The immunology of systemic lupus erythematosus.

Understanding the pathogenesis and clinical manifestations of systemic lupus erythematosus (SLE) has been a great challenge. Reductionist approaches to understand the nature of the disease have identified many pathogenetic contributors that parallel clinical heterogeneity. This Review outlines the immunological control of SLE and looks to experimental tools and approaches that are improving our understanding of the complex contribution of interacting genetics, environment, sex and immunoregulatory factors and their interface with processes inherent to tissue parenchymal cells. Efforts to advance precision medicine in the care of patients with SLE along with treatment strategies to correct the immune system hold hope and are also examined.

Glutathione peroxidase 4-regulated neutrophil ferroptosis induces systemic autoimmunity.

The linkage between neutrophil death and the development of autoimmunity has not been thoroughly explored. Here, we show that neutrophils from either lupus-prone mice or patients with systemic lupus erythematosus (SLE) undergo ferroptosis. Mechanistically, autoantibodies and interferon-α present in the serum induce neutrophil ferroptosis through enhanced binding of the transcriptional repressor CREMα to the glutathione peroxidase 4 (Gpx4, the key ferroptosis regulator) promoter, which leads to suppressed expression of Gpx4 and subsequent elevation of lipid-reactive oxygen species. Moreover, the findings that mice with neutrophil-specific Gpx4 haploinsufficiency recapitulate key clinical features of human SLE, including autoantibodies, neutropenia, skin lesions and proteinuria, and that the treatment with a specific ferroptosis inhibitor significantly ameliorates disease severity in lupus-prone mice reveal the role of neutrophil ferroptosis in lupus pathogenesis. Together, our data demonstrate that neutrophil ferroptosis is an important driver of neutropenia in SLE and heavily contributes to disease manifestations.

Autoimmunity and organ damage in systemic lupus erythematosus.

Impressive progress has been made over the last several years toward understanding how almost every aspect of the immune system contributes to the expression of systemic autoimmunity. In parallel, studies have shed light on the mechanisms that contribute to organ inflammation and damage. New approaches that address the complicated interaction between genetic variants, epigenetic processes, sex and the environment promise to enlighten the multitude of pathways that lead to what is clinically defined as systemic lupus erythematosus. It is expected that each patient owns a unique 'interactome', which will dictate specific treatment.

Phosphatase PP2A is requisite for the function of regulatory T cells.

Homeostasis of the immune system depends on the proper function of regulatory T cells (T(reg) cells). Compromised suppressive activity of T(reg) cells leads to autoimmune disease and graft rejection and promotes anti-tumor immunity. Here we report a previously unrecognized requirement for the serine-threonine phosphatase PP2A in the function of T(reg) cells. T(reg) cells exhibited high PP2A activity, and T(reg) cell-specific ablation of the PP2A complex resulted in a severe, multi-organ, lymphoproliferative autoimmune disorder. Mass spectrometry revealed that PP2A associated with components of the mTOR metabolic-checkpoint kinase pathway and suppressed the activity of the mTORC1 complex. In the absence of PP2A, T(reg) cells altered their metabolic and cytokine profile and were unable to suppress effector immune responses. Therefore, PP2A is required for the function of T(reg) cells and the prevention of autoimmunity.

Retraction Note: Microglia-dependent synapse loss in type I interferon-mediated lupus.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Reverse aging to treat lupus.

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with multifaceted pathogenetic processes, including abnormalities of T-cell subset distribution and function. Accumulation of senescent CD4+ T cells has been found to contribute to the development of the disease. In this issue, Jiang et al. provide compelling evidence that links an expanded pool of CD4+CD57+ senescent T cells in patients with SLE to disease activity favored by interleukin-15. Importantly, treatment of lupus-prone mice with a senolytic drug resulted in decreased autoimmune pathology. The findings of this study suggest possible novel therapeutics to treat patients with SLE.

IL-23 induces CLEC5A+ IL-17A+ neutrophils and elicit skin inflammation associated with psoriatic arthritis.

IL-23-activation of IL-17 producing T cells is involved in many rheumatic diseases. Herein, we investigate the role of IL-23 in the activation of myeloid cell subsets that contribute to skin inflammation in mice and man. IL-23 gene transfer in WT, IL-23RGFP reporter mice and subsequent analysis with spectral cytometry show that IL-23 regulates early innate immune events by inducing the expansion of a myeloid MDL1+CD11b+Ly6G+ population that dictates epidermal hyperplasia, acanthosis, and parakeratosis; hallmark pathologic features of psoriasis. Genetic ablation of MDL-1, a major PU.1 transcriptional target during myeloid differentiation exclusively expressed in myeloid cells, completely prevents IL-23-pathology. Moreover, we show that IL-23-induced myeloid subsets are also capable of producing IL-17A and IL-23R+MDL1+ cells are present in the involved skin of psoriasis patients and gene expression correlations between IL-23 and MDL-1 have been validated in multiple patient cohorts. Collectively, our data demonstrate a novel role of IL-23 in MDL-1-myelopoiesis that is responsible for skin inflammation and related pathologies. Our data open a new avenue of investigations regarding the role of IL-23 in the activation of myeloid immunoreceptors and their role in autoimmunity.

PPP2R2D Suppresses Effector T Cell Exhaustion and Regulatory T Cell Expansion and Inhibits Tumor Growth in Melanoma.

We had shown previously that the protein phosphatase 2A regulatory subunit PPP2R2D suppresses IL-2 production, and PPP2R2D deficiency in T cells potentiates the suppressive function of regulatory T (Treg) cells and alleviates imiquimod-induced lupus-like pathology. In this study, in a melanoma xenograft model, we noted that the tumor grew in larger sizes in mice lacking PPP2R2D in T cells (LckCreR2Dfl/fl) compared with wild type (R2Dfl/fl) mice. The numbers of intratumoral T cells in LckCreR2Dfl/fl mice were reduced compared with R2Dfl/fl mice, and they expressed a PD-1+CD3+CD44+ exhaustion phenotype. In vitro experiments confirmed that the chromatin of exhaustion markers PD-1, LAG3, TIM3, and CTLA4 remained open in LckCreR2Dfl/fl CD4 T conventional compared with R2Dfl/fl T conventional cells. Moreover, the percentage of Treg cells (CD3+CD4+Foxp3+CD25hi) was significantly increased in the xenografted tumor of LckCreR2Dfl/fl mice compared with R2Dfl/fl mice probably because of the increase in the percentage of IL-2-producing LckCreR2Dfl/fl T cells. Moreover, using adoptive T cell transfer in mice xenografted with melanoma, we demonstrated that PPP2R2D deficiency in T cells enhanced the inhibitory effect of Treg cells in antitumor immunity. At the translational level, analysis of publicly available data from 418 patients with melanoma revealed that PPP2R2D expression levels correlated positively with tumor-infiltration level of CD4 and CD8 T cells. The data demonstrate that PPP2R2D is a negative regulator of immune checkpoint receptors, and its absence exacerbates effector T cell exhaustion and promotes Treg cell expansion. We conclude that PPP2R2D protects against melanoma growth, and PPP2R2D-promoting regimens can have therapeutic value in patients with melanoma.

ADAM9 enhances Th17 cell differentiation and autoimmunity by activating TGF-ß1.

The a disintegrin and metalloproteinase (ADAM) family of proteinases alter the extracellular environment and are involved in the development of T cells and autoimmunity. The role of ADAM family members in Th17 cell differentiation is unknown. We identified ADAM9 to be specifically expressed and to promote Th17 differentiation. Mechanistically, we found that ADAM9 cleaved the latency-associated peptide to produce bioactive transforming growth factor ß1, which promoted SMAD2/3 phosphorylation and activation. A transcription factor inducible cAMP early repressor was found to bind directly to the ADAM9 promoter and to promote its transcription. Adam9-deficient mice displayed mitigated experimental autoimmune encephalomyelitis, and transfer of Adam9-deficient myelin oligodendrocyte globulin-specific T cells into Rag1-/- mice failed to induce disease. At the translational level, an increased abundance of ADAM9 levels was observed in CD4+ T cells from patients with systemic lupus erythematosus, and ADAM9 gene deletion in lupus primary CD4+ T cells clearly attenuated their ability to differentiate into Th17 cells. These findings revealed that ADAM9 as a proteinase provides Th17 cells with an ability to activate transforming growth factor ß1 and accelerates its differentiation, resulting in aberrant autoimmunity.

Lupus Nephritis Biomarkers: A Critical Review.

Lupus nephritis (LN), a major complication in individuals diagnosed with systemic lupus erythematosus, substantially increases morbidity and mortality. Despite marked improvements in the survival of patients with severe LN over the past 50 years, complete clinical remission after immunosuppressive therapy is achieved in only half of the patients. Therefore, timely detection of LN is vital for initiating prompt therapeutic interventions and improving patient outcomes. Biomarkers have emerged as valuable tools for LN detection and monitoring; however, the complex role of these biomarkers in LN pathogenesis remains unclear. Renal biopsy remains the gold standard for the identification of the histological phenotypes of LN and guides disease management. However, the molecular pathophysiology of specific renal lesions remains poorly understood. In this review, we provide a critical, up-to-date overview of the latest developments in the field of LN biomarkers.

Chronic stimulation with SARS-CoV-2 spike protein does not trigger autoimmunity.

Autoimmune manifestations were reported in people infected with SARS-CoV-2. Repetitive exposure of mice to foreign antigen may lead to the onset of autoimmunity. We therefore investigated whether repetitive exposure to the SARS-CoV-2 spike protein could result in autoimmunity. To address this hypothesis, we repeatedly immunized C57Bl/6 mice with spike protein injected intraperitoneally. At the end of the immunization, mice which received spike protein produced anti-spike IgG but none of them developed anti-dsDNA antibodies or proteinuria. In conclusion, repetitive immunization with SARS-CoV-2 spike protein does not induce autoimmunity in the present mice model. Albeit reassuring, these results need to be confirmed by large epidemiological study evaluating the incidence of autoimmune diseases in individuals with repetitive SARS-CoV-2 antigen exposure.

Pathogenesis of lupus nephritis: the contribution of immune and kidney resident cells.

PURPOSE OF REVIEW: Lupus nephritis is associated with significant mortality and morbidity. We lack effective therapeutics and biomarkers mostly because of our limited understanding of its complex pathogenesis. We aim to present an overview of the recent advances in the field to gain a deeper understanding of the underlying cellular and molecular mechanisms involved in lupus nephritis pathogenesis. RECENT FINDINGS: Recent studies have identified distinct roles for each resident kidney cell in the pathogenesis of lupus nephritis. Podocytes share many elements of innate and adaptive immune cells and they can present antigens and participate in the formation of crescents in coordination with parietal epithelial cells. Mesangial cells produce pro-inflammatory cytokines and secrete extracellular matrix contributing to glomerular fibrosis. Tubular epithelial cells modulate the milieu of the interstitium to promote T cell infiltration and formation of tertiary lymphoid organs. Modulation of specific genes in kidney resident cells can ward off the effectors of the autoimmune response including autoantibodies, cytokines and immune cells. SUMMARY: The development of lupus nephritis is multifactorial involving genetic susceptibility, environmental triggers and systemic inflammation. However, the role of resident kidney cells in the development of lupus nephritis is becoming more defined and distinct. More recent studies point to the restoration of kidney resident cell function using cell targeted approaches to prevent and treat lupus nephritis.

Essential role for the prolyl isomerase Pin1 in Toll-like receptor signaling and type I interferon-mediated immunity.

Toll-like receptors (TLRs) shape innate and adaptive immunity to microorganisms. The enzyme IRAK1 transduces signals from TLRs, but mechanisms for its activation and regulation remain unknown. We found here that TLR7 and TLR9 activated the isomerase Pin1, which then bound to IRAK1; this resulted in activation of IRAK1 and facilitated its release from the receptor complex to activate the transcription factor IRF7 and induce type I interferons. Consequently, Pin1-deficient cells and mice failed to mount TLR-mediated, interferon-dependent innate and adaptive immune responses. Given the critical role of aberrant activation of IRAK1 and type I interferons in various immune diseases, controlling IRAK1 activation via inhibition of Pin1 may represent a useful therapeutic approach.

Inhibition of calcium/calmodulin-dependent protein kinase IV in arthritis: dual effect on Th17 cell activation and osteoclastogenesis.

OBJECTIVE: To investigate the role of calcium/calmodulin-dependent protein kinase IV (CaMK4) in the development of joint injury in a mouse model of arthritis and patients with RA. METHODS: Camk4-deficient, Camk4flox/floxLck-Cre, and mice treated with CaMK4 inhibitor KN-93 or KN-93 encapsulated in nanoparticles tagged with CD4 or CD8 antibodies were subjected to collagen-induced arthritis (CIA). Inflammatory cytokine levels, humoral immune response, synovitis, and T-cell activation were recorded. CAMK4 gene expression was measured in CD4+ T cells from healthy participants and patients with active RA. Micro-CT and histology were used to assess joint pathology. CD4+ and CD14+ cells in patients with RA were subjected to Th17 or osteoclast differentiation, respectively. RESULTS: CaMK4-deficient mice subjected to CIA displayed improved clinical scores and decreased numbers of Th17 cells. KN-93 treatment significantly reduced joint destruction by decreasing the production of inflammatory cytokines. Furthermore, Camk4flox/floxLck-Cre mice and mice treated with KN93-loaded CD4 antibody-tagged nanoparticles developed fewer Th17 cells and less severe arthritis. CaMK4 inhibition mitigated IL-17 production by CD4+ cells in patients with RA. The number of in vitro differentiated osteoclasts from CD14+ cells in patients with RA was significantly decreased with CaMK4 inhibitors. CONCLUSION: Using global and CD4-cell-targeted pharmacologic approaches and conditionally deficient mice, we demonstrate that CaMK4 is important in the development of arthritis. Using ex vivo cell cultures from patients with RA, CaMK4 is important for both Th17 generation and osteoclastogenesis. We propose that CaMK4 inhibition represents a new approach to control the development of arthritis.

Targeted nanotherapy for kidney diseases: a comprehensive review.

Kidney diseases represent a major public health problem, affecting millions of people worldwide. Moreover, the treatment of kidney diseases is burdened by the problematic effects of conventional drug delivery, such as systemic drug toxicity, rapid drug clearance, and the absence of precise targeting of the kidney. Although the use of nanotechnology in medicine is in its early stage and lacks robust translational studies, nanomedicines have already shown great promise as novel drug-delivery systems for the treatment of kidney disease. On the basis of our current knowledge of renal anatomy and physiology, pathophysiology of kidney diseases, and physicochemical characteristics of nanoparticles, an expansive repertoire and wide use of nanomedicines could be developed for kidney diseases in the near future. Some limitations have slowed the transition of these agents from preclinical studies to clinical trials, however. In this review, we summarize the current knowledge on renal drug-delivery systems and recent advances in renal cell targeting; we also demonstrate their important potential as future paradigm-shifting therapies for kidney diseases.

The Regulatory Subunit PPP2R2A of PP2A Enhances Th1 and Th17 Differentiation through Activation of the GEF-H1/RhoA/ROCK Signaling Pathway.

Protein phosphatase 2A (PP2A) composed of a scaffold subunit, a catalytic subunit, and multiple regulatory subunits is a ubiquitously expressed serine/threonine phosphatase. We have previously shown that the PP2A catalytic subunit is increased in T cells from patients with systemic lupus erythematosus and promotes IL-17 production by enhancing the activity of Rho-associated kinase (ROCK) in T cells. However, the molecular mechanism whereby PP2A regulates ROCK activity is unknown. In this study, we show that the PP2A regulatory subunit PPP2R2A is increased in T cells from people with systemic lupus erythematosus and binds to, dephosphorylates, and activates the guanine nucleotide exchange factor GEF-H1 at Ser885, which in turn increases the levels of RhoA-GTP and the activity of ROCK in T cells. Genetic PPP2R2A deficiency in murine T cells reduced Th1 and Th17, but not regulatory T cell differentiation and mice with T cell-specific PPP2R2A deficiency displayed less autoimmunity when immunized with myelin oligodendrocyte glycoprotein peptide. Our studies indicate that PPP2R2A is the regulatory subunit that dictates the PP2A-directed enhanced Th1 and Th17 differentiation, and therefore, it represents a therapeutic target for pathologies linked to Th1 and Th17 cell expansion.

TNF-α Regulates Human Plasmacytoid Dendritic Cells by Suppressing IFN-α Production and Enhancing T Cell Activation.

Human plasmacytoid dendritic cells (pDCs) play a vital role in modulating immune responses. They can produce massive amounts of type I IFNs in response to nucleic acids via TLRs, but they are also known to possess weak Ag-presenting properties inducing CD4+ T cell activation. Previous studies showed a cross-regulation between TNF-α and IFN-α, but many questions remain about the effect of TNF-α in regulating human pDCs. In this study, we showed that TNF-α significantly inhibited the secretion of IFN-α and TNF-α of TLR-stimulated pDCs. Instead, exogenous TNF-α promoted pDC maturation by upregulating costimulatory molecules and chemokine receptors such as CD80, CD86, HLA-DR, and CCR7. Additionally, RNA sequencing analysis showed that TNF-α inhibited IFN-α and TNF-α production by downregulating IRF7 and NF-κB pathways, while it promoted Ag processing and presentation pathways as well as T cell activation and differentiation. Indeed, TNF-α-treated pDCs induced in vitro higher CD4+ T cell proliferation and activation, enhancing the production of Th1 and Th17 cytokines. In conclusion, TNF-α favors pDC maturation by switching their main role as IFN-α-producing cells to a more conventional dendritic cell phenotype. The functional status of pDCs might therefore be strongly influenced by their overall inflammatory environment, and TNF-α might regulate IFN-α-mediated aspects of a range of autoimmune and inflammatory diseases.

Cyclic AMP Response Element Modulator-α Suppresses PD-1 Expression and Promotes Effector CD4+ T Cells in Psoriasis.

Effector CD4+ T lymphocytes contribute to inflammation and tissue damage in psoriasis, but the underlying molecular mechanisms remain poorly understood. The transcription factor CREMα controls effector T cell function in people with systemic autoimmune diseases. The inhibitory surface coreceptor PD-1 plays a key role in the control of effector T cell function and its therapeutic inhibition in patients with cancer can cause psoriasis. In this study, we show that CD4+ T cells from patients with psoriasis and psoriatic arthritis exhibit increased production of IL-17 but decreased expression of IL-2 and PD-1. In genetically modified mice and Jurkat T cells CREMα expression was linked to low PD-1 levels. We demonstrate that CREMα is recruited to the proximal promoter of PDCD1 in which it trans-represses gene expression and corecruits DNMT3a-mediating DNA methylation. As keratinocytes limit inflammation by PD-1 ligand expression and, in this study, reported reduced expression of PD-1 on CD4+ T cells is linked to low IL-2 and high IL-17A production, our studies reveal a molecular pathway in T cells from people with psoriasis that can deserve clinical exploitation.