Genetic Mechanism of Human Neutrophil Antigen 2 Deficiency and Expression Variations

Abstract

Human neutrophil antigen 2 (HNA-2) deficiency is a common phenotype as 3–5% humans do not express HNA-2. HNA-2 is coded by CD177 gene that associates with human myeloproliferative disorders. HNA-2 deficient individuals are prone to produce HNA-2 alloantibodies that cause a number of disorders including transfusion-related acute lung injury and immune neutropenia. In addition, the percentages of HNA-2 positive neutrophils vary significantly among individuals and HNA-2 expression variations play a role in human diseases such as myelodysplastic syndrome, chronic myelogenous leukemia, and gastric cancer. The underlying genetic mechanism of HNA-2 deficiency and expression variations has remained a mystery. In this study, we identified a novel CD177 nonsense single nucleotide polymorphism (SNP 829A>T) that creates a stop codon within the CD177 coding region. We found that all 829TT homozygous individuals were HNA-2 deficient. In addition, the SNP 829A>T genotypes were significantly associated with the percentage of HNA-2 positive neutrophils. Transfection experiments confirmed that HNA-2 expression was absent on cells expressing the CD177 SNP 829T allele. Our data clearly demonstrate that the CD177 SNP 829A>T is the primary genetic determinant for HNA-2 deficiency and expression variations. The mechanistic delineation of HNA-2 genetics will enable the development of genetic tests for diagnosis and prognosis of HNA-2-related human diseases.

Molecular Genetics of the Human Neutrophil Antigens

“…A proportion of HNA-2-positive neutrophils in the blood with either intermediate or high expression between 1 and 100% has been demonstrated in different individuals. This proportion is a lifelong characteristic [10,59]. However, upon neutrophil activation in severe bacterial infections, in pregnancy and in newborns the expression can be upregulated [57,63,64,65,66].…”

“…Different SNPs have been attributed to a low or high HNA-2 expression or the presence of one or two antigen-positive subpopulations [67,68,69]. A dose effect of the wild-type CD177*787A or heterozygosity for both *787A and *787T has been correlated with the proportion of HNA-2-positive neutrophils [10,59]. Recently, gene silencing and a novel monoallelic expression pattern caused by disparate CpG and histone methylation have been described as basis for distinct neutrophil subsets thus introducing epigenetic mechanisms [70].…”

“…HNA. Although the coding genes of each of the currently known five HNA systems are published, even today some open questions on the causal connection between serological phenotypes and genotypes remain [10,11]. The following review will provide an overview of the molecular genetics, structures, and characteristics of the HNAs.…”

Towards a Regional Registry of Extended Typed Blood Donors: Molecular Typing for Blood Group, Platelet and Granulocyte Antigens

“…The most frequent cause of the HNA-2 null phenotype is the CD177 haplotype carrying the nonsense mutation c.787A>T (linked to additional 4 SNPs) in exon 7 [25]. However, the CD177P1 pseudogene with almost identical DNA sequence in the exon 4 to 9 region can also harbor this haplotype making CD177 -specific genotyping difficult.…”

“…Homozygosity for a nonsense mutation c.787A>T in CD177 was identified as the most frequent cause of the HNA-2 null phenotype [25]. But genotyping is hampered by the CD177P1 pseudogene with identical DNA sequence in the corresponding region.…”