Expression Of Vel Antigen Research Articles

Molecular screening for Vel- blood type and analysis of SMIM1 gene variants

To screen for Vel- rare blood type donors and determine the frequency of SMIM1 c.64_80del allele in Yili Prefecture of Xinjiang, China. DNA pooling and PCR-sequence-specific primers (PCR-SSP) was conducted to screen individuals carrying the SMIM1 c.64_80del variant, and Sanger sequencing of SMIM1 exon 3 was carried out to verify the genotype of those with the variation. SMIM1 intron 2 was also sequenced to identify single nucleotide polymorphisms (SNPs) that may affect the expression of Vel antigen. Among 3328 blood donors, 14 were identified as heterozygotes for the SMIM1 c.64_80del allele, its allele frequency was 0.21%; no homozygous SMIM1 c.64_80 deletions was found. For SNP rs1175550, all of the 14 individuals had an AA genotype, among whom 5 carried heterozygous 7111ins GCA variant in intron 2. The allelic frequency of SMIM1 c.64_80del in Yili area is approximately 0.21%, which is reported for the first time.

Identification of a novel single‐nucleotide mutation in SMIM1 gene that results in low Vel antigen expression

Identification of a novel single‐nucleotide mutation in <i>SMIM1</i> gene that results in low Vel antigen expression

SMIM1 intron 2 gene variations leading to variability in Vel antigen expression among Brazilian blood donors

BackgroundThere is a significant inter-individual heterogeneity of Vel antigen expression which can lead to inaccuracies on Vel phenotyping of blood donors and, potentially, to hemolytic post-transfusion reactions. Our aim was to evaluate the impact of genetic variants in the SMIM1 intron 2 on the expression of Vel antigen among Brazilian blood donors harboring the c.64_80del17 deletion in heterozygosity. MethodsDonors presenting the SMIM1 c.64_80del17 in heterozygosity were included in the study and subjected to SMIM1 intron 2 direct sequencing aiming to genotype the following polymorphisms: rs143702418, rs1181893, rs191041962, rs6673829, rs1175550 and rs9424296. ResultsSMIM1 intron 2 sequencing was performed on two hundred donors presenting one c.64_80del17 allele. The rs1175550 polymorphism significantly impacted on Vel antigen expression. Variations in the strength of agglutination on Vel phenotyping were also observed according to the rs6673829 genotype, but this difference did not persist with statistical relevance after multivariate analysis. ConclusionThe presence of the rs1175550A allele of SMIM1 is significantly and independently associated with a decrease in Vel antigen expression. Even though the population in Brazil is intensely mixed, the allele frequencies obtained in the current study were very similar to that reported for Europeans.

Development of a recombinant anti‐Vel immunoglobulin M to identify Vel‐negative donors

Alloimmunization against the high-frequency Vel blood group antigen may result in transfusion reactions or hemolytic disease of fetus and newborn. Patients with anti-Vel alloantibodies require Vel-negative blood but Vel-negative individuals are rare (1:4000). Identification of Vel-negative donors ensures availability of Vel-negative blood; however, accurate Vel blood group typing is difficult due to variable Vel antigen expression and limited availability of anti-Vel typing sera. We report the production of a recombinant anti-Vel that also identifies weak Vel expression. A recombinant anti-Vel monoclonal antibody was produced by cloning the variable regions from an anti-Vel-specific B cell isolated from an alloimmunized patient into a vector harboring the constant regions of immunoglobulin (Ig)G1-kappa or IgM-kappa. Antibody Vel specificity was tested by reactivity to SMIM1-transfected HEK293T cells and by testing various red blood cells (RBCs) of donors with normal, weak, or no Vel expression. High-throughput donor screening applicability was tested using an automated blood group analyzer. A Vel-specific IgM class antibody was produced. The antibody was able to distinguish between Vel-negative and very weak Vel antigen-expressing RBCs by direct agglutination and in high-throughput settings using a fully automated blood group analyzer and performed better than currently used human anti-Vel sera. High-throughput screening of 13,288 blood donations identified three new Vel-negative donors. We generated a directly agglutinating recombinant anti-Vel IgM, M3F5S-IgM, functional in manual, automated agglutination assays and flow cytometry settings. This IgM anti-Vel will improve diagnostics by facilitating the identification of Vel-negative blood donors.

The Polymorphism of SMIM1 Gene in Chinese Dividuals.

The SMIM1 gene, which encodes the high-frequency blood group antigen Vel, has not been systematicallyanalyzed at the molecular level in Chinese individuals. To better understand the SMIM1 genetic polymorphism, we assessed mutations among healthy Chinese individuals, patients with red blood cell autoantibodies and hematological disease. A total of 130 patients with hematological disease (case I group), 50 patients with red blood cell autoantibodies (case II group), and 500 healthy controls (control group) were enrolled. Exons 3 and 4 in the SMIM1 gene were sequenced to identify genetic variants or mutations. A polyclonal anti-Vel antibody was used to evaluate the expression of the Vel antigenon red blood cells in patients with novel alleles. The novel alleles of the SMIM1 gene were intron 3 position 193 (TT, CT, CC), 194 (GG, AG), 3' untranslated region positions 81 (CC, CA) and 87 (AA, CA). The single nucleotide polymorphism (SNP) frequencies of intron 3 position 193 TT, CT, CC were 13.1, 39.2, 47.7% in case group I, 6.7, 33.3, 60.0% in case group II and 8.5, 35.6, 56.2% in the control group, respectively. Other minor allele frequencies were all greater than 10% and all SNPs in Chinese showed Vel antigen expression on RBC membranes. The allele at intron 3 position 193 was the most frequent mutant allele found in the Chinese population and Vel antigen deficiency may not cause problems in Chinese patients with hematological diseases and RBC autoantibodies.

SMIM1 variants rs1175550 and rs143702418 independently modulate Vel blood group antigen expression

The Vel blood group antigen is expressed on the red blood cells of most individuals. Recently, we described that homozygosity for inactivating mutations in SMIM1 defines the rare Vel-negative phenotype. Still, Vel-positive individuals show great variability in Vel antigen expression, creating a risk for Vel blood typing errors and transfusion reactions. We fine-mapped the regulatory region located in SMIM1 intron 2 in Swedish blood donors, and observed a strong correlation between expression and rs1175550 as well as with a previously unreported tri-nucleotide insertion (rs143702418; C > CGCA). While the two variants are tightly linked in Caucasians, we separated their effects in African Americans, and found that rs1175550G and to a lesser extent rs143702418C independently increase SMIM1 and Vel antigen expression. Gel shift and luciferase assays indicate that both variants are transcriptionally active, and we identified binding of the transcription factor TAL1 as a potential mediator of the increased expression associated with rs1175550G. Our results provide insight into the regulatory logic of Vel antigen expression, and extend the set of markers for genetic Vel blood group typing.