New and emerging therapies for systemic lupus erythematosus.

Systemic Lupus Erythematosus (SLE) and lupus nephritis treatment is still based on non-specific immune suppression despite the first biological therapy for the disease having been approved more than a decade ago. Intense basic and translational research has uncovered a multitude of pathways that are actively being evaluated as treatment targets in SLE and lupus nephritis, with two new medications receiving FDA approval in the last 3 years. Herein we provide an overview of targeted therapies for SLE including medications targeting the B lymphocyte compartment, intracellular signaling, co-stimulation, and finally the interferons and other cytokines.

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.

Estimating glucocorticoid-related morbidity in lupus nephritis using the glucocorticoid toxicity index.

OBJECTIVE: Lupus nephritis (LN) is often treated with high doses of glucocorticoids (GCs). The glucocorticoid toxicity index (GTI) was developed by expert consensus to quantify GC toxicity. To date, the GTI has not been shown to correlate with GC exposure in patients with LN. METHODS: We performed a retrospective cohort study of patients with biopsy-confirmed LN between 2006 and 2016. Cumulative GC exposure and GTI scores were determined via medical record review. Both the aggregate improvement score (GTI-AIS) and the cumulative worsening score (GTI-CWS) were calculated. We performed linear regression to determine the association between GC exposure and GTI scores at 1 year and 5 years following kidney biopsy. RESULTS: This study included 49 patients with a mean age of 33.3 (SD 9.5) years. Mean GC exposure was 23.0 mg prednisone-equivalents per day through year 1 and 9.9 mg prednisone-equivalents per day through year 5. At 5 years, higher GC exposure was associated with higher GTI-AIS (p < 0.001) and GTI-CWS (p = 0.002), and this association persisted in multivariate analysis adjusting for age, sex, race, induction medication, and nephritis class (p = 0.026 for AIS, p = 0.012 for CWS). At 1 year, GC exposure was not associated with GTI scores (p = 0.70 for AIS; p = 0.58 for CWS). CONCLUSION: In this cohort study, the GTI was associated with cumulative steroid exposure at 5 years after diagnosis. In patients with LN, the GTI may serve as a useful outcome measure in future LN trials evaluating the steroid sparing effect of novel therapies.

Undifferentiated Connective Tissue Disease: Comprehensive Review.

PURPOSE OF REVIEW: Undifferentiated connective tissue disease (UCTD) is characterized by the presence of clinical symptoms of a systemic autoimmune disease in addition to laboratory evidence of autoimmunity with the patients not fulfilling any of the widely used classification criteria for classic autoimmune diseases. The presence of UCTD as a separate entity versus an early stage of such diseases as systemic lupus erythematosus (SLE) or scleroderma has long been debated. Given the uncertainty regarding this condition, we performed a systematic review on the topic. RECENT FINDINGS: UCTD can be subcategorized as evolving (eUCTD) or stable UCTD (sUCTD) based on its evolution towards a definable autoimmune syndrome. Analyzing the data from six UCTD cohorts published in the literature, we found that 28% of patients have an evolving course with the majority developing SLE or rheumatoid arthritis within 5-6 years of the UCTD diagnosis. From the remaining patients, 18% do achieve remission. Published treatment regimens were similar to other mild autoimmune diseases with low-dose prednisone, hydroxychloroquine, and NSAID. One-third of patients did need immune suppressive medications. Importantly, the reported outcomes were excellent with survival rates of more than 90% over 10 years. It has to be noted though that as data on patient related outcomes are not available to date, the exact impact of this condition on quality of life is unclear. UCTD is a mild autoimmune condition with generally good outcomes. There is still great uncertainty though regarding diagnosis and management. Going forward, consistent classification criteria are needed to advance UCTD research and eventually provide authoritative guidance on the management of the condition.

Prevalence and clinical significance of lymphadenopathy and its histological subtypes in patients with systemic lupus erythematosus: a retrospective cohort study.

The objective of this study was to evaluate the prevalence and the clinical significance of lymphadenopathy and its histological subtypes in patients with systemic lupus erythematosus. We conducted a retrospective cohort study of patients with SLE diagnosed using the 1997 ACR criteria, who were followed at our institution between 2008 and 2022. Patients were grouped based on the presence of SLE-attributed LAD and its histological phenotype, then compared in terms of demographic, clinical and laboratory characteristics. Of the 255 patients, 33.7% had SLE-attributed, 0.8% lymphoma-related and 0.4% tuberculosis-related LAD. Univariate analysis identified significant associations between the presence of LAD and fever (p < 0.0001), weight loss (p = 0.009), pericarditis (p = 0.004), myocarditis (p = 0.003), myositis (p = 0.034), leukopenia (p = 0.004), lymphopenia (p = 0.003), membranous nephritis (p = 0.004), anti-RNP (p = 0.001), anti-Smith (p = < 0.0001), and SSB antibodies (p = 0.038), and hypocomplementemia (C3:p = 0.019; C4:p < 0.0001). Logistic regression confirmed the associations of LAD with fever (OR = 3.277, 95% C.I 1.657-6.481), pericarditis (OR = 4.146, 95% C.I:1.577-10.899), membranous nephritis (OR = 3.586, 95% C.I:1.305-9.854), and leukopenia (OR = 2.611, 95%C.I:1.319-5.166), but not with weight loss, myocarditis, or myositis. Biopsy in a subset of patients (33.7% of total) revealed reactive/proliferative (62.1%) or necrotizing (37.9%) histological patterns. When we compared the histologic patterns, necrotizing LAD was associated with fever (p = 0.052), sicca (p = 0.018), and malar rash (p = 0.005). Most patients received corticosteroids, hydroxychloroquine, and/or DMARDs with relatively quick clinical improvement. In conclusion, LAD is a common SLE manifestation, associated with constitutional symptoms, myo-/pericarditis, myositis, cytopenia, and membranous nephritis. Despite relatively high prevalence of LAD in SLE, a biopsy may still be needed to rule out lymphoma.

Predictors of a weak antibody response to COVID-19 mRNA vaccine in systemic lupus erythematosus.

OBJECTIVES: To characterize the antibody response to COVID-19 mRNA vaccination in patients with Systemic Lupus Erythematosus (SLE) and identify predictors of poor response. METHODS: SLE patients who are followed at the Beth Israel Deaconess Medical Center Lupus Cohort (BID-LC) were enrolled. SARS-CoV-2 IgG Spike antibody was measured in patients who received two doses of either the BNT162b2 (Pfizer-BioNTech) or the mRNA-1273 (Moderna) COVID-19 vaccine (n = 62). We defined non-responders as patients with an IgG Spike antibody titer less than two-fold (< 2) the index value of the test and responders as patients with antibody levels greater or equal to two-fold (≥ 2). A web-based survey was used to collect information regarding immunosuppressive medication use and SLE flares after vaccination. RESULTS: In our cohort of lupus patients, 76% were vaccine responders. The use of two or more immunosuppressive drugs was associated with being a non-responder (Odds Ratio 5.26; 95% CI 1.23-22.34, p = 0.02). Both Belimumab use and higher Prednisone dose were associated with vaccine non-response (p = 0.04 and p = 0.04). The non-responder group had higher mean levels of serum IL-18 than the responder group (p = 0.04) as well as lower C3 levels (p = 0.01). Lupus flares and breakthrough infections were uncommon post-vaccination. CONCLUSIONS: Immunosuppressive medications have a negative impact on vaccine humoral response in SLE individuals. We observed a trend towards vaccine no-response in BNT162b2 recipients and a relationship between IL-18 and impaired antibody response that merits further investigation.

Immunogenicity of SARS-CoV-2 vaccination in rituximab-treated patients: Effect of timing and immunologic parameters.

Rituximab (RTX), an important therapeutic option for patients with rheumatic diseases, has been shown to reduce immune responses to various vaccines. We asked whether following SARS-CoV-2 vaccination, response rates in RTX treated patients are reduced and whether specific patient characteristics influence the responses. We recruited patients on chronic RTX therapy undergoing anti-SARS-CoV2 vaccination and measured the post-vaccination anti-spike IgG antibody levels. The median time from pre-vaccination RTX infusion to vaccination and from vaccination to the post-vaccination RTX infusion was 20.5 weeks and 7.2 weeks respectively. Only 36.5% of patients developed measurable titers of IgG anti-SARS-CoV-2 spike antibody after vaccination. Hypogammaglobulinemia (IgG and/or IgM) but not timing of vaccination, B cell numbers, or concomitant immune suppressive medications, correlated with sero-negativity (p = 0.004). Our results underscore the fact that even after B cell reconstitution, RTX induced chronic hypogammaglobulinemia significantly impairs the ability of the immune system to respond to SARS-CoV-2 vaccination.

Seroconversion among rituximab-treated patients following SARS-CoV-2 vaccine supplemental dose.

Rituximab (RTX) is a very effective treatment for autoimmune rheumatic diseases (AIRD), but it increases infection risk and impairs vaccine responses. Herein we evaluated the antibody response of RTX-treated patients to the supplemental COVID-19 vaccine. After the supplemental dose, 53.1% of patients had detectable antibody titers. Only 36% of patients who did not mount an antibody response after the original vaccine series did have detectable antibodies after the supplemental dose (seroconversion). Patients with undetectable CD20+ cell levels did not seroconvert while hypogammaglobulinemia was associated with a 15-times decrease in the likelihood of seroconversion. Although we noted 11 COVID-19 infections after the supplemental dose, no patients who received monoclonal antibodies pre-exposure prophylaxis had COVID-19 afterwards. We propose that patients receiving RTX should continue to be prioritized for prophylaxis measures and that vaccination should be timed after B cell recovery wherever possible.

Splicing factor SRSF1 limits IFN-γ production via RhoH and ameliorates experimental nephritis.

OBJECTIVE: CD4 T helper 1 (Th1) cells producing IFN-γ contribute to inflammatory responses in the pathogenesis of SLE and lupus nephritis. Moreover, elevated serum type II IFN levels precede the appearance of type I IFNs and autoantibodies in patient years before clinical diagnosis. However, the molecules and mechanisms that control this inflammatory response in SLE remain unclear. Serine/arginine-rich splicing factor 1 (SRSF1) is decreased in T cells from SLE patients, and restrains T cell hyperactivity and systemic autoimmunity. Our objective here was to evaluate the role of SRSF1 in IFN-γ production, Th1 differentiation and experimental nephritis. METHODS: T cell-conditional Srsf1-knockout mice were used to study nephrotoxic serum-induced nephritis and evaluate IFN-γ production and Th1 differentiation by flow cytometry. RNA sequencing was used to assess transcriptomics profiles. RhoH was silenced by siRNA transfections in human T cells by electroporation. RhoH and SRSF1 protein levels were assessed by immunoblots. RESULTS: Deletion of Srsf1 in T cells led to increased Th1 differentiation and exacerbated nephrotoxic serum nephritis. The expression levels of RhoH are decreased in Srsf1-deficient T cells, and silencing RhoH in human T cells leads to increased production of IFN-γ. Furthermore, RhoH expression was decreased and directly correlated with SRSF1 in T cells from SLE patients. CONCLUSION: Our study uncovers a previously unrecognized role of SRSF1 in restraining IFN-γ production and Th1 differentiation through the control of RhoH. Reduced expression of SRSF1 may contribute to pathogenesis of autoimmune-related nephritis through these molecular mechanisms.

Rituximab-associated hypogammaglobulinemia in autoimmune rheumatic diseases: a single-center retrospective cohort study.

B-cell targeted therapies, such as rituximab (RTX), are used widely in autoimmune rheumatic diseases (AIRD). RTX can cause hypogammaglobulinemia and predispose patients to infections. Herein, we asked whether the underlying diagnosis influences the risk for hypogammaglobulinemia in patients treated with RTX. All patients who received RTX infusions and carried a diagnosis of rheumatoid arthritis (RA), ANCA-associated vasculitis (AAV), or connective tissue disease (CTD) were included in this single-center retrospective cohort study. We used STATA® for analysis: Chi-square test was used for comparing categorical variables. Based on distribution, continuous variables were compared using the t test/ANOVA or the Wilcoxon/Kruskal-Wallis tests. Of the 163 patients who received RTX for an AIRD, 60 with pre- and post- RTX immunoglobulins were analyzed. A higher incidence of post-treatment hypogammaglobulinemia was seen in AAV (45%) compared to RA (22%) and CTD (9.1%) groups (p = 0.03). Glucocorticoid exposure of 10 mg or more was identified as a significant risk factor for hypogammaglobulinemia. Finally, we observed a higher number of clinically significant infections per person in the AAV group than in the RA and CTD groups. We observed an increased incidence of hypogammaglobulinemia in the RTX-treated AAV group, with almost half of patients developing post-RTX hypogammaglobulinemia. The rate of infections per person was highest in the AAV group. Screening immunoglobulins were not consistently measured pre- and post-RTX. Results highlight a need for increased awareness of the role of immunoglobulin measurement before maintenance doses of RTX, especially in patients with AAV and steroid exposure.

Pyruvate dehydrogenase phosphatase catalytic subunit 2 limits Th17 differentiation.

Th17 cells favor glycolytic metabolism, and pyruvate dehydrogenase (PDH) is the key bifurcation enzyme, which in its active dephosphorylated form advances the oxidative phosphorylation from glycolytic pathway. The transcriptional factor, inducible cAMP early repressor/cAMP response element modulator (ICER/CREM), has been shown to be induced in Th17 cells and to be overexpressed in CD4+ T cells from the patients with systemic lupus erythematosus (SLE). We found that glycolysis and lactate production in in vitro Th17-polarized T cells was reduced and that the expression of pyruvate dehydrogenase phosphatase catalytic subunit 2 (PDP2), an enzyme that converts the inactive PDH to its active form, and PDH enzyme activity were increased in Th17 cells from ICER/CREM-deficient animals. ICER was found to bind to the Pdp2 promoter and suppress its expression. Furthermore, forced expression of PDP2 in CD4+ cells reduced the in vitro Th17 differentiation, whereas shRNA-based suppression of PDP2 expression increased in vitro Th17 differentiation and augmented experimental autoimmune encephalomyelitis. At the translational level, PDP2 expression was decreased in memory Th17 cells from patients with SLE and forced expression of PDP2 in CD4+ T cells from lupus-prone MRL/lpr mice and patients with SLE suppressed Th17 differentiation. These data demonstrate the direct control of energy production during Th17 differentiation in health and disease by the transcription factor ICER/CREM at the PDH metabolism bifurcation level.

Splicing factor SRSF1 controls T cell homeostasis and its decreased levels are linked to lymphopenia in systemic lupus erythematosus.

OBJECTIVE: Lymphopenia is a frequent clinical manifestation and risk factor for infections in SLE, but the underlying mechanisms are not fully understood. We previously identified novel roles for the RNA-binding protein serine arginine-rich splicing factor 1 (SRSF1) in the control of genes involved in signalling and cytokine production in human T cells. SRSF1 is decreased in T cells from patients with SLE and associates with severe disease. Because SRSF1 controls the expression of apoptosis-related genes, we hypothesized that SRSF1 controls T cell homeostasis and, when reduced, leads to lymphopenia. METHODS: We evaluated SRSF1 expression in T cells from SLE patients by immunoblots and analysed its correlation with clinical parameters. T cell conditional Srsf1 knockout mice were used to evaluate lymphoid cells and apoptosis by flow cytometry. Quantitative PCR and immunoblots were used to assess Bcl-xL mRNA and protein expression. SRSF1 overexpression was performed by transient transfections by electroporation. RESULTS: We found that low SRSF1 levels correlated with lymphopenia in SLE patients. Selective deletion of Srsf1 in T cells in mice led to T cell lymphopenia, with increased apoptosis and decreased expression of the anti-apoptotic Bcl-xL. Lower SRSF1 expression correlated with low Bcl-xL levels in T cells and lower Bcl-xL levels associated with lymphopenia in SLE patients. Importantly, overexpression of SRSF1 rescued survival of T cells from patients with SLE. CONCLUSION: Our studies uncovered a previously unrecognized role for SRSF1 in the control of T cell homeostasis and its reduced expression as a molecular defect that contributes to lymphopenia in systemic autoimmunity.

Interleukin 23 is elevated in the serum of patients with SLE.

Aim: Interleukin-23 (IL-23) is a cytokine that promotes the differentiation of T cells into pro-inflammatory Th17. We have previously shown that IL-23 is upregulated in systemic lupus erythematosus (SLE) patients and lupus prone mice. As SLE is highly heterogeneous, we asked whether IL-23 production correlates with different manifestations of the disease.Methods: We recruited 56 subjects who fulfilled the ACR criteria for SLE. Interleukin-23 was measured in the serum by ELISA.Results: IL-23 levels were positively correlated with the overall SLE disease activity as measured with the SLEDAI. Moreover, IL-23 correlated with the skin, renal domains of SLEDAI and arthritis but not with cytopenias or serositis. IL-23 did also correlate with anti-dsDNA antibody positivity and inversely correlated with C3 levels. We found no relationship between patients' demographics, prior disease manifestations, medications, or autoantibody profile and IL-23 levels. No immunomodulatory medication seemed to be affecting IL-23 levels suggesting that current medications used in SLE are not as effective in shutting down the IL-23/IL-17 axis. Conclusions: IL-23 levels track SLE disease activity mostly in the renal, skin and musculoskeletal domains. Our data suggest that IL-23 inhibitors may be helpful in combination with current standard of care in alleviating arthritis, renal and cutaneous manifestations of the disease.

Downregulation of CD3ζ in NK Cells from Systemic Lupus Erythematosus Patients Confers a Proinflammatory Phenotype.

Cytotoxic function and cytokine profile of NK cells are compromised in patients with systemic lupus erythematosus (SLE). CD3ζ, an important molecule for NK cell activation, is downregulated in SLE T cells and contributes to their altered function. However, little is known about the role of CD3ζ in SLE NK cells. We studied CD3ζ levels and its contribution to cytotoxic, degranulation, and cytokine production capacity of NK cells from patients with SLE. Furthermore, we studied the human NK cell line, NKL, in which manipulation of CD3ζ levels was achieved using small interfering RNA and NK cells from Rag2 mice deficient in CD3ζ. We found reduced CD3ζ expression in NK cells from SLE patients independent of disease activity. Downregulation of CD3ζ expression in NK cells is mediated, at least in part, by Caspase 3, the activity of which is higher in NK cells from patients with SLE compared with NK cells from healthy donors. CD3ζ levels correlated inversely with natural cytotoxicity and the percentage of cells capable of producing the proinflammatory cytokines IFN-γ and TNF. In contrast, CD3ζ levels showed a direct correlation with levels of Ab-dependent cellular cytotoxicity. Experiments performed in CD3ζ-silenced NKL and CD3ζ-deficient NK cells from Rag2 mice confirmed the dependence of NK cell function on CD3ζ levels. Our results demonstrate a differential role for CD3ζ in natural cytotoxicity and Ab-dependent cellular cytotoxicity. We conclude that downregulated CD3ζ confers a proinflammatory phenotype to SLE NK cells and contributes to their altered function in patients with SLE.

Targeting cytokines to treat autoimmunity.

Monoclonal antibodies, small molecules and soluble receptors that target cytokines have revolutionized the treatment of autoimmune and autoinflammatory diseases. The articles that are presented in this special issue of Clinical Immunology analyze the basic science, the clinical implications and the future directions of cytokine targeting in these diseases.

IL-23 Limits the Production of IL-2 and Promotes Autoimmunity in Lupus.

The IL-23/IL-17 pathway is important in multiple autoimmune diseases, but its effect on lupus pathology remains unclear, with opposing trials in murine models of the disease. In this study, we show a disease activity-related upregulation of serum IL-23 and IL-23 receptor in patients with systemic lupus erythematosus (SLE) as compared with healthy controls. When added in SLE T cell in vitro cultures, IL-23 induced IL-17 and limited IL-2 production, whereas T follicular helper and double negative (DN) T cells significantly expanded. To further dissect the role of IL-23 in the expression of autoimmunity and related pathology, we generated IL-23 receptor-deficient MRL.lpr mice. These IL-23R-/-MRL.lpr mice displayed attenuated lupus nephritis with a striking decrease in the accumulation of DN T cells in the kidneys and secondary lymphoid organs. Moreover, T cells from IL-23R-/-MRL.lpr mice produced increased amounts of IL-2 and reduced amounts of IL-17 compared with T cells from wild type animals. In vitro IL-23 treatment promoted IL-17 production and downregulated IL-2 production. The IL-23R-/-MRL.lpr had fewer T follicular helper cells, B cells, and plasma cells, leading to decreased production of anti-dsDNA Abs. Our results show that IL-23 accounts for the main aspects of human and murine lupus including the expansion of DN T cells, decreased IL-2, and increased IL-17 production. We propose that blockade of IL-23 should have a therapeutic value in patients with SLE.

Cathepsin K Deficiency Ameliorates Systemic Lupus Erythematosus-like Manifestations in Faslpr Mice.

Cysteinyl cathepsin K (CatK) is expressed in osteoclasts to mediate bone resorption, but is also inducible under inflammatory conditions. Faslpr mice on a C57BL/6 background develop spontaneous systemic lupus erythematosus-like manifestations. Although normal mouse kidneys expressed negligible CatK, those from Faslpr mice showed elevated CatK expression in the glomeruli and tubulointerstitial space. Faslpr mice also showed elevated serum CatK levels. CatK deficiency in Faslpr mice reduced all tested kidney pathologies, including glomerulus and tubulointerstitial scores, glomerulus complement C3 and IgG deposition, chemokine expression and macrophage infiltration, and serum autoantibodies. CatK contributed to Faslpr mouse autoimmunity and pathology in part by its activity in TLR-7 proteolytic processing and consequent regulatory T (Treg) cell biology. Elevated TLR7 expression and proteolytic processing in Faslpr mouse kidneys and Tregs showed significantly reduced levels in CatK-deficient mice, leading to increased spleen and kidney Treg content. Purified CD4+CD25highFoxp3+ Tregs from CatK-deficient mice doubled their immunosuppressive activity against T effector cells, compared with those from CatK-sufficient mice. In Faslpr mice, repopulation of purified Tregs from CatK-sufficient mice reduced spleen sizes, autoantibody titers, and glomerulus C3 and IgG deposition, and increased splenic and kidney Treg contents. Tregs from CatK-deficient mice had significantly more potency than CatK-sufficient Tregs in reducing spleen sizes, serum autoantibody titers, and glomerulus C3 deposition, and in increasing splenic and kidney Treg content. This study established a possible role of CatK in TLR7 proteolytic activation, Treg immunosuppressive activity, and lupus autoimmunity and pathology.

CD74 Deficiency Mitigates Systemic Lupus Erythematosus-like Autoimmunity and Pathological Findings in Mice.

CD74 mediates MHC class-II antigenic peptide loading and presentation and plays an important role in the pathogenesis of autoimmune diseases, including systemic lupus erythematosus. C57BL/6 Faslpr mice that develop spontaneous lupus-like autoimmunity and pathology showed elevated CD74 expression in the inflammatory cell infiltrates and the adjacent tubular epithelial cells (TECs) in kidneys affected by lupus nephritis but negligible levels in kidneys from age-matched wild-type mice. The inflammatory cytokine IFN-γ or IL-6 induced CD74 expression in kidney TECs in vitro. The presence of kidney TECs from Faslpr mice, rather than from wild-type mice, produced significantly stronger histones, dsDNA, and ribonucleoprotein-Smith Ag complex-induced CD4+ T cell activation. Splenocytes from CD74-deficient FaslprCd74-/- mice had muted responses in a MLR and to the autoantigen histones. Compared with FaslprCd74+/+ mice, FaslprCd74-/- mice had reduced kidney and spleen sizes, splenic activated T cells and B cells, serum IgG and autoantibodies, urine albumin/creatinine ratio, kidney Periodic acid-Schiff score, IgG and C3 deposition, and serum IL-6 and IL-17A levels, but serum IL-2 and TGF-ß levels were increased. Study of chronic graft-versus-host C57BL/6 mice that received donor splenocytes from B6.C-H2bm12 /KhEg mice and those that received syngeneic donor splenocytes yielded similar observations. CD74 deficiency reduced lupus-like autoimmunity and kidney pathology in chronic graft-versus-host mice. This investigation establishes the direct participation of CD74 in autoimmunity and highlights a potential role for CD74 in kidney TECs, together with professional APCs in systemic lupus erythematosus.

Engagement of SLAMF3 enhances CD4+ T-cell sensitivity to IL-2 and favors regulatory T-cell polarization in systemic lupus erythematosus.

Signaling lymphocytic activation molecule family 3 (SLAMF3/Ly9) is a coregulatory molecule implicated in T-cell activation and differentiation. Systemic lupus erythematosus (SLE) is characterized by aberrant T-cell activation and compromised IL-2 production, leading to abnormal regulatory T-cell (Treg) development/function. Here we show that SLAMF3 functions as a costimulator on CD4(+) T cells and influences IL-2 response and T helper cell differentiation. SLAMF3 ligation promotes T-cell responses to IL-2 via up-regulation of CD25 in a small mothers against decapentaplegic homolog 3 (Smad3)-dependent mechanism. This augments the activation of the IL-2/IL-2R/STAT5 pathway and enhances cell proliferation in response to exogenous IL-2. SLAMF3 costimulation promotes Treg differentiation from naïve CD4(+) T cells. Ligation of SLAMF3 receptors on SLE CD4(+) T cells restores IL-2 responses to levels comparable to those seen in healthy controls and promotes functional Treg generation. Taken together, our results suggest that SLAMF3 acts as potential therapeutic target in SLE patients by augmenting sensitivity to IL-2.

Decreased SAP Expression in T Cells from Patients with Systemic Lupus Erythematosus Contributes to Early Signaling Abnormalities and Reduced IL-2 Production.

T cells from patients with systemic lupus erythematosus (SLE) display a number of abnormalities, including increased early signaling events following engagement of the TCR. Signaling lymphocytic activation molecule family cell surface receptors and the X-chromosome-defined signaling lymphocytic activation molecule-associated protein (SAP) adaptor are important in the development of several immunocyte lineages and modulating the immune response. We present evidence that SAP protein levels are decreased in T cells and in their main subsets isolated from 32 women and three men with SLE, independent of disease activity. In SLE T cells, SAP protein is also subject to increased degradation by caspase-3. Forced expression of SAP in SLE T cells normalized IL-2 production, calcium (Ca(2+)) responses, and tyrosine phosphorylation of a number of proteins. Exposure of normal T cells to SLE serum IgG, known to contain anti-CD3/TCR Abs, resulted in SAP downregulation. We conclude that SLE T cells display reduced levels of the adaptor protein SAP, probably as a result of continuous T cell activation and degradation by caspase-3. Restoration of SAP levels in SLE T cells corrects the overexcitable lupus T cell phenotype.