Evidence for gene recombination in FCGR3 gene variants

Primary structure of human neutrophil antigens 1a and 1b

BACKGROUND

Neutrophil specific Fcγ receptor IIIb (CD16b) is a low-affinity IgG receptor. Its polymorphic variants are associated with human neutrophil antigens (HNA). HNA-1a and HNA-1b differ in four amino acids. Immunization can lead to the production of alloantibodies. The exact contribution of four amino acid exchanges for the formation of HNA-1a, -1b epitopes is currently unknown.

STUDY DESIGN AND METHODS

Permutation of each polymorphic amino acid from wild-type CD16b cDNA constructs was performed and expressed on HEK293 cells. All 16 receptor variants were produced and tested against 19 well-characterized HNA antisera in an antigen capture assay.

RESULTS

Analyzing the reaction pattern revealed that anti-HNA-1a antibodies can bind whenever asparagine (N) is present in position 65, regardless of the three other positions (CD16b *N**). Anti-HNA-1b antibodies can bind when serine (S) is present in position 36 (CD16b S***), when N is present in position 82 (CD16b **N*), or both (CD16b S*N*). CD16b variants with N65 and S36 and/or N82 (such as CD16b SNN*) bind both, anti-HNA-1a and anti-HNA-1b alloantibodies. If these specific amino acids are missing (as in CD16b RSD*), no antibodies will bind.

CONCLUSION

Whereas the primary structure of HNA-1a and HNA-1b usually differs in four amino acids, epitope composition is not "antithetical". N65 alone determines the presence of HNA-1a, and S36 and/or N82 determine the presence of HNA-1b. Amino acid 106 does not participate in epitope formation. Our findings are of specific relevance when a HNA-1 phenotype is predicted from a genotype.

Genotyping of human neutrophil antigens 1, 3, 4 and 5 using a novel multiplex polymerase chain reaction

OBJECTIVES

Our study aimed to establish a novel multiplex polymerase chain reaction (PCR) for rapid simultaneous detection of all relevant human neutrophil antigen (HNA)-1, -3, -4 and -5 alleles.

BACKGROUND

Granulocyte-reactive antibodies are involved in several diseases, such as neonatal alloimmune neutropenia, autoimmune neutropenia and transfusion-related acute lung injury. A panel of well-defined test granulocytes is required for diagnostic antibody detection and prospective blood donor screening. Several genotyping methods for the detection of HNA alleles have been described, but most approaches require separate amplification of each HNA allele or at least a separate amplification of the HNA-1 alleles.

METHODS

The new method is based on simultaneous detection in one reaction tube, where each HNA-1 allele is amplified by two allele-specific primers, one primer of which is labelled with a fluorescent dye (HEX, FAM). Allelic polymorphisms for HNA-3, -4 and -5 were amplified with one common unlabelled primer and two fluorescence-labelled (HEX, FAM) allele-specific primers. DNA fragments of HNA alleles are analysed on a Genetic Analyser 3130xl by amplicon size and fluorescent dye. A total of 110 blood donors with known genotypes were studied.

RESULTS

In the 110 DNA samples studied, all HNA-1, -3, -4 and -5 alleles could be detected precisely. All results matched perfectly with those from reference typing by PCR-sequence-specific primer. Amplification performed well even at low DNA concentrations (10 ng μL^-1 ).

CONCLUSION

Our method enables fast and easy genotyping of all relevant HNA-alleles in one PCR reaction. Results are easy to analyse due to different amplicon sizes and fluorescent dyes. Furthermore, the method is suitable for high sample throughput.

Molecular Genetics of the Human Neutrophil Antigens

BACKGROUND AND OBJECTIVE

Antibodies to human neutrophil antigens (HNAs) have been implicated in transfusion-related acute lung injury and allo- and autoimmune neutropenia. To date, five HNA systems are assigned, and during the last decades enormous efforts have been undertaken to identify the underlying genes and to characterize the antigens. This review of the literature will provide the current genetic, molecular and functional information on HNAs.

RECENT FINDINGS

New information on alleles and antigens has been added to nearly each of the five HNA systems. HNA-1d has been added as the antithetical epitope to HNA-1c that is located on the glycoprotein encoded by FCGR3B*02 but not by FCGR3B. FCGR3B*04 and *05 now are included as new alleles. A CD177*787A>T substitution was demonstrated as the main reason for the HNA-2-negative phenotype on neutrophils. The target glycoprotein of HNA-3 antibodies could be identified as choline transporter-like protein 2 (CTL2) encoded by SLC44A2. The conformation sensitive epitope discriminates between arginine and glutamine at position 152 resulting in HNA-3a and HNA-3b. An additional Leu151Phe substitution can impair HNA-3a antibody binding. Recently an alloantibody against HNA-4b which discriminates from HNA-4a by an Arg61His exchange of the glycoprotein encoded by the ITGAM gene was reported in neonatal alloimmune neutropenia. An update of the current HNA nomenclature based on the new findings was provided in 2016 by the ISBT Granulocyte Immunobiology Working Party nomenclature subcommittee.

CONCLUSIONS

The molecular basis of each of the five HNA antigen systems has been decoded during the past decades. This enables reliable molecular typing strategies, antibody detection and specification as well as development of new assays based on recombinant antigens. However, research on HNA alleles, antigens, and antibodies is not finally terminated and also in the future will add new findings.

Fc gamma receptor IIIb polymorphism and systemic lupus erythematosus: association with disease susceptibility and identification of a novel FCGR3B*01 variant

OBJECTIVE

The objective of this study was to evaluate the association between Fc gamma receptor IIIb polymorphism and susceptibility to systemic lupus erythematosus and clinical traits of the disease.

METHODS

Genomic DNA was obtained from 303 consecutive systemic lupus erythematosus patients and 300 healthy blood donors from the southeastern region of Brazil. The polymorphic region of the FCGR3B gene was sequenced and the alleles FCGR3B*01, FCGR3B*02 and FCGR3B*03 were analyzed.

RESULTS

The FCGR3B*01 allele was more frequent in systemic lupus erythematosus patients (43.1%) while the FCGR3B*02 allele prevailed among controls (63.7%) (P = 0.001). The FCGR3B*03 allele was found equally in both groups. The FCGR3B*01/*01 (20.7%) and FCGR3B*01/*02 (41.1%) genotypes were more frequent among systemic lupus erythematosus patients (P = 0.028 and P = 0.012, respectively) while the FCGR3B*02/*02 genotype was more frequent in controls (45.5%) (P < 0.001). One variant of the FCGR3B*01 allele previously described in Germany was found in only one control. A new variant of the FCGR3B*01 allele with two substitutions (A227G/G277A) was found in one control. Three variants of the FCGR3B*02 allele previously described in African-Americans, Brazilians, Chinese and Japanese were found in ten 10 patients and two controls. In addition, several single nucleotide polymorphisms at non-polymorphic positions were identified in both patients and controls.

CONCLUSION

Susceptibility to systemic lupus erythematosus was associated with the FCGR3B*01 allele, as well as with the FCGR3B*01/*01 and FCGR3B*01/*02 genotypes. No association was found between FCGR3B genotypes and clinical manifestations, disease severity or the presence of autoantibodies.

Fc γ receptor IIIB (FcγRIIIB) polymorphisms are associated with clinical malaria in Ghanaian children

Plasmodium falciparum malaria kills nearly a million people annually. Over 90% of these deaths occur in children under five years of age in sub-Saharan Africa. A neutrophil mediated mechanism, the antibody dependent respiratory burst (ADRB), was recently shown to correlate with protection from clinical malaria. Human neutrophils constitutively express Fc gamma receptor-FcγRIIA and FcγRIIIB by which they interact with immunoglobulin (Ig) G (IgG)-subclass antibodies. Polymorphisms in exon 4 of FCGR2A and exon 3 of FCGR3B genes encoding FcγRIIA and FcγRIIIB respectively have been described to alter the affinities of both receptors for IgG. Here, associations between specific polymorphisms, encoding FcγRIIA p.H166R and FcγRIIIB-NA1/NA2/SH variants with clinical malaria were investigated in a longitudinal malaria cohort study. FcγRIIA-p.166H/R was genotyped by gene specific polymerase chain reaction followed by allele specific restriction enzyme digestion. FCGR3B-exon 3 was sequenced in 585 children, aged 1 to 12 years living in a malaria endemic region of Ghana. Multivariate logistic regression analysis found no association between FcγRIIA-166H/R polymorphism and clinical malaria. The A-allele of FCGR3B-c.233C>A (rs5030738) was significantly associated with protection from clinical malaria under two out of three genetic models (additive: p=0.0061; recessive: p=0.097; dominant: p=0.0076) of inheritance. The FcγRIIIB-SH allotype (CTGAAA) containing the 233A-allele (in bold) was associated with protection from malaria (p=0.049). The FcγRIIIB-NA2*03 allotype (CTGCGA), a variant of the classical FcγRIIIB-NA2 (CTGCAA) was associated with susceptibility to clinical malaria (p=0.0092). The present study is the first to report an association between a variant of FcγRIIIB-NA2 and susceptibility to clinical malaria and provides justification for further functional characterization of variants of the classical FcγRIIIB allotypes. This would be crucial to the improvement of neutrophil mediated functional assays such as the ADRB assay aimed at assessing the functionality of antibodies induced by candidate malaria vaccines.

FCGR3B*03 allele inheritance pattern in Brazilian families and some new variants of gene FCGR3B

BACKGROUND

The FCGR3B gene encoding the FcyRIIIb receptor for immunoglobulin G has three polymorphic forms known as HNA-1a, HNA-1b, and HNA-1c, encoded by the alleles FCGR3B*01, FCGR3B*02, and FCGR3B*03, respectively. It is not clear whether the inheritance of the FCGR3B*03 allele, which encodes the HNA-1c, is linked or not to the other two alleles. The objective of this study was to identify the inheritance pattern of the FCGR3B*03 allele in Brazilians.

STUDY DESIGN AND METHODS

Blood samples from nine families with at least one FCGR3B*03(+) member, totalizing 47 individuals, were studied. The presence of the FCGR3B*01, FCGR3B*02, and FCGR3B*03 alleles was detected by the polymerase chain reaction with sequence-specific priming method, and all DNA samples were sequenced.

RESULTS

In three of the nine studied families, the FCGR3B*03 was passed down with the FCGR3B*02, while in one family the FCGR3B*03 was inherited in linkage with FCGR3B*01. The other families were not informative regarding FCGR3B*03 inheritance. Sequencing showed for the first time one single-nucleotide polymorphism at Position 264 resulting from a simple substitution C→T; three other different substitutions at Position 230, T→A, T→G; and the presence of three nucleotides at Position 230 (T, G, and A). The previously reported variants FCGR3B*01A227G and FCGR3BG330T were also found.

CONCLUSION

In this Brazilian FCGR3B*03(+) group we found that the inheritance of FCGR3B*03 took place by a linkage to FCGR3B*02 or to FCGR3B*01. Linkage of FCGR3B*03 to FCGR3B*02 was the most common. Additionally, we report SNPs that have not been described, suggesting that they might be more common than previously thought.