Neutrophil-specific antigen NB1 is anchored via a glycosyl-phosphatidylinositol linkage

CD177 is a novel IgG Fc receptor and CD177 genetic variants affect IgG-mediated function

CD177 plays an important role in the proliferation and differentiation of myeloid lineage cells including neutrophils, myelocytes, promyelocytes, megakaryocytes, and early erythroblasts in bone marrow. CD177 deficiency is a common phenotype in humans. Our previous studies revealed genetic mechanisms of human CD177 deficiency and expression variations. Up to now, immune functions of CD177 remain undefined. In the current study, we revealed human IgG as a ligand for CD177 by using flow cytometry, bead-rosette formation, and surface plasmon resonance (SPR) assays. In addition, we show that CD177 variants affect the binding capacity of CD177 for human IgG. Furthermore, we show that the CD177 genetic variants significantly affect antibody-dependent cell-mediated cytotoxicity (ADCC) function. The demonstration of CD177 as a functional IgG Fc-receptor may provide new insights into CD177 immune function and genetic mechanism underlying CD177 as biomarkers for human diseases.

The CD177 c.1291A Allele Leads to a Loss of Membrane Expression and Mimics a CD177-Null Phenotype

CD177 is a glycosyl phosphatidyl inositol (GPI)-linked, neutrophil-specific glycoprotein that in 3-5% of normal individuals is absent from all neutrophils. The molecular mechanism behind the absence of CD177 has not been unravelled completely. Here, we analyse the impact of the recently described CD177 c.1291G>A variant on CD177 expression. Recombinant CD177 c.1291G>A was expressed in HEK293F cells and its expression on the cell surface, inside the cell, and in the culture supernatant was investigated. The CD177 c.1291G>A protein was characterised serologically and its interaction with proteinase 3 (PR3) was demonstrated by confocal laser scanning microscopy. Our experiments show that CD177 c.1291G>A does not interfere with CD177 protein biosynthesis but affects the membrane expression of CD177, leading to very low copy numbers of the protein on the cellular surface. The mutation does not interfere with the ability of the protein to bind PR3 or human polyclonal antibodies against wild-type CD177. Carriers of the c.1291G>A allele are supposed to be phenotyped as CD177-negative, but the protein is present in soluble form. The presence of CD177 c.1291A leads to the production of an unstable CD177 protein and an apparent "CD177-null" phenotype.

CD177 is a novel IgG Fc receptor and CD177 genetic variants affect IgG-mediated function

CD177 plays an important role in the proliferation and differentiation of myeloid lineage cells including neutrophils, myelocytes, promyelocytes, megakaryocytes, and early erythroblasts in bone marrow. CD177 deficiency is a common phenotype in humans. Our previous studies revealed genetic mechanisms of human CD177 deficiency and expression variations. Up to now, immune functions of CD177 remain undefined. In the current study, we revealed human IgG as a ligand for CD177 by using flow cytometry, bead-rosette formation, and surface plasmon resonance (SPR) assays. In addition, we show that CD177 variants affect the binding capacity of CD177 for human IgG. Furthermore, we showed that the CD177 genetic variants significantly affect antibody-dependent cell-mediated cytotoxicity (ADCC) function. The demonstration of CD177 as a functional IgG Fc-receptor may provide new insights into CD177 immune function and genetic mechanism underlying CD177 as biomarkers for human diseases.

The neutrophil subset defined by CD177 expression is preferentially recruited to gingival crevicular fluid in periodontitis

In recent years, the concept of distinct subpopulations of human neutrophils has attracted much attention. One bona fide subset marker, exclusively expressed by a proportion of circulating neutrophils in a given individual, and therefore dividing neutrophils in two distinct subpopulations, is the glycoprotein CD177. CD177 is expressed on the plasma and granule membranes of 0-100% of circulating neutrophils depending on the donor. Several in vitro studies have linked CD177 to neutrophil transmigration, yet very few have looked at the role of CD177 for tissue recruitment in vivo. We investigate whether the CD177⁺ and CD177^- neutrophil subsets differ in their propensity to migrate to both aseptic- and microbe-triggered inflamed human tissues. Microbe-triggered neutrophil migration was evaluated in samples of gingival crevicular fluid (GCF) from patients with periodontitis, whereas neutrophil migration to aseptic inflammation was evaluated in synovial fluid from patients with inflammatory arthritis, as well as in exudate from experimental skin chambers applied on healthy donors. We found that the proportion of CD177⁺ neutrophils was significantly higher in GCF from patients with periodontitis, as compared to blood from the same individuals. Such accumulation of CD177⁺ neutrophils was not seen in the two models of aseptic inflammation. Moreover, the proportion of CD177⁺ neutrophils in circulation was significantly higher in the periodontitis patient group, as compared to healthy donors. Our data indicate that the CD177⁺ neutrophil subset is preferentially recruited to the gingival crevice of periodontitis patients, and may imply that this subtype is of particular importance for situations of microbe-driven inflammation.

A novel nonsense mutation found in the CD177 gene of Thai individuals with the HNA-2 null phenotype

OBJECTIVES

The aim of this study is to explore the molecular basis and to develop a simple sequence-specific primer polymerase chain reaction (PCR-SSP) technique for screening genotypes associated with the human neutrophil antigen-2 (HNA-2) null phenotype among Thai blood donors.

BACKGROUND

Single-nucleotide polymorphisms (SNPs) c.787A>T of the CD177 gene is well known to be primarily demonstrated as a genetic determinant for HNA-2 deficiency.

METHODS

The SNPs in the CD177 gene (exons 7 and 9) of 49 Thai blood donors with the known percentage of CD177 expression by flow cytometry including 48 HNA-2 positive and 1 HNA-2 null individuals were identified by long-range PCR amplification and sequencing. Moreover, screening for the c.1254G>A mutation was developed using an in-house PCR-SSP technique and tested among 771 unrelated donor samples.

RESULTS

A HNA-2 null sample from the first cohort was heterozygous for c.787A/T and homozygous for c.1291G/G, namely, a 787A-1291G/787T-1291G (AG/TG) genotype. Interestingly, we could identify SNP c.1254G>A (rs188387562, p. Trp418Ter) that caused a nonsense mutation of the CD177 gene in exon 9. This individual might have the 787A-1254A-1291G/787T-1254G-1291G genotype. From the second cohort (771 unrelated donors), the 1254GG homozygote was the most common (96.37%), followed by the 1254GA heterozygote (3.50%) and 1254AA homozygote (0.13%). Blood samples of two individuals with 787AT-1254GA-1291GG and 787AA-1254AA-1291GG genotypes were tested and the HNA-2 antigen expressions were 0.03% and 0.16% in rank.

CONCLUSIONS

The c.787A>T is a primary genetic hallmark to determine the HNA-2 null phenotype. Additional screening of the novel c.1254G>A in combination with c.787A>T is a suitable, convenient and effective diagnosis among Thais.

The nonconservative CD177 single-nucleotide polymorphism c.1291G>A is a genetic determinant for human neutrophil antigen-2 atypical/low expression and deficiency

BACKGROUND

Human neutrophil antigen-2 (HNA-2) is exclusively expressed on neutrophils. HNA-2-deficient individuals (HNA-2 null) are susceptible to produce isoantibodies. The nonsense CD177 coding single-nucleotide polymorphism (SNP) c.787A>T has been demonstrated as the primary genetic mechanism for HNA-2 deficiency. We hypothesized that the other genetic variants also contribute to HNA-2 expression variation and deficiency.

STUDY DESIGN AND METHODS

The deficiency, density, and percentage of HNA-2 antigen on neutrophils from 292 healthy blood donors were determined in flow cytometry. CD177 genotypes were determined by genomic DNA sequence analyses. The full-length CD177 cDNAs were amplified and sequenced. Additionally, the whole CD177 genomic sequence in eight HNA-2-null immunized women and four HNA-2-positive donors were analyzed with next-generation sequencing. The associations of CD177 SNP genotypes with HNA-2 expression variation were statistically analyzed.

RESULTS

A functional CD177 SNP c.1291G>A was identified in the current study. Atypical (trimodal) HNA-2 expression phenotype was consistently observed in donors carrying the heterozygous c.1291G/A genotype. Phenotype-genotype analyses of SNP c.787A>T and SNP c.1291G>A revealed that all homozygous 787T-1291G (TG/TG) genotype donors were HNA-2 null in healthy blood donors. On the other hand, five of eight HNA-2-immunized females were homozygous for the 787T-1291G (TG/TG) genotype while the other three HNA-2-immunized females had the 787T-1291G/787A-1291A (TG/AA) genotype and the lowest HNA-2 expression was observed in healthy subjects with the 787T-1291G/787A-1291A (TG/AA) and 787A-1291A/787A-1291A (AA/AA) genotype.

CONCLUSION

The CD177 SNP c.1291G>A is a genetic determinant for the atypical and low HNA-2 expression, which also contributes to HNA-2 deficiency phenotype.

Heterogeneity of Human Neutrophil CD177 Expression Results from CD177P1 Pseudogene Conversion

Most humans harbor both CD177neg and CD177pos neutrophils but 1-10% of people are CD177null, placing them at risk for formation of anti-neutrophil antibodies that can cause transfusion-related acute lung injury and neonatal alloimmune neutropenia. By deep sequencing the CD177 locus, we catalogued CD177 single nucleotide variants and identified a novel stop codon in CD177null individuals arising from a single base substitution in exon 7. This is not a mutation in CD177 itself, rather the CD177null phenotype arises when exon 7 of CD177 is supplied entirely by the CD177 pseudogene (CD177P1), which appears to have resulted from allelic gene conversion. In CD177 expressing individuals the CD177 locus contains both CD177P1 and CD177 sequences. The proportion of CD177hi neutrophils in the blood is a heritable trait. Abundance of CD177hi neutrophils correlates with homozygosity for CD177 reference allele, while heterozygosity for ectopic CD177P1 gene conversion correlates with increased CD177neg neutrophils, in which both CD177P1 partially incorporated allele and paired intact CD177 allele are transcribed. Human neutrophil heterogeneity for CD177 expression arises by ectopic allelic conversion. Resolution of the genetic basis of CD177null phenotype identifies a method for screening for individuals at risk of CD177 isoimmunisation.

Genetic mechanism of human neutrophil antigen 2 deficiency and expression variations

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.

NB1 mediates surface expression of the ANCA antigen proteinase 3 on human neutrophils

Antineutrophil cytoplasmic antibodies (ANCAs) with specificity for proteinase 3 (PR3) are central to a form of ANCA-associated vasculitis. Membrane PR3 (mPR3) is expressed only on a subset of neutrophils. The aim of this study was to determine the mechanism of PR3 surface expression on human neutrophils. Neutrophils were isolated from patients and healthy controls, and hematopoietic stem cells from cord blood served as a model of neutrophil differentiation. Surface expression was analyzed by flow cytometry and confocal microscopy, and proteins were analyzed by Western blot experiments. Neutrophil subsets were separated by magnetic cell sorting. Transfection experiments were carried out in HEK293 and HL60 cell lines. Using neutrophils from healthy donors, patients with vasculitis, and neutrophilic differentiated stem cells we found that mPR3 display was restricted to cells expressing neutrophil glycoprotein NB1, a glycosylphosphatidylinositol (GPI)–linked surface receptor. mPR3 expression was decreased by enzymatic removal of GPI anchors from cell membranes and was absent in a patient with paroxysmal nocturnal hemoglobinuria. PR3 and NB1 coimmunoprecipitated from and colocalized on the neutrophil plasma membrane. Transfection with NB1 resulted in specific PR3 surface binding in different cell types. We conclude that PR3 membrane expression on neutrophils is mediated by the NB1 receptor.

Sex-dependent up regulation of CD 177-specific mRNA expression in cord blood due to different stimuli

BACKGROUND

The neutrophil-specific CD 177 molecule (NB1 glycoprotein/HNA-2a) has gained clinical interest because of its involvement in severe antibody-dependent diseases like transfusion-related acute lung injury and neonatal alloimmune neutropenia. Up regulation of CD 177 in response to different stimuli (granulocyte-colony-stimulating factor, N-formyl-Met-Leu-Phe, bacterial infections) has been described in adults.

STUDY DESIGN AND METHODS

The regulation of CD 177 expression was evaluated on mRNA and glycoprotein levels from cord blood neutrophils of 56 neonates, 38 of them with complications during pregnancy or delivery. Real-time polymerase chain reaction and flow cytometry were used for quantification.

RESULTS

White blood cells from neonates of both sexes showed significantly elevated glycoprotein and mRNA levels compared to adults. In addition, there was a significant mRNA up regulation in female newborns predominantly occurring in cases with pathologic cardiotocogram, premature rupture of the amniotic membrane, and health disorders of the mother.

CONCLUSION

These findings show a significantly increased CD 177 expression in neutrophils from newborns compared to adults, which suggests the existence of additional factors being able to stimulate CD 177 expression.

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.

Lack of NB1 GP (CD177/HNA-2a) gene transcription in NB1 GP- neutrophils from NB1 GP-expressing individuals and association of low expression with NB1 gene polymorphisms

The human neutrophil NB1 glycoprotein (NB1 GP, HNA-2a, CD177) has gained clinical importance for being involved in pulmonary transfusion reactions and immune neutropenias. The NB1 GP shows the unique feature of being expressed only on a neutrophil subpopulation. Recently, we identified splicing defects responsible for an NB1 GP deficiency. In this study, we have investigated the molecular basis of the heterogeneous expression of NB1 GP by separating the 2 neutrophil subpopulations using immunofluorescence followed by single-cell picking or by fluorescence-activated cell sorter. We found a lack of NB1 mRNA in the NB1 GP- cells that remained constant even after granulocyte colony-stimulating factor (G-CSF) administration. Comparing the cDNA sequences of donors with a large (> 60%) and those with a small (< 40%) NB1 GP-expressing subpopulation, we found 6 polymorphisms. Of the 6, 3 were significantly associated with a small NB1 GP-expressing subpopulation, indicating a genetic basis for NB1 GP nonexpression.

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.

The use of bioinformatics to identify the genomic structure of the gene that encodes neutrophil antigen NB1, CD177

The gene encoding neutrophil alloantigen NB1, CD177, is highly homologous to a gene overexpressed in polycythemia vera neutrophils, polycythemia rubra vera-1 (PRV-1). The cDNAs of both genes have been cloned, but their genomic structure is unknown. The purpose of this study was to determine the intron-exon organization of NB1 and PRV-1 and discern if they are separate members of a homologous gene family or alleles of the same gene. GenBank's human genome sequences were probed in silico with PRV-1's 1605-nucleotide coding sequence. Searches identified two adjacent bacterial artificial chromosomes (BACs) on chromosome 19q13.2: BC338531 and BC52850. BC338531 contained sequences 100% homologous to the first 654 nucleotides of PRV-1. Comparison of coding and genomic sequences allowed us to separate this region into exons 1 through 5, interrupted by five introns. BC52850 contained sequences 95% homologous to nucleotides 413 through 1605 of PRV-1, organized into exons 4 through 9. However, the orientation of PRV-1-homologous in the first BAC was plus-plus and of the second was plus-minus, indicating they could not be portions of the same gene. The GenBank sequence of BC338531 was incomplete, creating a sequence gap in chromosome 19q13.2. Evaluation of BC338531's unfinished sequences in Joint Genome Institute public databases allowed us to complete the gap and revealed that BC338531 contained sequences 98% homologous to all nine PRV-1 exons followed by a second gene consisting of exons 9 through 4. Most likely, NB1 and PRV-1 are alleles of the same gene, CD177, and the duplication of exons 4 through 9 is a pseudo gene.

Variations in the expression of granulocyte antigen NB1

BACKGROUND

Between 87 and 97 percent of whites express NB1 alloantigen on some but not all of their granulocytes. The expression of NB1 has not been compared among large groups of adults of different sexes, ages, and ethnic groups. Previous testing of whites suggests that the expression of NB1 is variable.

STUDY DESIGN AND METHODS

Serologic testing of granulocytes from 224 persons with two examples of MoAb to NB1 (1B5 and 7D8) was performed to distinguish phenotypic differences among age, sex, and ethnic groups and differences in reactivity to MoAbs. The donors were from 17 to 82 years of age, and 87 were female. They were from four ethnic backgrounds: 54 were African American (black), 10 were Asian, 9 Hispanic, and 152 white. Granulocytes were tested by flow cytometry. Parallel testing with MoAbs to CD16, CD11b, and CD45 served as controls. The size of the granulocyte population reacting with 1B5 and 7D8 and the respective mean, median, and peak cell fluorescence intensities were analyzed.

RESULTS

The expression of 7D8 and 1B5 was greater on granulocytes from female donors. The expression of 7D8 fell in older women but not in men. There were no differences among the four racial groups in either the frequency of NB1 as determined by 1B5 or 7D8 or in the size of the population of granulocytes reacting with either antibody. When the fluorescence intensities of the antibody reactions were compared among groups, there were no differences in reactivity with 1B5. However, reactions with 7D8 were all greater in blacks. Comparison of the size of the antigen-positive granulocyte population, as determined by antibody reactivity, showed that only 30 donors differed by more than 10 percent. These discordant results were more likely to occur in whites than in blacks (18% vs. 4%, p<0.02).

CONCLUSIONS

NB1 is composed of at least two epitopes as determined by serologic studies. The expression of both antigens is greater in females. The 7D8-reactive epitope appears to be more prevalent or more accessible on granulocytes of blacks. Variations in the expression of NB1 are more likely to occur in whites. The biochemical and molecular basis of these variations are not known.

The chemical and immunoglobulin structural features necessary for reactions of quinine-dependent antibodies to neutrophils

BACKGROUND

Previously described were three patients with quinine-dependent antibodies to neutrophils, platelets, and red cells who had episodic pancytopenia and renal failure. The nature of the antibody-drug-neutrophil interactions was investigated with sera from these patients.

STUDY DESIGN AND METHODS

Sera from all three patients were tested against neutrophils in flow cytometry in the presence of several compounds related to quinine. IgG and Fab and F(ab')2 fragments were prepared from the serum of one patient and tested against neutrophils in flow cytometry and immunoprecipitation in the presence of quinine and related compounds.

RESULTS

In flow cytometry, sera from all three patients plus quinidine reacted with neutrophils. Sera from Patients 1 and 3 reacted with neutrophils in the presence of cinchonidine (desmethoxy-quinine) and serum from Patient 3 also reacted with neutrophils in the presence of cinchonine (desmethoxy-quinidine). None of the sera reacted with neutrophils in the presence of chloroquine or primaquine. Serum from Patient 3 plus quinolinic acid, a tryptophan metabolite, reacted with neutrophils, but sera from the other two patients did not. Patient 3 serum plus tryptophan or another tryptophan metabolite, quinalidic acid, did not react with neutrophils. IgG from Patient 3 serum reacted with neutrophils in flow cytometry in the presence of quinine, quinidine, cinchonidine, cinchonine, and quinolinic acid. F(ab')2 fragments plus quinine or cinchonidine also reacted with neutrophils, but Fab fragments plus quinine did not. In the presence of quinine, Patient 3 IgG immunoprecipitated the 85- and 60-kDa molecules and F(ab')2 fragments immunoprecipitated the 85-kDa molecule. Patient 3 serum plus quinidine, cinchonidine, cinchonine, and quinolinic acid immunoprecipitated the 130- and 85-kDa molecules, but not the 60-kDa molecule.

CONCLUSION

Quinine-dependent neutrophil antibodies often react with neutrophils in the presence of quinidine and related compounds. These reactions were mediated by the F(ab')2 domain of IgG.

CELL-SURFACE ANTIGENS

The cell surface is covered with protein molecules that are held in the membrane by hydrophobic transmembrane segments or glycosyl–phosphatidylinositol (GPI) anchors. Antigens found on cell surfaces comprise not only those encoded by the cell itself but also the products of intracellular parasites. Soluble ligands may be bound to receptor structures on the cell membrane or lectin-like molecules bound to cell-surface carbohydrate structures. The molecules that form an integral part of the cell surface may be proteins, glycoproteins, or glycolipids. They subserve one of three major functions: adhesion, antigen recognition, or receptors for soluble mediators. However, many cell-surface molecules possess more than one function—for example, molecules involved in cell–cell or cell–extracellular matrix adhesion can also themselves be involved in signal transduction. The cell-surface antigens of leukocytes have been intensively studied because of ease of access to this cellular compartment.

Further characterization of the NB 1 antigen as a variably expressed 56-62 kD GPI-linked glycoprotein of plasma membranes and specific granules of neutrophils

The human neutrophil-specific alloantigen NB1 was identified as a glycosyl-phosphatidylinositol (GPI)-anchored N-glycosylated protein of M(r) 56-62 kD under reducing conditions. Under non-reducing conditions its M(r) was 49-55 kD. This glycoprotein antigen was found to be expressed by only a subpopulation of normal donor neutrophils, and could not be detected on other blood cells. The allotypic epitope recognized by human anti-NB1 IgG was also recognized by the mouse monoclonal antibody 1B5. The percentage of neutrophils stained by these antibodies varied greatly among healthy donors (range 0-100%). When 16 donors were repeatedly tested, the NB1-positive neutrophil fraction appeared to remain remarkably constant over time in most donors, but significant fluctuations were seen in some. NB1 antigen was found to be expressed not only on the plasma membrane, but also intracellularly on the membranes of small vesicles and specific granules. The neutrophils which expressed NB1 antigen on the plasma membrane were the same as those with intracellular expression of this antigen. Crosslinking of NB1 antigen on the plasma membrane with monoclonal antibody 1B5 and goat-anti-mouse Ig resulted in internalization of the complex, while in-vitro stimulation of neutrophils caused an increase of the intensity of plasma membrane staining with anti-NB1, but only of those cells that were positive already prior to stimulation. The NB1 glycoprotein thus appears to identify a distinct subset of neutrophils, the size of which greatly varies among healthy donors. The function of the NB1 glycoprotein remains unclear, but its behaviour upon crosslinking and chemotactic peptide stimulation suggests a possible role as receptor molecule.

Dodecyl maltoside detergent improves resolution of hepatic membrane proteins in two-dimensional gels

This report describes the incorporation of an alkyl maltoside detergent in two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) sample lysis buffer in order to improve resolution of protein patterns separated by nonequilibrium pH gradient electrophoresis. Membrane-associated proteins with alkaline isoelectric points form horizontal streaks on two-dimensional electrophoretograms when solubilized with conventional nonionic detergent. Dodecyl maltoside enhances protein delipidation during solubilization and improves pattern resolution and protein mobility.