Introduction

Systemic lupus erythematosus (SLE) is a chronic, multiorgan, and systemic autoimmune disorder [1]. SLE is characterized by defective functioning of the immune system, resulting in autoantibody production and inflammatory manifestations in several organs [1]. Immune cells from SLE patients display various aberrations, including skewed cytokine production, defective function of CD4+ T cells, abnormal activation of B cells, and reduction of cytotoxic T cell function [2–6]. Occupational exposure, drugs, chemicals, food, viruses and other infectious factors may contribute to this alteration in the immune system [7, 8]. Genetic factors also play a significant role in the susceptibility to SLE incidence [9–11]. In particular, numerous genes encoding disparate proteins regulating the immune system pathways are candidates to be the susceptibility locus in the development of SLE [9].

Chemokines encompass a collection of small molecular weight (8–14 kDa) chemotactic cytokines, which bind to specific G-protein-coupled plasma cell membrane receptors [12]. Chemokines recruit hematopoietic and immune cells to sites of differentiation and inflammation, respectively [12, 13]. Stromal cell-derived factor-1 (SDF1), which is currently also designated CXCL12, is a chemokine involved in organogenesis, lymphopoiesis, and myelopoiesis [14, 15].

In the lupus model NZB/W mice, SDF1 contributes to the chemotaxis, proliferation, and survival of PerB1a lymphocyte subpopulations that express a self-reactive repertoire of antibodies [16, 17]. Balabanian et al. [17] showed that SDF1 played a significant role in the production of anti-dsDNA antibodies, nephritis, and death in NZB/W mice.

It has been demonstrated that SDF1 has a G801A transition at position 801 in the 3′-untranslated region of the transcript, known as SDF1-3′A (rs 1801157) [18, 19]. This polymorphism may have an important regulatory function via an increase in the biosynthesis of SDF1 protein [18, 19]. We investigated the prevalence of SDF1-3′ G801A genotypes and alleles in patients with SLE (n = 150) and controls (n = 300) from a Polish cohort. We also examined the association of SDF1-3′ G801A genotypes with clinical manifestations and the presence of autoantibodies in patients with SLE.

Patients and methods

Patients and controls

One hundred and fifty consecutive SLE patients (all women) enrolled at the Institute of Rheumatology in Warsaw, Poland were included in the present study (Table 1). Patients fulfilled at least four of the American College of Rheumatology 1982 revised criteria for SLE [20, 21]. Both patients and control groups were of Polish Caucasian origin. The control group included three hundred healthy women. The mean age of healthy individuals was 37.6 ± 8.6 years. The protocol of the investigation was approved by the Local Ethical Committee of Poznań University of Medical Sciences. Written informed consent was signed by all participating individuals.

Table 1 Association of the polymorphism with clinical manifestation and production of autoantibodies in patients with SLE
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Genotyping

DNA was obtained from peripheral blood leucocytes by salt extraction. Polymorphic variants of SDF1-3′ G801A (rs 1801157) were identified using PCR with the primer pair 5′-TTATTGTACTTGCCTTATTAGAG-3′ and 5-′GTAGTTCACCCCAAAGGACC-3′; enzyme digestion followed the identification process. The PCR-amplified fragments of SDF1 that were 732 bp in length were isolated and subjected to digestion with MspI (C/CGG). The SDF1-3′G allele was digested into 456 and 276 bp fragments, whereas the SDF1-3′A allele stayed uncut at a size of 732 bp. DNA fragments were separated by electrophoresis on 3% agarose gel and visualized by ethidium bromide staining. Polymorphism confirmation was performed by sequencing analysis.

Statistical analysis

The distribution of genotypes in all groups was tested for deviation from Hardy–Weinberg equilibrium. Fisher exact test was used to determine differences in the genotypic and allelic distribution between patients and controls. Moreover, the Odds Ratio (OR) and 95% Confidence Intervals (CI) were calculated. A P value <0.05 was considered statistically significant. Associations between clinical manifestations, the production of autoantibodies, and polymorphism distribution in patients with SLE were determined by Fisher exact test.

Results

Genotype assessment of SDF1 G801A polymorphisms disclosed no significant deviation from Hardy–Weinberg equilibrium in any group.

We found a significant association between SDF1-3′ A/A and G/A genotypes (recessive model) and, respectively, renal manifestations of the disease OR = 3.042 (95% CI = 1.527–6.058, P = 0.002), and the P value stayed statistically significant after Bonferroni correction (p corr = 0.032) (Table 1). However, the statistically significant association of SDF1-3′ A/A and G/A genotypes (recessive model) with dermal manifestations OR = 2.510 (95% CI = 1.247–5.052, P = 0.0122), (p corr = 0.1952) did not remain statistically significant after Bonferroni correction (Table 1).

We did not observe a significant variation in the distribution of SDF1 G801A polymorphic variants in SLE patients and controls (Table 2). OR for SLE patients with SDF1-3′ A/A genotype was 2.034 (95% CI = 0.5796–7.142, P = 0.3123) and OR of the SDF1-3′ A/A and A/G genotypes was 1.309 (95% CI = 0.8660–1.978), P = 0.2029 (Table 2). We also did not find a correlation between the SDF1-3′ A allele or AA genotype with SLE disease activity.

Table 2 Association of the SDF1 G801A polymorphisms in SLE patients and controls
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Discussion

The human genome project disclosed more than ten million single nucleotide polymorphisms. Despite this vast number of polymorphisms, the role of most of them in the incidence of various disorders remains elusive [22].

The human SDF1 gene is located at 10q11.1 and its transcription produces alpha and beta alternative splice variants [23]. Translation of both transcripts produces the SDF1 chemokine, which binds to only one receptor, CXCR4 [24]. SDF1 is a chemoattractant for lymphocytes, megakaryocytes, endothelial cells, and stem cells [24–26], and is involved in the development of neuronal, cardiac, vascular, and craniofacial systems [27].

To date, the SDF1-3′A gene variant has been considered a factor in increased susceptibility to lymphoma, oral and squamous carcinomas, and cancers of the breast, lung, and prostate [28–33]. Schröppel et al. [34] observed that the SDF1-3′A variant is significantly associated with higher mortality in liver allograft recipients. Moreover, the SDF1-3′A allele has been associated with the microvascular involvement in systemic sclerosis and with age-at-onset of type 1 diabetes mellitus in the Japanese population [35, 36].

We did not observe a difference in the contribution of the SDF1-3′A gene variant between SLE patients and healthy individuals. These findings are consistent with Lima et al. [37], who also did not find differences between SDF1-3′ G801A genotypes and allele prevalence in SLE patients and controls. However, they found that SLE patients with antiphospholipid syndrome exhibited a higher distribution of SDF1-3′ A/A genotype frequencies compared with patients without this syndrome [37].

We did not observe a contribution of SDF1-3′ G801A genotypes to antiphospholipid syndrome (results not shown). However, we observed a significant association of SDF1-3′ AA and GA genotypes with renal manifestations of SLE. There was also a higher distribution of SDF1-3′ A/A and A/G genotypes in patients with dermal manifestations compared with patients without dermal manifestations. The discrepancies between Lima’s and our findings can be due to differences in the racial structure of these investigated groups. Moreover, exposure to varying environmental factors in patients with distinct SDF1-3′ G801A genotypes can also have a disparate effect on SLE manifestation [7].

The SDF1 receptor, CXCR4, is also considered a co-receptor for entry of the human immunodeficiency virus (HIV) into immune cells [38]. The genetic association analysis of 2,857 patients disclosed that homozygous SDF1-3′A/A individuals had delayed onset of AIDS [18]. Since SDF1 competes with HIV for entry into target cells, this delay in the onset of AIDS may suggest that SDF1-3′A variants are responsible for higher SDF1 biosynthesis [18].

Balabanian et al. [17] observed an increased production of SDF1 in the podocytes of glomeruli of NZB/W mice. They also reversed lupus nephritis in NZB/W mice following SDF1 neutralization [17]. Moreover, Robak et al. [39] indicated that patients with SLE exhibited a higher median serum level of SDF1 than healthy individuals.

Our observations suggest that the SDF1-3′A variant, which may lead to a higher production of the SDF1 chemokine, may be associated with renal manifestations of SLE. The SDF1-3′A can also be associated with a gene with which SDF1 interacts and is not in linkage disequilibrium but this gene contributes to renal SLE manifestations. However, to more precisely determine the significance of the SDF1-3′A G801A polymorphism in SLE manifestation or incidence, additional examination of the prevalence of these variants in other cohorts is required.