The 5′ promoter region of MHC class I chain-related gene B

Genetic polymorphism analysis of MICB gene in Jing ethnic minority of Southern China

In the present study, the polymorphism in the 5'-upstream regulation region (5'-URR), coding region (exons 2-4), and the 3'-untranslated region (3'-UTR) of MICB gene were investigated for 150 healthy unrelated Jing individuals in Guangxi Zhuang Autonomous Region, by using PCR-SBT method. A total of 14 variation sites in the 5'-URR, 9 in coding region, and 6 in the 3'-UTR were detected in the Jing population. The MICB gene seems to present two different lineages showing functional variations mainly in nucleotides of the promoter region. Nineteen different MICB extended haplotypes (EHs) encompassing the 5'-URR, exons 2-4, and 3'-UTR were found in this population, and the most frequent was EH2 (20.33%). The findings here are of importance for future studies on the potential role of regulation region of MICB gene in disease association, transplantation, viral infection, and tumor progression among Jing population.

Functional Characterisation and Analysis of the Soluble NKG2D Ligand Repertoire Detected in Umbilical Cord Blood Plasma

We previously reported that cord blood plasma (CBP) contains significantly more soluble NKG2D ligands (sNKG2DLs), such as sMICB and sULBP1, than healthy adult plasma. Viral infection or malignant transformation upregulates expression of NKG2D ligand on affected cells, leading to NK group 2, member D (NKG2D)-mediated natural killer (NK) cell lysis. Conversely, sNKG2DL engagement of NKG2D decreases NK cell cytotoxicity leading to viral or tumour immune escape. We hypothesised that sNKG2DLs detected in CBP may represent an additional fetal–maternal tolerance mechanism. To further understand the role of sNKG2DL in pregnancy and individual contributions of the various ligand types, we carried out functional analysis using 181 CBP samples. To test the ability of CBP to suppress the function of NK cells in vitro, we measured expression of NKG2D, CD107a, and IFN-γ in NK cells from control donors after exposure to 181 individual CBP samples and characterised the sMICA, sMICB, and sULBP1 content of each one. Furthermore, to detect possible allelic differences between samples that may also affect function, we carried out umbilical cord blood typing for MHC class I-related chain A (MICA) and MHC class I-related chain B (MICB) coding and promoter allelic types. Strongest functional correlations related to increasing concentration of exosomal sULBP1, which was present in all CBP samples tested. In addition, common MICB alleles, such as MICB*005:02, resulted in increased concentration of sMICB. Interestingly, MICB*005:02 uniquely associated with eight different promoter types. Among promoter polymorphisms, P2 resulted in the highest expression of sMICB and P9 the least and was confirmed using luciferase reporter assays. Higher levels of sMICB associated with lower IFN-γ production, indicating that sMICB also suppressed NK cell function. We also examined the MICA functional dimorphism encoding methionine (met) or valine (val) at residue 129 associated with strong or weak NKG2D binding, respectively. Most sMICA associated with val/val, some with met/val but none with met/met and, counter-intuitively, the presence of sMICA in CBP increased NK cell cytotoxicity. We propose a model for fetal–maternal tolerance, whereby NK cell activity is limited by sULBP1 and sMICB in CBP. The release of 129val sMICA with weak NKG2D signalling may reduce the overall net suppressive signal and break tolerance thus allowing fetal NK cells to overcome immunological threats in utero.

Further diversity of the 5' promoter region of the MHC class I-related chain B gene

We have now found a total of 15 individual MICB promoter sequences, varying by combination of 18 polymorphic positions within the MICB minimal promoter sequence. Sequence-based typing and cloning characterized the three new 5' promoter sequences as MICB-P13, MICB-P14 and MICB-P15.

Two novel 5' promoter sequences of the MHC class I-related chain A gene

In this study, we have characterized two novel polymorphism of the 5' promoter sequence of MICA gene, MICA-P13 and MICA-P14, by sequence-based typing and cloning.

MHC class I-related chain B gene polymorphism is associated with virological response to pegylated interferon plus ribavirin therapy in patients with chronic hepatitis C infection

The outcome of antiviral therapy is associated with viral and host factors. In the present study, the association between MHC class I-related chain B (MICB) genotypes and therapeutic response to pegylated interferon plus ribavirin (PEG-IFN/RBV) therapy was investigated in hepatitis C virus (HCV)-infected patients. In total, 107 patients with chronic HCV infection (74 with HCV serotype 1 and 33 with serotype 2) were enrolled. Genotyping of MICB single-nucleotide polymorphism (SNP) rs3828913 and interleukin-28B (IL28B) SNP rs8099917 was performed using TaqMan^® SNP genotyping assays. The genotype distribution of the MICB alleles was: CC, 79.4%; CA, 17.8%; and AA, 2.8%. Sustained virological response (SVR) was achieved by 55.1% (59/107) of the HCV patients. The SVR rate of patients with MICB major (CC) alleles was 62.3% and this rate was significantly higher than that of the patients with MICB minor (CA and AA) alleles (27.2%) (P=0.0068). A multivariate logistic model showed that the MICB major genotype was an independent factor contributing to SVR (OR, 4.47; 95% CI, 1.46-13.70; P=0.009). In addition, the MICB genotype was identified as the sole independent factor contributing to SVR and non-virological response in HCV serotype 1 patients with the IL28B major genotype. In HCV serotype 2 patients, the MICB genotype was the sole significant factor contributing to SVR (OR, 30.68; 95% CI, 2.72-346.3; P=0.006). In conclusion, the MICB genotype is a strong predictive factor for virological response to PEG-IFN/RBV therapy in HCV patients.

Diversity and characterization of polymorphic 5' promoter haplotypes of MICA and MICB genes

The major histocompatibility complex (MHC) class I-related chain A (MICA) and B (MICB) are ligands for the natural killer group 2, member D (NKG2D) activating receptor expressed on natural killer (NK) cells, natural killer T (NKT) cells, CD8+ T cells and γδ T cells. Natural killer group 2, member D (NKG2D) ligand expression is stress-related and upregulated by infected or oncogenic cells leading to cytolysis. MICA and MICB genes display considerable polymorphism among individuals and studies have investigated allelic association with disease and relevance of MICA in transplantation, with variable success. It is now known that promoters of MICA and MICB are polymorphic with some polymorphisms associating with reduced expression. We sequenced International Histocompatibility Workshop (IHW) cell line DNA to determine promoter types and alleles encoded by exons 2-6. We found 8 of 12 known MICA promoter polymorphisms and although promoter P7 dominated, other promoters associated with the same allele. For example, MICA*002:01 had promoters P3, P4 or P7 and the common MICA*008:01/04 type had P1, P6 or P7. Similarly, we sequenced 8 of 12 known MICB promoter haplotypes. Some coding region defined MICB alleles had a single promoter, for example, MICB*002:01 and promoter P9, whereas the promiscuous MICB*005 allele had promoters P1, P2, P5, P6, P10 or P12. The results indicate potential for variation in expression of MICA and MICB ligands between individuals with the same allelic types. If differential expression by polymorphic MICA and MICB promoters is confirmed by functional studies, involvement of these genes in disease susceptibility or adverse transplantation outcomes may require knowledge of both promoter and allelic types to make meaningful conclusions.