Dantu Blood Group Erythrocytes Form Large Plasmodium falciparum Rosettes Less Commonly

Dantu erythrocytes, which express a hybrid glycophorin B/A protein, are protective against severe malaria. Recent studies have shown that Dantu impairs Plasmodium falciparum invasion by increasing erythrocyte membrane tension, but its effects on pathological host-parasite adhesion interactions such as rosetting, the binding of uninfected erythrocytes to P. falciparum-infected erythrocytes, have not been investigated previously. The expression of several putative host rosetting receptors-including glycophorin A (GYPA), glycophorin C (GYPC), complement receptor 1 (CR1), and band 3, which complexes with GYPA to form the Wrightb blood group antigen-are altered on Dantu erythrocytes. Here, we compare receptor expression, and rosetting at both 1 hour and 48 hours after mixing with mature trophozoite-stage Kenyan laboratory-adapted P. falciparum strain 11019 parasites in Dantu and non-Dantu erythrocytes. Dantu erythrocytes showed lower staining for GYPA and CR1, and greater staining for band 3, as observed previously, whereas Wrightb and GYPC staining did not vary significantly. No significant between-genotype differences in rosetting were seen after 1 hour, but the percentage of large rosettes was significantly less in both Dantu heterozygous (mean, 16.4%; standard error of the mean [SEM], 3.2) and homozygous donors (mean, 15.4%; SEM, 1.4) compared with non-Dantu erythrocytes (mean, 32.9%; SEM, 7.1; one-way analysis of variance, P = 0.025) after 48 hours. We also found positive correlations between erythrocyte mean corpuscular volume (MCV), the percentage of large rosettes (Spearman's rs = 0.5970, P = 0.0043), and mean rosette size (rs = 0.5206, P = 0.0155). Impaired rosetting resulting from altered erythrocyte membrane receptor expression and reduced MCV might add to the protective effect of Dantu against severe malaria.

The Dantu blood group prevents parasite growth in vivo: Evidence from a controlled human malaria infection study

Background

The long co-evolution of Homo sapiens and Plasmodium falciparum has resulted in the selection of numerous human genetic variants that confer an advantage against severe malaria and death. One such variant is the Dantu blood group antigen, which is associated with 74% protection against severe and complicated P. falciparum malaria infections in homozygous individuals, similar to that provided by the sickle haemoglobin allele (HbS). Recent in vitro studies suggest that Dantu exerts this protection by increasing the surface tension of red blood cells, thereby impeding the ability of P. falciparum merozoites to invade them and reducing parasite multiplication. However, no studies have yet explored this hypothesis in vivo.

Methods

We investigated the effect of Dantu on early phase P. falciparum (Pf) infections in a controlled human malaria infection (CHMI) study. 141 sickle-negative Kenyan adults were inoculated with 3.2 × 10³ aseptic, purified, cryopreserved Pf sporozoites (PfSPZ Challenge) then monitored for blood-stage parasitaemia for 21 days by quantitative polymerase chain reaction (qPCR)analysis of the 18S ribosomal RNA P. falciparum gene. The primary endpoint was blood-stage P. falciparum parasitaemia of ≥500/μl while the secondary endpoint was the receipt of antimalarial treatment in the presence of parasitaemia of any density. On study completion, all participants were genotyped both for Dantu and for four other polymorphisms that are associated with protection against severe falciparum malaria: α⁺-thalassaemia, blood group O, G6PD deficiency, and the rs4951074 allele in the red cell calcium transporter ATP2B4.

Results

The primary endpoint was reached in 25/111 (22.5%) non-Dantu subjects in comparison to 0/27 (0%) Dantu heterozygotes and 0/3 (0.0%) Dantu homozygotes (p=0.01). Similarly, 49/111 (44.1%) non-Dantu subjects reached the secondary endpoint in comparison to only 7/27 (25.9%) and 0/3 (0.0%) Dantu heterozygotes and homozygotes, respectively (p=0.021). No significant impacts on either outcome were seen for any of the other genetic variants under study.

Conclusions

This study reveals, for the first time, that the Dantu blood group is associated with high-level protection against early, non-clinical, P. falciparum malaria infections in vivo. Learning more about the mechanisms involved could potentially lead to new approaches to the prevention or treatment of the disease. Our study illustrates the power of CHMI with PfSPZ Challenge for directly testing the protective impact of genotypes previously identified using other methods.

Funding

The Kenya CHMI study was supported by an award from Wellcome (grant number 107499). SK was supported by a Training Fellowship (216444/Z/19/Z), TNW by a Senior Research Fellowship (202800/Z/16/Z), JCR by an Investigator Award (220266/Z/20/Z), and core support to the KEMRI-Wellcome Trust Research Programme in Kilifi, Kenya (203077), all from Wellcome. The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication. For the purpose of Open Access, the authors have applied a CC BY public copyright license to any Author Accepted Manuscript version arising from this submission.

Clinical trial number

NCT02739763.

BIRC6 modifies risk of invasive bacterial infection in Kenyan children

Invasive bacterial disease is a major cause of morbidity and mortality in African children. Despite being caused by diverse pathogens, children with sepsis are clinically indistinguishable from one another. In spite of this, most genetic susceptibility loci for invasive infection that have been discovered to date are pathogen specific and are not therefore suggestive of a shared genetic architecture of bacterial sepsis. Here, we utilise probabilistic diagnostic models to identify children with a high probability of invasive bacterial disease among critically unwell Kenyan children with Plasmodium falciparum parasitaemia. We construct a joint dataset including 1445 bacteraemia cases and 1143 severe malaria cases, and population controls, among critically unwell Kenyan children that have previously been genotyped for human genetic variation. Using these data, we perform a cross-trait genome-wide association study of invasive bacterial infection, weighting cases according to their probability of bacterial disease. In doing so, we identify and validate a novel risk locus for invasive infection secondary to multiple bacterial pathogens, that has no apparent effect on malaria risk. The locus identified modifies splicing of BIRC6 in stimulated monocytes, implicating regulation of apoptosis and autophagy in the pathogenesis of sepsis in Kenyan children.

Red blood cell tension protects against severe malaria in the Dantu blood group

Malaria has had a major effect on the human genome, with many protective polymorphisms-such as the sickle-cell trait-having been selected to high frequencies in malaria-endemic regions1,2. The blood group variant Dantu provides 74% protection against all forms of severe malaria in homozygous individuals3-5, a similar degree of protection to that afforded by the sickle-cell trait and considerably greater than that offered by the best malaria vaccine. Until now, however, the protective mechanism has been unknown. Here we demonstrate the effect of Dantu on the ability of the merozoite form of the malaria parasite Plasmodium falciparum to invade red blood cells (RBCs). We find that Dantu is associated with extensive changes to the repertoire of proteins found on the RBC surface, but, unexpectedly, inhibition of invasion does not correlate with specific RBC-parasite receptor-ligand interactions. By following invasion using video microscopy, we find a strong link between RBC tension and merozoite invasion, and identify a tension threshold above which invasion rarely occurs, even in non-Dantu RBCs. Dantu RBCs have higher average tension than non-Dantu RBCs, meaning that a greater proportion resist invasion. These findings provide both an explanation for the protective effect of Dantu, and fresh insight into why the efficiency of P. falciparum invasion might vary across the heterogenous populations of RBCs found both within and between individuals.

Human genetics and malaria resistance

Malaria has been the pre-eminent cause of early mortality in many parts of the world throughout much of the last five thousand years and, as a result, it is the strongest force for selective pressure on the human genome yet described. Around one third of the variability in the risk of severe and complicated malaria is now explained by additive host genetic effects. Many individual variants have been identified that are associated with malaria protection, but the most important all relate to the structure or function of red blood cells. They include the classical polymorphisms that cause sickle cell trait, α-thalassaemia, G6PD deficiency, and the major red cell blood group variants. More recently however, with improving technology and experimental design, others have been identified that include the Dantu blood group variant, polymorphisms in the red cell membrane protein ATP2B4, and several variants related to the immune response. Characterising how these genes confer their effects could eventually inform novel therapeutic approaches to combat malaria. Nevertheless, all together, only a small proportion of the heritable component of malaria resistance can be explained by the variants described so far, underscoring its complex genetic architecture and the need for continued research.

Mapping Variation in Cellular and Transcriptional Response to 1,25-Dihydroxyvitamin D3 in Peripheral Blood Mononuclear Cells

The active hormonal form of vitamin D, 1,25-dihydroxyvitamin D (1,25D) is an important modulator of the immune system, inhibiting cellular proliferation and regulating transcription of immune response genes. In order to characterize the genetic basis of variation in the immunomodulatory effects of 1,25D, we mapped quantitative traits of 1,25D response at both the cellular and the transcriptional level. We carried out a genome-wide association scan of percent inhibition of cell proliferation (Imax) induced by 1,25D treatment of peripheral blood mononuclear cells from 88 healthy African-American individuals. Two genome-wide significant variants were identified: rs1893662 in a gene desert on chromosome 18 (p = 2.32 x 10-8) and rs6451692 on chromosome 5 (p = 2.55 x 10-8), which may influence the anti-proliferative activity of 1,25D by regulating the expression of nearby genes such as the chemokine gene, CCL28, and the translation initiation gene, PAIP1. We also identified 8 expression quantitative trait loci at a FDR<0.10 for transcriptional response to 1,25D treatment, which include the transcriptional regulator ets variant 3-like (ETV3L) and EH-domain containing 4 (EHD4). In addition, we identified response eQTLs in vitamin D receptor binding sites near genes differentially expressed in response to 1,25D, such as FERM Domain Containing 6 (FRMD6), which plays a critical role in regulating both cell proliferation and apoptosis. Combining information from the GWAS of Imax and the response eQTL mapping enabled identification of putative Imax-associated candidate genes such as PAIP1 and the transcriptional repressor gene ZNF649. Overall, the variants identified in this study are strong candidates for immune traits and diseases linked to vitamin D, such as multiple sclerosis.

Genetic analysis of the pathogenic molecular sub-phenotype interferon-alpha identifies multiple novel loci involved in systemic lupus erythematosus

Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disorder characterized by inflammation of multiple organ systems and dysregulated interferon responses. SLE is both genetically and phenotypically heterogeneous, greatly reducing the power of case-control studies in SLE. Elevated circulating interferon alpha (IFN-α) is a stable, heritable trait in SLE, which has been implicated in primary disease pathogenesis. 40–50% of patients have high IFN-α, and high levels correspond with clinical differences. To study genetic heterogeneity in SLE, we performed a case-case study comparing patients with high vs. low IFN-α in over 1550 SLE cases, including GWAS and replication cohorts. In meta-analysis, the top associations in European ancestry were PRKG1 rs7897633 (P_Meta=2.75 × 10⁻⁸) and PNP rs1049564 (P_Meta=1.24 × 10⁻⁷). We also found evidence for cross-ancestral background associations with the ANKRD44 and PLEKHF2 loci. These loci have not been previously identified in case-control SLE genetic studies. Bioinformatic analyses implicated these loci functionally in dendritic cells and natural killer cells, both of which are involved in IFN-α production in SLE. As case-control studies of heterogeneous diseases reach a limit of feasibility with respect to subject number and detectable effect size, the study of informative pathogenic subphenotypes becomes an attractive strategy for genetic discovery in complex disease.

Brief Report: IRF5 systemic lupus erythematosus risk haplotype is associated with asymptomatic serologic autoimmunity and progression to clinical autoimmunity in mothers of children with neonatal lupus

OBJECTIVE

Variation in the interferon regulatory factor 5 (IRF5) gene has been associated with risk of developing systemic lupus erythematosus (SLE), and this association is largely dependent upon anti-Ro autoantibodies. This study was undertaken to determine if the IRF5 genotype is associated with maternal diagnosis or progression of autoimmunity.

METHODS

Genotyping of haplotype-tagging polymorphisms in IRF5 was performed in 93 subjects of European ancestry who were recruited to the Research Registry for Neonatal Lupus. All subjects had high-titer anti-Ro autoantibodies and had a child with neonatal lupus (NL); allele frequencies were compared to those in nonautoimmune controls. The mothers had SLE, Sjögren's syndrome (SS), or undifferentiated autoimmune syndrome (UAS), or were asymptomatic.

RESULTS

The SLE risk haplotype of IRF5 was enriched in all anti-Ro-positive subjects except in those with SS (odds ratio [OR] 2.55, P = 8.8 × 10(-4) ). The SLE risk haplotype was even enriched in asymptomatic individuals with anti-Ro antibodies (OR 2.69, P = 0.019). The same haplotype was more prevalent in subjects who were initially asymptomatic but developed symptomatic SLE during followup (OR 5.83, P = 0.0024). Interestingly, SS was associated with 2 minor IRF5 haplotypes, and these same haplotypes were decreased in frequency in mothers with SLE and those with UAS.

CONCLUSION

The IRF5 SLE risk haplotype was associated with anti-Ro antibody positivity in asymptomatic individuals, as well as with progression to SLE in asymptomatic anti-Ro-positive individuals. SS in mothers of children with NL was associated with different IRF5 haplotypes. These data suggest that IRF5 polymorphisms play a role in serologic autoimmunity in humans and may promote the progression to clinical autoimmunity.

IRF5 haplotypes demonstrate diverse serological associations which predict serum interferon alpha activity and explain the majority of the genetic association with systemic lupus erythematosus

OBJECTIVE

High serum interferon α (IFNα) activity is a heritable risk factor for systemic lupus erythematosus (SLE). Auto-antibodies found in SLE form immune complexes which can stimulate IFNα production by activating endosomal Toll-like receptors and interferon regulatory factors (IRFs), including IRF5. Genetic variation in IRF5 is associated with SLE susceptibility; however, it is unclear how IRF5 functional genetic elements contribute to human disease.

METHODS

1034 patients with SLE and 989 controls of European ancestry, 555 patients with SLE and 679 controls of African-American ancestry, and 73 patients with SLE of South African ancestry were genotyped at IRF5 polymorphisms, which define major haplotypes. Serum IFNα activity was measured using a functional assay.

RESULTS

In European ancestry subjects, anti-double-stranded DNA (dsDNA) and anti-Ro antibodies were each associated with different haplotypes characterised by a different combination of functional genetic elements (OR>2.56, p<1.9×10(-14) for both). These IRF5 haplotype-auto-antibody associations strongly predicted higher serum IFNα in patients with SLE and explained >70% of the genetic risk of SLE due to IRF5. In African-American patients with SLE a similar relationship between serology and IFNα was observed, although the previously described European ancestry-risk haplotype was present at admixture proportions in African-American subjects and absent in African patients with SLE.

CONCLUSIONS

The authors define a novel risk haplotype of IRF5 that is associated with anti-dsDNA antibodies and show that risk of SLE due to IRF5 genotype is largely dependent upon particular auto-antibodies. This suggests that auto-antibodies are directly pathogenic in human SLE, resulting in increased IFNα in cooperation with particular combinations of IRF5 functional genetic elements. SLE is a systemic autoimmune disorder affecting multiple organ systems including the skin, musculoskeletal, renal and haematopoietic systems. Humoral autoimmunity is a hallmark of SLE, and patients frequently have circulating auto-antibodies directed against dsDNA, as well as RNA binding proteins (RBP). Anti-RBP autoantibodies include antibodies which recognize Ro, La, Smith (anti-Sm), and ribonucleoprotein (anti-nRNP), collectively referred to as anti-retinol-binding protein). Anti-retinol-binding protein and anti-dsDNA auto-antibodies are rare in the healthy population. These auto-antibodies can be present in sera for years preceding the onset of clinical SLE illness and are likely pathogenic in SLE.

Autoimmune disease risk variant of IFIH1 is associated with increased sensitivity to IFN-α and serologic autoimmunity in lupus patients

Increased IFN-α signaling is a heritable risk factor for systemic lupus erythematosus (SLE). IFN induced with helicase C domain 1 (IFIH1) is a cytoplasmic dsRNA sensor that activates IFN-α pathway signaling. We studied the impact of the autoimmune-disease-associated IFIH1 rs1990760 (A946T) single nucleotide polymorphism upon IFN-α signaling in SLE patients in vivo. We studied 563 SLE patients (278 African-American, 179 European-American, and 106 Hispanic-American). Logistic regression models were used to detect genetic associations with autoantibody traits, and multiple linear regression was used to analyze IFN-α-induced gene expression in PBMCs in the context of serum IFN-α in the same blood sample. We found that the rs1990760 T allele was associated with anti-dsDNA Abs across all of the studied ancestral backgrounds (meta-analysis odds ratio = 1.34, p = 0.026). This allele also was associated with lower serum IFN-α levels in subjects who had anti-dsDNA Abs (p = 0.0026). When we studied simultaneous serum and PBMC samples from SLE patients, we found that the IFIH1 rs1990760 T allele was associated with increased IFN-induced gene expression in PBMCs in response to a given amount of serum IFN-α in anti-dsDNA-positive patients. This effect was independent of the STAT4 genotype, which modulates sensitivity to IFN-α in a similar way. Thus, the IFIH1 rs1990760 T allele was associated with dsDNA Abs, and in patients with anti-dsDNA Abs this risk allele increased sensitivity to IFN-α signaling. These studies suggest a role for the IFIH1 risk allele in SLE in vivo.

Trait-stratified genome-wide association study identifies novel and diverse genetic associations with serologic and cytokine phenotypes in systemic lupus erythematosus

Introduction

Systemic lupus erythematosus (SLE) is a highly heterogeneous disorder, characterized by differences in autoantibody profile, serum cytokines, and clinical manifestations. SLE-associated autoantibodies and high serum interferon alpha (IFN-α) are important heritable phenotypes in SLE which are correlated with each other, and play a role in disease pathogenesis. These two heritable risk factors are shared between ancestral backgrounds. The aim of the study was to detect genetic factors associated with autoantibody profiles and serum IFN-α in SLE.

Methods

We undertook a case-case genome-wide association study of SLE patients stratified by ancestry and extremes of phenotype in serology and serum IFN-α. Single nucleotide polymorphisms (SNPs) in seven loci were selected for follow-up in a large independent cohort of 538 SLE patients and 522 controls using a multi-step screening approach based on novel metrics and expert database review. The seven loci were: leucine-rich repeat containing 20 (LRRC20); protein phosphatase 1 H (PPM1H); lysophosphatidic acid receptor 1 (LPAR1); ankyrin repeat and sterile alpha motif domain 1A (ANKS1A); protein tyrosine phosphatase, receptor type M (PTPRM); ephrin A5 (EFNA5); and V-set and immunoglobulin domain containing 2 (VSIG2).

Results

SNPs in the LRRC20, PPM1H, LPAR1, ANKS1A, and VSIG2 loci each demonstrated strong association with a particular serologic profile (all odds ratios > 2.2 and P < 3.5 × 10^-4). Each of these serologic profiles was associated with increased serum IFN-α. SNPs in both PTPRM and LRRC20 were associated with increased serum IFN-α independent of serologic profile (P = 2.2 × 10^-6 and P = 2.6 × 10^-3 respectively). None of the SNPs were strongly associated with SLE in case-control analysis, suggesting that the major impact of these variants will be upon subphenotypes in SLE.

Conclusions

This study demonstrates the power of using serologic and cytokine subphenotypes to elucidate genetic factors involved in complex autoimmune disease. The distinct associations observed emphasize the heterogeneity of molecular pathogenesis in SLE, and the need for stratification by subphenotypes in genetic studies. We hypothesize that these genetic variants play a role in disease manifestations and severity in SLE.

African-derived genetic polymorphisms in TNFAIP3 mediate risk for autoimmunity

The TNF alpha-induced protein 3 (TNFAIP3) is an ubiquitin-modifying enzyme and an essential negative regulator of inflammation. Genome-wide association studies have implicated the TNFAIP3 locus in susceptibility to autoimmune disorders in European cohorts, including rheumatoid arthritis, coronary artery disease, psoriasis, celiac disease, type 1 diabetes, inflammatory bowel disease, and systemic lupus erythematosus (SLE). There are two nonsynonymous coding polymorphisms in the deubiquitinating (DUB) domain of TNFAIP3: F127C, which is in high-linkage disequilibrium with reported SLE-risk variants, and A125V, which has not been previously studied. We conducted a case-control study in African-American SLE patients using these coding variants, along with tagging polymorphisms in TNFAIP3, and identified a novel African-derived risk haplotype that is distinct from previously reported risk variants (odds ratio=1.6, p=0.006). In addition, a rare protective haplotype was defined by A125V (odds ratio=0.31, p=0.027). Although A125V was associated with protection from SLE, surprisingly the same allele was associated with increased risk of inflammatory bowel disease. We tested the functional activity of nonsynonymous coding polymorphisms within TNFAIP3, and found that the A125V coding-change variant alters the DUB activity of the protein. Finally, we used computer modeling to depict how the A125V amino acid change in TNFAIP3 may affect the three-dimensional structure of the DUB domain to a greater extent than F127C. This is the first report of an association between TNFAIP3 polymorphisms and autoimmunity in African-Americans.

The PTPN22 C1858T polymorphism is associated with skewing of cytokine profiles toward high interferon-alpha activity and low tumor necrosis factor alpha levels in patients with lupus

OBJECTIVE

The C1858T polymorphism in PTPN22 has been associated with the risk of systemic lupus erythematosus (SLE) as well as multiple other autoimmune diseases. We have previously shown that high serum interferon-alpha (IFNalpha) activity is a heritable risk factor for SLE. The aim of this study was to determine whether the PTPN22 risk variant may shift serum cytokine profiles to higher IFNalpha activity, resulting in risk of disease.

METHODS

IFNalpha was measured in 143 patients with SLE, using a functional reporter cell assay, and tumor necrosis factor alpha (TNFalpha) was measured by enzyme-linked immunosorbent assay. The rs2476601 single-nucleotide polymorphism in PTPN22 (C1858T) was genotyped in the same patients. Patients were grouped, using a clustering algorithm, into 4 cytokine groups (IFNalpha predominant, IFNalpha and TNFalpha correlated, TNFalpha predominant, and both IFNalpha and TNFalpha low).

RESULTS

SLE patients carrying the risk allele of PTPN22 had higher serum IFNalpha activity than patients lacking the risk allele (P = 0.027). TNFalpha levels were lower in carriers of the risk allele (P = 0.030), and the risk allele was more common in patients in the IFNalpha-predominant and IFNalpha and TNFalpha-correlated groups as compared with patients in the TNFalpha-predominant and both IFNalpha and TNFalpha-low groups (P = 0.001). Twenty-five percent of male patients carried the risk allele, compared with 10% of female patients (P = 0.024); however, cytokine skewing was similar in both sexes.

CONCLUSION

The autoimmune disease risk allele of PTPN22 is associated with skewing of serum cytokine profiles toward higher IFNalpha activity and lower TNFalpha levels in vivo in patients with SLE. This serum cytokine pattern may be relevant in other autoimmune diseases associated with the PTPN22 risk allele.

Genetic variation at the IRF7/PHRF1 locus is associated with autoantibody profile and serum interferon-alpha activity in lupus patients

OBJECTIVE

Interferon-alpha (IFNalpha) is a heritable risk factor for systemic lupus erythematosus (SLE). Genetic variation near IRF7 is implicated in SLE susceptibility. SLE-associated autoantibodies can stimulate IFNalpha production through the Toll-like receptor/IRF7 pathway. This study was undertaken to determine whether variants of IRF7 act as risk factors for SLE by increasing IFNalpha production and whether autoantibodies are important to this phenomenon.

METHODS

We studied 492 patients with SLE (236 African American, 162 European American, and 94 Hispanic American subjects). Serum levels of IFNalpha were measured using a reporter cell assay, and single-nucleotide polymorphisms (SNPs) in the IRF7/PHRF1 locus were genotyped.

RESULTS

In a joint analysis of European American and Hispanic American subjects, the rs702966 C allele was associated with the presence of anti-double-stranded DNA (anti-dsDNA) antibodies (odds ratio [OR] 1.83, P = 0.0069). The rs702966 CC genotype was only associated with higher serum levels of IFNalpha in European American and Hispanic American patients with anti-dsDNA antibodies (joint analysis P = 4.1 x 10(-5) in anti-dsDNA-positive patients and P = 0.99 in anti-dsDNA-negative patients). In African American subjects, anti-Sm antibodies were associated with the rs4963128 SNP near IRF7 (OR 1.95, P = 0.0017). The rs4963128 CT and TT genotypes were associated with higher serum levels of IFNalpha only in African American patients with anti-Sm antibodies (P = 0.0012). In African American patients lacking anti-Sm antibodies, an effect of anti-dsDNA-rs702966 C allele interaction on serum levels of IFNalpha was observed, similar to the other patient groups (overall joint analysis P = 1.0 x 10(-6)). In European American and Hispanic American patients, the IRF5 SLE risk haplotype showed an additive effect with the rs702966 C allele on IFNalpha level in anti-dsDNA-positive patients.

CONCLUSION

Our findings indicate that IRF7/PHRF1 variants in combination with SLE-associated autoantibodies result in higher serum levels of IFNalpha, providing a biologic relevance for this locus at the protein level in human SLE in vivo.

Genetic regulation of serum cytokines in systemic lupus erythematosus

Genetic association studies in systemic lupus erythematosus (SLE) have been extremely successful in recent years, identifying several loci associated with disease susceptibility. Much work remains to integrate these loci into the functional pathogenic pathways that characterize the disease. Our working hypothesis is that many genetic variations linked to SLE and autoimmunity mediate the risk of disease by altering cytokine profiles or responses to cytokine signaling. Genetic polymorphisms that affect cytokine signaling could alter thresholds for immune responses, resulting in proinflammatory presentation of self-antigens and the subsequent misdirection of adaptive immunity against self, which is observed in autoimmune disease. SLE is clinically heterogeneous and genetically complex, and we expect that individual genes and cytokine patterns will be more or less important to different disease manifestations and subgroups of patients. Defining these genotype-cytokine-phenotype relationships will increase our understanding of both initial disease pathogenesis as well as subsequent response/nonresponse to various therapies. In this review, we summarize some recent work in the area of SLE cytokine genetics and describe the implications for SLE, autoimmunity, and immune system homeostasis, which are revealed by these investigations.

Elevated serum interferon-alpha activity in juvenile dermatomyositis: associations with disease activity at diagnosis and after thirty-six months of therapy

OBJECTIVE

Interferon-alpha (IFNalpha) has been implicated in the pathogenesis of juvenile dermatomyositis (DM). The aim of this study was to examine serum IFNalpha activity in a cohort of children with juvenile DM to determine relationships between IFNalpha and indicators of disease activity and severity.

METHODS

Thirty-nine children with definite/probable juvenile DM were included in the study. Serum samples were obtained at the time of diagnosis from 18 untreated patients with juvenile DM. Second samples from 11 of these patients were obtained at 24 months, while they were receiving treatment, and third samples were obtained from 7 of these patients at 36 months. The remaining 21 children were studied 36 months after their initial diagnosis. Serum IFNalpha activity was measured using a functional reporter cell assay.

RESULTS

Patients with juvenile DM had higher serum IFNalpha activity than both pediatric and adult healthy control subjects. In untreated patients, serum IFNalpha activity was positively correlated with serum muscle enzyme levels (P<0.05 for creatine kinase, aspartate aminotransferase, and aldolase) and inversely correlated with the duration of untreated disease (P=0.017). The tumor necrosis factor alpha -308A allele was associated with higher serum IFNalpha levels only in untreated patients (P=0.030). At 36 months, serum IFNalpha levels were inversely correlated with muscle enzyme levels in those patients still requiring therapy and with the skin Disease Activity Score in those patients who had completed therapy (P=0.002).

CONCLUSION

Serum IFNalpha activity was associated with higher serum levels of muscle-derived enzymes and a shorter duration of untreated disease in patients with newly diagnosed juvenile DM and was inversely correlated with measures of chronic disease activity at 36 months postdiagnosis. These data suggest that IFNalpha could play a role in disease initiation in juvenile DM.

Age- and gender-specific modulation of serum osteopontin and interferon-alpha by osteopontin genotype in systemic lupus erythematosus

Osteopontin (OPN) is a multifunctional cytokine involved in long bone remodeling and immune system signaling. Additionally, OPN is critical for interferon-alpha (IFN-alpha) production in murine plasmacytoid dendritic cells. We have previously shown that IFN-alpha is a heritable risk factor for systemic lupus erythematosus (SLE). Genetic variants of OPN have been associated with SLE susceptibility, and one study suggests that this association is particular to men. In this study, the 3' UTR SLE-risk variant of OPN (rs9138C) was associated with higher serum OPN and IFN-alpha in men (P=0.0062 and P=0.0087, respectively). In women, the association between rs9138 C and higher serum OPN and IFN-alpha was restricted to younger subjects, and risk allele carriers showed a strong age-related genetic effect of rs9138 genotype on both serum OPN and IFN-alpha (P<0.0001). In African-American subjects, the 5' region single nucleotide polymorphisms, rs11730582 and rs28357094, were associated with anti-RNP antibodies (odds ratio (OR)=2.9, P=0.0038 and OR=3.9, P=0.021, respectively). Thus, we demonstrate two distinct genetic influences of OPN on serum protein traits in SLE patients, which correspond to previously reported SLE-risk variants. This study provides a biologic relevance for OPN variants at the protein level, and suggests an influence of this gene on the IFN-alpha pathway in SLE.

Cutting edge: autoimmune disease risk variant of STAT4 confers increased sensitivity to IFN-alpha in lupus patients in vivo

Increased IFN-alpha signaling is a primary pathogenic factor in systemic lupus erythematosus (SLE). STAT4 is a transcription factor that is activated by IFN-alpha signaling, and genetic variation of STAT4 has been associated with risk of SLE and rheumatoid arthritis. We measured serum IFN-alpha activity and simultaneous IFN-alpha-induced gene expression in PBMC in a large SLE cohort. The risk variant of STAT4 (T allele; rs7574865) was simultaneously associated with both lower serum IFN-alpha activity and greater IFN-alpha-induced gene expression in PBMC in SLE patients in vivo. Regression analyses confirmed that the risk allele of STAT4 was associated with increased sensitivity to IFN-alpha signaling. The IFN regulatory factor 5 SLE risk genotype was associated with higher serum IFN-alpha activity; however, STAT4 showed dominant influence on the sensitivity of PBMC to serum IFN-alpha. These data provide biologic relevance for the risk variant of STAT4 in the IFN-alpha pathway in vivo.