Gunnar V. Alm

Polymorphisms in the tyrosine kinase 2 and interferon regulatory factor 5 genes are associated with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex systemic autoimmune disease caused by both genetic and environmental factors. Genome scans in families with SLE point to multiple potential chromosomal regions that harbor SLE susceptibility genes, and association studies in different populations have suggested several susceptibility alleles for SLE. Increased production of type I interferon (IFN) and expression of IFN-inducible genes is commonly observed in SLE and may be pivotal in the molecular pathogenesis of the disease. We analyzed 44 single-nucleotide polymorphisms (SNPs) in 13 genes from the type I IFN pathway in 679 Swedish, Finnish, and Icelandic patients with SLE, in 798 unaffected family members, and in 438 unrelated control individuals for joint linkage and association with SLE. In two of the genes--the tyrosine kinase 2 (TYK2) and IFN regulatory factor 5 (IRF5) genes--we identified SNPs that displayed strong signals in joint analysis of linkage and association (unadjusted P<10(-7)) with SLE. TYK2 binds to the type I IFN receptor complex and IRF5 is a regulator of type I IFN gene expression. Thus, our results support a disease mechanism in SLE that involves key components of the type I IFN system.

Autoimmunity after alpha-interferon therapy for malignant carcinoid tumors.

OBJECTIVE To determine the incidence of autoantibodies and autoimmune disease and their influence on therapeutic results during alpha-interferon treatment in patients with malignant midgut carcinoid tumors. DESIGN Consecutive sample of patients. SETTING University hospital. PATIENTS One hundred thirty-five patients (70 women, 65 men; median age, 59 years) with biopsy-proven tumors, liver metastases, and no autoimmune disease. INTERVENTIONS Leukocyte alpha-interferon (n = 88) or alpha-interferon 2b (n = 47) three times a week. MAIN OUTCOME MEASURES Signs and symptoms of autoimmune disease or development of autoantibodies to thyroid antigens, nuclear antigens, or gastric parietal cells. Tumor responses were determined by reduced liver metastases or reduced urinary 5-hydroxyindole acetic acid excretion, or both. RESULTS Twenty-five patients (19%) developed the following autoimmune disorders after a median of 9 months of therapy: thyroid disease (n = 18), systemic lupus erythematosus (n = 1), pernicious anemia (n = 4), and vasculitis (n = 2). Antibodies to microsomal thyroid antigen or thyroglobulin were detected in 16 patients before therapy and in another 11 patients during therapy. Antinuclear antibodies were detected in 16 patients before and in another 19 patients during therapy. Clinical thyroid disease developed in more than 60% of patients who had or developed thyroid antibodies but in only 7% of initially autoantibody-negative patients. Autoimmunity did not correlate with objective tumor response. CONCLUSION Patients with malignant carcinoid tumors may develop autoimmune disease during alpha-interferon therapy, especially when autoantibodies are present. They should therefore be monitored for autoimmunity, which does not appear, however, to influence tumor responses.

Activation of type I interferon system in systemic lupus erythematosus correlates with disease activity but not with antiretroviral antibodies

The objective was to investigate the relation between serum levels of interferon-α (IFN-α), the activity of an endogenous IFN-a inducing factor (SLE-IIF), clinical and immunological disease activity as well as serum levels of antiretroviral antibodies in SLE. Serum levels of IFN-α were measured in serial sera from 30 patients sampled at different stages of disease activity (SLEDAI score). The SLE-IIF activity was measured by its ability to induce IFN-α production in cultures of normal peripheral blood mononuclear cells. Both serum IFN-α and SLE-IIF increased markedly at flare in serially followed patients. The SLEDAI score, levels of anti-dsDNA antibodies and IL-10 correlated positively, and complement components Clq, C3 and leukocytes correlated inversely with serum concentrations of IFN-α. The extent of multiple organ involvement correlated with serum IFN-α. No relation between concentrations of retroviral peptide binding antibodies and IFN-α or SLE-IIF activity was found. The close relationship between disease activity in SLE patients and IFN-α serum levels suggests that activation of the type I IFN system might be of importance in the disease process.

Patients with systemic lupus erythematosus (SLE) have a circulating inducer of interferon-alpha (IFN-alpha) production acting on leucocytes resembling immature dendritic cells.

Patients with active SLE often have an ongoing production of IFN‐α. We therefore searched for an endogenous IFN‐α‐inducing factor (IIF) in SLE patients and found that their sera frequently induced production of IFN‐α in cultures of peripheral blood mononuclear cells (PBMC) from healthy blood donors, especially when the PBMC were costimulated with the cytokines IFN‐α2b and granulocyte‐macrophage colony‐stimulating factor (GM‐CSF). The phenotype of the IFN‐α‐producing cells (IPC) as determined by flow cytometry corresponded to that of the natural IPC, resembling immature dendritic cells. The IIF activity in SLE sera was sometimes as high as that of a virus and was present especially in patients with active disease and with measurable IFN‐α levels in serum. The IIF had an apparent molecular weight of 300–1000 kD and appeared to consist of both immunoglobulin and DNA, possibly being immune complexes. This endogenous IFN‐α inducer may be of pathogenic significance, since a reported occasional adverse effect of IFN‐α therapy in patients with non‐autoimmune disorders is development of anti‐dsDNA antibodies and SLE.

A risk haplotype of STAT4 for systemic lupus erythematosus is over-expressed, correlates with anti-dsDNA and shows additive effects with two risk alleles of IRF5

Systemic lupus erythematosus (SLE) is the prototype autoimmune disease where genes regulated by type I interferon (IFN) are over-expressed and contribute to the disease pathogenesis. Because signal transducer and activator of transcription 4 (STAT4) plays a key role in the type I IFN receptor signaling, we performed a candidate gene study of a comprehensive set of single nucleotide polymorphism (SNPs) in STAT4 in Swedish patients with SLE. We found that 10 out of 53 analyzed SNPs in STAT4 were associated with SLE, with the strongest signal of association (P = 7.1 × 10−8) for two perfectly linked SNPs rs10181656 and rs7582694. The risk alleles of these 10 SNPs form a common risk haplotype for SLE (P = 1.7 × 10−5). According to conditional logistic regression analysis the SNP rs10181656 or rs7582694 accounts for all of the observed association signal. By quantitative analysis of the allelic expression of STAT4 we found that the risk allele of STAT4 was over-expressed in primary human cells of mesenchymal origin, but not in B-cells, and that the risk allele of STAT4 was over-expressed (P = 8.4 × 10−5) in cells carrying the risk haplotype for SLE compared with cells with a non-risk haplotype. The risk allele of the SNP rs7582694 in STAT4 correlated to production of anti-dsDNA (double-stranded DNA) antibodies and displayed a multiplicatively increased, 1.82-fold risk of SLE with two independent risk alleles of the IRF5 (interferon regulatory factor 5) gene.

An etiopathogenic role for the type I IFN system in SLE

The type I interferon (IFN) system plays a pivotal role in the etiopathogenesis of systemic lupus erythematosus (SLE). The initial appearance of autoantibody-producing B cells can be precipitated by infection-induced type I IFNs, but the further, significant generation of autoimmune T and B cells is caused by the prolonged production of IFN-alpha, which is maintained by a vicious circle mechanism. This involves the activation of immature dendritic cells, known as natural IFN-producing cells, by continuously formed endogenous IFN-alpha inducers. These IFN-alpha inducers consist of complexes of autoantibodies with nucleic-acid-containing autoantigens derived from apoptotic cells.

The Combination of Apoptotic U937 Cells and Lupus IgG Is a Potent IFN-α Inducer

Patients with active systemic lupus erythematosus (SLE) have signs of an ongoing IFN-α production, that may be of pathogenic significance in the disease. We previously showed that SLE patients have an IFN-α-inducing factor in blood, probably consisting of complexes containing anti-DNA Abs and immunostimulatory DNA. The DNA component could be derived from apoptotic cells, because SLE patients have been reported to have both increased apoptosis and reduced clearance of apoptotic cell material. In the present study, we therefore investigated whether apoptotic cells, together with IgG from SLE patients, could act as an IFN-α inducer in normal PBMC in vitro. We found that apoptotic cells of the myeloid leukemia cell line U937 as well as four other cell lines (MonoMac6, H9, Jurkat, U266) could induce IFN-α production in PBMC when combined with IgG from SLE patients. The IFN-α production by PBMC was much enhanced when PBMC were costimulated by IFN-α2b. The ability of IgG from different SLE patients to promote IFN-α induction by apoptotic U937 cells was associated with the presence of anti-ribonucleoprotein Abs, but not clearly with occurrence of anti-DNA Abs. These results suggest that apoptotic cells in the presence of autoantibodies can cause production of a clearly immunostimulatory cytokine, which is IFN-α. This mechanism for induction of IFN-α production could well be operative also in vivo, explain the IFN-α production seen in SLE patients, and be important in the pathogenesis of SLE.

Interferon-β is required for interferon-α production in mouse fibroblasts

The type I interferons — interferon-a (IFN-a) and interferon-b (IFN-b) — are critical for protection against viruses during the acute stage of viral infection [1,2]. Furthermore, type I interferons have been implicated as important mediators in the regulation of lymphocyte development [3], immune responses [4,5] and the maintenance of immunological memory of cytotoxic T cells [6,7]. The different IFN-a subtypes are encoded by 12 genes in the mouse [8] whereas IFN-b is encoded for by only one gene [9]. IFN-a and IFN-b have a high degree of sequence homology and are thought to interact with the same surface receptor on target cells [10,11]. As an approach to analysing the different biological functions of IFN-a and IFN-b, we have generated a mouse strain with an inactivated IFN-b gene. We report here that embryonic fibroblasts from such mice produce neither IFN-b nor IFN-a upon Sendai virus infection, whereas the production of IFN-a by leukocytes from the same strain of mice is intact. IFN-a production in embryonic fibroblasts from IFN-b–/– mice could be rescued by ‘priming’ the cells using exogenous IFN-b. These results imply a unique role for IFN-b in the induction of type I interferons in peripheral tissues.

The type I interferon system in the development of lupus

The type I interferon (IFN) system induces inhibition of viral replication, but can also activate the innate and adaptive immune system. An important role of the type I IFN system in autoimmune diseases, including lupus, is suggested by the observation that these disorders display a prominent over-expression of type I IFN regulated genes. The development of autoimmune diseases in some individuals treated with IFN-α directly supports a pivotal role for this cytokine in breaking tolerance and inducing autoimmune reactions. A genetic setup that promotes type I IFN production and/or response and the presence of endogenous inducers of IFN-α production have been described in patients with lupus. Several known environmental risk factors for development of lupus or disease flares may contribute to the ongoing type I IFN production. In the present review we will describe the possible role of the type I IFN system in the lupus disease process. The possible connection between the type I IFN system and some environmental and genetic risk factors for lupus is also discussed.

Role of Natural Interferon-α Producing Cells (Plasmacytoid Dendritic Cells) in Autoimmunity

The type I interferons (IFNs) have antiviral, cytostatic and prominent immunomodulatory effects, which all are of great importance during viral infections. However, prolonged exposure of the immune system to type I IFN can break tolerance and initiate an autoimmune reaction, eventually leading to autoimmune disease. Recent observations in patients with systemic lupus erythematosus (SLE) have revealed that such individuals have endogenous IFN-α inducers, causing an ongoing IFN-α production and consequently a continuous stimulation of the immune system. These IFN-α inducers consist of small immune complexes (IC) containing DNA or RNA and act on the principal IFN-α producing cell, the natural IFN-α producing cell (NIPC), also termed the plasmacytoid dendritic cell (PDC). The NIPC/PDC is a key cell in both the innate and adaptive immune response but can also, either directly or via produced IFN-α, have a pivotal role in autoimmunity. In this review we summarize recent data concerning NIPC/PDC, including their activation, regulation, function and possible role in autoimmune diseases, especially SLE.