An accurate and reliable real time SNP genotyping assay for the HLA-G +3142 bp C>G polymorphism

Rapid high-resolution melting method to identify human leukocyte antigen-G (HLA-G) 3' untranslated region polymorphism +3142C/G (rs1063320)

Background

HLA‐G is a non‐classical class I gene of the human Major Histocompatibility encoding molecules with immune‐modulatory properties. Expression of HLA‐G is being largely studied in pathological conditions, such as tumors, viral infections, inflammation, and autoimmune diseases, grafted tissues, among others. HLA‐G +3142C/G (rs1063320: dbSNP database) polymorphism is located in 3′ UTR of HAL‐G and plays a key role in determining the magnitude of gene and protein expression. The detection of HLA‐G +3142C/G polymorphism in the most published report is done through polymerase chain reaction followed by enzymatic digestion. Therefore, it is so interesting to develop a rapid and sensitive assay to genotype HLA‐G +3142C/G polymorphism. High‐resolution melt analysis (HRM) is a technology that is based on the analysis of the melting profile of PCR products through gradual temperature increase. The aim of this work is to apply high‐resolution melt method for genotyping the HLA‐G +3142C/G polymorphism.

Methods

DNA from 118 individuals was extracted from whole blood with QIAamp^® DNA blood mini kit (Qiagen, Germany). Primer couple was designed using Primer 3 online tools so as to have only one SNP in the target sequence for high HRM efficiency. Positive Controls were identified using DNA sequencing and used as reference when assigning genotypes for trial samples.

Results

We were able to recognize the three genotypes with similar accuracy than DNA sequencing using high resolution melting method. Hardy‐Weinberg equilibrium test shows that our population is in equilibrium for the studied SNP. Genotypes frequencies of +3142C/G polymorphism in Tunisian general population are 0.475 for heterozygote G/C, 0.186 for homozygote G/G and 0.339 for homozygote C/C.

Conclusion

HRM is a cost‐effective method suitable for SNP genotyping.

Upregulation of Soluble HLA-G in Chronic Left Ventricular Systolic Dysfunction

Left ventricular systolic dysfunction (LVSD) defined by ejection fraction (EF) <40% is common, serious but treatable, and correct diagnosis is the cornerstone of effective treatment. Biomarkers may help to diagnose LVSD and give insight into the pathophysiology. The immune system is activated in LVSD, and the immunomodulatory molecule human leukocyte antigen-G (HLA-G) may be involved. The primary aim was to measure soluble HLA-G (sHLA-G) in the blood in different stages of LVSD (<30% and 30–40%), in the midrange EF 40–50%, and in preserved EF ≥ 50% and to validate sHLA-G as a LVSD biomarker. The secondary aim was to examine associations between HLA-G gene polymorphisms influencing expression levels and LVSD. The 260 study participants were ≥75 years old, many with risk factors for heart disease or with known heart disease. Soluble HLA-G was significantly and uniformly higher in the groups with EF < 50% (<30, 30–40, and 40–50%) compared to EF > 50% (p < 0.0001). N-terminal fragment-pro-B-type natriuretic peptide (NT-proBNP) and uric acid values were inversely related to EF. According to Receiver Operating Characteristic (ROC) curves NT-proBNP outperformed both sHLA-G and uric acid as biomarkers of LVSD. Soluble HLA-G in blood plasma was elevated in LVSD regardless of EF. A novel finding was that a combined 14 bp ins-del/+3142 SNP HLA-G haplotype was associated with EF < 40%.

14-bp ins/del polymorphism and +3142C>G SNP of the HLA-G gene have a significant impact on acute rejection after liver transplantation

Expression of human leukocyte antigen G (HLA-G) has been associated with increased graft survival and decreased rejection episodes. It has been described that the HLA-G 14-base pair (bp) insertion/deletion (ins/del) (rs66554220) and +3142C>G (rs1063320) gene polymorphisms modify the expression level of HLA-G. The aim of the study was to investigate whether these HLA-G polymorphisms have an impact on acute rejection after liver transplantation. In total, 146 liver transplant recipients (57 with acute rejection and 89 without acute rejection) and 99 corresponding liver donors were genotyped for both polymorphisms. In liver transplantation the 14-bp ins/ins and the +3142GG genotypes are more frequent in recipients without rejection compared to recipients with rejection (3.5% vs. 31.5%, p=<0.001; 12.3% vs. 41.6%, p=<0.001) demonstrating an association with protection from acute rejection. In contrast, in liver donors we could not reveal an association. We conclude that 14-bp ins/ins and +3142GG genotypes of HLA-G in liver transplant recipients are of importance for prediction of acute rejection after liver transplantation. Thus genotyping of liver recipients for both polymorphisms might be useful to stratify liver transplant recipients according to the risk of acute liver transplant rejection.

Fetal cell microchimerism: a protective role in autoimmune thyroid diseases

OBJECTIVE

The physiological persistence of fetal cells in the circulation and tissue of a previously pregnant woman is called fetal cell microchimerism (FCM). It has been hypothesized to play a role in systemic autoimmune disease; however, only limited data are available regarding its role in autoimmune thyroid disease (AITD).

DESIGN

Circulating FCM was analyzed in a large series of previously pregnant women with Graves' disease (GD), Hashimoto's thyroiditis (HT), or no disease (healthy controls (HCs)). To exclude the possible bias related to placental factors, the polymorphic pattern of human leukocyte antigen-G (HLA-G) gene, which is known to be involved in the tolerance of fetal cells by the maternal immune system, was investigated.

METHODS

FCM was evaluated by PCR in the peripheral blood, and the Y chromosome was identified by fluorescence in situ hybridization in some GD tissues. HLA-G polymorphism typing was assessed by real-time PCR.

RESULTS

FCM was significantly more frequent in HC (63.6%) than in GD (33.3%) or HT (27.8%) women (P=0.0004 and P=0.001 respectively). A quantitative analysis confirmed that circulating male DNA was more abundant in HC than it was in GD or HT. Microchimeric cells were documented in vessels and in thyroid follicles. In neither GD/HT patients nor HC women was the HLA-G typing different between FCM-positive and FCM-negative cases.

CONCLUSION

The higher prevalence of FCM in HC as compared to GD and HT patients suggests that it plays a possible protective role in autoimmune thyroid disorders. Placental factors have been excluded as determinants of the differences found. The vascular and tissue localization of microchimeric cells further highlights the ability of those cells to migrate to damaged tissues.

A polymorphism in HLA-G modifies statin benefit in asthma

Several reports have shown that statin treatment benefits patients with asthma, however inconsistent effects have been observed. The mir-152 family (148a, 148b and 152) has been implicated in asthma. These microRNAs suppress HLA-G expression, and rs1063320, a common SNP in the HLA-G 3’UTR which is associated with asthma risk, modulates miRNA binding. We report that statins up-regulate mir-148b and 152, and affect HLA-G expression in an rs1063320 dependent fashion. In addition, we found that individuals who carried the G minor allele of rs1063320 had reduced asthma related exacerbations (emergency department visits, hospitalizations or oral steroid use) compared to non-carriers (p=0.03) in statin users ascertained in the Personalized Medicine Research Project at the Marshfield Clinic (n=421). These findings support the hypothesis that rs1063320 modifies the effect of statin benefit in asthma, and thus may contribute to variation in statin efficacy for the management of this disease.

Transcriptional and posttranscriptional regulations of the HLA-G gene

HLA-G has a relevant role in immune response regulation. The overall structure of the HLA-G coding region has been maintained during the evolution process, in which most of its variable sites are synonymous mutations or coincide with introns, preserving major functional HLA-G properties. The HLA-G promoter region is different from the classical class I promoters, mainly because (i) it lacks regulatory responsive elements for IFN-γ and NF-κB, (ii) the proximal promoter region (within 200 bases from the first translated ATG) does not mediate transactivation by the principal HLA class I transactivation mechanisms, and (iii) the presence of identified alternative regulatory elements (heat shock, progesterone and hypoxia-responsive elements) and unidentified responsive elements for IL-10, glucocorticoids, and other transcription factors is evident. At least three variable sites in the 3' untranslated region have been studied that may influence HLA-G expression by modifying mRNA stability or microRNA binding sites, including the 14-base pair insertion/deletion, +3142C/G and +3187A/G polymorphisms. Other polymorphic sites have been described, but there are no functional studies on them. The HLA-G coding region polymorphisms might influence isoform production and at least two null alleles with premature stop codons have been described. We reviewed the structure of the HLA-G promoter region and its implication in transcriptional gene control, the structure of the HLA-G 3'UTR and the major actors of the posttranscriptional gene control, and, finally, the presence of regulatory elements in the coding region.

Role of HLA-G 14bp deletion/insertion and +3142C>G polymorphisms in the production of sHLA-G molecules in relapsing-remitting multiple sclerosis

HLA-G is believed to act as an anti-inflammatory molecule in Multiple Sclerosis (MS). The 3' untranslated region of the HLA-G gene is characterized by two polymorphisms, DEL/INS14bp and +3142C>G, which control soluble HLA-G (sHLA-G) production. The influence of these two HLA-G variants on sHLA-G serum and cerebrospinal fluid (CSF) levels was investigated in 69 Relapsing-Remitting MS patients grouped in magnetic resonance imaging (MRI) inactive and active disease. Serum and CSF sHLA-G levels were more elevated in high than in low DEL/INS 14bp and +3142C>G sHLA-G producers and were different among the various combined HLA-G genotypes in both MRI inactive and active diseases. The highest and the lowest sHLA-G values were identified in MS patients with C/C,DEL/DEL and G/G,INS/INS genotypes, respectively. Our preliminary findings suggest that serum and CSF sHLA-G levels in MS could be influenced by HLA-G polymorphisms irrespective of the inflammatory microenvironment.