Human Fc gamma RIII: cloning, expression, and identification of the chromosomal locus of two Fc receptors for IgG

Interaction with cellular CD4 exposes HIV-1 envelope epitopes targeted by antibody-dependent cell-mediated cytotoxicity

Anti-HIV-1 envelope glycoprotein (Env) antibodies without broadly neutralizing activity correlated with protection in the RV144 clinical trial, stimulating interest in other protective mechanisms involving antibodies, such as antibody-dependent cell-mediated cytotoxicity (ADCC). Env epitopes targeted by many antibodies effective at mediating ADCC are poorly exposed on the unliganded Env trimer. Here we investigated the mechanism of exposure of ADCC epitopes on Env and showed that binding of Env and CD4 within the same HIV-1-infected cell effectively exposes these epitopes. Env capacity to transit to the CD4-bound conformation is required for ADCC epitope exposure. Importantly, cell surface CD4 downregulation by Nef and Vpu accessory proteins and Vpu-mediated BST-2 antagonism modulate exposure of ADCC-mediating epitopes and reduce the susceptibility of infected cells to this effector function in vitro. Significantly, Env conformational changes induced by cell surface CD4 are conserved among Env from HIV-1 and HIV-2/SIVmac lineages. Altogether, our observations describe a highly conserved mechanism required to expose ADCC epitopes that might help explain the evolutionary advantage of downregulation of cell surface CD4 by the HIV-1 Vpu and Nef proteins.

IMPORTANCE

HIV-1 envelope epitopes targeted by many antibodies effective at mediating antibody-dependent cell-mediated cytotoxicity (ADCC) are poorly exposed on the unliganded envelope trimer. Here we investigated the mechanism of exposure of these epitopes and found that envelope interaction with the HIV-1 CD4 receptor is required to expose some of these epitopes. Moreover, our results suggest that HIV-1 CD4 downregulation might help avoid the killing of HIV-1-infected cells by this immune mechanism.

Analysis of MIF, FCGR2A and FCGR3A gene polymorphisms with susceptibility to pulmonary tuberculosis in Moroccan population

In order to investigate the influence of functional polymorphisms of macrophage migration inhibitory factor (MIF), Fcg receptors CD16A (FCGR3A) and CD32A (FCGR2A) genes on susceptibility to pulmonary tuberculosis (PTB) in the Moroccan population, we analyzed 123 patients with PTB and 154 healthy controls. The genotyping for MIF-173 (G/C) (rs755622), FCGR2A-131H/R (rs1801274) and FCGR3A-158V/F (rs396991) was carried out using TaqMan SNP Genotyping Assay method. We found a statistically significant increase of the MIF -173CC homozygote genotype and MIF -173*C allele frequencies in PTB patients compared with healthy controls (17.07%versus 5.84%, P = 0.003; and 35.37%versus 26.30%, P = 0.02; respectively). In contrast, no association was observed between FCGR2A-131H/R and FCGR3A-158V/F polymorphisms and tuberculosis disease. Our finding suggests that MIF -173*C variant may play an important role in the development of active tuberculosis.

[Implications of receptors for the Fc portion of IgG (FcgammaRs) in mechanism of action of therapeutic antibodies]

From several years ago, recombinant monoclonal antibodies have allowed a revolution in therapeutic approach of cancer patients. Whereas the clinical efficacy of many antibodies is now demonstrated, their mechanism of action in patients remains elusive. For antibodies targeting membrane antigens, they particularly resort to cytotoxic effectors, which expressed receptors for Fc portion of IgG (FcgammaRs). This review analyses different functions depending of FcgammaR and their potential role in mechanism of action of therapeutic antibodies. A better knowledge of these functions should allow in the next future the optimisation of these treatments.

Dimers and multimers of monoclonal IgG1 exhibit higher in vitro binding affinities to Fcgamma receptors

The in vitro binding of monomeric, dimeric and multimeric forms of monoclonal IgG1 molecules, designated mAb1 and mAb2, to the extracellular domains of Fcgamma receptors RI, RIIA and RIIIB were investigated using a surface plasmon resonance (SPR) based biosensor technique. Stable noncovalent and covalent dimers of mAb1 and mAb2, respectively, were isolated from CHO cell expressed materials. The dissociation constants of monomeric mAb1 and mAb2 were determined to be 1 nM for the FcgammaRI-binding and 6-12 microM for the FcgammaRIIA- and FcgammaRIIIB-binding. Dimeric mAb1 and mAb2 exhibited increased affinities, by 2-3 fold for FcgammaRI and 200-800 fold for FcgammaRIIA and FcgammaRIIIB. Further increases in binding were observed when the antibodies formed large immune complexes with multivalent antigens, but not in a linear relation with size. The binding properties of monomeric mAb2 were identical with and without a bound monovalent antigen, indicating that antigen-binding alone does not induce measurable change in binding of antibodies to Fcgamma receptors. Dimerization is sufficient to show enhancement in the receptor binding. Given the wide distribution of the low-affinity Fcgamma receptors on immune effector cells, the increased affinities to aggregated IgG may lead to some biological consequences, depending on the subsequent signal transduction events. The SPR-based in vitro binding assay is useful in evaluating Fcgamma receptor binding of various species in antibody-based biotherapeutics.

Distribution of FcγRIIa and FcγRIIIb Genotypes in Patients With Generalized Aggressive Periodontitis

BACKGROUND

Polymorphisms in FcgammaR have been associated with different forms of periodontitis. This study determined the frequency of FcgammaRIIa and FcgammaRIIIb alleles/genotypes in patients with generalized aggressive periodontitis (GAgP).

METHODS

Thirty-one GAgP and 49 periodontally healthy Brazilian subjects participated in the study. Full-mouth periodontal examinations were carried out, and mouthwash samples were collected for human DNA isolation. FcgammaR genotyping was performed by polymerase chain reaction and hybridization with allele-specific oligonucleotide probes. Significant differences between groups were sought by Mann-Whitney, chi2, and Fisher exact tests and configural frequency analysis.

RESULTS

FcgammaRIIa-H131 (53.8%) and FcgammaRIIIb-NA1 (75%) were the most prevalent alleles in this sample population. A significant overrepresentation of FcgammaRIIIb-NA2 was observed in the GAgP group, whereas FcgammaRIIIb-NA1 was detected more often in healthy individuals (odds ratio, 32.5; 95% confidence interval [CI], 10.6 to 99.8; P<0.001). No significant differences in the distribution of the FcgammaRIIa genotypes were observed between the groups. The prevalence of FcgammaRIIIb-NA2/NA2 was higher in GAgP patients, whereas FcgammaRIIIb-NA1/NA1 was predominant in the healthy group (chi2=45.1; P<0.001). The combination of the genotypes FcgammaRIIIb-NA2/NA2 plus FcgammaRIIa-H/H131 was observed more frequently in GAgP subjects than expected from marginal frequencies (chi2=12.5; P<0.001).

CONCLUSIONS

The data suggest that the FcgammaRIIIb-NA2 allele and/or FcgammaRIIIb-NA2/NA2 genotype and the composite genotype FcgammaRIIIb-NA2/NA2 plus FcgammaRIIa-H/H131 may be associated with GAgP, whereas FcgammaRIIIb-NA1 and/or FcgammaRIIIb-NA1/NA1 may be related to periodontal health in this sample of the Brazilian population.

Neonatal alloimmune neutropenia attributed to maternal immunoglobulin G antibodies against the neutrophil alloantigen HNA-1c (SH): a report of five cases

BACKGROUND

Neonatal alloimmune neutropenia (NAN) occurs when maternal immunoglobulin G (IgG) antibodies enter fetal circulation and destroy neonatal neutrophils. Whether antibodies specific for the neutrophil antigen HNA-1c (SH) can cause NAN is uncertain, because in three of four reported cases, other neutrophil-specific antibodies were present. In this report, we describe five cases of NAN, in which only anti-HNA-1c was detected in maternal serum.

STUDY DESIGN AND METHODS

HNA-1c antibodies were detected with flow cytometry immunofluorescence (FCI) and the monoclonal antibody (MoAb) immobilization of granulocyte antigens (MAIGA) assay. Genotyping for HNA-1c was performed by allele-specific polymerase chain reaction amplification of DNA.

RESULTS

All five maternal serum samples contained IgG antibodies with specificity for HNA-1c detected in both FCI and MAIGA assay. Of CD16-specific MoAbs evaluated, only MBC238.7 was optimal for detection of antibody by MAIGA assay. Recombinant human granulocyte-colony-stimulating factor (rHuG-CSF) was effective in raising neutrophil counts in the two infants treated in this manner.

CONCLUSION

Severe NAN can be caused by maternal antibodies specific for HNA-1c (SH) alone. Use of an appropriate MoAb is critical for detection of anti-HNA-1c by MAIGA assay. rHuG-CSF is an effective therapy in infants with NAN caused by anti-HNA-1c.

Fcgamma receptor IIA genotype and susceptibility to P. aeruginosa infection in patients with cystic fibrosis

It has been suggested that genes other than CFTR could modulate the severity of lung disease in cystic fibrosis (CF). Neutrophil Fcgamma receptor II (FcgammaRII) is involved in host defense against microorganisms and in inflammatory response. We evaluated the association between genetic variability of this gene and both airway infection with Pseudomonas aeruginosa and severity of lung disease in patients with CF. We studied 167 Italian unrelated patients with CF and 50 control subjects. The distribution of FcgammaRIIA genotypes in CF patients was compared with that in control subjects and the different genotypes were related with the presence or absence of P. aeruginosa infection and markers of disease severity in CF patients. The distribution of FcgammaRIIA genotypes was not significantly different between CF patients and controls. We observed that in CF patients with the same CFTR genotype (DeltaF508/DeltaF508), those carrying the R allele of FcgammaRIIA had an increased risk of acquiring chronic P. aeruginosa infection (P=0.042, R.R.: 4.38; 95% CI: 1.17/22.4). Moreover, the frequency of R/R genotype in patients with chronic P. aeruginosa infection seems to be higher than that of control subjects and patients without chronic infection. The observation that CF patients carrying the R allele of FcgammaRIIA are at higher risk of acquiring chronic P. aeruginosa infection suggests that the FcgammaRII loci genetic variation is contributing to this infection susceptibility.

Polymorphisms in FcγRIIIA (CD16) Receptor Expression Are Associated With Clinical Response to Rituximab in Waldenström’s Macroglobulinemia

Purpose

Rituximab is an important therapeutic for Waldenström’s macroglobulinemia (WM). Polymorphisms in FcγRIIIA (CD16) receptor expression modulate human immunoglobulin G1 binding and antibody-dependent cell-mediated cytotoxicity, and may therefore influence responses to rituximab.

Patients and Methods

Sequence analysis of the entire coding region of FcγRIIIA was undertaken in 58 patients with WM whose outcomes after rituximab were known.

Results

Variations in five codons of FcγRIIIA were identified. Two were commonly observed (FcγRIIIA-48 and FcγRIIIA-158) and predicted for amino acid polymorphisms at FcγRIIIA-48: leucine/leucine (L/L), leucine/arginine (L/R), and leucine/histidine (L/H). Polymorphisms at FcγRIIIA-158 were phenylalanine/phenylalanine (F/F), phenylalanine/valine (F/V), and valine/valine (V/V). A clear linkage between these polymorphisms was detected and all patients with FcγRIIIA-158F/F were always FcγRIIIA-48L/L, and patients with either FcγRIIIA-L/R or -L/H always expressed at least one valine at FcγRIIIA-158 (P ≤ .001). The response trend was higher for patients with FcγRIIIA-48L/H (38.5%) versus -48L/R (25.0%) and LL (22.0%), and was significantly higher for patients with FcγRIIIA-158V/V (40.0%) and -V/F (35%) versus -158F/F (9.0%; P = .030). Responses for patients with FcγRIIIA-48L/L were higher when at least one valine was present at FcγRIIIA-158 (P = .057), thereby supporting a primary role for FcγRIIIA-158 polymorphisms in predicting rituximab responses. With a median follow-up of 13 months, no significant differences in the median time to progression and progression-free survival were observed when patients were grouped according to their FcγRIIIA-48 and -158 polymorphisms.

Conclusion

The results of these studies therefore support a predictive role for FcγRIIIA-158 polymorphisms and responses to rituximab in WM.

Characterization of human FCGR3B*02 (HNA-1b, NA2) cDNAs and IMGT standardized description of FCGR3B alleles

The low-affinity Fc gamma receptor IIIb (Fc gamma RIIIb and CD16b) is constituted by a unique FCGR3B polypeptide chain that comprises two extracellular immunoglobulin-like domains, and is expressed as a glycosylphosphatidyl inositol-anchored receptor on the neutrophils. The FCGR3B chain bears allotypes that define the human neutrophil antigen-1 (HNA-1 and NA) system involved in major post-transfusional reactions. FCGR3B is highly homologous to FCGR3A, which is expressed as a transmembrane receptor on natural killer cells and monocytes/macrophages. Its transcription products were not yet fully characterized. In the present work, we sequenced FCGR3B cDNAs with complete 3' untranslated region from purified granulocytes of HNA-1b/HNA-1b (NA2/NA2) genotyped donors. We characterized two FCGR3B cDNAs of different lengths corresponding to two polyadenylation sites. This result was corroborated by data raised by serial analysis of gene expression (SAGE). FCGR3B allele polymorphisms, from this article [FCGR3B*02 (HNA-1b, NA2)] and from the literature, are described for the first time according to the IMGT standardized nomenclature and to the IMGT unique numbering for C-LIKE-DOMAIN (http://imgt.cines.fr). These rules, described in the IMGT Scientific chart, are based on the IMGT-ONTOLOGY concepts. IMGT allele alignments and IMGT Collier de Perles graphical two-dimensional representations are provided for the two Ig-like domains (or C-LIKE-DOMAINs) [D1] and [D2] of FCGR3B*02. The standardized description of FCGR3B allele polymorphisms was approved by the IMGT Nomenclature Committee (IMGT-NC) and is freely available in IMGT repertoire at IMGT, http://imgt.cines.fr.

Fucose Depletion from Human IgG1 Oligosaccharide Enhances Binding Enthalpy and Association Rate Between IgG1 and FcγRIIIa

Depletion of fucose from human IgG1 oligosaccharide improves its affinity for Fcgamma receptor IIIa (FcgammaRIIIa). This is the first case where a glycoform modification is shown to improve glycoprotein affinity for the receptors without carbohydrate-binding capacity, suggesting a novel glyco-engineering strategy to improve ligand-receptor binding. To address the mechanisms of affinity improvement by the fucose depletion, we used isothermal titration calorimetry (ITC) and biosensor analysis with surface plasmon resonance. ITC demonstrated that IgG1-FcgammaRIIIa binding was driven by favorable binding enthalpy (DeltaH) but opposed by unfavorable binding entropy change (DeltaS). Fucose depletion from IgG1 enhanced the favorable DeltaH, leading to the increase in the binding constant of IgG1 for the receptor by a factor of 20-30. The increase in the affinity was mainly attributed to an enhanced association rate. A triple amino acid substitution in IgG1, S298A/E333A/K334A, is also known to improve IgG1 affinity for FcgammaRIIIa. ITC demonstrated that the amino acid substitution attenuated the unfavorable DeltaS resulting in a three- to fourfold increase in the binding constant. The affinity enhancement by the amino acid substitution was due to a reduced dissociation rate. These results indicate that the mechanism of affinity improvement by the fucose depletion is quite distinct from that by the amino acid substitution. Defucosylated IgG1 exhibited higher antibody-dependent cellular cytotoxicity (ADCC) than S298A/E333A/K334A-IgG1, showing a correlation between IgG1 affinity for FcgammaRIIIa and ADCC. We also examined the effect of FcgammaRIIIa polymorphism (Val158/Phe158) on IgG1-FcgammaRIIIa binding. The Phe to Val substitution increased FcgammaRIIIa affinity for IgG1 in an enthalpy-driven manner with the reduced dissociation rate. These results together highlight the distinctive functional improvement of affinity by IgG1 defucosylation and suggest that engineering of non-interfacial monosaccharides can improve glycoprotein affinity for receptors via an enthalpy-driven and association rate-assisted mechanism.

Genetic deficiency of CD16, the low-affinity receptor for immunoglobulin G, has no impact on the functional capacity of polymorphonuclear neutrophils

BACKGROUND

Of the three receptors for immunoglobulin G (IgG), the low-affinity receptor CD16 is constitutively expressed on polymorphonuclear neutrophils (PMNs), monocytes and NK-cells. CD16 participates in various effector functions, notably phagocytosis of opsonized particles or of immune complexes, and in antibody-dependent cellular cytotoxicity (ADCC). In the present study we report a case of total CD16 deficiency on PMNs and monocytes.

DESIGN

Polymorphonuclear neutrophils, monocytes and NK-cells were analyzed for surface-receptor expression by cytofluorometry and laser scan microscopy. Moreover, CD16-specific mRNA was assessed by RT-PCR. As functional parameters, phagocytosis of opsonized bacteria was tested, as was superoxide production.

RESULTS

Polymorphonuclear neutrophils and monocytes totally deficient in CD16 were detected by chance in an apparently healthy individual. Further analysis revealed that two more members of his family, his father and sister, were also deficient in CD16. All were healthy and there was no evidence of an increased frequency, or of exceptionally severe or persistent infections. Despite the lack of CD16, phagocytosis of antibody-coated bacteria was within the normal range, as was the superoxide production.

CONCLUSION

Deficiency of CD16 does not compromise the host defence. Apparently, the other receptors for IgG, CD32 and CD64, can compensate for the lack of CD16.

Establishment ofFUT8 knockout Chinese hamster ovary cells: An ideal host cell line for producing completely defucosylated antibodies with enhanced antibody-dependent cellular cytotoxicity

To generate industrially applicable new host cell lines for antibody production with optimizing antibody-dependent cellular cytotoxicity (ADCC) we disrupted both FUT8 alleles in a Chinese hamster ovary (CHO)/DG44 cell line by sequential homologous recombination. FUT8 encodes an alpha-1,6-fucosyltransferase that catalyzes the transfer of fucose from GDP-fucose to N-acetylglucosamine (GlcNAc) in an alpha-1,6 linkage. FUT8(-/-) cell lines have morphology and growth kinetics similar to those of the parent, and produce completely defucosylated recombinant antibodies. FUT8(-/-)-produced chimeric anti-CD20 IgG1 shows the same level of antigen-binding activity and complement-dependent cytotoxicity (CDC) as the FUT8(+/+)-produced, comparable antibody, Rituxan. In contrast, FUT8(-/-)-produced anti-CD20 IgG1 strongly binds to human Fcgamma-receptor IIIa (FcgammaRIIIa) and dramatically enhances ADCC to approximately 100-fold that of Rituxan. Our results demonstrate that FUT8(-/-) cells are ideal host cell lines to stably produce completely defucosylated high-ADCC antibodies with fixed quality and efficacy for therapeutic use.

Glycosylation of FcgammaRIII in N163 as mechanism of regulating receptor affinity

Human FcgammaRIII (CD16) is a low-affinity receptor for immunoglobulin G (IgG). There are two different isoforms of this protein: CD16a (transmembranous, expressed on natural killer cells and on macrophages) and CD16b (glycosylphosphatidylinositol-linked, expressed on neutrophilic granulocytes in two allelic forms NA1 and NA2). Both forms of the protein have a variable glycosylation pattern. The NA1 allele of CD16B has four asparagine (N)-linked glycosylation sites. One of them (N163) is localized in the ligand-binding site of domain II. This site is shared by the NA2 allele and CD16A. To examine the functional role of the glycosylation we mutated the four glycosylation sites of the NA1 allele (N39, N75, N163, N170) into glutamine (Q). HEK293 cells were stably transfected with the single mutants and wild-type CD16 as control. We determined binding of human IgG to transfected cells using immunofluorescence studies with anti-human IgG antibody. Monomeric IgG bound to N163Q transfectants with higher affinity than to other transfectants, showing that glycosylation in N163 influences the affinity of CD16 to its ligand. In addition, preincubation of WT-CD16-transfected cells with Tunicamycin (an inhibitor of N-glycosylation) resulted in an increased binding of monomeric IgG whereas N163Q-CD16-transfected cells remained unaffected. Therefore, glycosylation in N163 is a mechanism of regulating affinity of FcgammaRIII to its ligand IgG.

Transmembrane domains in the functions of Fc receptors

In the present study, we use a novel method, PHDhtm, to predict the exact locations and extents of the transmembrane (TM) domains of multisubunit immunoglobulin Fc-receptors. Whereas most previous studies have used single residue hydrophobicity plots for characterizing of these domains, PHDhtm utilizes a system of neural networks and the evolutionary information contained in multiple alignments of related sequences to predict the above. Present PHDhtm application predicts TM domains of immunoglobulin Fc-receptors that in many cases differ significantly from those derived by using earlier methods. Comparisons of helical wheel projections of the presently derived TM domains from PHDhtm with those produced earlier reveal different hydrophobic moments as well as hydrophobic and hydrophilic surfaces. These differences probably alter the character of subunit association within the receptor complexes. This new algorithm can also be used for other membrane protein complexes and may advance both understanding the principles underlying such complexes formation and design of peptides that can interfere with such TM domain association so as to modulate specific cellular responses.

Evidence for non-random distribution of Fcgamma receptor genotype combinations

Human IgG receptors (FcgammaR) display considerable heterogeneity, and are crucial immune response modulating molecules. FcgammaRIIA, FcgammaRIIIA, and FcgammaRIIIB display functional biallelic polymorphisms. FcgammaR polymorphisms have been found associated with susceptibility to infectious and autoimmune diseases. Linked transmission of FcgammaR alleles was studied by determining the distribution of FcgammaRIIA-FcgammaRIIIA-FcgammaRIIIB genotype combinations in 514 Dutch Caucasian, and 149 Japanese blood donors. The structure of the FcgammaR locus was studied by radiation hybrid mapping of FcgammaRIA, FcgammaRIIA, FcgammaRIIB, FcgammaRIIIA, FcgammaRIIIB, and adjacent genes from the pentraxin family. In addition, crossing-over frequencies within the FcgammaR locus were determined in 63 Dutch Caucasian families, encompassing 183 individuals. FcgammaRII and FcgammaRIII subclasses were mapped in close proximity (0.47-3.14 cR). Accordingly, crossing-over frequencies within the FcgammaRII-III locus in Dutch families were low. Analysis of combined FcgammaR genotypes strongly suggested non-random distribution of FcgammaRIIA-FcgammaRIIIA-, and FcgammaRIIIA-FcgammaRIIIB genotypes in Dutch donors (P<0.001 and P<0.00001, respectively), and of FcgammaRIIA-FcgammaRIIIb genotypes in Japanese blood donors (P<0.02). Frequencies of FcgammaRII-FcgammaRIII haplotypes differed significantly between Dutch and Japanese (P<0.00001). This study provides important information for the interpretation of studies reporting associations of FcgammaR alleles with disease, and underscores the apparent differences in FcgammaR heterogeneity between ethnic groups.

The Fc gamma RIIIA-F158 allele is a risk factor for the development of lupus nephritis: a meta-analysis

BACKGROUND

The Fc gamma RIIIA-V/F158 polymorphism affects immunoglobulins (Ig)G1- and IgG3-binding capacity and may modulate the expression of renal disease in patients with systemic lupus erythematosus (SLE). We aimed to determine whether this polymorphism confers risk for the development of lupus nephritis and SLE in general.

METHODS

A meta-analysis was performed based on the Medline and Embase databases (last update, August 2002), perusal of abstracts from major meetings (1999 to 2001), assessment of bibliographies of pertinent articles, and additional data gathered after contact with primary investigators.

RESULTS

A total of 16 comparisons from 11 studies involving V/F158 genotyping of 1154 patients with lupus nephritis, 1261 SLE patients without nephritis, and 1455 disease-free controls were included. Comparison of lupus nephritis patients with non-nephritis SLE subjects revealed a significant overrepresentation of the low-binding F158 allele among patients who developed renal disease [odds ratio (OR) 1.20, 95% confidence interval (95% CI) 1.06 to 1.36, P = 0.003)], without significant between-study heterogeneity. FF homozygotes had the highest risk of renal disease as compared to VV homozygotes (OR 1.47, 95% CI 1.11 to 1.93, P = 0.006). It was uncertain whether the F158 allele influenced susceptibility to SLE per se (OR 1.19, 95% CI 0.99 to 1.43, P = 0.063 for SLE patients without nephritis versus disease-free controls; 0.01 < P < 0.10 for heterogeneity) and the observed trend for an association was driven mostly by the smaller studies (P = 0.058 for publication bias). No such bias was detected for analyses on susceptibility to lupus nephritis.

CONCLUSION

The Fc gamma RIIIA-V/F158 polymorphism has a significant impact on the development of lupus nephritis.

Distribution of variant genotypes of Fc gamma receptor IIIa in healthy Chinese population of Zhengzhou City

To investigate the distribution of variant genotypes of Fc gamma receptor IIIa (Fc gamma R IIIa) in healthy Chinese population of Zhengzhou city, genomic DNA was extracted from peripheral blood of healthy donators. The genotypes of Fc gamma R IIIa-158 were determined by nested polymerase chain reaction (PCR) in 137 healthy people in Zhengzhou city. The results showed that frequencies of variant genotypes FF, VV and VF were 42.3%, 48.9% and 8.8% respectively. The distribution of Fc gamma R IIIa-158 in healthy Chinese population of Zhengzhou city was polymorphic and different from that of African Americans (AA) and Caucasian Americans (CA).

FcgammaRIII expression on cultured human keratinocytes and upregulation by interferon-gamma

Keratinocytes of human epidermis are actively involved in inflammatory and autoimmune reactions of the skin and interact with resident or infiltrating immunocompetent cells via cytokines, chemokines, and intercellular adhesion mechanisms. Most immunocompetent cells have been reported to express Fcgamma receptors (FcgammaR), which are important for immunoregulatory functions. In this study we investigate FcgammaRIII expression on cultured human keratinocytes and upregulation by interferon-gamma. By real-time polymerase chain reaction, we show basal mRNA expression of both subclasses FcgammaRIIIA and FcgammaRIIIB, but after interferon-gamma treatment mRNA of FcgammaRIIIA and FcgammaRIIIB is increased 4.4 and 6.5 times, respectively. FcgammaRIII protein expression and its increase after interferon-gamma treatment were shown on cultured human keratinocytes by indirect immunofluorescence. In immunoblotting experiments, a bonified anti-CD16 antibody revealed reactivity to a polypeptide of 50-65 kDa on lysates of treated and untreated keratinocytes. In summary, we demonstrate expression of mRNA specific for the FcgammaRIIIA and FcgammaRIIIB subclasses and their upregulation by interferon-gamma on human keratinocytes in vitro, and confirm FcgammaRIII protein expression by indirect immunofluorescence and by immunoblotting experiments.

Fcgamma receptor gene polymorphisms in Japanese patients with systemic lupus erythematosus: contribution of FCGR2B to genetic susceptibility

OBJECTIVE

Human low-affinity Fcgamma receptors (FcgammaR) constitute a clustered gene family located on chromosome 1q23, that consists of FcgammaRIIA, IIB, IIC, IIIA, and IIIB genes. FcgammaRIIB is unique in its ability to transmit inhibitory signals, and recent animal studies demonstrated a role for FcgammaRIIB deficiency in the development of autoimmunity. Genetic variants of FcgammaRIIA, IIIA, and IIIB and their association with systemic lupus erythematosus (SLE) have been extensively studied in various populations, but the results were inconsistent. To examine the possibility that another susceptibility gene of primary significance exists within the FcgammaR region, we screened for polymorphisms of the human FCGR2B gene, and examined whether these polymorphisms are associated with SLE.

METHODS

Variation screening of FCGR2B was performed by direct sequencing and polymerase chain reaction (PCR)-single-strand conformation polymorphism methods using complementary DNA samples. Genotyping of the detected polymorphism was done using genomic DNA, with a specific genotyping system based on nested PCR and hybridization probing. Association with SLE was analyzed in 193 Japanese patients with SLE and 303 healthy individuals. In addition, the same groups of patients and controls were genotyped for the previously known polymorphisms of FCGR2A, FCGR3A, and FCGR3B.

RESULTS

We detected a single-nucleotide polymorphism in FCGR2B, (c.695T>C), coding for a nonsynonymous substitution, Ile232Thr (I232T), within the transmembrane domain. The frequency of the 232T/T genotype was significantly increased in SLE patients compared with healthy individuals. When the same patients and controls were also genotyped for FCGR2A-131R/H, FCGR3A-176V/F, and FCGR3B-NA1/2 polymorphisms, FCGR3A-176F/F showed significant association. Two-locus analyses suggested that both FCGR2B and FCGR3A may contribute to SLE susceptibility, while the previously reported association of FCGR3B was considered to be secondary and derived from strong linkage disequilibrium with FCGR2B.

CONCLUSION

These results demonstrate the association of a new polymorphism of FCGR2B (I232T) with susceptibility to SLE in the Japanese.

Patterns of low-affinity immunoglobulin receptor polymorphisms in stroke and homozygous sickle cell disease

Symptomatic stroke is a major complication of homozygous sickle cell (SS) disease, with a prevalence of approximately 10%. An elevated peripheral leukocyte count has been identified as a risk factor for hemorrhagic stroke in adults with SS disease. It has been observed that sickle cells coated with immunoglobulin have increased adherence to endothelial cells or phagocytes, possibly via binding to the low-affinity Fcgamma receptors. Common polymorphisms have been described in three low-affinity receptors: FCGR2A, FCGR3A, and FCGR3B; each has been shown to alter biological function, and each has also been associated with disease susceptibility. On the basis of this information, we evaluated common genetic variants of the low-affinity Fcgamma receptors for an association with symptomatic stroke in SS disease in a pilot case-control study of 51 Jamaican adult SS disease stroke cases and 51 SS disease-matched controls. Comparison of allelic distributions between cases and controls at 3 loci, FCGR2A (P = 0.39), FCGR3A (P = 0.67), FCGR3B (P = 0.35), failed to demonstrate a significant association. In a separate analysis, the FCGR2A/FCGR3A two-locus combination does not appear to segregate randomly (P(COR) = 0.0053), suggesting that these two loci could be linked in this population. We conclude that polymorphisms of the low-affinity Fcgamma receptors are not associated with stroke in SS disease.

Therapeutic activity of humanized anti-CD20 monoclonal antibody and polymorphism in IgG Fc receptor FcgammaRIIIa gene

Given that the FcgammaRIIIa receptor 158V allotype displays a higher affinity for human immunoglobulin G1 and increased antibody-dependent cellular cytotoxicity, the aim of this study was to determine the influence of that FCGR3A polymorphism on the therapeutic response to rituximab, an anti-CD20 humanized immunoglobulin G1 increasingly used in the treatment of non-Hodgkin lymphomas. The FCGR3A-158V/F genotype was determined in 49 patients having received rituximab for a previously untreated follicular non-Hodgkin lymphoma. The clinical response and the disappearance of the BCL2-JH gene rearrangement in both peripheral blood and bone marrow were evaluated at 2 months (M2) and at 1 year (M12). The study population consisted of 20% FCGR3A-158V homozygous patients, 35% FCGR3A-158F homozygous patients, and 45% heterozygous patients (FCGR3A-158F carriers). The objective response rates at M2 and M12 were 100% and 90%, respectively, in FCGR3A-158V homozygous patients compared with 67% (P =.03) and 51% (P =.03), respectively, in FCGR3A-158F carriers. A disappearance of the BCL2-JH gene rearrangement in both peripheral blood and marrow was observed at M12 in 5 of 6 of homozygous FCGR3A-158V patients compared with 5 of 17 of FCGR3A-158F carriers (P =.03). The homozygous FCGR3A-158V genotype was confirmed to be the single parameter associated with clinical and molecular responses by multivariate analysis. This study showed an association between the FCGR3A genotype and clinical and molecular responses to rituximab. This finding will certainly give rise to new pharmacogenetic approaches to the management of patients with non-Hodgkin lymphomas.

Granulocyte function disorders: aspects of development, genetics and management

The field of phagocytic disorders has attained major biologic and clinical significance in the past 40 years. The development of exciting new techniques in molecular biology and the cellular physiology of signal transduction have made it possible to identify the genetic defects involved in many of these disorders. Moreover through immunopharmacologic intervention, bone marrow or peripheral or cord blood stem cell transplantation along with the prospect of gene therapy, we have begun attempts to at least partially correct genetic defects in cell development and activation pathways in the entire spectrum of phagocyte disorders. Carrier detection and prenatal diagnosis employing with chain reaction techniques or direct nucleotide sequencing in fetal blood have made these diseases potentially preventable or treatable in utero or shortly after birth.

Human receptors for immunoglobulin G: key elements in the pathogenesis of rheumatic disease

The structural diversity of Fc gammaR provides a mechanism by which IgG can elicit a broad range of cell responses. Fc gammaR vary in their affinity for IgG, their preference for IgG subclasses, the cell types in which they are expressed, and the intracellular signals which they elicit--stimulatory or inhibitory. Expansion in our knowledge of structure-function relationships among Fc gammaR has identified them as heritable risk factors for disease susceptibility and valuable targets for therapeutic modulation of the immune system.

Variant genotypes of FcγRIIIA influence the development of Kaposi's sarcoma in HIV-infected men

Disturbances in inflammatory cytokine production and immune regulation coupled with human herpesvirus-8 (HHV-8) infection underlie the current understanding of the pathogenesis of Kaposi's sarcoma (KS), the most common HIV-associated malignancy. The low affinity Fc gamma receptors (FcγR) for IgG link humoral and cellular immunity by mediating interaction between antibodies and effector cells, such as phagocytes and natural killer cells. We examined the frequency of polymorphic forms of the low affinityFcγRs, FcγRIIA,FcγRIIIA, and FcγRIIIB in 2 cohorts of HIV-infected men with KS and found that theFcγRIIIA genotype exerts a significant influence on susceptibility to or protection from KS. The FF genotype was underrepresented in patients with KS, whereas the VF genotype was associated with development of KS. A similar association was observed between FcγRIIIA genotypes and HHV-8 seropositivity. These observations suggest a possible role forFcγRIIIA in the development of KS during HIV infection.

Variant genotypes of FcγRIIIA influence the development of Kaposi's sarcoma in HIV-infected men

Disturbances in inflammatory cytokine production and immune regulation coupled with human herpesvirus-8 (HHV-8) infection underlie the current understanding of the pathogenesis of Kaposi's sarcoma (KS), the most common HIV-associated malignancy. The low affinity Fc gamma receptors (FcγR) for IgG link humoral and cellular immunity by mediating interaction between antibodies and effector cells, such as phagocytes and natural killer cells. We examined the frequency of polymorphic forms of the low affinityFcγRs, FcγRIIA,FcγRIIIA, and FcγRIIIB in 2 cohorts of HIV-infected men with KS and found that theFcγRIIIA genotype exerts a significant influence on susceptibility to or protection from KS. The FF genotype was underrepresented in patients with KS, whereas the VF genotype was associated with development of KS. A similar association was observed between FcγRIIIA genotypes and HHV-8 seropositivity. These observations suggest a possible role forFcγRIIIA in the development of KS during HIV infection.

Bovine FcgammaRIII with a single extracellular domain

The full length of gene encoding Fc receptor types III for bovine immunoglobulin G (boFcgammaRIII, CD16) was obtained with PCR from the c DNA library of bovine alveolar macrophages. Through molecular cloning and sequencing it is shown that the coding gene has 507 bp and codes for 168 amino acids. There are signal peptide, transmembrane spanning domain and three potential N-linked glycosylation sites in the sequence. Compared with the boFcgammaRIII cDNA sequence cloned by Collins et al, it deletes 82 amino acids and has only one extracellular domain. It is suggested that this cDNA fragment is a special form of the gene structure of bovine FcgammaRIIIA (CD16-II).

The IgG Fc receptor, FcgammaRIIB, is a target for deregulation by chromosomal translocation in malignant lymphoma

Rearrangement of chromosomal bands 1q21-23 is one of the most frequent chromosomal aberrations observed in hematological malignancy. The genes affected by these rearrangements remain poorly characterized. Typically, 1q21-23 rearrangements arise during tumor evolution and accompany disease-specific chromosomal rearrangements such as t(14;18) (BCL2) and t(8;14) (MYC), where they are thus thought to play an important role in tumor progression. The pathogenetic basis of this 1q21-23-associated disease progression is currently unknown. In this setting, we surveyed our series of follicular lymphoma for evidence of recurring 1q21-23 breaks and identified three cases in which a t(14;18)(q32;q21) was accompanied by a novel balanced t(1;22)(q22;q11). Molecular cloning of the t(1;22) in a cell line (B593) derived from one of these cases and detailed fluorescent in situ hybridization mapping in the two remaining cases identified the FCGR2B gene, which encodes the immunoreceptor tyrosine-based inhibition motif-bearing IgG Fc receptor, FcgammaRIIB, as the target gene of the t(1;22)(q22;q11). We demonstrate deregulation of FCGR2B leading to hyperexpression of FcgammaRIIb2 as the principal consequence of the t(1;22). This is evidence that IgG Fc receptors can be targets for deregulation through chromosomal translocation in lymphoma. It suggests that dysregulation of FCGR2B may play a role in tumor progression in follicular lymphoma.

Mining variations in genes of innate and phagocytic immunity: current status and future prospects

The large number of sequence variations in human genes reflects the diversity of human populations and the response to prior environmental and pathogen challenges. Currently, major efforts are under way to identify and catalog single-nucleotide polymorphisms for use in genetic studies designed to explore the contribution of common variants to both disease susceptibility and interindividual differences in outcomes. So far, the most productive approach has been to search with candidate genes for which there is a scientific rationale (eg, prior data on the biologic implications of one or more variant alleles). Recently, there has been an explosion in the number of genetic association studies seeking to correlate one or more well-defined outcomes with variant alleles. These studies provide a foundation for identifying and applying genetic risk factors to clinical medicine. However, a number of challenges must be met before widespread use in clinical medicine can be undertaken. These include more efficient bioinformatics, basic insights into the significance of the variant alleles, ethical issues, and the availability of cost-effective, high-throughput platforms for genotype analysis.

Variant Genotypes of the Low-Affinity Fcγ Receptors in Two Control Populations and a Review of Low-Affinity Fcγ Receptor Polymorphisms in Control and Disease Populations

Fcγ-receptors (FcγR) provide a critical link between humoral and cellular immunity. The genes of the low-affinity receptors for IgG and their isoforms, namely, FcγRIIa, FcγRIIb, FcγRIIIa, FcγRIIIb, and SH-FcγRIIIb, are located in close proximity on chromosome 1q22. Variant alleles may differ in biologic activity and a number of studies have reported the frequencies of variant FcγR alleles in both disease and control populations. No large study has evaluated the possibility of a nonrandom distribution of variant genotypes. We analyzed 395 normal individuals (172 African Americans [AA] and 223 Caucasians [CA]) at the following loci: FcγRIIa, FcγRIIIa, and FcγRIIIb, including the SH-FcγRIIIb. The genotypic distributions of FcγRIIa, FcγRIIIa, and FcγRIIIb conform to the Hardy-Weinberg law in each group. There was no strong evidence that combinations of 2-locus genotypes of the 3 loci deviated from random distributions in these healthy control populations. The distribution of SH-FcγRIIIb is underrepresented in CA compared with AA (P &lt; .0001) controls. A previously reported variant FcγRIIb was not detected in 70 normal individuals, indicating that this allele, if it exists, is very rare (&lt;1%). In conclusion, we present data that should serve as the foundation for the interpretation of association studies involving multiple variant alleles of the low-affinity FcγR.

Variant Genotypes of the Low-Affinity Fcγ Receptors in Two Control Populations and a Review of Low-Affinity Fcγ Receptor Polymorphisms in Control and Disease Populations

Fcγ-receptors (FcγR) provide a critical link between humoral and cellular immunity. The genes of the low-affinity receptors for IgG and their isoforms, namely, FcγRIIa, FcγRIIb, FcγRIIIa, FcγRIIIb, and SH-FcγRIIIb, are located in close proximity on chromosome 1q22. Variant alleles may differ in biologic activity and a number of studies have reported the frequencies of variant FcγR alleles in both disease and control populations. No large study has evaluated the possibility of a nonrandom distribution of variant genotypes. We analyzed 395 normal individuals (172 African Americans [AA] and 223 Caucasians [CA]) at the following loci: FcγRIIa, FcγRIIIa, and FcγRIIIb, including the SH-FcγRIIIb. The genotypic distributions of FcγRIIa, FcγRIIIa, and FcγRIIIb conform to the Hardy-Weinberg law in each group. There was no strong evidence that combinations of 2-locus genotypes of the 3 loci deviated from random distributions in these healthy control populations. The distribution of SH-FcγRIIIb is underrepresented in CA compared with AA (P < .0001) controls. A previously reported variant FcγRIIb was not detected in 70 normal individuals, indicating that this allele, if it exists, is very rare (<1%). In conclusion, we present data that should serve as the foundation for the interpretation of association studies involving multiple variant alleles of the low-affinity FcγR.

Soluble CD16 in the treatment of murine lupus nephritis

To determine if soluble CD16 (sCD16) could alter the expression of lupus-like disease, groups of 10 female NZB/NZW mice (age 16-20 weeks) were given sCD16 three times a week for 5 weeks (control; 100 microg; 200 microg/dose) after onset of proteinuria. Results of this study indicate that the administration of sCD16 after onset of disease lowered anti-DNA levels, delayed the development of proteinuria, and significantly prolonged survival while the mice were on treatment. These results indicate that sCD16 alters the expression of autoantibodies and the progression of renal disease in NZB/NZW mice, suggesting that therapies directed at Fc receptors may be useful in the treatment of SLE.

Serum IgG2 level, Gm(23) allotype and FcgammaRIIa and FcgammaRIIIb receptors in refractory periodontal disease

The purpose of this investigation was to compare the levels of serum IgG2, the frequency of detection of Gm(23)-negative allotype and frequency of detection of FcgammaRIIa and FcgammaRIIIb receptor haplotypes in 32 refractory, 54 successfully treated and 27 periodontally healthy individuals. Refractory subjects showed mean full mouth attachment loss and/or >3 sites with attachment loss >2.5 mm within 1 year after both scaling and root planing, and surgery plus systemically administered tetracycline. Successfully treated subjects showed mean attachment level gain and no sites with attachment loss >2.5 mm 1 year post-therapy. Periodontally healthy subjects exhibited no pocket depth or attachment level >3 mm, and no evidence of progressing disease during 1 year of monitoring. Blood was obtained from each subject at baseline. Serum IgG2 and Gm(23) allotype were determined using radial immunodiffusion. DNA was extracted from whole blood and the FcgammaR genotypes determined using PCR and allele specific oligonucleotide probes. Significance of differences among clinical groups were sought using the Kruskal-Wallis or chi-square tests. Associations between 2 or more variables were tested using regression analysis. Refractory subjects exhibited higher mean attachment loss and pocket depth than successfully treated or periodontally healthy subjects. Smoking status did not differ significantly among groups. No significant differences in serum IgG2 levels and frequency of detection of Gm(23)-negative allotype were observed among the clinical groups. Serum IgG2 level was positively associated with the number of serum antibody responses to subgingival species (r=0.51, p<0.001). Subjects with the Gm(23)-negative allotype exhibited lower mean levels of serum IgG2 (3.06+/-0.3 versus 3.9+/-0.2, p<0.01) and mean number of serum antibodies to subgingival species (17.7+/-1.7 versus 23.3+/-1.4, p<0.05) than allotype positive individuals. No significant differences in FcgammaR haplotype distribution were observed among the 3 clinical groups. Associations of serum IgG2 level, Gm(23) allotype, FcgammaRIIa and FcgammaRIIIb receptor haplotypes and smoking status were weakly related or not related to clinical status. This lack of relationship may have been due to a reality of no relationship, or the inadvertent pooling of subjects where these factors were of primary importance with subjects in whom these factors played a less important role.

FcγRIIIB Gene Duplication: Evidence for Presence and Expression of Three Distinct FcγRIIIB Genes in NA(1+,2+)SH(+) Individuals

Recently, a new alloantigen on IgG Fc receptor type IIIb (FcγRIIIb), SH, was described (Bux et al, Blood 89:1027, 1997). We identified three healthy individuals whose neutrophils reacted positively with the SH antiserum. The neutrophil antigen (NA) phenotype of all three donors was NA(1+,2+). Analysis of genomic DNA showed that the three donors were positive for the described SH-encoding mutation in the NA2-FcγRIIIB gene, 266C→A. However, NA(1,2) genotyping and nucleotide sequencing of an NA2-specific fragment amplified from the genomic DNA fragment showed that these individuals carried three FcγRIIIBgenes, namely, NA1-FcγRIIIB, NA2-FcγRIIIB, andSH-FcγRIIIB, encoding NA1-FcγRIIIb, NA2-FcγRIIIb, and SH-FcγRIIIb, respectively. Southern blot analysis confirmed these findings. Furthermore, all three transcripts were isolated from neutrophil mRNA. To investigate whether the presence of threeFcγRIIIB genes resulted in a higher membrane expression of FcγRIIIb, we measured the reactivity of neutrophils from NA(1+,2+)SH(+) individuals with a panel of CD16 monoclonal antibodies (MoAbs) in comparison with neutrophils from NA(1+,2+)SH(−) controls. Reactivity of four different anti–pan-FcγRIII MoAbs and NA2-specific MoAb GRM1 was higher with SH(+) neutrophils compared with controls, whereas that of NA1-specific MoAbs was similar, which is in concordance with the results from the genomic analysis. We observed that reactivity with NA2-specific CD16 MoAb PEN1 was sixfold higher in SH(+) individuals compared with controls. Apparently, the 60Ala→Asp substitution in SH-FcγRIIIb influences the epitope recognized by PEN1. In conclusion, we identified three NA(1+,2+)SH(+) individuals carrying three FcγRIIIB genes and observed a clear gene-dosage effect on the level of expression of neutrophil FcγRIIIb.

FcγRIIIB Gene Duplication: Evidence for Presence and Expression of Three Distinct FcγRIIIB Genes in NA(1+,2+)SH(+) Individuals

Recently, a new alloantigen on IgG Fc receptor type IIIb (FcγRIIIb), SH, was described (Bux et al, Blood 89:1027, 1997). We identified three healthy individuals whose neutrophils reacted positively with the SH antiserum. The neutrophil antigen (NA) phenotype of all three donors was NA(1+,2+). Analysis of genomic DNA showed that the three donors were positive for the described SH-encoding mutation in the NA2-FcγRIIIB gene, 266C→A. However, NA(1,2) genotyping and nucleotide sequencing of an NA2-specific fragment amplified from the genomic DNA fragment showed that these individuals carried three FcγRIIIBgenes, namely, NA1-FcγRIIIB, NA2-FcγRIIIB, andSH-FcγRIIIB, encoding NA1-FcγRIIIb, NA2-FcγRIIIb, and SH-FcγRIIIb, respectively. Southern blot analysis confirmed these findings. Furthermore, all three transcripts were isolated from neutrophil mRNA. To investigate whether the presence of threeFcγRIIIB genes resulted in a higher membrane expression of FcγRIIIb, we measured the reactivity of neutrophils from NA(1+,2+)SH(+) individuals with a panel of CD16 monoclonal antibodies (MoAbs) in comparison with neutrophils from NA(1+,2+)SH(−) controls. Reactivity of four different anti–pan-FcγRIII MoAbs and NA2-specific MoAb GRM1 was higher with SH(+) neutrophils compared with controls, whereas that of NA1-specific MoAbs was similar, which is in concordance with the results from the genomic analysis. We observed that reactivity with NA2-specific CD16 MoAb PEN1 was sixfold higher in SH(+) individuals compared with controls. Apparently, the 60Ala→Asp substitution in SH-FcγRIIIb influences the epitope recognized by PEN1. In conclusion, we identified three NA(1+,2+)SH(+) individuals carrying three FcγRIIIB genes and observed a clear gene-dosage effect on the level of expression of neutrophil FcγRIIIb.

Saliva: a convenient source of DNA for analysis of bi-allelic polymorphisms of Fc gamma receptor IIA (CD32) and Fc gamma receptor IIIB (CD16)

Genetic polymorphisms of low-affinity IgG Fc receptors (Fc gamma R) have been found to influence binding of human IgG subclass antibodies, and may influence susceptibility to certain types of infectious and autoimmune diseases. Phenotypic and/or genotypic analyses of Fc gamma R polymorphisms have traditionally employed peripheral venous blood as a source of leukocytes or genomic DNA, respectively. The present study was undertaken to determine whether human salivary DNA is a suitable alternative to DNA extracted from blood for genetic analysis of FC gamma R allelic polymorphisms. Genomic DNA was extracted from whole saliva of 69 healthy adult volunteers using a commercial DNA purification kit. The average quantity of genomic DNA isolated per ml of saliva was 19.2 +/- 14.1 micrograms. To assess intrasubject variation in yield of salivary DNA, ten saliva samples were collected from a single donor over a 3-month period. The average yield of DNA recovered from these samples was 25.2 +/- 13.7 micrograms. Volumes of saliva as small as 100 microliters, as well as saliva samples stored at -70 degrees C for prolonged periods (up to 6 years), provided DNA in amounts sufficient for PCR-based genetic analysis. Two comparative PCR assays were performed using DNA extracted from both peripheral blood and saliva from a number of individuals. The assays were able to detect a single nucleotide substitution (G-->A) in the Fc gamma RIIA gene, as well as two codominant alleles encoding the NA polymorphism in Fc gamma RIIIB, respectively. Furthermore, Fc gamma RIIA and Fc gamma RIIIB genotype results were confirmed by quantitative flow cytometry using specific monoclonal antibodies. Complete concordance was achieved between the typing results of our salivary DNA, and blood DNA-based assays. Therefore, saliva appears to be an excellent source of DNA for studies of Fc gamma RIIA and Fc gamma RIIIB polymorphisms.

A novel polymorphism of FcgammaRIIIa (CD16) alters receptor function and predisposes to autoimmune disease

A novel polymorphism in the extracellular domain 2 (EC2) of FcgammaRIIIA affects ligand binding by natural killer (NK) cells and monocytes from genotyped homozygous normal donors independently of receptor expression. The nonconservative T to G substitution at nucleotide 559 predicts a change of phenylalanine (F) to valine (V) at amino acid position 176. Compared with F/F homozygotes, FcgammaRIIIa expressed on NK cells and monocytes in V/V homozygotes bound more IgG1 and IgG3 despite identical levels of receptor expression. In response to a standard aggregated human IgG stimulus, FcgammaRIIIa engagement on NK cells from V/V (high-binding) homozygotes led to a larger rise in [Ca2+]i, a greater level of NK cell activation, and a more rapid induction of activation-induced cell death (by apoptosis). Investigation of an independently phenotyped normal cohort revealed that all donors with a low binding phenotype are F/F homozygotes, while all phenotypic high binding donors have at least one V allele. Initial analysis of 200 patients with SLE indicates a strong association of the low binding phenotype with disease, especially in patients with nephritis who have an underrepresentation of the homozygous high binding phenotype. Thus, the FcgammaRIIIa polymorphism at residue 176 appears to impact directly on human biology, an effect which may extend beyond autoimmune disease characterized by immune complexes to host defense mechanisms.

Mapping of bovine FcgammaR (FCGR) genes by sperm typing allows extended use of human map information

Polymorphic sites within the bovine FcgammaRI (FCGR1), FcgammaRII (FCGR2), and FcgammaRIII (FCGR3) genes were used for proximal mapping of these genes to bovine Chromosome (Chr) 3 (BTA3) with paternal half-sib families from Norwegian Cattle. A fine-structure genetic map of the region was obtained by the analysis of 288 sperm cells from three bulls that were heterozygous for the loci included in the study. No recombinants were observed between FCGR2 and FCGR3 (242 sperm cells). Considering FCGR2 and FCGR3 as a single locus, a three-point linkage analysis for [FCGR2/FCGR3], FCGR1, and INRA003 was carried out. The best-supported order of the loci was found to be INRA003-FCGR1-[FCGR2/FCGR3]. Map distances in a two-point linkage analysis were 10.3 cM between [FCGR2/FCGR3] and FCGR1, and 25.5 cM between FCGR1 and INRA003, respectively. This linkage mapping of the bovine FCGR gene family resembles the human situation where all FCGR genes are located at Chr 1 (HSA1), at position q21-q24. Moreover, the results locate the evolutionary breakpoint between HSA1q and BTA3 within the human 1q24 region.

Separate promoters from proximal and medial control regions contribute to the natural killer cell-specific transcription of the human FcgammaRIII-A (CD16-A) receptor gene

The molecular events governing the differentiation pathway of natural killer (NK) cells are not well understood. The phenotype of mature NK cells is specified by the expression of the low affinity Fc receptor for IgG (human FcgammaRIII, CD16) encoded by the FcgammaRIII-A gene. Here we report that the Pprox promoter (-198/-10) of FcgammaRIII-A stimulated by its own intron enhancer (+10/+712) was only one of the cis-elements that target the expression of a reporter gene in the immature NK cell line, YT. The transcription start sites of the FcgammaRIII-A a2/3 and a5/6 splice alternatives in NK cells were mapped to the medial -1817/-850 FcgammaRIII-A control region. Two promoters, Pmed1 (-942/-850) and Pmed2 (-1376/-1123) resided in this region and controlled for the initiation of these transcript classes encoding the known FcgammaRIII-A receptor protein. Deletion mapping studies demonstrated that the 93 base pairs -942/-850 Pmed1 sequence was sufficient to confer cell type-specific expression in YT cells. The 5' end of Pmed1 (-942 to -921) was required for full promoter function indicating the presence of an important sequence motif recognized by a YT-specific factor. Our data suggest that this motif might be a useful tool for subsequent identification of putative transcription factors uniquely active in YT and NK cells.

CD45 modulates phosphorylation of both autophosphorylation and negative regulatory tyrosines of Lyn in B cells

CD45 is a tyrosine phosphatase that is required for normal B cell receptor (BCR)-mediated signaling. It has been shown that Src-family tyrosine kinases such as Lyn could be a potential substrate for CD45. In vitro studies indicate that activities of Src family tyrosine kinases are regulated by tyrosine phosphorylation; C-terminal phosphorylation is inhibitory, and autophosphorylation is stimulatory. We report here that both autophosphorylation and C-terminal negative regulatory tyrosines of Lyn were hyperphosphorylated in CD45-deficient DT40 B cells. In this mutant cell, BCR-induced protein-tyrosine phosphorylation and calcium mobilization were severely compromised, as seen in Lyn-deficient cells. Consistent with this observation, Lyn activation upon receptor ligation was profoundly decreased in CD45-deficient cells. Taken together, our results suggest that dephosphorylation of tyrosine residues at both autophosphorylation and negative regulatory sites is mediated by CD45 in vivo, and that dephosphorylation of C-terminal tyrosine is a prerequisite for participation of Lyn in BCR signaling.

Natural Killer (NK) cell deficiency associated with an epitope-deficient Fc receptor type IIIA (CD16-II)

Susceptibility to herpes virus infections has been described in experimental animals depleted of NK cells and in patients with defective NK cell function. We have identified a child with recurrent infections, especially with herpes simplex virus, who had a decreased number of CD56(+)CD3(-) NK cells in circulation. Her NK cells expressed an altered form of the Fc receptor for IgG type IIIA (Fc gamma RIIIA or CD16-II) which was not reactive with the anti-CD16-II MoAb B73.1. Sequence analysis revealed the patient to be homozygous for a T to A substitution at position 230 of CD16-II cDNA, predicting a Leu(66) to His(66) change in the first immunoglobulin domain of CD16-II at the B73.1 recognition site. Spontaneous NK cell activity of the patient's peripheral blood mononuclear cells (PBMC) was markedly decreased, while antibody-dependent cellular cytotoxicity (ADCC) was unaffected. These results suggest that this child suffers from a defect affecting the development and function of NK cells, resulting in NK cytopenia and clinically significant immunodeficiency. The role of the CD16-II mutant in the pathogenesis of the patient's NK cell deficiency is discussed.

The IgG binding site of human FcgammaRIIIB receptor involves CC' and FG loops of the membrane-proximal domain

Fc gamma receptors for the Fc part of IgG are the mediators for antibody effector functions. FcgammaRIII and FcgammaRII are low affinity receptors that, through the interaction with immune complexes, initiate a variety of immunological responses, such as phagocytosis, antibody-dependent cellular cytotoxicity, and release of inflammatory mediators. We set out to define the IgG binding site on human FcgammaRIII. We assumed that potential beta-turns in Ig-like domains are the most probable determinants for ligand binding, and chimeric FcgammaRIIIB/FcepsilonRI receptors as well as single residue mutants were constructed in these regions of FcgammaRIIIB. Substitution of four amino acids in the membrane-proximal domain (Gln126, Arg156, Lys162, Val164) resulted in decreased binding of human IgG1. Lys162 and Val164 were found also to be crucial for the interaction with the IgG-binding inhibitory monoclonal antibody 3G8. In a putative three-dimensional model constructed in this study, these residues map on the CC loop (Gln126), on F beta-sheet (Arg156), and on the FG loop (Lys162, Val164). Our data are consistent with the study about human FcgammaRII (Hulett, M. D., Witort, E., Brinkworth, R. I., McKenzie, I. F. C., and Hogarth, P. M. (1994) J. Biol. Chem. 269, 15287-15293), suggesting that common structural determinants, i.e. FG loop or the GFC surface of the membrane-proximal domain, can be involved in interactions with IgG by both low affinity receptor classes FcgammaRII and FcgammaRIII.

Defining a similarity threshold for a functional protein sequence pattern: the signal peptide cleavage site

When preparing data sets of amino acid or nucleotide sequences it is necessary to exclude redundant or homologous sequences in order to avoid overestimating the predictive performance of an algorithm. For some time methods for doing this have been available in the area of protein structure prediction. We have developed a similar procedure based on pair-wise alignments for sequences with functional sites. We show how a correlation coefficient between sequence similarity and functional homology can be used to compare the efficiency of different similarity measures and choose a nonarbitrary threshold value for excluding redundant sequences. The impact of the choice of scoring matrix used in the alignments is examined. We demonstrate that the parameter determining the quality of the correlation is the relative entropy of the matrix, rather than the assumed (PAM or identity) substitution mode. Results are presented for the case of prediction of cleavage sites in signal peptides. By inspection of the false positives, several errors in the database were found. The procedure presented may be used as a general outline for finding a problem-specific similarity measure and threshold value for analysis of other functional amino acid or nucleotide sequence patterns.

Fine mapping of the human pentraxin gene region on chromosome 1q23

The 1q21 to 25 region of human chromosome 1 contains genes which encode proteins with immune- and inflammation-associated functions. These include the pentraxin genes, for C-reactive protein (CRP), serum amyloid P (SAP) protein (APCS),a nd a CRP pseudogene (CRPP1). The region of chromosome 1 containing this cluster is syntenic with distal mouse chromosome 1. We constructed an approximately 1.4 megabase yeast artificial chromosome (YAC) contig with the pentraxin genes at its core. This four-YAC contig includes other genes with immune functions including the FCER1A gene, which encodes the alpha-subunit of the IgE high-affinity Fc receptor and the IFI-16 gene, an interferon-gamma-induced gene. In addition, it contains the histone H3F2 and H4F2 genes and the gene for erythroid alpha-spectrin (SPTA1). The gene order is cen.-SPTA1-H4F2-H3F2-IFI-16-CRP-CRPP1-APCS -FCER1A- tel. The contig thus consists of a cluster of genes whose products either have immunological importance, bind DNA, or both.

Molecular cloning of a novel myeloid granule protein

Granulocytes are recognized by the presence of granules, including primary (azurophilic) and secondary types. Each granule type contains distinct and characteristic families of enzymes. We have screened a murine bone marrow cDNA library to obtain a series of sequences corresponding to mRNAs which are both myeloid-specific and appear to be expressed only in immature bone marrow cells. A 1,160 bp sequence (B9) has been isolated, which shows restricted expression in murine bone marrow, with the highest levels in cultures enriched for promyelocytes. Translation yields a single open reading frame of 167 amino acids and a calculated MW of 19.33 kd. A single potential N-glycosylation site is present. Evaluation of the amino terminal sequence shows 2 polar amino acids flanking a hydrophobic region, suggesting a signal sequence and the possibility of post-translational modification. An extensive search of the protein data base reveals 30% identity over 90 amino acids with porcine cathelin, a cystatin-like cysteine proteinase inhibitor. This sequence identity includes conservation of the 4 cysteine residues noted in all members of the cystatin superfamily. In an attempt to further characterize this novel sequence, a polyclonal antiserum was prepared by immunization with a 20 amino acid synthetic peptide corresponding to a unique portion of the carboxy terminus. Immunoelectron microscopy localized B9 to neutrophilic granules. We have identified a novel myeloid-specific granule protein related to porcine cathelin, but showing important structural differences. This may represent the first isolated member of a new cystatin family. More importantly, the small size of the B9 gene and its tight pattern of early expression make B9 an excellent reporter molecule for the study of new factors important in myeloid differentiation.

Abnormal neutrophil phenotype and neutrophil FcRIII deficiency corrected by bone marrow transplantation

BACKGROUND

Neutrophils from a patient in first remission of acute myeloid leukemia were found to lack NA1 and NA2 alloantigens. This NA null phenotype was converted to the normal phenotype of NA1, NB2 by the transplantation of bone marrow from an HLA-identical sibling. To investigate the inherited or acquired nature of this rare phenotype, a combination of conventional neutrophil serology and recently developed restriction fragment length polymorphism (RFLP) and polymerase chain reaction (PCR) assays was used.

STUDY DESIGN AND METHODS

Diagnosis, remission, and posttransplant patient peripheral blood samples were used for neutrophil phenotyping by granulocyte agglutination and immunofluorescence tests. The presence and dose of the gene for neutrophil Fc gamma RIIIb (Fc gamma RIIIB) were tested for with RFLP and Southern analysis and PCR-based RFLP tests. Plasma levels of circulating soluble Fc gamma RIII (sFc gamma RIII) were measured with radioimmunoassay. The sibling bone marrow donor and the patient's parents were also studied.

RESULTS

RFLP analysis of DNA obtained from the patient at the time of diagnosis showed that she lacked the Fc gamma RIIIB gene for neutrophil Fc gamma RIII (i.e., Fc gamma RIIIb), but that, in DNA prepared from posttransplant samples, the Fc gamma RIIIB gene was present. Quantitation of plasma levels of soluble FcRIII (sFcRIII) demonstrated a complete absence of sFcRIII in the patient's pretransplant plasma. However, 20 units of sFcRIII were detected in the patient's plasma by 160 days after graft. Hair samples from the patient provided sufficient nonhematopoietic, genomic DNA to confirm that her genotype was NA0NA0. DNA prepared from lymphocytes of both parents and the sibling marrow donor was used to quantitate their Fc gamma RIIIB gene dose. The mother and brother had only one Fc gamma RIIIB gene each, while the father apparently had a normal complement of two Fc gamma RIIIB genes.

CONCLUSION

In this case, an inherited absence of Fc gamma RIIIB gene in a patient with acute myeloid leukemia was unintentionally corrected by the transplantation of bone marrow from a sibling donor who himself carried only one Fc gamma RIIIB gene.