CD177 polymorphisms: correlation between high-frequency single nucleotide polymorphisms and neutrophil surface protein expression

BACKGROUND

Human neutrophil antigen-2a (NB1) is located on NB1 glycoprotein, which is expressed on subpopulations of neutrophils. PRV-1 is a gene that is over-expressed in neutrophils from patients with polycythemia rubra vera. The gene encoding NB1 differs from PRV-1 at four nucleotides. The purpose of this study was to determine if PRV-1 and NB1 are alleles of the same gene or two separate genes; and, moreover, if they are alleles, to explore potential correlations to NB1 glycoprotein expression.

STUDY DESIGN AND METHODS

Primer pairs were used to amplify WBC DNA in the regions surrounding the four NB1 polymorphic sites. The four resulting amplicons were sequenced. The size of the neutrophil population in each donor that stained brightly with CD177 antibody was assessed by flow cytometry.

RESULTS

If PRV-1 and NB1 are separate genes, then all people should be heterozygous for the PRV-1/NB1 polymorphisms. Because 11 of 23 donors were homozygous for PRV-1 polymorphisms at all four sites, PRV-1 and NB1 are alleles of the same gene, CD177. When the sequenced exons were compared with PRV-1, 13 single nucleotide polymorphisms (SNPs) that result in amino acid changes were found. The G42C NB1 polymorphism, found in 10 donors, was the most common SNP. The size of the CD177 bright-staining neutrophil population was greater in 42C/C donors than in 42G/G donors (66 +/- 20% vs. 41 +/- 21%, p = 0.004).

CONCLUSIONS

PRV-1 and NB1 are alleles of the polymorphic gene CD177. The most common SNP in bp 42 predicted an amino acid change that may have an effect on protein expression.

Expression of human neutrophil antigen-2a (NB1) is increased in pregnancy

BACKGROUND

The expression of human neutrophil antigen-2a (HNA-2a) or NB1 is highly variable. This study investigated variations in neutrophil expression of HNA-2a by comparing the expression of epitopes recognized by three HNA-2a-specific CD177 antibodies among healthy adults and pregnant women.

STUDY DESIGN AND METHODS

Flow cytometry was used to compare the neutrophil reactions of three CD177 antibodies (MEM-166, TAG4, and 7D8) among 52 healthy adults. Because HNA-2a expression is greater in women than men, neutrophils were studied from 21 women early in pregnancy and 23 women late in pregnancy.

RESULTS

All three CD177 antibodies reacted with two populations of neutrophils: a brightly staining population and a dimly staining population. Among the 52 healthy adults, there was no difference in the mean size of the brightly reactive population of neutrophils recognized by each antibody (46 +/- 23% for MEM-166, 49 +/- 23% for TAG4, and 49 +/- 23% for 7D8), and all three antibodies were specific for HNA-2a. For all three antibodies the size of the antigen bright neutrophil population was greater on neutrophils collected both early and late in pregnancy than in healthy adults. There was no difference in the size of the antigen bright population among neutrophils tested early and late in pregnancy.

CONCLUSION

HNA-2a antigen expression increases in pregnancy. Some of the variations in neutrophil expression of HNA-2a among individuals is likely due to differences in gene regulation or differences in post-translational protein modifications rather than gene polymorphisms.

Molecular basis of NB1 (HNA-2a, CD177) deficiency

Alloimmunization to the neutrophil antigen NB1 (HNA-2a, CD177) can result in immune neutropenia and transfusion-related acute lung injury. Recently, we were able to elucidate the primary structure of NB1. To shed light also on the molecular basis of the NB1-negative phenotype, we studied the neutrophils of 2 women with NB1-specific alloantibodies for intracellular and extracellular NB1 expression, NB1-specific mRNA production, and the presence of the NB1 gene. No antibody binding to neutrophils was observed by immunofluorescence and immunoblot using a variety of human and monoclonal NB1-specific antibodies. By reverse transcription-polymerase chain reaction with NB1-specific primers we could not detect NB1 cDNAs without accessory sequences, which were found to be introns. The NB1 gene was present in the genome of both patients. Our data indicate that the NB1-negative phenotype is the result of different off-frame insertions on RNA level, resulting in NB1 deficiency on neutrophils.

Fcgamma receptors in autoimmune diseases

Fcgamma-receptors (Fcgamma-R) recognise the Fc portion of IgG and thus form a link between humoral and cellular immunity. These receptors are expressed by a variety of immune cells, and they function in the binding of immune complexes or IgG-opsonised particles, such as microbial pathogens. The are three major types of Fcgamma-R, namely Fcgamma-RI (CD64), Fcgamma-RII (CD32) and Fcgamma-RIII (CD16), and these differ in their ability to bind IgG and complexes. There are many isoforms of these receptors and a number of recently identified polymorphisms in their structure. This review describes the structure and function of these Fcgamma-Rs, and highlights how gene deficiencies and polymorphisms may contribute to the pathology of human diseases.

Characterization of a New Alloantigen (SH) on the Human Neutrophil Fcγreceptor IIIb

Polymorphic structures of the neutrophil Fcγreceptor IIIb (FcγRIIIb) result in alloantibody formation that causes alloimmune neonatal neutropenia and transfusion reactions. Alloantigens located on FcγRIIIb include the antigens NA1 and NA2. In four cases of alloimmune neonatal neutropenia, granulocyte-specific alloantibodies directed against a thus far unknown antigen were detected by granulocyte agglutination and immunofluorescence tests in the maternal sera. By the use of the monoclonal antibody–specific immobilization of granulocyte antigens (MAIGA) assay, the new antigen, termed SH, was located on the FcγRIIIb. Nucleotide sequence analysis of the FcγRIIIb coding region from a SH(+) individual showed a single-base C→A mutation at position 266, which results in an Ala78Asp amino acid substitution. A family study confirmed that this nucleotide difference is inherited, and corresponds to the SH phenotype. Serologic typing of 309 randomly selected individuals showed an antigen frequency of 5% in the white population. The same frequency was found by genotyping, for which a technique based on polymerase chain reaction (PCR) using sequence-specific primers (PCR-SSP) was developed. Typing of all SH(+) individuals for NA1 and NA2, and PCR-restriction fragment length polymorphism analysis of the NA-specific PCR products from five SH(+) individuals using the SH-specific endonuclease SfaN I showed that SH antigen is very probably the result of an additional mutational event in the NA2 form of the FcγRIIIB gene. Immunochemical studies also demonstrated that the SH determinants reside on the 65- to 80-kD NA2 isoform of the FcγRIIIb. Our findings show the existence of an additional polymorphism of the FcγRIIIb, which can result in alloantibody formation causing alloimmune neonatal neutropenia.