Pui Y. Lee

Induction of autoimmunity by pristane and other naturally-occurring hydrocarbons

Tetramethylpentadecane (TMPD, or commonly known as pristane)-induced lupus is a murine model of systemic lupus erythematosus (SLE). Renal disease and autoantibody production strictly depend on signaling through the interferon (IFN)-I receptor. The major source of IFN-I is immature monocytes bearing high levels of the surface marker Ly6C. Interferon production is mediated exclusively by signaling through TLR7 and the adapter protein MyD88. It is likely that endogenous TLR7 ligands such as components of small nuclear ribonucleoprotein complexes are involved in triggering disease. Lupus autoantibodies are produced in ectopic lymphoid tissue developing in response to TMPD. This model is well suited for examining links between dysregulated IFN-I production and the pathogenesis of human SLE, which like TMPD-lupus, is associated with high levels of IFN-I.

TLR7-dependent and FcγR-independent production of type I interferon in experimental mouse lupus

Increased type I interferon (IFN-I) production and IFN-stimulated gene (ISG) expression are linked to the pathogenesis of systemic lupus erythematosus (SLE). Although the mechanisms responsible for dysregulated IFN-I production in SLE remain unclear, autoantibody-mediated uptake of endogenous nucleic acids is thought to play a role. 2,6,10,14-tetramethylpentadecane (TMPD; also known as pristane) induces a lupus-like disease in mice characterized by immune complex nephritis with autoantibodies to DNA and ribonucleoproteins. We recently reported that TMPD also causes increased ISG expression and that the development of the lupus is completely dependent on IFN-I signaling (Nacionales, D.C., K.M. Kelly-Scumpia, P.Y. Lee, J.S. Weinstein, R. Lyons, E. Sobel, M. Satoh, and W.H. Reeves. 2007. Arthritis Rheum. 56:3770–3783). We show that TMPD elicits IFN-I production, monocyte recruitment, and autoantibody production exclusively through a Toll-like receptor (TLR) 7– and myeloid differentiation factor 88 (MyD88)–dependent pathway. In vitro studies revealed that TMPD augments the effect of TLR7 ligands but does not directly activate TLR7 itself. The effects of TMPD were amplified by the Y-linked autoimmune acceleration cluster, which carries a duplication of the TLR7 gene. In contrast, deficiency of Fcγ receptors (FcγRs) did not affect the production of IFN-I. Collectively, the data demonstrate that TMPD-stimulated IFN-I production requires TLR7/MyD88 signaling and is independent of autoantibody-mediated uptake of ribonucleoproteins by FcγRs.

The Nuclear IκB Protein IκBNS Selectively Inhibits Lipopolysaccharide-Induced IL-6 Production in Macrophages of the Colonic Lamina Propria

Macrophages play an important role in the pathogenesis of chronic colitis. However, it remains unknown how macrophages residing in the colonic lamina propria are regulated. We characterized colonic lamina proprial CD11b-positive cells (CLPMφ). CLPMφ of wild-type mice, but not IL-10-deficient mice, displayed hyporesponsiveness to TLR stimulation in terms of cytokine production and costimulatory molecule expression. We compared CLPMφ gene expression profiles of wild-type mice with IL-10-deficient mice, and identified genes that are selectively expressed in wild-type CLPMφ. These genes included nuclear IκB proteins such as Bcl-3 and IκBNS. Because Bcl-3 has been shown to specifically inhibit LPS-induced TNF-α production, we analyzed the role of IκBNS in macrophages. Lentiviral introduction of IκBNS resulted in impaired LPS-induced IL-6 production, but not TNF-α production in the murine macrophage cell line RAW264.7. IκBNS expression led to constitutive and intense DNA binding of NF-κB p50/p50 homodimers. IκBNS was recruited to the IL-6 promoter, but not to the TNF-α promoter, together with p50. Furthermore, small interference RNA-mediated reduction in IκBNS expression in RAW264.7 cells resulted in increased LPS-induced production of IL-6, but not TNF-α. Thus, IκBNS selectively suppresses LPS-induced IL-6 production in macrophages. This study established that nuclear IκB proteins differentially regulate LPS-induced inflammatory cytokine production in macrophages.

A Novel Type I IFN-Producing Cell Subset in Murine Lupus

Excess type I IFNs (IFN-I) have been linked to the pathogenesis of systemic lupus erythematosus (SLE). Therapeutic use of IFN-I can trigger the onset of SLE and most lupus patients display up-regulation of a group of IFN-stimulated genes (ISGs). Although this “IFN signature” has been linked with disease activity, kidney involvement, and autoantibody production, the source of IFN-I production in SLE remains unclear. 2,6,10,14-Tetramethylpentadecane-induced lupus is at present the only model of SLE associated with excess IFN-I production and ISG expression. In this study, we demonstrate that tetramethylpentadecane treatment induces an accumulation of immature Ly6Chigh monocytes, which are a major source of IFN-I in this lupus model. Importantly, they were distinct from IFN-producing dendritic cells (DCs). The expression of IFN-I and ISGs was rapidly abolished by monocyte depletion whereas systemic ablation of DCs had little effect. In addition, there was a striking correlation between the numbers of Ly6Chigh monocytes and the production of lupus autoantibodies. Therefore, immature monocytes rather than DCs appear to be the primary source of IFN-I in this model of IFN-I-dependent lupus.

B cells enhance early innate immune responses during bacterial sepsis

Type I interferon–responsive B cells provide early protection against bacterial sepsis.

Type I Interferon Modulates Monocyte Recruitment and Maturation in Chronic Inflammation

Chronic inflammation is characterized by continuous recruitment and activation of immune cells such as monocytes in response to a persistent stimulus. Production of proinflammatory mediators by monocytes leads to tissue damage and perpetuates the inflammatory response. However, the mechanism(s) responsible for the sustained influx of monocytes in chronic inflammation are not well defined. In chronic peritonitis induced by pristane, the persistent recruitment of Ly6C(hi) inflammatory monocytes into the peritoneum was abolished in type I interferon (IFN-I) receptor-deficient mice but was unaffected by the absence of IFN-gamma, tumor necrosis factor-alpha, interleukin-6, or interleukin-1. IFN-I signaling stimulated the production of chemokines (CCL2, CCL7, and CCL12) that recruited Ly6C(hi) monocytes via interactions with the chemokine receptor CCR2. Interestingly, after 2,6,10,14-tetramethylpentadecane treatment, the rapid turnover of inflammatory monocytes in the inflamed peritoneum was associated with a lack of differentiation into Ly6C(lo) monocytes/macrophages, a more mature subset with enhanced phagocytic capacity. In contrast, Ly6C(hi) monocytes differentiated normally into Ly6C(lo) cells in IFN-I receptor-deficient mice. The effects of IFN-I were specific for monocytes as granulocyte migration was unaffected in the absence of IFN-I signaling. Taken together, our findings reveal a novel role of IFN-I in promoting the recruitment of inflammatory monocytes via the chemokine receptor CCR2. Continuous monocyte recruitment and the lack of terminal differentiation induced by IFN-I may help sustain the chronic inflammatory response.

Monocyte and Macrophage Abnormalities in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with profound effects on multiple organ systems. In patients with SLE, the immune system is subverted to target numerous self antigens and the ensuing inflammatory response elicits a vicious cycle of immune-cell activation and tissue damage. Both genetic and environmental factors are essential for the development of this debilitating condition, although the exact cause remains unclear. Early studies on the pathogenesis of lupus centered on the adaptive immune system as lymphocyte abnormalities were thought to be the primary cause of autoimmunity. In the past decade, however, this paradigm has shifted with rapid advances in the field of innate immunity. These developments have yielded important insights into how the autoimmune response in SLE is initiated and maintained. Monocytes and macrophages are an essential arm of the innate immune system with a multitude of immunological functions, including antigen presentation, phagocytosis, and cytokine production. Aberrations of monocyte/macrophage phenotype and function are increasingly recognized in SLE and animal models of the disease. In this review we summarize the current knowledge of monocyte/macrophage abnormalities in human SLE and discuss their implications for understanding the pathogenesis of lupus.

Ly6 family proteins in neutrophil biology

The murine Ly6 complex was identified 35 years ago using antisera to lymphocytes. With advances in mAb development, molecular cloning, and genome sequencing, >20 structurally related genes have been identified within this complex on chromosome 15. All members of the Ly6 family and their human homologues share the highly conserved LU domain and most also possess a GPI anchor. Interestingly, many Ly6 proteins are expressed in a lineage‐specific fashion, and their expression often correlates with stages of differentiation. As a result, Ly6 proteins are frequently used as surface markers for leukocyte subset identification and targets for antibody‐mediated depletion. Murine neutrophils display prominent surface expression of several Ly6 proteins, including Ly6B, Ly6C, and Ly6G. Although the physiology of most Ly6 proteins is not well understood, a role in neutrophil functions, such as migration, is recognized increasingly. In this review, we will provide an overview of the Ly6 complex and discuss, in detail, the specific Ly6 proteins implicated in neutrophil biology.

Toll-like receptor 3 ligands induce CD80 expression in human podocytes via an NF-κB-dependent pathway

BACKGROUND Recent studies suggest that CD80 (also known as B7.1) is expressed on podocytes in minimal-change disease (MCD) and may have a role in mediating proteinuria. CD80 expression is known to be induced by Toll-like receptor (TLR) ligands in dendritic cells. We therefore evaluated the ability of TLR to induce CD80 in human cultured podocytes. METHODS Conditionally immortalized human podocytes were evaluated for TLR expression. Based on high expression of TLR3, we evaluated the effect of polyinosinic-polycytidylic acid (polyIC), a TLR3 ligand, to induce CD80 expression in vitro. RESULTS TLR1-6 and 9 messenger RNA (mRNA) were expressed in podocytes. Among TLR ligands 1-9, CD80 mRNA expression was significantly induced by polyIC and lipopolysaccharide (TLR4 ligand) with the greatest stimulation by polyIC (6.8 ± 0.7 times at 6 h, P < 0.001 versus control). PolyIC induced increased expression of Cathepsin L, decreased synaptopodin expression and resulted in actin reorganization which suggested a similar injury pattern as observed with lipopolyssaccharide. PolyIC induced type I and type II interferon signaling, nuclear factor kappa B (NF-κB) activation and the induction of CD80 expression. Knockdown of CD80 protected against actin reorganization and reduced synaptopodin expression in response to polyIC. Dexamethasone, a corticosteroid commonly used to treat MCD, also blocked both basal and polyIC-stimulated CD80 expression, as did inhibition of NF-κB. CONCLUSIONS Activation of TLR3 on cultured human podocytes induces CD80 expression and phenotypic change via an NF-κB-dependent mechanism and is partially blocked by dexamethasone. These studies provide a mechanism by which viral infections may cause proteinuria.

Idiopathic Nephrotic Syndrome and Atopy: Is There a Common Link?

Numerous reports during the last 60 years have reported a strong association between idiopathic nephrotic syndrome and atopic disorders. Idiopathic nephrotic syndrome can be precipitated by allergic reactions and has been associated with both aeroallergens (pollens, mold, and dust) and food allergies. Patients with idiopathic nephrotic syndrome also may show increased serum immunoglobulin E (IgE) levels. A review of the literature suggests that although some idiopathic nephrotic syndrome cases may be associated with allergies, evidence that it is a type of allergic disorder or can be induced by a specific allergen is weak. Rather, it is likely that the proteinuria and increased IgE levels in patients with idiopathic nephrotic syndrome are caused by increased levels of interleukin 13 observed in these patients. Recent studies suggest that interleukin 13, a known stimulator of IgE response, may mediate proteinuria in patients with minimal change disease because of its ability to directly induce CD80 expression on the podocyte.