The role of HLA-G in gastrointestinal inflammatory disease and malignancy

Serum levels of soluble HLA-G correlate with disease activity in pediatric patients with Crohn's disease

BACKGROUND

Human leukocyte antigen (HLA)-G, a member of the HLA family, is crucial for fetomaternal tolerance. Transmembrane or circulating/soluble HLA-G (sHLA-G) is elevated in autoimmune conditions and the tumor microenvironment. Circulating sHLA-G levels and their association with disease activity have not yet been assessed in pediatric patients with inflammatory bowel disease (IBD). This study aimed to quantify the serum sHLA-G levels of pediatric patients with IBD and assess the association of serum sHLA-G with disease activity.

METHODS

: We enrolled 24 pediatric IBD patients Crohn's disease (CD) and ulcerative colitis (UC), n = 12 each] and 24 healthy controls. Based on the disease activity index, five and seven of the CD patients had mild and moderate/severe disease, respectively, whereas six of the UC patients were in remission and six had mild disease. Serum was collected and sHLA-G levels were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

: Pediatric patients with CD had significantly higher sHLA-G levels compared with patients with UC and healthy controls. Notably, serum sHLA-G levels were significantly higher in patients with moderate/severe CD than in those with mild CD.

CONCLUSIONS

: Serum sHLA-G levels correlate with disease activity in pediatric patients with CD and are higher in CD patients than in UC patients. Thus, sHLA-G is a potential biomarker for disease activity in CD.

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.

Increased HLA-G Expression in Tissue-Infiltrating Cells in Inflammatory Bowel Diseases

BACKGROUND

Since HLA-G is an immune checkpoint molecule and since Crohn's disease (CD) and ulcerative colitis (UC) exhibit deregulated immune-mediated mechanisms, we aimed to evaluate intestinal HLA-G expression and soluble HLA-G (sHLA-G) levels in CD/UC patients stratified according to the CD phenotype/localization and UC extension.

METHODS

HLA-G tissue expression was assessed by immunohistochemistry in biopsies collected from 151 patients (90 CD, 61 UC) and in surgical resection specimens (28 CD, 12 UC). Surgical material from 24 healthy controls was also assessed. Plasma sHLA-G levels (97 CD, 81 UC, and 120 controls) were evaluated using ELISA.

RESULTS

HLA-G expression was similarly observed in the intestinal epithelial cells of control and CD/UC specimens. However, in biopsies, the plasma cells/lymphocytes infiltrating the lamina propria in CD/UC presented (1) increased HLA-G expression compared to controls (P < 0.0001), (2) greater cell staining in UC cells than in CD cells irrespective of disease extent (P = 0.0011), and (3) an increased number of infiltrating cells in the inflammatory CD phenotype compared to that in the stenosing and fistulizing phenotypes (P = 0.0407). In surgical specimens, CD/UC patients exhibited higher infiltrating cell HLA-G expression in lesion areas than in margins. sHLA-G levels were higher in UC/CD patients (P < 0.0001) than in controls, but no difference was observed between diseases.

CONCLUSIONS

Increased infiltrating cell HLA-G expression associated with increased sHLA-G levels in CD/UC patients may reflect ongoing host strategies to suppress chronic inflammation.

Susceptibility role of soluble HLA-G and HLA-G 14-bp insertion/deletion polymorphism in inflammatory bowel disease

Background

Inflammatory bowel disease (IBD) is a group of chronic inflammatory disorders of the gastrointestinal tract. It is fundamentally related to a dysregulated immune response in the intestinal mucosa against microbiota in genetically predisposed individuals. Among the genetic and immunological factors that are suggested to have role in etiology and pathogenesis of IBD are human leukocyte antigen (HLA)-G molecules. Therefore, soluble HLA-G (sHLA-G) serum level and genetic association with HLA-G 14-bp insertion (Ins)/deletion (Del) polymorphism was analyzed in 100 IBD patients; 50 ulcerative colitis (UC) and 50 Crohn’s disease (CD), and 100 controls.

Results

sHLA-G level was significantly elevated in IBD patients compared to controls (174.7 ± 27.1 vs. 126.8 ± 15.1; corrected probability [pc] < 0.001). The level was also elevated in UC patients compared to CD patients but the difference was not significant (180.5 ± 27.1 vs. 168.9 ± 26.3; p = 0.059). Receiver operating characteristic analysis confirmed the significance of sHLA-G in total IBD, UC, and CD patients (area under curve = 0.944, 0.961, and 0.927, respectively). The genetic association was analyzed under five genetic models (allele, recessive, dominant, overdominant, and codominant). At the allele level, Del allele frequency was significantly increased in total IBD patients (Odds ratio [OR] = 1.93; 95% confidence interval [CI] = 1.27–2.94; pc = 0.018) and CD patients (OR = 2.08; 95% CI = 1.23–3.54; pc = 0.042) compared to controls. Among UC patients, a similar increased frequency was observed, but the pc value was not significance (OR = 1.79; 95% CI = 1.07–3.00; p = 0.031). At the genotypic level, Del/Del genotype was associated with a significantly increased IBD-risk in total patients under codominant model (OR = 4.06; 95% CI = 1.56–10.56; pc = 0.024). sHLA-G level was not influenced by the Ins/Del polymorphism.

Conclusions

This study demonstrated a significant increase in serum level of sHLA-G in UC and CD patients. Further, HLA-G 14-bp Ins/Del polymorphism may be associated with susceptibility to IBD, particularly CD.

HLA-G expression in gastric carcinoma: clinicopathological correlations and prognostic impact

To analyze expression of human leukocyte antigen-G (HLA-G) in gastric adenocarcinoma and correlate its expression with histological and clinical variables. A continuous series of 94 unselected patients with gastric adenocarcinoma (stage I to III) were selected. All histological and clinical variables were collected including the intensity of intra- and peri-tumor lymphocytic infiltration. HLA-G expression was investigated using immunohistochemistry. All histological samples analyzed for HLA-G expression were taken from the primary gastric lesion and included non-neoplastic mucosa. Evaluation of HLA-G expression was performed on the transition zone between tumor and non-neoplastic mucosa, and the invasive front of the tumor and assessment was performed as follows: percentage of positive (strong expression vs weak) cells. A variable amount of HLA-G-positive tumor cells was found in 24 out of 94 cases (25.5%). No significant correlation was found between HLA-G expression and other clinicopathological variables (sex, age, stage, grade, histotype). The overall median survival was worse in patients with HLA-G-positive adenocarcinoma (24.3 months, CI95% 7.7-41.0) compared to those with HLA-G-negative tumors (66.3 months, CI95% 53.0-79.7; p < 0.0001). Two- and 5-year survival rates of HLA-G-negative patients were 88 and 44%, respectively, while were 42 and 11% in those HLA-G-positive. This trend was observed in all stages but was more marked in stage III. HLA-G expression is associated with poor survival in stage III gastric cancer patients and represents a possible immunoescape mechanism of cancer cells.

The role of gene polymorphism in HLA class I splicing

Among the large number of human leucocyte antigen (HLA) alleles, only a few have been identified with a nucleotide polymorphism impairing correct splicing. Those alleles show aberrant expression levels, due to either a direct effect of the polymorphism on the normal splice site or to the creation of an alternative splice site. Furthermore, in several studies, the presence of alternatively spliced HLA transcripts co-expressed with the mature spliced transcripts was reported. We evaluated the splice site sequences of all known HLA class I alleles and found that, beside the consensus GT and AG sequences at the intron borders, there were some other highly conserved nucleotides for the different class I genes. In this review, we summarize the splicing mechanism and evaluate what is known today about alternative splicing of HLA class I genes.

Inflammation in Alzheimer's Disease and Molecular Genetics: Recent Update

Alzheimer's disease (AD) is a complex age-related neurodegenerative disorder of the central nervous system. Since the first description of AD in 1907, many hypotheses have been established to explain its causes. The inflammation theory is one of them. Pathological and biochemical studies of brains from AD individuals have provided solid evidence of the activation of inflammatory pathways. Furthermore, people with long-term medication of anti-inflammatory drugs have shown a reduced risk to develop the disease. After three decades of genetic study in AD, dozens of loci harboring genetic variants influencing inflammatory pathways in AD patients has been identified through genome-wide association studies (GWAS). The most well-known GWAS risk factor that is responsible for immune response and inflammation in AD development should be APOE ε4 allele. However, a growing number of other GWAS risk AD candidate genes in inflammation have recently been discovered. In the present study, we try to review the inflammation in AD and immunity-associated GWAS risk genes like HLA-DRB5/DRB1, INPP5D, MEF2C, CR1, CLU and TREM2.