfering with beneficial responses against pathogens and cancers. A major mediator of this B cell regulatory function is their secretion of IL-10. There is considerable interest in identifying the mechanisms inducing the expression of IL-10 in B cells during the course of their activation. Here, we review the molecular mechanisms controlling IL-10 expression in B cells, and the evidence that IL-10-producing B cells play a protective role in human autoimmune diseases, underlying the relevance of this immunosuppressive axis for therapy.

International audience; OBJECTIVE:The two related tumor necrosis factor members a proliferation-inducing ligand (APRIL) and B-cell activation factor (BAFF) are currently targeted in autoimmune diseases as B-cell regulators. In multiple sclerosis (MS), combined APRIL/BAFF blockade led to unexpected exacerbated inflammation in the central nervous system (CNS) of patients. Here, we investigate the role of the APRIL/BAFF axis in the CNS.METHODS:APRIL expression was analyzed in MS lesions by immunohistochemistry. The in vivo role of APRIL was assessed in the murine MS model, experimental autoimmune encephalitis (EAE). Functional in vitro studies were performed with human and mouse astrocytes.RESULTS:APRIL was expressed in lesions from EAE. In its absence, the disease was worst. Lesions from MS patients also showed APRIL expression upon infiltration of macrophages. Notably, all the APRIL secreted by these macrophages specifically targeted astrocytes. The upregulation of chondroitin sulfate proteoglycan, sometimes bearing chondroitin sulfate of type E sugar moieties, binding APRIL, in reactive astrocytes explained the latter selectivity. Astrocytes responded to APRIL by producing a sufficient amount of IL-10 to dampen antigen-specific T-cell proliferation and pathogenic cytokine secretion. Finally, an intraspinal delivery of recombinant APRIL before disease onset, shortly reduced EAE symptoms. Repeated intravenous injections of recombinant APRIL before and even at disease onset also had an effect.INTERPRETATION:Our data show that APRIL mediates an anti-inflammatory response from astrocytes in MS lesions. This protective activity is not shared with BAFF. ANN NEUROL 2019;85:406-420.© 2019 American Neurological Association.

International audience

Multiple myeloma (MM) is a non-curable tumor developing in the bone marrow (BM). The BM microenvironment rich in hematopoietic precursors is suspected to have a role in MM development. Here we show that a proliferation-inducing ligand (APRIL) mediated in vivo MM promotion. In MM-infiltrated BM, APRIL originated from differentiating myeloid cells with an expression peak in precursor cells. Notably, APRIL expression stayed stable in BM despite MM infiltration. The pool of APRIL-producing cells changed upon MM infiltration. Although CD16(+) mature myeloid cells constituted about half of the APRIL-producing cells in healthy BM, CD16(-) Elastase(+) myeloid precursor cells were predominant in MM-infiltrated BM. Myeloid precursor cells secreted all the APRIL they produced, and binding of secreted APRIL to MM cells, strictly dependent of heparan sulfate carried by CD138, resulted in an in situ internalization by tumor cells. This indicated APRIL consumption by MM in BM. Taken together, our data show that myelopoiesis dysregulation characterized by an increased proportion of precursor cells occurs in MM patients. Such dysregulation correlates with a stable expression of the MM-promoting factor APRIL in infiltrated BM.

IL-6, a cytokine with broad functions in inflammation and immunity, has been extensively studied for its role on normal antibody-producing plasma cells. In addition, IL-6 is recognized as a proliferative factor for multiple myeloma (MM), a malignant plasma cell tumor developing in the bone marrow. Blocking IL-6 signaling was thus developed into a therapeutic approach for MM already early after its discovery, in 1991. Unfortunately, the first clinical trials did not demonstrate a clear benefit, but despite this apparent failure hopes on IL-6 antagonism are still high and trials ongoing. The cellular source of IL-6 has long been a matter of debate. IL-6 was first recognized as an autocrine factor produced by the malignant plasma cells themselves, but later reports clearly showed that IL-6 was a paracrine factor, produced by the microenvironment, mostly by cells from the myeloid lineage. Recently, we have confirmed that IL-6 originates from myeloid lineage cells, mainly from myeloid precursors. We have also demonstrated that IL-6 amplifies the pool of myeloid cells producing a second key factor for MM, a proliferation inducing ligand (APRIL). These findings form a new rationale for IL-6 inhibition in MM and for new ways to use IL-6 blocking in the clinics.

Multiple myeloma (MM) invariably develops in the bone marrow (BM), indicating the strong requirement of this tumor for the peculiar BM microenvironment, rich in cytokine and hematopoietic precursor cells. Interleukin-6 (IL-6) and a proliferation inducing ligand (APRIL) are key cytokines implicated in MM development. Here, we show that MM cells changed the hematopoietic microenvironment early upon BM infiltration by strongly downregulating hematopoietic precursor cells from all lineages except myeloid precursor cells. Myeloid precursor cells constituted a major source of APRIL in MM-infiltrated BM, and their proliferative response to IL-6 upregulation explained their relative resistance to MM infiltration. The osteolytic molecule receptor activator of NF-kB ligand (RANK-L) expressed by MM cells started this myeloid proliferation by inducing in a contact-dependent manner IL-6 production by myeloid precursor cells themselves. Taken together, our data demonstrate that MM cells do not simply displace hematopoietic cells upon BM infiltration, but rather selectively modulate the BM microenvironment to preserve a pool of high APRIL-producing myeloid precursor cells. Our data also identify a positive regulation of APRIL by IL-6 in myeloid precursor cells.