RIPK3-MLKL-Mediated Neutrophil Death Requires Concurrent Activation of Fibroblast Activation Protein-α.

Cytokine-primed neutrophils can undergo a nonapoptotic type of cell death using components of the necroptotic pathway, including receptor-interacting protein kinase-3 (RIPK3), mixed lineage kinase-like (MLKL) and NADPH oxidase. In this report, we provide evidence for a potential role of serine proteases in CD44-mediated necroptotic death of GM-CSF-primed human neutrophils. Specifically, we observed that several inhibitors known to block the enzymatic function of fibroblast activation protein-α (FAP-α) were able to block CD44-mediated reactive oxygen species production and cell death, but not FAS receptor-mediated apoptosis. To understand how FAP-α is involved in this nonapoptotic death pathway, we performed immunoblotting experiments in the presence and absence of inhibitors of RIPK3, MLKL, p38 MAPK, PI3K, and FAP-α. The results of these experiments suggested that FAP-α is active in parallel with RIPK3, MLKL, and p38 MAPK activation but proximal to PI3K and NADPH oxidase activation. Interestingly, neutrophils isolated from the joints of patients suffering from rheumatoid arthritis underwent a GM-CSF-independent necroptosis following CD44 ligation; this effect was also blocked by both FAP-α and MLKL inhibitors. Taken together, our evidence shows that the RIPK3-MLKL pathway activates NADPH oxidase but requires, in addition to p38 MAPK and PI3K, a serine protease activity, whereby FAP-α is the most likely candidate. Thus, FAP-α could be a potential drug target in neutrophilic inflammatory responses to avoid exaggerated nonapoptotic neutrophil death, leading to tissue damage.

Human "TH9" cells are a subpopulation of PPAR-γ+ TH2 cells.

Although TH1, TH2, and TH17 cells are well-defined TH cell lineages in humans, it remains debated whether IL-9-producing TH cells represent a bona fide "TH9" lineage. Our understanding of the cellular characteristics and functions of IL-9-producing TH cells in humans is still nascent. Here, we report that human IL-9-producing TH cells express the chemokine receptors CCR4 and CCR8, produce high levels of IL-5 and IL-13, and express TH2 lineage-associated transcription factors. In these cells, IL-9 production is activation dependent, transient, and accompanied by down-regulation of TH2 cytokines, leading to an apparent "TH9" phenotype. IL-9+ TH2 cells can be distinguished from "conventional" TH2 cells based on their expression of the transcription factor PPAR-γ. Accordingly, PPAR-γ is induced in naïve TH cells by priming with IL-4 and TGF-ß ("TH9" priming) and is required for IL-9 production. In line with their identity as early activated TH2 cells, IL-9+ TH2 cells are found in acute allergic skin inflammation in humans. We propose that IL-9-producing TH cells are a phenotypically and functionally distinct subpopulation of TH2 cells that depend on PPAR-γ for full effector functions.

Immuno-monitoring reveals an extended subclinical disease activity in tocilizumab-treated giant cell arteritis.

Objective: Tocilizumab is effective in inducing and maintaining remission of GCA. Despite clinical and serological control of disease, magnetic resonance angiography may show persistence of inflammatory signals of unknown significance in arterial walls. Thus, there is an unmet need for tools to detect subclinical disease activity. Methods: Immune-inflammatory markers were measured in prospectively collected sera of the first randomized, double-blind, placebo-controlled trial investigating the use of tocilizumab in GCA. As a comparison, immune-inflammatory markers were also measured in sera from age- and sex-matched healthy volunteers. The biomarkers were quantified using luminex technology. Results: Of all the parameters determined, only MMP-3, pentraxin-3 and sTNFR2 were significantly elevated, while ICAM-1 and CD163 were significantly decreased during the early stages of the study, at time points of full clinical remission under treatment with tocilizumab plus glucocorticoids. In contrast, tocilizumab monotherapy towards the end of the study resulted in an almost complete normalization of immune-inflammatory molecules, as defined by the healthy controls. MMP-3 levels showed a weak association with magnetic resonance signal intensity; none of the biomarkers predicted relapse occurring within 6 months after study end. Conclusion: The data documented a subclinical disease activity in GCA that was more pronounced during the early stages of treatment and almost disappeared towards the study end. They indicated that tocilizumab treatment of at least 52 weeks is necessary in order to reset a broad range of immune-inflammatory pathways. Trial registration: ClinicalTrials.gov, http://clinicaltrials.gov, NCT01450137.

Magnetic resonance angiography in giant cell arteritis: results of a randomized controlled trial of tocilizumab in giant cell arteritis.

Objective: To analyse magnetic resonance angiographic (MRA) vessel wall signals from a randomized controlled trial of tocilizumab (TCZ) to treat GCA. Methods: Participants were assigned in a 2:1 ratio to receive either TCZ + glucocorticoids (GCs) or placebo + GC infusions at 4-week intervals for 52 weeks. GCs were started at 1 mg/kg/day, then tapered to 0.1 mg/kg/day at week 12 and thereafter down to zero. Patients with initial positive MRA findings underwent control MRA at weeks 12 and 52. Vessel wall signals were scored from 0 (normal) to 3 (intense late enhancement). Outcomes were the number of patients with complete MRA remission at weeks 12 and 52, and changes in vasculitis score, vessel anatomy and atherosclerosis. Results: Of the 30 randomized participants, nine TCZ and two placebo patients had no vessel wall enhancement on initial MRA. At week 12, MRAs were performed in nine TCZ and four placebo patients (nine and three in clinical remission, respectively). Three (33%) TCZ patients showed normalization of vessel wall signals compared with one (25%) placebo patient. At week 52, there was additional MRA improvement in some TCZ patients, but one-third showed persistent or increased late vessel wall enhancement. There was no formation of aneurysms or stenosis and no increase in atherosclerosis. Conclusions: Although TCZ resulted in complete clinical and laboratory remission of GCA over 52 weeks, MRA signals in vessel walls normalized in only one-third of patients. Whether these signals are of prognostic importance remains to be determined.

Tocilizumab for induction and maintenance of remission in giant cell arteritis: a phase 2, randomised, double-blind, placebo-controlled trial.

BACKGROUND: Giant cell arteritis is an immune-mediated disease of medium and large-sized arteries that affects mostly people older than 50 years of age. Treatment with glucocorticoids is the gold-standard and prevents severe vascular complications but is associated with substantial morbidity and mortality. Tocilizumab, a humanised monoclonal antibody against the interleukin-6 receptor, has been associated with rapid induction and maintenance of remission in patients with giant cell arteritis. We therefore aimed to study the efficacy and safety of tocilizumab in the first randomised clinical trial in patients with newly diagnosed or recurrent giant cell arteritis. METHODS: In this single centre, phase 2, randomised, double-blind, placebo-controlled trial, we recruited patients aged 50 years and older from University Hospital Bern, Switzerland, who met the 1990 American College of Rheumatology criteria for giant cell arteritis. Patients with new-onset or relapsing disease were randomly assigned (2:1) to receive either tocilizumab (8 mg/kg) or placebo intravenously. 13 infusions were given in 4 week intervals until week 52. Both groups received oral prednisolone, starting at 1 mg/kg per day and tapered down to 0 mg according to a standard reduction scheme defined in the study protocol. Allocation to treatment groups was done using a central computerised randomisation procedure with a permuted block design and a block size of three, and concealed using central randomisation generated by the clinical trials unit. Patients, investigators, and study personnel were masked to treatment assignment. The primary outcome was the proportion of patients who achieved complete remission of disease at a prednisolone dose of 0·1 mg/kg per day at week 12. All analyses were intention to treat. This trial is registered with ClinicalTrials.gov, number NCT01450137. RESULTS: Between March 3, 2012, and Sept 9, 2014, 20 patients were randomly assigned to receive tocilizumab and prednisolone, and ten patients to receive placebo and glucocorticoid; 16 (80%) and seven (70%) patients, respectively, had new-onset giant cell arteritis. 17 (85%) of 20 patients given tocilizumab and four (40%) of ten patients given placebo reached complete remission by week 12 (risk difference 45%, 95% CI 11-79; p=0·0301). Relapse-free survival was achieved in 17 (85%) patients in the tocilizumab group and two (20%) in the placebo group by week 52 (risk difference 65%, 95% CI 36-94; p=0·0010). The mean survival-time difference to stop glucocorticoids was 12 weeks in favour of tocilizumab (95% CI 7-17; p<0·0001), leading to a cumulative prednisolone dose of 43 mg/kg in the tocilizumab group versus 110 mg/kg in the placebo group (p=0·0005) after 52 weeks. Seven (35%) patients in the tocilizumab group and five (50%) in the placebo group had serious adverse events. INTERPRETATION: Our findings show, for the first time in a trial setting, the efficacy of tocilizumab in the induction and maintenance of remission in patients with giant cell arteritis. FUNDING: Roche and the University of Bern.

Deletion of exon 8 from the EXT1 gene causes multiple osteochondromas (MO) in a family with three affected members.

Multiple osteochondromas (also called hereditary multiple exostoses) is an autosomal dominant disorder characterized by multiple cartilaginous tumors, which are caused by mutations in the genes for exostosin-1 (EXT1) and exostosin-2 (EXT2). The goal of this study was to elucidate the genetic alterations in a family with three affected members. Isolation of RNA from the patients' blood followed by reverse transcription and PCR amplification of selected fragments showed that the three patients lack a specific region of 90 bp from their EXT1 mRNA. This region corresponds to the sequence of exon 8 from the EXT1 gene. No splice site mutation was found around exon 8. However, long-range PCR amplification of the region from intron 7 to intron 8 indicated that the three patients contain a deletion of 4318 bp, which includes exon 8 and part of the flanking introns. There is evidence that the deletion was caused by non-homologous end joining because the breakpoints are not located within a repetitive element, but contain multiple copies of the deletion hotspot sequence TGRRKM. Exon 8 encodes part of the active site of the EXT1 enzyme, including the DXD signature of all UDP-sugar glycosyltransferases. It is conceivable that the mutant protein exerts a dominant negative effect on the activity of the EXT glycosyltransferase since it might interact with normal copies of the enzyme to form an inactive hetero-oligomeric complex. We suggest that sequencing of RNA might be superior to exome sequencing to detect short deletions of a single exon.

A mouse model of HIES reveals pro- and anti-inflammatory functions of STAT3.

Mutations of STAT3 underlie the autosomal dominant form of hyperimmunoglobulin E syndrome (HIES). STAT3 has critical roles in immune cells and thus, hematopoietic stem cell transplantation (HSCT), might be a reasonable therapeutic strategy in this disease. However, STAT3 also has critical functions in nonhematopoietic cells and dissecting the protean roles of STAT3 is limited by the lethality associated with germline deletion of Stat3. Thus, predicting the efficacy of HSCT for HIES is difficult. To begin to dissect the importance of STAT3 in hematopoietic and nonhematopoietic cells as it relates to HIES, we generated a mouse model of this disease. We found that these transgenic mice recapitulate multiple aspects of HIES, including elevated serum IgE and failure to generate Th17 cells. We found that these mice were susceptible to bacterial infection that was partially corrected by HSCT using wild-type bone marrow, emphasizing the role played by the epithelium in the pathophysiology of HIES.

A systems analysis identifies a feedforward inflammatory circuit leading to lethal influenza infection.

For acutely lethal influenza infections, the relative pathogenic contributions of direct viral damage to lung epithelium versus dysregulated immunity remain unresolved. Here, we take a top-down systems approach to this question. Multigene transcriptional signatures from infected lungs suggested that elevated activation of inflammatory signaling networks distinguished lethal from sublethal infections. Flow cytometry and gene expression analysis involving isolated cell subpopulations from infected lungs showed that neutrophil influx largely accounted for the predictive transcriptional signature. Automated imaging analysis, together with these gene expression and flow data, identified a chemokine-driven feedforward circuit involving proinflammatory neutrophils potently driven by poorly contained lethal viruses. Consistent with these data, attenuation, but not ablation, of the neutrophil-driven response increased survival without changing viral spread. These findings establish the primacy of damaging innate inflammation in at least some forms of influenza-induced lethality and provide a roadmap for the systematic dissection of infection-associated pathology.

Congenital B cell lymphocytosis explained by novel germline CARD11 mutations.

Nuclear factor-κB (NF-κB) controls genes involved in normal lymphocyte functions, but constitutive NF-κB activation is often associated with B cell malignancy. Using high-throughput whole transcriptome sequencing, we investigated a unique family with hereditary polyclonal B cell lymphocytosis. We found a novel germline heterozygous missense mutation (E127G) in affected patients in the gene encoding CARD11, a scaffolding protein required for antigen receptor (AgR)-induced NF-κB activation in both B and T lymphocytes. We subsequently identified a second germline mutation (G116S) in an unrelated, phenotypically similar patient, confirming mutations in CARD11 drive disease. Like somatic, gain-of-function CARD11 mutations described in B cell lymphoma, these germline CARD11 mutants spontaneously aggregate and drive constitutive NF-κB activation. However, these CARD11 mutants rendered patient T cells less responsive to AgR-induced activation. By reexamining this rare genetic disorder first reported four decades ago, our findings provide new insight into why activating CARD11 mutations may induce B cell expansion and preferentially predispose to B cell malignancy without dramatically perturbing T cell homeostasis.

The folliculin-FNIP1 pathway deleted in human Birt-Hogg-Dubé syndrome is required for murine B-cell development.

Birt-Hogg-Dubé (BHD) syndrome is an autosomal dominant disorder characterized by cutaneous fibrofolliculomas, pulmonary cysts, and kidney malignancies. Affected individuals carry germ line mutations in folliculin (FLCN), a tumor suppressor gene that becomes biallelically inactivated in kidney tumors by second-hit mutations. Similar to other factors implicated in kidney cancer, FLCN has been shown to modulate activation of mammalian target of rapamycin (mTOR). However, its precise in vivo function is largely unknown because germ line deletion of Flcn results in early embryonic lethality in animal models. Here, we describe mice deficient in the newly characterized folliculin-interacting protein 1 (Fnip1). In contrast to Flcn, Fnip1(-/-) mice develop normally, are not susceptible to kidney neoplasia, but display a striking pro-B cell block that is entirely independent of mTOR activity. We show that this developmental arrest results from rapid caspase-induced pre-B cell death, and that a Bcl2 transgene reconstitutes mature B-cell populations, respectively. We also demonstrate that conditional deletion of Flcn recapitulates the pro-B cell arrest of Fnip1(-/-) mice. Our studies thus demonstrate that the FLCN-FNIP complex deregulated in BHD syndrome is absolutely required for B-cell differentiation, and that it functions through both mTOR-dependent and independent pathways.

TGF-ß and retinoic acid induce the microRNA miR-10a, which targets Bcl-6 and constrains the plasticity of helper T cells.

Distinct CD4(+) T cell subsets are critical for host defense and immunoregulation. Although these subsets can act as terminally differentiated lineages, they have been increasingly noted to demonstrated plasticity. MicroRNAs are factors that control T cell stability and plasticity. Here we report that naturally occurring regulatory T cells (T(reg) cells) had high expression of the microRNA miR-10a and that miR-10a was induced by retinoic acid and transforming growth factor-ß (TGF-ß) in inducible T(reg) cells. By simultaneously targeting the transcriptional repressor Bcl-6 and the corepressor Ncor2, miR-10a attenuated the phenotypic conversion of inducible T(reg) cells into follicular helper T cells. We also found that miR-10a limited differentiation into the T(H)17 subset of helper T cells and therefore represents a factor that can fine-tune the plasticity and fate of helper T cells.

Deep-sequencing identification of the genomic targets of the cytidine deaminase AID and its cofactor RPA in B lymphocytes.

The cytidine deaminase AID hypermutates immunoglobulin genes but can also target oncogenes, leading to tumorigenesis. The extent of AID's promiscuity and its predilection for immunoglobulin genes are unknown. We report here that AID interacted broadly with promoter-proximal sequences associated with stalled polymerases and chromatin-activating marks. In contrast, genomic occupancy of replication protein A (RPA), an AID cofactor, was restricted to immunoglobulin genes. The recruitment of RPA to the immunoglobulin loci was facilitated by phosphorylation of AID at Ser38 and Thr140. We propose that stalled polymerases recruit AID, thereby resulting in low frequencies of hypermutation across the B cell genome. Efficient hypermutation and switch recombination required AID phosphorylation and correlated with recruitment of RPA. Our findings provide a rationale for the oncogenic role of AID in B cell malignancy.

Regulation of microRNA expression and abundance during lymphopoiesis.

Although the cellular concentration of miRNAs is critical to their function, how miRNA expression and abundance are regulated during ontogeny is unclear. We applied miRNA-, mRNA-, and ChIP-Seq to characterize the microRNome during lymphopoiesis within the context of the transcriptome and epigenome. We show that lymphocyte-specific miRNAs are either tightly controlled by polycomb group-mediated H3K27me3 or maintained in a semi-activated epigenetic state prior to full expression. Because of miRNA biogenesis, the cellular concentration of mature miRNAs does not typically reflect transcriptional changes. However, we uncover a subset of miRNAs for which abundance is dictated by miRNA gene expression. We confirm that concentration of 5p and 3p miRNA strands depends largely on free energy properties of miRNA duplexes. Unexpectedly, we also find that miRNA strand accumulation can be developmentally regulated. Our data provide a comprehensive map of immunity's microRNome and reveal the underlying epigenetic and transcriptional forces that shape miRNA homeostasis.

The B cell mutator AID promotes B lymphoid blast crisis and drug resistance in chronic myeloid leukemia.

Chronic myeloid leukemia (CML) is induced by BCR-ABL1 and can be effectively treated for many years with Imatinib until leukemia cells acquire drug resistance through BCR-ABL1 mutations and progress into fatal B lymphoid blast crisis (LBC). Despite its clinical significance, the mechanism of progression into LBC is unknown. Here, we show that LBC but not CML cells express the B cell-specific mutator enzyme AID. We demonstrate that AID expression in CML cells promotes overall genetic instability by hypermutation of tumor suppressor and DNA repair genes. Importantly, our data uncover a causative role of AID activity in the acquisition of BCR-ABL1 mutations leading to Imatinib resistance, thus providing a rationale for the rapid development of drug resistance and blast crisis progression.

Identification and characterization of a human CD5+ pre-naive B cell population.

We have identified a distinct pre-naive B cell population circulating in human peripheral blood that exhibits an intermediate phenotype between transitional and naive B cells. Like human transitional B cells, these cells express CD5 but have intermediate densities of CD38, CD10, CD9, and the ABCB1 transporter compared with transitional and naive B cells. These pre-naive B cells account for a majority of circulating human CD5(+) B cells. Importantly, CD5(+) pre-naive B cells could be induced to differentiate into cells with a naive phenotype in vitro. CD5(+) pre-naive B cells show only partial responses to BCR stimulation and CD40 ligation and undergo more spontaneous apoptosis and cell death than do naive B cells, whereas BAFF/BLyS (B cell-activating factor belonging to the TNF family) did not enhance their survival compared with naive B cells. In contrast, CD5(+) pre-naive B cells carry out certain functions comparable to naive B cells, including the capacity to differentiate into plasma cells and the ability to function as APCs. Notably, an increased proportion of CD5(+) pre-naive B cells were found in peripheral blood of patients with systemic lupus erythematosus. These results have identified a unique intermediate in human naive B cell development within the peripheral blood and derangements of its homeostasis in patients with systemic lupus erythematosus.

The role of IL-21 in regulating B-cell function in health and disease.

SUMMARY: Interleukin-21 (IL-21) belongs to a family of cytokines that includes IL-2, IL-4, IL-7, IL-9, and IL-15, all of which bind to private (or shared) receptors as well as the common cytokine receptor gamma-chain as a component. Most cytokines in this family are critically important for both the maintenance and function of T cells and B cells. The receptor for IL-21 is widely distributed on lymphohematopoietic cells, and IL-21 plays many biologic roles, including maintenance and function of CD8(+) memory T cells and natural killer cells, as well as promoting the generation of Th17 cells in the mouse. One principal non-redundant role of IL-21 is the promotion of B-cell activation, differentiation or death during humoral immune responses. Furthermore, increased IL-21 production is characteristic of certain autoimmune diseases and is likely to contribute to autoantibody production as well as pathologic features of autoimmune disease. In contrast, IL-21 may function as a co-adjuvant to enhance antibody responses and thereby facilitate host defense to malignances and infectious diseases. The critical role of IL-21 in promoting humoral immune responses makes it an important focus of potential therapeutic interventions in conditions characterized by either overproduction of pathogenic autoantibodies or under production of protective antibodies.

Essential role of IL-21 in B cell activation, expansion, and plasma cell generation during CD4+ T cell-B cell collaboration.

During T cell-B cell collaboration, plasma cell (PC) differentiation and Ig production are known to require T cell-derived soluble factors. However, the exact nature of the cytokines produced by activated T cells that costimulate PC differentiation is not clear. Previously, we reported that costimulation of purified human B cells with IL-21 and anti-CD40 resulted in efficient PC differentiation. In this study, we addressed whether de novo production of IL-21 was involved in direct T cell-induced B cell activation, proliferation, and PC differentiation. We found that activated human peripheral blood CD4(+) T cells expressed mRNA for a number of cytokines, including IL-21, which was confirmed at the protein level. Using a panel of reagents that specifically neutralize cytokine activity, we addressed which cytokines are essential for B cell activation and PC differentiation induced by anti-CD3-activated T cells. Strikingly, neutralization of IL-21 with an IL-21R fusion protein (IL-21R-Fc) significantly inhibited T cell-induced B cell activation, proliferation, PC differentiation, and Ig production. Inhibition of PC differentiation was observed even when the addition of IL-21R-Fc was delayed until after initial B cell activation and expansion had occurred. Importantly, IL-21 was found to be involved in PC differentiation from both naive and memory B cells. Finally, IL-21R-Fc did not inhibit anti-CD3-induced CD4(+) T cell activation, but rather directly blocked T cell-induced B cell activation and PC differentiation. These data are the first to document that B cell activation, expansion, and PC differentiation induced by direct interaction of B cells with activated T cells requires IL-21.