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

Background:The human neutrophil antigen 2 (HNA-2), which is expressed on CD177, is undetectable in 3-5% of the normal population. Exposure of these HNA-2(null) individuals to HNA-2-positive cells can cause immunization and pro-duction of HNA-2 antibodies, which can induce immune neutropenia and transfusion-related acute lung injury. In HNA-2-positive individuals, neutrophils are divided into a CD177(pos.) and a CD177(neg.) subpopulation. The molecular background of HNA-2 deficiency and the bimodal expression pattern, however, are not completely decoded.Study Design:An international collaboration was conducted on the genetic analysis of HNA-2-phenotyped blood samples, including HNA-2-deficient individuals, mothers, and the respective children with neonatal immune neutropenia and regular blood donors.Results:From a total of 54 HNA-2(null) individuals, 43 were homozygous for theCD177*787A>Tsubstitution. Six carried theCD177*c.1291G>Asingle nucleotide polymorphism. All HNA-2-positive samples with >40% CD177(pos.) neutrophils carried the *787Awild-type allele, whereas a lower rate of CD177(pos.) neutrophils was preferentially associated with *c.787ATheterozygosity. Interestingly, only the *c.787Aallele sequence was detected in complementary DNA (cDNA) sequence analysis carried out on all *c.787ATheterozygous individuals. However, cDNA analysis after sorting of CD177(pos.) and CD177(neg.) neutrophil subsets from HNA-2-positive individuals showed identical sequences, which makes regulatory elements within the promoter unlikely to affectCD177gene transcription in different CD177 neutrophil subsets.Conclusion:This comprehensive study clearly demonstrates the impact of single nucleotide polymorphisms on the expression of HNA-2 on the neutrophil surface but challenges the hypothesis of regulatory epigenetic effects being implicated in the bimodal CD177 expression pattern.