Lupus activity and outcomes in lupus patients undergoing maintenance dialysis.

OBJECTIVES: Lupus activity has long been considered to decline after initiation of maintenance dialysis (MD). This assumption is based on limited historical data. We aimed to describe the natural history of lupus in patients undergoing MD. METHODS: We assembled a national retrospective cohort of lupus patients who started dialysis between 2008 and 2011, included in the REIN registry with a 5-year follow-up. We analysed healthcare consumption from the National Health Data System. We evaluated the proportion of patients 'off-treatment' (i.e. receiving 0-5 mg/d of corticosteroids, without any immunosuppressive therapy) after the start of MD. We describe the cumulative incidences of non-severe and severe lupus flares, cardiovascular events, severe infections, kidney transplantation and survival. RESULTS: We included 137 patients (121 females and 16 males), with a median age of 42 years. The proportion of patients 'off-treatment' at dialysis initiation was 67.7% (95% CI: 61.8, 73.8%), and increased to 76.0% (95% CI: 73.3, 78.8) at 1 year and 83.4% (95% CI: 81.0, 85.9%) at 3 years, with a lower proportion in younger patients. Lupus flares mainly occurred in the first year after MD initiation, and at 12 months 51.6% of patients had presented a non-severe lupus flare and 11.6% a severe lupus flare. In addition, 42.2% (95% CI: 32.9, 50.3%) and 23.7% (95% CI: 16.0, 30.7%) of patients at 12 months had been hospitalized for cardiovascular events or infections, respectively. CONCLUSION: The proportion of lupus patients off-treatment increases after MD initiation, but non-severe and severe lupus flares continue to occur, mainly during the first year. This calls for the continued follow-up of lupus patients by lupus specialists after dialysis initiation.

Impact of BNT162b2 mRNA anti-SARS-CoV-2 vaccine on interferon-alpha production by plasmacytoid dendritic cells and autoreactive T cells in patients with systemic lupus erythematosus: The COVALUS project.

OBJECTIVE: To evaluate the specific response of SLE patients to BNT162b2 vaccination and its impact on autoimmunity defined as in vivo production of interferon-alpha (IFNα) by plasmacytoid dendritic cells (pDCs) and autoreactive immune responses. METHODS: Our prospective study included SLE patients and healthy volunteers (HV) who received 2 doses of BNT162b2 vaccine 4 weeks apart. Subjects under immunosuppressive drugs or with evidence of prior COVID-19 were excluded. IgG anti-Spike SARS-CoV-2 (anti-S) antibodies, anti-S specific-B cells, anti-S specific T cells, in vivo INF-α production by pDCs, activation marker expression by pDCs and autoreactive anti-nuclear T cells were quantified before first injection, before second injection, and 3 and 6 months after first injection. RESULTS: Vaccinated SLE patients produced significantly lower IgG antibodies and specific B cells against SARS-CoV-2 as compared to HV. In contrast, anti-S T cell response did not significantly differ between SLE patients and HV. Following vaccination, the surface expression of HLA-DR and CD86 and the in vivo production of IFNα by pDCs significantly increased in SLE patients. The boosted expression of HLA-DR on pDCs induced by BNT162b2 vaccine correlated with the overall immune responses against SARS-CoV-2 (anti-S antibodies: r = 0.27 [0.05-0.46], p = 0.02; anti-S B cells: r = 0.19 [-0.03-0.39], p = 0.09); anti-S T cells: r = 0.28 [0.05-0.47], p = 0.016). Eventually, anti-SARS-CoV-2 vaccination was associated with an overall decrease of autoreactive T cells (slope = - 0.00067, p = 0.015). CONCLUSION: BNT162b2 vaccine induces a transient in vivo activation of pDCs in SLE that contributes to the immune responses against SARS-CoV-2. Unexpectedly BNT162b2 vaccine also dampens the pool of circulating autoreactive T cells, suggesting that vaccination may have a beneficial impact on SLE disease.

Autoreactive IgE: Pathogenic role and therapeutic target in autoimmune diseases.

Autoimmunity is the break of tolerance to self-antigens that leads to organ-specific or systemic diseases often characterized by the presence of pathogenic autoreactive antibodies (AAb) produced by plasmablast and/or plasma cells. AAb are prevalent in the general population and not systematically associated with clinical symptoms. In contrast, in some individuals, these AAb are pathogenic and drive the development of signs and symptoms of antibody-mediated autoimmune diseases (AbAID). AAb production, isotype profiles, and glycosylations are promoted by pro-inflammatory triggers linked to genetic, environmental, and hormonal parameters. Recent evidence supports a role for pathogenic AAb of the IgE isotype in a number of AbAID. Autoreactive IgE can drive the activation of mast cells, basophils, and other types of FcεRI-bearing cells and may play a role in promoting autoantibody production and other pro-inflammatory pathways. In this review, we discuss the current knowledge on the pathogenicity of autoreactive IgE in AbAID and their status as therapeutic targets. We also highlight unresolved issues including the need for assays that reproducibly quantify IgE AAbs, to validate their diagnostic and prognostic value, and to further study their pathophysiological contributions to AbAID.

Basophils and IgE contribute to mixed connective tissue disease development.

BACKGROUND: Mixed connective tissue disease (MCTD) is a rare and complex autoimmune disease that presents mixed features with other connective tissue diseases, such as systemic lupus erythematosus, systemic sclerosis, and myositis. It is characterized by high levels of anti-U1 small nuclear ribonucleoprotein 70k autoantibodies and a high incidence of life-threatening pulmonary involvement. The pathophysiology of MCTD is not well understood, and no specific treatment is yet available for the patients. Basophils and IgE play a role in the development of systemic lupus erythematosus and thus represent new therapeutic targets for systemic lupus erythematosus and other diseases involving basophils and IgE in their pathogenesis. OBJECTIVE: We sought to investigate the role of basophils and IgE in the pathophysiology of MCTD. METHODS: Basophil activation status and the presence of autoreactive IgE were assessed in peripheral blood of a cohort of patients with MCTD and in an MCTD-like mouse model. Basophil depletion and IgE-deficient animals were used to investigate the contribution of basophils and IgE in the lung pathology development of this mouse model. RESULTS: Patients with MCTD have a peripheral basopenia and activated blood basophils overexpressing C-C chemokine receptor 3. Autoreactive IgE raised against the main MCTD autoantigen U1 small nuclear ribonucleoprotein 70k were found in nearly 80% of the patients from the cohort. Basophil activation and IgE anti-U1 small nuclear ribonucleoprotein 70k were also observed in the MCTD-like mouse model along with basophil accumulation in lymph nodes and lungs. Basophil depletion dampened lung pathology, and IgE deficiency prevented its development. CONCLUSIONS: Basophils and IgE contribute to MCTD pathophysiology and represent new candidate therapeutic targets for patients with MCTD.

Non-IgE mediated mast cell activation.

Mast cells (MCs) are innate immune cells that are scattered in tissues throughout the organism being particularly abundant at sites exposed to the environment such as the skin and mucosal surfaces. Generally known for their role in IgE-mediated allergies, they have also important functions in the maintenance of tissue integrity by constantly sensing their microenvironment for signals by inflammatory triggers that can comprise infectious agents, toxins, hormones, alarmins, metabolic states, etc. When triggered their main function is to release a whole set of inflammatory mediators, cytokines, chemokines, and lipid products. This allows them to organize the ensuing innate immune and inflammatory response in tight coordination with resident tissue cells, other rapidly recruited immune effector cells as well as the endocrine and exocrine systems of the body. To complete these tasks, MCs are endowed with a large repertoire of receptors allowing them to respond to multiple stimuli or directly interact with other cells. Here we review some of the receptors expressed on MCs (ie, receptors for Immunoglobulins, pattern recognition receptors, nuclear receptors, receptors for alarmins, and a variety of other receptors) and discuss their functional implication in the immune and inflammatory response focusing on non-IgE-mediated activation mechanisms.

CD62L on blood basophils: a first pre-treatment predictor of remission in severe lupus nephritis.

BACKGROUND: Basophils were recently shown to contribute to lupus nephritis (LN). This study assessed blood basophil activation markers (BAMs) for the diagnosis of LN severity and as pre-treatment prognostic markers of the response to treatment in patients with severe LN. METHOD: The diagnostic study included all the patients of a monocentric prospective observational cohort built with consecutive patients diagnosed with LN on the basis of a renal biopsy. The prognostic study selected patients of this cohort according to the following inclusion criteria: ≥18 years old, Class III or IV A ± C ± Class V or pure Class V LN at the time of inclusion and treated with an induction treatment for LN. Clinical data and BAMs were obtained at the time of the kidney biopsy. LN remission status was recorded 12 months after induction therapy initiation. Associations between baseline data and histological severity of LN or LN remission were assessed using logistic regression. RESULTS: No significant association was found between BAMs and the histological severity of LN in 101 patients. Among the 83 patients included in the prognostic study, 64 reached renal remission. CD62L expression on blood basophils at baseline was independently negatively associated with remission at 12 months [odds ratio = 0.26, 95% confidence interval 0.08-0.82, P = 0.02 for quantitative CD62L expression >105 (geometric fluorescent intensity) gMFI]. CD62L <105 gMFI was associated with a probability of 0.87 of LN remission in the next 12 months after the start of induction therapy. CONCLUSION: Pre-treatment CD62L expression on blood basophils could be a first predictive biomarker of renal response to induction therapy at 12 months in patients with severe LN.

TLR4 Receptor Induces 2-AG-Dependent Tolerance to Lipopolysaccharide and Trafficking of CB2 Receptor in Mast Cells.

Mast cells (MCs) contribute to the control of local inflammatory reactions and become hyporesponsive after prolonged TLR4 activation by bacterial LPS. The molecular mechanisms involved in endotoxin tolerance (ET) induction in MCs are not fully understood. In this study, we demonstrate that the endocannabinoid 2-arachidonoylglycerol (2-AG) and its receptor, cannabinoid receptor 2 (CB2), play a role in the establishment of ET in bone marrow-derived MCs from C57BL/6J mice. We found that CB2 antagonism prevented the development of ET and that bone marrow-derived MCs produce 2-AG in a TLR4-dependent fashion. Exogenous 2-AG induced ET similarly to LPS, blocking the phosphorylation of IKK and the p65 subunit of NF-κB and inducing the synthesis of molecular markers of ET. LPS caused CB2 receptor trafficking in Rab11-, Rab7-, and Lamp2-positive vesicles, indicating recycling and degradation of the receptor. 2-AG also prevented LPS-induced TNF secretion in vivo, in a MC-dependent model of endotoxemia, demonstrating that TLR4 engagement leads to 2-AG secretion, which contributes to the negative control of MCs activation. Our study uncovers a functional role for the endocannabinoid system in the inhibition of MC-dependent innate immune responses in vivo.

Mast cell chymase protects against acute ischemic kidney injury by limiting neutrophil hyperactivation and recruitment.

Here we investigated the role of murine mast cell protease 4 (MCPT4), the functional counterpart of human mast cell chymase, in an experimental model of renal ischemia reperfusion injury, a major cause of acute kidney injury. MCPT4-deficient mice had worsened kidney function compared to wildtype mice. MCPT4 absence exacerbated pathologic neutrophil infiltration in the kidney and increased kidney myeloperoxidase expression, cell death and necrosis. In kidneys with ischemia reperfusion injury, when compared to wildtype mice, MCPT4-deficient mice showed increased surface expression of adhesion molecules necessary for leukocyte extravasation including neutrophil CD162 and endothelial cell CD54. In vitro, human chymase mediated the cleavage of neutrophil expressed CD162 and also CD54, P- and E-Selectin expressed on human glomerular endothelial cells. MCPT4 also dampened systemic neutrophil activation after renal ischemia reperfusion injury as neutrophils expressed more CD11b integrin and produced more reactive oxygen species in MCPT4-deficient mice. Accordingly, after renal injury, neutrophil migration to an inflammatory site distal from the kidney was increased in MCPT4-deficient versus wildtype mice. Thus, contrary to the described overall aggravating role of mast cells, one granule-released mediator, the MCPT4 chymase, exhibits a potent anti-inflammatory function in renal ischemia reperfusion injury by controlling neutrophil extravasation and activation thereby limiting associated damage.

Mast cell interleukin-2 production contributes to suppression of chronic allergic dermatitis.

The incidence of chronic allergic dermatitis is rapidly increasing. Regulatory control of this disease has not been adequately explored. Here we report that mast cell-derived interleukin-2 (IL-2) contributes to the suppression of chronic allergic dermatitis. Mice deficient in IL-2 production, or deficient in mast cells (Kit(W-sh/W-sh)), showed exacerbated dermatitis upon repeated oxazolone challenge when compared to their wild-type counterparts. Adoptive transfer of wild-type, but not Il2(-/-), mast cells into Kit(W-sh/W-sh) mice dampened the inflammatory response. During the course of disease, mast cell expansion occurred at the site of inflammation and also in the spleen, where production of IL-2 by mast cells was markedly enhanced. In the absence of mast cell IL-2 production, the ratio of activated to regulatory T cells at the site of inflammation was increased. Thus, MC-derived IL-2 contributes to the maintenance of suppression in chronic allergic skin inflammation.

Mast Cell Chymase and Kidney Disease.

A sizable part (~2%) of the human genome encodes for proteases. They are involved in many physiological processes, such as development, reproduction and inflammation, but also play a role in pathology. Mast cells (MC) contain a variety of MC specific proteases, the expression of which may differ between various MC subtypes. Amongst these proteases, chymase represents up to 25% of the total proteins in the MC and is released from cytoplasmic granules upon activation. Once secreted, it cleaves the targets in the local tissue environment, but may also act in lymph nodes infiltrated by MC, or systemically, when reaching the circulation during an inflammatory response. MC have been recognized as important components in the development of kidney disease. Based on this observation, MC chymase has gained interest following the discovery that it contributes to the angiotensin-converting enzyme's independent generation of angiotensin II, an important inflammatory mediator in the development of kidney disease. Hence, progress regarding its role has been made based on studies using inhibitors but also on mice deficient in MC protease 4 (mMCP-4), the functional murine counterpart of human chymase. In this review, we discuss the role and actions of chymase in kidney disease. While initially believed to contribute to pathogenesis, the accumulated data favor a more subtle view, indicating that chymase may also have beneficial actions.

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.

Basophil involvement in lupus nephritis: a basis for innovation in daily care.

Lupus nephritis (LN) affects a large proportion of patients with systemic lupus erythematosus (SLE). LN can lead to end-stage renal disease depending on when it is diagnosed and on the adequacy of the treatment administered to the patient based on the class of LN. Determination of the class and activity of LN is only possible by histological analysis of kidney biopsies. In this context, the development of non-invasive early diagnostic tools for determining the class of LN and biomarkers predicting the response to treatment would greatly benefit patients with SLE. Basophils, which are one of the rarest types of circulating leucocytes, are well-established effectors of allergic and parasitic diseases. Recent advances in the understanding of the immune regulatory role of basophils in several auto immune conditions, including SLE and LN, have demonstrated their involvement in the amplification of auto-antibody production and LN pathogenesis in both human SLE and lupus-like mouse models. The present review summarizes the currently available literature describing dysregulation of basophil counts, basophil activation status and basophil activating factors in patients with SLE and the involvement of basophils in the pathogenesis of SLE. We also discuss the potential utility of these biological and immunological parameters as diagnostic and prognostic biomarkers, used alone or in combination with other known SLE and LN activity biomarkers. Finally, considering basophils as contributors to the disease, they may also constitute a future treatment target for the management of SLE and LN.

Early Phase Mast Cell Activation Determines the Chronic Outcome of Renal Ischemia-Reperfusion Injury.

Ischemia-reperfusion injury (IRI) is an important cause of acute kidney injury that can lead to end-stage renal failure. Although the ensuing inflammatory response can restore homeostasis, a consecutive maladaptive repair and persistent inflammation represent important risk factors for postischemic chronic kidney disease development. In this study, we investigated the role of mast cells in both the early and late phases of the inflammatory response in experimental models of acute and chronic renal IRI using our recently developed mouse model that allows conditional ablation of mast cells. Depletion of mast cells prior to IRI resulted in improved renal function due to diminished local inflammatory cytokine/chemokine levels and neutrophil recruitment to the kidneys after the acute injury phase (48 h post-IRI). Furthermore, although not completely protected, mast cell-depleted mice displayed less organ atrophy and fibrosis than did wild-type mice during the chronic phases (2 and 6 wk post-IRI) of disease development. Conversely, mast cell ablation after the acute phase of IRI had no impact on organ atrophy, tubular necrosis, or fibrosis. Thus, our results suggest a deleterious role of mast cells during the acute inflammatory phase of IRI promoting subsequent fibrosis development, but not during the chronic phase of the disease.

Lyn kinase controls basophil GATA-3 transcription factor expression and induction of Th2 cell differentiation.

T helper 1 (Th1)-Th2 cell balance is key to host defense and its dysregulation has pathophysiological consequences. Basophils are important in Th2 cell differentiation. However, the factors controlling the onset and extent of basophil-mediated Th2 cell differentiation are unknown. Here, we demonstrate that Lyn kinase dampened basophil expression of the transcription factor GATA-3 and the initiation and extent of Th2 cell differentiation. Lyn-deficient mice had a marked basophilia, a constitutive Th2 cell skewing that was exacerbated upon in vivo challenge of basophils, produced antibodies to a normally inert antigen, and failed to appropriately respond to a Th1 cell-inducing pathogen. The Th2 cell skewing was dependent on basophils, immunoglobulin E, and interleukin-4, but was independent of mast cells. Our findings demonstrate that basophil-expressed Lyn kinase exerts regulatory control on Th2 cell differentiation and function.

Cyclosporine A impairs nucleotide binding oligomerization domain (Nod1)-mediated innate antibacterial renal defenses in mice and human transplant recipients.

Acute pyelonephritis (APN), which is mainly caused by uropathogenic Escherichia coli (UPEC), is the most common bacterial complication in renal transplant recipients receiving immunosuppressive treatment. However, it remains unclear how immunosuppressive drugs, such as the calcineurin inhibitor cyclosporine A (CsA), decrease renal resistance to UPEC. Here, we investigated the effects of CsA in host defense against UPEC in an experimental model of APN. We show that CsA-treated mice exhibit impaired production of the chemoattractant chemokines CXCL2 and CXCL1, decreased intrarenal recruitment of neutrophils, and greater susceptibility to UPEC than vehicle-treated mice. Strikingly, renal expression of Toll-like receptor 4 (Tlr4) and nucleotide-binding oligomerization domain 1 (Nod1), neutrophil migration capacity, and phagocytic killing of E. coli were significantly reduced in CsA-treated mice. CsA inhibited lipopolysaccharide (LPS)-induced, Tlr4-mediated production of CXCL2 by epithelial collecting duct cells. In addition, CsA markedly inhibited Nod1 expression in neutrophils, macrophages, and renal dendritic cells. CsA, acting through inhibition of the nuclear factor of activated T-cells (NFATs), also markedly downregulated Nod1 in neutrophils and macrophages. Silencing the NFATc1 isoform mRNA, similar to CsA, downregulated Nod1 expression in macrophages, and administration of the 11R-VIVIT peptide inhibitor of NFATs to mice also reduced neutrophil bacterial phagocytosis and renal resistance to UPEC. Conversely, synthetic Nod1 stimulating agonists given to CsA-treated mice significantly increased renal resistance to UPEC. Renal transplant recipients receiving CsA exhibited similar decrease in NOD1 expression and neutrophil phagocytosis of E. coli. The findings suggest that such mechanism of NFATc1-dependent inhibition of Nod1-mediated innate immune response together with the decrease in Tlr4-mediated production of chemoattractant chemokines caused by CsA may contribute to sensitizing kidney grafts to APN.

CD4+CXCR3+ T cells and plasmacytoid dendritic cells drive accelerated atherosclerosis associated with systemic lupus erythematosus.

Cardiovascular disease due to accelerated atherosclerosis is the leading cause of death in patients with systemic lupus erythematosus (SLE). Noteworthy, accelerated atherosclerosis in SLE patients appears to be independant of classical Framingham risk factors. This suggests that aggravated atherosclerosis in SLE patients may be a result of increased inflammation and altered immune responses. However, the mechanisms that mediate the acceleration of atherosclerosis in SLE remain elusive. Based on experimental data which includes both humans (SLE patients and control subjects) and rodents (ApoE-/- mice), we herein propose a multi-step model in which the immune dysfunction associated with SLE (i.e. high level of IFN-α production by TLR 9-stimulated pDCs) is associated with, first, an increased frequency of circulating pro inflammatory CD4+CXCR3+ T cells; second, an increased production of CXCR3 ligands by endothelial cells; third, an increased recruitment of pro-inflammatory CD4+CXCR3+ T cells into the arterial wall, and fourth, the development of atherosclerosis. In showing how SLE may promote accelerated atherosclerosis, our model also points to hypotheses for potential interventions, such as pDCs-targeted therapy, that might be studied in the future.

Cutting edge: persistence of increased mast cell numbers in tissues links dermatitis to enhanced airway disease in a mouse model of atopy.

The development of chronic allergic dermatitis in early life has been associated with increased onset and severity of allergic asthma later in life. However, the mechanisms linking these two diseases are poorly understood. In this study, we report that the development of oxazolone-induced chronic allergic dermatitis, in a mouse model, caused enhanced OVA-induced allergic asthma after the resolution of the former disease. Our findings show that oxazolone-induced dermatitis caused a marked increase in tissue mast cells, which persisted long after the resolution of this disease. Subsequent OVA sensitization and airway challenge of mice that had recovered from dermatitis resulted in increased allergic airway hyperreactivity. The findings demonstrate that the accumulation of mast cells during dermatitis has the detrimental effect of increasing allergic airway hypersensitivity. Importantly, our findings also show that exposure to a given allergen can modify the immune response to an unrelated allergen.