Andrei Alexsson

IFN-α production by plasmacytoid dendritic cell associations with polymorphisms in gene loci related to autoimmune and inflammatory diseases

The type I interferon (IFN) system is persistently activated in systemic lupus erythematosus (SLE) and many other systemic autoimmune diseases. Studies have shown an association between SLE and several gene variants within the type I IFN system. We investigated whether single-nucleotide polymorphisms (SNPs) associated with SLE and other autoimmune diseases affect the IFN-α production in healthy individuals. Plasmacytoid dendritic cells (pDCs), B cells and NK cells were isolated from peripheral blood of healthy individuals and stimulated with RNA-containing immune complexes (ICs), herpes simplex virus (HSV) or the oligonucleotide ODN2216. IFN-α production by pDCs alone or in cocultures with B or NK cells was measured by an immunoassay. All donors were genotyped with the 200K ImmunoChip, and a 5 bp CGGGG length polymorphism in the IFN regulatory factor 5 gene (IRF5) was genotyped by PCR. We found associations between IFN-α production and 18-86 SNPs (P ≤ 0.001), depending on the combination of the stimulated cell types. However, only three of these associated SNPs were shared between the cell-type combinations. Several SNPs showed novel associations to the type I IFN system among all the associated SNPs, whereas some loci have been described earlier for their association with SLE. Furthermore, we found that the SLE-risk variant of the IRF5 CGGGG-indel was associated with lower IFN-α production. We conclude that the genetic variants affecting the IFN-α production highlight the intricate regulation of the type I IFN system and the importance of understanding the mechanisms behind the dysregulated type I IFN system in SLE.

Novel risk genes for systemic lupus erythematosus predicted by random forest classification

Genome-wide association studies have identified risk loci for SLE, but a large proportion of the genetic contribution to SLE still remains unexplained. To detect novel risk genes, and to predict an individual’s SLE risk we designed a random forest classifier using SNP genotype data generated on the “Immunochip” from 1,160 patients with SLE and 2,711 controls. Using gene importance scores defined by the random forest classifier, we identified 15 potential novel risk genes for SLE. Of them 12 are associated with other autoimmune diseases than SLE, whereas three genes (ZNF804A, CDK1, and MANF) have not previously been associated with autoimmunity. Random forest classification also allowed prediction of patients at risk for lupus nephritis with an area under the curve of 0.94. By allele-specific gene expression analysis we detected cis-regulatory SNPs that affect the expression levels of six of the top 40 genes designed by the random forest analysis, indicating a regulatory role for the identified risk variants. The 40 top genes from the prediction were overrepresented for differential expression in B and T cells according to RNA-sequencing of samples from five healthy donors, with more frequent over-expression in B cells compared to T cells.

DNA methylation mapping identifies gene regulatory effects in patients with systemic lupus erythematosus

Objectives Systemic lupus erythematosus (SLE) is a chronic autoimmune condition with heterogeneous presentation and complex aetiology where DNA methylation changes are emerging as a contributing factor. In order to discover novel epigenetic associations and investigate their relationship to genetic risk for SLE, we analysed DNA methylation profiles in a large collection of patients with SLE and healthy individuals. Methods DNA extracted from blood from 548 patients with SLE and 587 healthy controls were analysed on the Illumina HumanMethylation 450 k BeadChip, which targets 485 000 CpG sites across the genome. Single nucleotide polymorphism (SNP) genotype data for 196 524 SNPs on the Illumina ImmunoChip from the same individuals were utilised for methylation quantitative trait loci (cis-meQTLs) analyses. Results We identified and replicated differentially methylated CpGs (DMCs) in SLE at 7245 CpG sites in the genome. The largest methylation differences were observed at type I interferon-regulated genes which exhibited decreased methylation in SLE. We mapped cis-meQTLs and identified genetic regulation of methylation levels at 466 of the DMCs in SLE. The meQTLs for DMCs in SLE were enriched for genetic association to SLE, and included seven SLE genome-wide association study (GWAS) loci: PTPRC (CD45), MHC-class III, UHRF1BP1, IRF5, IRF7, IKZF3 and UBE2L3. In addition, we observed association between genotype and variance of methylation at 20 DMCs in SLE, including at the HLA-DQB2 locus. Conclusions Our results suggest that several of the genetic risk variants for SLE may exert their influence on the phenotype through alteration of DNA methylation levels at regulatory regions of target genes.

Plasmacytoid dendritic cells and RNA-containing immune complexes drive expansion of peripheral B cell subsets with an SLE-like phenotype

Background Hyperactive B cells and a continuous interferon (IFN)-α production by plasmacytoid dendritic cells (pDCs) play a key role in systemic lupus erythematosus (SLE). We asked whether the interaction between B cells and pDCs stimulated with RNA-containing immune complexes affects peripheral B cell subsets. Methods B cells and pDCs were isolated from blood of healthy individuals and stimulated with immune complexes consisting of SLE-IgG and U1snRNP (RNA-IC). Expression of cell surface molecules as well as IL-6 and IL-10 production were determined by flow cytometry and immunoassays. Gene expression profiles were determined by a NanoString nCounter expression array. Results We found a remarkable increase of double negative CD27-IgD- B cells, from 7% within fresh CD19+ B cells to 37% in the RNA-IC-stimulated co-cultures of B cells and pDCs, comparable to the frequency of double negative B cells in SLE patients. Gene expression analysis of the double negative CD27-IgD- and the CD27+IgD- memory B cells revealed that twenty-one genes were differentially expressed between the two B cell subsets (≥ 2-fold, p<0.001). The, IL21R, IL4R, CCL4, CCL3, CD83 and the IKAROS Family Zinc Finger 2 (IKZ2) showed higher expression in the double negative CD27-IgD- B cells. Conclusion The interactions between B cells and pDCs together with RNA-containing IC led to an expansion of B cells with similar phenotype as seen in SLE, suggesting that the pDC-B cell crosstalk contributes to the autoimmune feed-forward loop in SLE.

Novel gene variants associated with cardiovascular disease in systemic lupus erythematosus and rheumatoid arthritis

Objectives Patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) have increased risk of cardiovascular disease (CVD). We investigated whether single nucleotide polymorphisms (SNPs) at autoimmunity risk loci were associated with CVD in SLE and RA. Methods Patients with SLE (n=1045) were genotyped using the 200K Immunochip SNP array (Illumina). The allele frequency was compared between patients with and without different manifestations of CVD. Results were replicated in a second SLE cohort (n=1043) and in an RA cohort (n=824). We analysed publicly available genetic data from general population, performed electrophoretic mobility shift assays and measured cytokine levels and occurrence of antiphospholipid antibodies (aPLs). Results We identified two new putative risk loci associated with increased risk for CVD in two SLE populations, which remained after adjustment for traditional CVD risk factors. An IL19 risk allele, rs17581834(T) was associated with stroke/myocardial infarction (MI) in SLE (OR 2.3 (1.5 to 3.4), P=8.5×10−5) and RA (OR 2.8 (1.4 to 5.6), P=3.8×10−3), meta-analysis (OR 2.5 (2.0 to 2.9), P=3.5×10−7), but not in population controls. The IL19 risk allele affected protein binding, and SLE patients with the risk allele had increased levels of plasma-IL10 (P=0.004) and aPL (P=0.01). An SRP54-AS1 risk allele, rs799454(G) was associated with stroke/transient ischaemic attack in SLE (OR 1.7 (1.3 to 2.2), P=2.5×10−5) but not in RA. The SRP54-AS1 risk allele is an expression quantitative trait locus for four genes. Conclusions The IL19 risk allele was associated with stroke/MI in SLE and RA, but not in the general population, indicating that shared immune pathways may be involved in the CVD pathogenesis in inflammatory rheumatic diseases.

S4D:5 Targeted next-generation sequencing suggests novel risk loci in juvenile onset systemic lupus erythematosus

Purpose Childhood onset systemic lupus erythematosus (SLE) is associated with a more aggressive disease course and higher mortality risk than adult onset SLE. It has been suggested that juvenile onset SLE cases could have a more genetically determined disease. To identify genetic risk loci in juvenile onset SLE we performed targeted DNA resequencing in a cohort of Swedish SLE patients and control individuals. Methods Coding and regulatory regions of 1853 genes selected from pathways involved in immunological diseases were resequenced in 958 patients with SLE and in 1030 healthy individuals. All patients fulfilled at least four ACR 1982 classification criteria for SLE. For 117 of the SLE patients the disease onset was at age 18 or younger, 105 of whom were women and 12 men. Capturing of the targeted genes was performed with a Roche NimbleGen custom-made liquid capture library followed by Illumina HiSeq2500 sequencing. 97 264 single nucleotide variants (SNVs) passed quality control and had a minor allele frequency of at least 1%. Results Single variant case-control association analysis revealed that 40 SNVs were associated with juvenile onset SLE (false-discovery rate <5%). These 40 SNVs were enriched for missense variants (8% vs 1.8% for all SNPs) and were annotated to 15 genes. Two coding SNVs on chromosome 1q25 showed the strongest evidence of association with juvenile onset SLE (p-values<5E-08), one of which results in a predicted deleterious amino acid change. Interestingly, this association exceeded the signal from the human leukocyte antigen region on chromosome 6. Conclusion Using targeted sequencing we have identified coding SNVs in novel candidate risk loci in juvenile onset SLE. Our finding suggests differences in the genetic risk for childhood and adult onset SLE and provides insight into the genetic aetiology of juvenile onset SLE.