TLR tolerance reduces IFN-alpha production despite plasmacytoid dendritic cell expansion and anti-nuclear antibodies in NZB bicongenic mice

Altered Balance of Pro-Inflammatory Immune Cells to T Regulatory Cells Differentiates Symptomatic From Asymptomatic Individuals With Anti-Nuclear Antibodies

Systemic Autoimmune Rheumatic Diseases (SARDs) are characterized by the production of anti-nuclear antibodies (ANAs). ANAs are also seen in healthy individuals and can be detected years before disease onset in SARD. Both the immunological changes that promote development of clinical symptoms in SARD and those that prevent autoimmunity in asymptomatic ANA+ individuals (ANA+ NS) remain largely unexplored. To address this question, we used flow cytometry to examine peripheral blood immune populations in ANA+ individuals, with and without SARD, including 20 individuals who subsequently demonstrated symptom progression. Several immune populations were expanded in ANA+ individuals with and without SARD, as compared with ANA- healthy controls, particularly follicular and peripheral T helper, and antibody-producing B cell subsets. In ANA+ NS individuals, there were significant increases in T regulatory subsets and TGF-ß1 that normalized in SARD patients, whereas in SARD patients there were increases in Th2 and Th17 helper cell levels as compared with ANA+ NS individuals, resulting in a shift in the balance between inflammatory and regulatory T cell subsets. Patients with SARD also had increases in the proportion of pro-inflammatory innate immune cell populations, such as CD14+ myeloid dendritic cells, and intermediate and non-classical monocytes, as compared to ANA+ NS individuals. When comparing ANA+ individuals without SARD who progressed clinically over the subsequent 2 years with those who did not, we found that progressors had significantly increased T and B cell activation, as well as increased levels of LAG3+ T regulatory cells and TGF-ß1. Collectively, our findings suggest that active immunoregulation prevents clinical autoimmunity in ANA+ NS and that this becomes impaired in patients who progress to SARD, resulting in an imbalance favoring inflammation.

Potential role of viral infection and B cells as a linker between innate and adaptive immune response in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease that involves several organ systems. Although B cells play a key role in SLE pathogenesis, the mechanisms behind B cell dysregulation in SLE development remained controversial. Finding the modules containing highly co-expressed genes in B cells could explain biological pathways involved in the pathogenesis of SLE, which may further support the reasons for the altered function of B cells in SLE disease. A total of three microarray gene expression datasets were downloaded from Gene Expression Omnibus. SLE samples were prepared from the purified B lymphocyte cells of the patients who have not received immunosuppressive drugs as well as high dose immunocytotoxic therapies or steroids. A weighted gene co-expression network was then constructed to find the relevant modules implicated in the SLE progression. Among 17 identified modules, 3 modules were selected through mapping to STRING and finding the ones that had highly connection at the protein level. These modules clearly indicate the involvement of several pathways in the pathogenesis of SLE including viral infection, adaptive immune response, and innate immune response in B lymphocytes. The WGCN analysis further revealed the co-expressed genes involved in both innate and adaptive immune systems. Mix infections and primary immunodeficiency might also dysregulate B lymphocytes, which may facilitate SLE development. As such, identifying novel biomarkers and pathways in lupus would be of importance.

IFI27 Is a Useful Genetic Marker for Diagnosis of Immunoglobulin A Nephropathy and Membranous Nephropathy Using Peripheral Blood

Diagnosis of chronic glomerulonephritis (CGN) depends primarily on renal biopsy, which is expensive and requires hospitalization, creating a demand for noninvasive diagnostic method for this disease. We used DNA microarray analysis to search for genes whose expression levels in peripheral blood mononuclear cells (PBMCs) could distinguish between patients with CGN and healthy volunteers (HVs). We selected immunoglobulin A nephropathy (IgAN) and membranous nephropathy (MN) as typical forms of CGN. The mRNA level of the gene encoding interferon (IFN)-alpha-inducible protein 27, IFI27, which is preferentially expressed in podocytes of glomeruli, was lower in PBMCs of IgAN and MN patients than in those of HVs. This result was confirmed by quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). Moreover, qRT-PCR analysis revealed that the IFI27 mRNA level was reduced in PBMCs of patients with other types of chronic glomerulonephritis. IFI27 immunohistochemical staining of biopsied specimens also confirmed reduced expression of IFI27 protein in IgAN and MN patients. Based on these results, we propose that IFI27 could serve as a noninvasive diagnostic marker for CGNs using peripheral blood.

Breakdown of Immune Tolerance in Systemic Lupus Erythematosus by Dendritic Cells

Dendritic cells (DC) play an important role in the pathogenesis of systemic lupus erythematosus (SLE), an autoimmune disease with multiple tissue manifestations. In this review, we summarize recent studies on the roles of conventional DC and plasmacytoid DC in the development of both murine lupus and human SLE. In the past decade, studies using selective DC depletions have demonstrated critical roles of DC in lupus progression. Comprehensive in vitro and in vivo studies suggest activation of DC by self-antigens in lupus pathogenesis, followed by breakdown of immune tolerance to self. Potential treatment strategies targeting DC have been developed. However, many questions remain regarding the mechanisms by which DC modulate lupus pathogenesis that require further investigations.

Cutting Edge: Plasmacytoid Dendritic Cells in Late-Stage Lupus Mice Defective in Producing IFN-α

Plasmacytoid dendritic cells (pDCs) are professional type I IFN producers believed to promote lupus. However, questions exist about whether they function at the same level throughout the course of lupus disease. We analyzed high-purity pDCs sorted from lupus mice. Although pDCs produced a large amount of IFN-α during disease initiation, those sorted from late-stage lupus mice were found to be defective in producing IFN-α. These pDCs expressed an increased level of MHC, suggesting a functional drift to Ag presentation. We examined the potential mechanism behind the defect and identified a novel transcriptional factor, Foxj2, which repressed the expression of several genes in pDCs, but not IFN-α. Dysregulation in pDCs appears to be predisposed, because they exhibited an altered transcriptional profile before the onset of clinical signs. Our results suggest that pDCs do not function the same throughout the disease course and lose the ability to produce IFN-α in late-stage lupus mice.

Paradoxical effects of all-trans-retinoic acid on lupus-like disease in the MRL/lpr mouse model

Roles of all-trans-retinoic acid (tRA), a metabolite of vitamin A (VA), in both tolerogenic and immunogenic responses are documented. However, how tRA affects the development of systemic autoimmunity is poorly understood. Here we demonstrate that tRA have paradoxical effects on the development of autoimmune lupus in the MRL/lpr mouse model. We administered, orally, tRA or VA mixed with 10% of tRA (referred to as VARA) to female mice starting from 6 weeks of age. At this age, the mice do not exhibit overt clinical signs of lupus. However, the immunogenic environment preceding disease onset has been established as evidenced by an increase of total IgM/IgG in the plasma and expansion of lymphocytes and dendritic cells in secondary lymphoid organs. After 8 weeks of tRA, but not VARA treatment, significantly higher pathological scores in the skin, brain and lung were observed. These were accompanied by a marked increase in B-cell responses that included autoantibody production and enhanced expression of plasma cell-promoting cytokines. Paradoxically, the number of lymphocytes in the mesenteric lymph node decreased with tRA that led to significantly reduced lymphadenopathy. In addition, tRA differentially affected renal pathology, increasing leukocyte infiltration of renal tubulointerstitium while restoring the size of glomeruli in the kidney cortex. In contrast, minimal induction of inflammation with tRA in the absence of an immunogenic environment in the control mice was observed. Altogether, our results suggest that under a predisposed immunogenic environment in autoimmune lupus, tRA may decrease inflammation in some organs while generating more severe disease in others.

Prolonged Clinical Remission in Patients with Systemic Lupus Erythematosus

Objective.

Systemic lupus erythematosus (SLE) is typically a relapsing/remitting disease. However, some patients experience prolonged remission. These patients may provide further insights into SLE pathophysiology. In this study we characterize their clinical course.

Methods.

Prolonged remission was defined as Systemic Lupus Erythematosus Disease Activity Index (SLEDAI-2K) = 0, = 2, or = 4 (based on serology) for ≥ 5 consecutive years, with visits ≤ 18 months apart. The patients could be taking antimalarials, but not corticosteroids or immunosuppressives. Flare was defined as clinical activity on SLEDAI-2K, or by corticosteroid/immunosuppressive initiation. Each patient’s preremission course was classified as monophasic, relapsing/remitting, or chronic active. These patients were compared to matched SLE controls and patients achieving remission on medications.

Results.

A total of 38/1613 (2.4%) patients achieved prolonged remission while taking no medications. The mean duration was 11.5 ± 6.4 years. Twenty-seven patients (71.0%) had relapsing/remitting disease, 11 (28.9%) had monophasic illness, and none had chronic active disease prior to remission. They differed from matched controls in ethnicity, disease activity at first visit, and cumulative organ damage. There were 34/1613 patients (2.1%) who achieved prolonged remission while taking steroids and/or immunosuppressives, with mean duration 8.5 ± 2.9 years. Twelve patients (35.3%) experienced disease flare. They were younger at diagnosis, with more disease activity prior to remission than patients taking no medications.

Conclusion.

Prolonged remission is an infrequent outcome among patients and is preceded by an atypically monophasic clinical course in a significant minority. Those taking medications represent a heterogeneous group: those who will tolerate eventual taper, and those whose disease activity was merely suppressed by ongoing immunosuppression. Prolonged remission may reflect unique pathophysiologic mechanisms, and warrants further investigation.

Reduced B lymphoid kinase (Blk) expression enhances proinflammatory cytokine production and induces nephrosis in C57BL/6-lpr/lpr mice

BLK, which encodes B lymphoid kinase, was recently identified in genome wide association studies as a susceptibility gene for systemic lupus erythematosus (SLE), and risk alleles mapping to the BLK locus result in reduced gene expression. To determine whether BLK is indeed a bona fide susceptibility gene, we developed an experimental mouse model, namely the Blk^+/−.lpr/lpr (Blk^+/−.lpr) mouse, in which Blk expression levels are reduced to levels comparable to those in individuals carrying a risk allele. Here, we report that Blk is expressed not only in B cells, but also in IL-17-producing γδ and DN αβ T cells and in plasmacytoid dendritic cells (pDCs). Moreover, we found that solely reducing Blk expression in C57BL/6-lpr/lpr mice enhanced proinflammatory cytokine production and accelerated the onset of lymphoproliferation, proteinuria, and kidney disease. Together, these findings suggest that BLK risk alleles confer susceptibility to SLE through the dysregulation of a proinflammatory cytokine network.

T cell and dendritic cell abnormalities synergize to expand pro-inflammatory T cell subsets leading to fatal autoimmunity in B6.NZBc1 lupus-prone mice

We have previously shown that B6 congenic mice with a New Zealand Black chromosome 1 (c1) 96-100 cM interval produce anti-nuclear Abs and that at least two additional genetic loci are required to convert this subclinical disease to fatal glomerulonephritis in mice with a c1 70-100 cM interval (c1(70-100)). Here we show that the number of T follicular helper and IL-21-, IFN-γ-, and IL-17-secreting CD4(+) T cells parallels disease severity and the number of susceptibility loci in these mice. Immunization of pre-autoimmune mice with OVA recapitulated these differences. Differentiation of naïve T cells in-vitro under polarizing conditions and in-vivo following adoptive transfer of OVA-specific TCR transgenic cells into c1(70-100) or B6 recipient mice, revealed T cell functional defects leading to increased differentiation of IFN-γ- and IL-17-producing cells in the 96-100 cM and 88-96 cM intervals, respectively. However, in-vivo enhanced differentiation of pro-inflammatory T cell subsets was predominantly restricted to c1(70-100) recipient mice, which demonstrated altered dendritic cell function, with increased production of IL-6 and IL-12. The data provide support for the role of pro-inflammatory T cells in the conversion of subclinical disease to fatal autoimmunity and highlight the importance of synergistic interactions between individual susceptibility loci in this process.

Wiskott-Aldrich syndrome protein-mediated actin dynamics control type-I interferon production in plasmacytoid dendritic cells

Wiskott-Aldrich Syndrome protein (WASp)–mediated actin polymerization controls intracellular trafficking and compartmentalization of TLR9 ligands in plasmacytoid dendritic cells.

Mutations in Wiskott-Aldrich syndrome (WAS) protein (WASp), a regulator of actin dynamics in hematopoietic cells, cause WAS, an X-linked primary immunodeficiency characterized by recurrent infections and a marked predisposition to develop autoimmune disorders. The mechanisms that link actin alterations to the autoimmune phenotype are still poorly understood. We show that chronic activation of plasmacytoid dendritic cells (pDCs) and elevated type-I interferon (IFN) levels play a role in WAS autoimmunity. WAS patients display increased expression of type-I IFN genes and their inducible targets, alteration in pDCs numbers, and hyperresponsiveness to TLR9. Importantly, ablating IFN-I signaling in WASp null mice rescued chronic activation of conventional DCs, splenomegaly, and colitis. Using WASp-deficient mice, we demonstrated that WASp null pDCs are intrinsically more responsive to multimeric agonist of TLR9 and constitutively secrete type-I IFN but become progressively tolerant to further stimulation. By acute silencing of WASp and actin inhibitors, we show that WASp-mediated actin polymerization controls intracellular trafficking and compartmentalization of TLR9 ligands in pDCs restraining exaggerated activation of the TLR9–IFN-α pathway. Together, these data highlight the role of actin dynamics in pDC innate functions and imply the pDC–IFN-α axis as a player in the onset of autoimmune phenomena in WAS disease.