Interferon-alpha: a new target for therapy in systemic lupus erythematosus?

Gene expression profiling in the study of the pathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease with a complex pathogenesis involving multiple genetic and environmental contributions. DNA microarray technology has recently been applied to unravel some of this complexity through genomewide profiling. Early studies using microarray analysis of peripheral blood mononuclear cells (PBMCs) from SLE patients revealed dysregulation of inflammatory cytokines, chemokines, and immune response-related genes, as well as genes involved in apoptosis, signal transduction, and the cell cycle. More recently, using arrays containing many more genes, 4 independent research groups have found that interferon (IFN)-regulated genes are highly overexpressed in the peripheral blood and kidney glomeruli of SLE patients, supporting a crucial role for interferon in SLE. Future studies focusing on target tissues or organs in lupus, including the kidney, may further contribute to our understanding of lupus pathogenesis while providing new targets for therapy.

Induction of Systemic TH1-Like Innate Immunity in Normal Volunteers Following Subcutaneous but Not Intravenous Administration of CPG 7909, a Synthetic B-Class CpG Oligodeoxynucleotide TLR9 Agonist

Subcutaneous injection of normal human volunteers with a B-class CpG oligodeoxynucleotide (ODN) TLR9 agonist, CPG 7909, induced a TH1-like pattern of systemic innate immune activation manifested by expression of IL-6, IL-12p40, IFN-alpha, and IFN-inducible chemokines. Serum IP-10 was found to be the most sensitive assay for subcutaneous CPG 7909 stimulation; its level was significantly increased in all subjects at all dose levels, including the lowest tested dose of just 0.0025 mg/kg. This pattern of chemokine and cytokine induction was markedly different from that previously reported to be induced by TLR9 stimulation in rodents, most likely reflecting species-specific differences in the cell types expressing TLR9. Subcutaneous CPG 7909 injection induced transient shifts in blood neutrophils, lymphocytes, and monocytes, consistent with the increased chemokine expression. Levels of acute phase reactants such as C-reactive protein were also increased. A second subcutaneous CPG 7909 injection administered 2 weeks after the first elicited similar immune responses, showing little or no tolerance to the effects of repeated in vivo TLR9 stimulation. Subjects developed dose-dependent transient injection site reactions and flu-like symptoms but otherwise tolerated injection well, with no evidence of organ toxicity or systemic autoimmunity. The activation of innate immunity was dependent on the route of ODN administration, since intravenous injection caused no such effects. These studies indicate that in vivo activation of TLR9 by subcutaneous administration of CPG 7909 could be a well-tolerated immunotherapeutic approach for induction of TH1 innate immune activation.

Microarray analysis of interferon-regulated genes in SLE

Altered regulation of interferon-alpha (IFNalpha) in systemic lupus erythematosus (SLE) was first demonstrated nearly 25 years ago. However, only recently has due attention been directed towards the central role of this cytokine family in SLE. Several laboratories have used large-scale microarray technology to study global gene expression patterns in heterogeneous populations of peripheral blood cells from lupus patients and control subjects. The results of these studies demonstrate that IFN-regulated genes are among the most significantly overexpressed in SLE mononuclear cells. In view of the protean effects of IFNs on immune system function, increased activity of IFNs may account for many of the immune system alterations that characterize SLE and contribute to autoimmunity. Definition of the nature of the major IFNs, or other factors, that drive the IFN-regulated gene expression signature noted in SLE is an important area for investigation that may lead to new approaches to targeted therapy of SLE.

Interferon-α in systemic lupus erythematosus

PURPOSE OF REVIEW

To describe the lines of evidence supporting a significant role for interferon-alpha (IFNalpha) in the pathogenesis of systemic lupus erythematosus (SLE) and to propose potential mechanisms by which IFNalpha contributes to the autoimmunity and immune dysfunction of SLE.

RECENT FINDINGS

Long-standing data indicating elevated levels of IFNalpha in the circulation of patients with SLE have recently been supplemented by reports from clinical practice, gene expression data, analysis of patient cells studied ex vivo, and studies of mechanisms of induction of IFNalpha production to provide complementary data strongly supporting a pathogenic role for IFNalpha in SLE. Recombinant IFNalpha, when administered as a therapy to patients with malignancy or hepatitis infection, can induce SLE. IFNalpha-regulated genes are highly expressed in SLE peripheral blood cells compared with cells from control subjects. Functional alterations of SLE mononuclear cells have been attributed to effects of IFNalpha. In addition, immune complexes bearing lupus autoantibodies and RNA or DNA have been shown to induce IFNalpha production. Finally, progress in understanding the role of Toll-like receptors (TLR) in the activation of the innate immune response has suggested potential mechanisms by which adjuvant-like factors act through TLR to induce IFNalpha as well as effective processing of self-antigens, resulting in activation of an adaptive immune response directed against self, as well as cytokine-mediated immune dysfunction.

SUMMARY

Substantial evidence supports a significant role for IFNalpha in the pathogenesis of lupus. The IFNalpha pathway represents a promising target for therapeutic intervention in patients with SLE.

Gene expression profiling in peripheral blood mononuclear cells from lupus patients with active and inactive disease

Systemic lupus erythematosus (SLE) is characterized by periods of flare and remission. The search for parameters associated with disease activity has been an area of intense investigation. To identify genes that best differentiate patients with active from those with inactive disease, the expression pattern of 375 genes was analyzed in peripheral blood mononuclear cells (PBMC) from 12 patients with active and 14 patients with inactive disease. Using the "nearest shrunken centroids" method, 29 genes were found to best discriminate the two groups. Among these genes, 14 were upregulated and 15 were downregulated in patients with active compared to those with inactive disease. Fourteen of these genes also correlated with SELENA-SLEDAI with correlation coefficients ranging from 0.4 to 0.7. Most of these genes have not been previously associated with disease activity and belong to a variety of families such as adhesion molecules, proteases, TNF superfamily, and neurotrophic factors. Using a cross-validation method, the error rate for classifying samples in the two groups was 30%. These results highlight the potential use of microarray data in identifying genes associated with disease activity in SLE, which could become potential biomarkers or future therapeutic targets.

Transcriptional down-regulation of the platelet ADP receptor P2Y(12) and clusterin in patients with systemic lupus erythematosus

Cardiovascular complications are common in systemic lupus erythematosus (SLE) and myocardial infarctions are the leading cause of increased mortality. The ADP receptor P2Y(12) plays a central role in platelet activation and the P2Y(12) blocker clopidogrel reduces the incidence of cardiovascular events. Clusterin, a complement inhibitory protein suggested to be involved in the pathogenesis of SLE, has been found recently in a microarray study to be expressed at very high levels in platelets. Using a new protocol for mRNA quantification in platelets we set out to study if gene expression is altered in SLE patients compared with a healthy control group. Quantitative assay based on real-time PCR was used to measure mRNA expression, Western blot for P2 receptor protein expression and PFA-100 for platelet aggregation. The P2Y(12) receptor expression was decreased in SLE compared to the controls (P < 0.05), while expression of P2Y(1) and P2X(1) were unaltered. These findings were consistent at the protein level. The clusterin mRNA expression was very high. However, SLE patients had significantly lower levels than controls (P < 0.05). Platelet aggregation was similar in both groups. It may be suggested that a decreased level of P2Y(12) receptors could represent a protective response in SLE against thrombotic complications. Lowered clusterin levels could be involved in the pathogenesis of SLE due to decreased protective effects. These findings could help to achieve a better understanding of the platelet function in SLE and serve as a guide for further research and drug use.

Microarray analysis of gene expression in lupus

Recent advances in the study of global patterns of gene expression with the use of microarray technology, coupled with data analysis using sophisticated statistical algorithms, have provided new insights into pathogenic mechanisms of disease. Complementary and reproducible data from multiple laboratories have documented the feasibility of analysis of heterogeneous populations of peripheral blood mononuclear cells from patients with rheumatic diseases through use of this powerful technology. Although some patterns of gene expression, including increased expression of immune system cell surface activation molecules, confirm previous data obtained with other techniques, some novel genes that are differentially expressed have been identified. Most interesting is the dominant pattern of interferon-induced gene expression detected among blood mononuclear cells from patients with systemic lupus erythematosus and juvenile dermatomyositis. These data are consistent with longstanding observations indicating increased circulating interferon-alpha in the blood of patients with active lupus, but draw attention to the dominance of the interferon pathway in the hierarchy of gene expression pathways implicated in systemic autoimmunity.