Multicenter Study on Differential Human Neutrophil Antigen 2 Expression and Underlying Molecular Mechanisms

Area of Science:

• Immunology
• Genetics
• Hematology

Background:

• Human neutrophil antigen 2 (HNA-2) is expressed on CD177, with HNA-2 null individuals comprising 3-5% of the population.
• HNA-2 null individuals can develop HNA-2 antibodies upon exposure to HNA-2 positive cells, potentially causing immune neutropenia and transfusion-related acute lung injury.
• Neutrophils in HNA-2 positive individuals exhibit a bimodal expression of CD177 (CD177pos. and CD177neg. subpopulations), the molecular basis of which is not fully understood.

Purpose of the Study:

• To investigate the genetic basis of HNA-2 deficiency and the bimodal CD177 expression pattern in neutrophils.
• To determine the role of single nucleotide polymorphisms (SNPs) and potential epigenetic factors in HNA-2 expression.

Main Methods:

• International collaboration involving genetic analysis of HNA-2 phenotyped blood samples.
• Inclusion of HNA-2 deficient individuals, mothers, and children with neonatal immune neutropenia, alongside regular blood donors.
• Genotyping for CD177 SNPs and complementary DNA (cDNA) sequence analysis of sorted neutrophil subsets.

Main Results:

• Of 54 HNA-2 null individuals, 43 were homozygous for the CD177 *787A>T substitution, and 6 carried the CD177 *c.1291G>A SNP.
• HNA-2 positive individuals with >40% CD177pos. neutrophils predominantly carried the *787A wild-type allele; heterozygosity (*c.787AT) was associated with lower CD177pos. neutrophil rates.
• cDNA analysis revealed identical sequences in both CD177pos. and CD177neg. neutrophil subsets from HNA-2 positive individuals, suggesting promoter regulatory elements are unlikely to influence CD177 transcription.

Conclusions:

• Single nucleotide polymorphisms significantly influence HNA-2 expression on the neutrophil surface.
• The study challenges the hypothesis that regulatory epigenetic effects are responsible for the bimodal CD177 expression pattern.
• Genetic variations, specifically SNPs in CD177, are key determinants of HNA-2 expression and neutrophil subpopulations.