Some theoretical considerations regarding the effects of steric hindrance and intrinsic global coupling on the flexibility of Fc-anchored immunoglobulins

Nanosecond fluorescence depolarization studies reported in the accompanying companion paper showed that the long rotational correlation time, phi L, increased somewhat when rabbit IgG anti-dansyl antibodies were anchored in staphylococcal protein A (SpA) soluble complexes. The increases in phi L upon anchoring IgG probably resulted from "global coupling" effects caused by: increased steric hindrance of the antibody segments in the SpA complexes and intrinsic structural constraints already present in the monomeric IgG. Global coupling results from a restriction in the angular range of a flexible segment and is manifest when flexible motions alone cannot depolarize all of the fluorescence, so that the slower global tumbling of the entire particle is also required. Such effects cannot be resolved directly from experimental anisotropy data, however, because only a single long correlation time, phi L, is well defined over the limited time range of most fluorophores. In this paper, estimates of the anisotropy contributions from flexible and global motions of the IgG-SpA complexes are determined by contrasting theoretical and measured decays. For this analysis it was assumed that each of the experimental phi L-values is a weighted composite of the rotational correlation time associated with the less restricted flexible motions of the Fab arms, phi F, and the correlation time associated with global tumbling of the entire particle, phi G. A general two-exponential expression was used to relate phi F and phi G to phi L. This approach was meaningful because phi G-values of the various SpA complexes had been calculated from hydrodynamic measurements. The theoretical decays clearly show that, even if phi G is much longer than phi F, these two rotational motions still cannot be resolved over the experimentally accessible time range. Families of emission anisotropy decay curves for IgG antibodies with different amounts of intrinsic global coupling and for anchored antibodies with different amounts of steric hindrance were simulated by varying the preexponential weighting factors of the flexible and global terms. By comparing the calculated curves with the measured decays, it is evident that the rabbit IgG anti-dansyl antibodies do not have much intrinsic global coupling, but rather they are highly flexible. The curves also indicate that even for the exceptionally compact IgG4-SpA2 17-S complex, which showed the most steric hindrance in electron micrographs, the appropriate phi G weighting factor is only 0.28. Thus, as supposed earlier, the anchored antibodies exhibit considerable segmental flexibility. In closing, the above concepts are used to examine the results of     

Use of enzyme-linked immunosorbent assay to detect antibodies to staphylococcal protein A in the rabbit

An ELISA technique is described which employs both solid phase and labelled free SpA. The technique allows the detection of anti-SpA antibodies in the rabbit. It is not suited for the same purpose with human sera, because human immunoglobulins are not saturated by non-specific interaction with solid phase SpA.     

A critical study of the use of staphylococci containing protein A for separation of IgG and IgM antibodies

This study was to determine the best conditions for using staphylococci bearing protein A to separate IgG from IgM. The validity of the technique was evaluated for detection of IgM with antimicrobial activity and for typing monoclonal IgM. The results indicate that separation of IgG and IgM is not entirely satisfactory in normal sera and worse in hyperglobulinemic sera. The detection and titration of IgM antimicrobial antibodies (rubella and hepatitis B core (HBc) specific IgM) was unreliable because IgG was only partially absorbed by staphylococcal cells, while a significant portion of IgM was bound. The use of higher concentrations of staphylococci did not improve the results because the more IgG was absorbed, the more IgM was also bound. It is shown that with anti-HBc specific IgM the risk of misinterpretation is very high with a sensitive radioimmunoassay technique allowing detection of trace amounts of nonabsorbed IgG. In contrast staphylococcal protein A proved useful in typing monoclonal IgM.     

Binding of immunoglobulins to protein A and immunoglobulin levels in mammalian sera

The use of protein A from S. aureus (SpA) as an anti-IgG reagent in immunological techniques has extended in recent years, together with knowledge about its interaction with immunoglobulins of different species. Current data with respect to the binding of protein A to immunoglobulins and to the levels of immunoglobulins in the sera of some mammalian species are reviewed.     

母体IgG对N-甲基-D-天冬氨酸诱导乳鼠痉挛发作模型的作用及其对脑FOS蛋白的影响

目的探讨母体IgG对N-甲基-D-天冬氨酸（NMDA）诱导Wistar乳鼠痉挛发作模型抗痉挛的作用机制及其对脑内FOS蛋白的影响。方法从母鼠取血后提取γ球蛋白,采用离子交换法（DEAE-52）提纯大鼠母体IgG。将30只Wistar乳鼠随机分为3组：对照组（n=6）,NMDA组（n=12）和母体IgG组（n=12）。母体IgG组生后第11天起,于8：00时连续给予皮下注射所提取的各自母体IgG10mg·kg^-1·d^-1,所有注射剂量均稀释至5mL。对照组和NMDA组同时同部位注射等剂量生理盐水。NMDA组和母体IgG组生后第15天在分别注射生理盐水和母体IgG1h后,给予腹腔注射NMDA15mg·kg^-1·d^-1,诱发大鼠痉挛发作,制作Wishar乳鼠痉挛发作模型。对照组则在皮下注射生理盐水1h后腹腔注射生理盐水15mL·kg^-1。观察比较NMDA组和母体IgG组痉挛发作情况,采用免疫组化法观察各组乳鼠脑神经细胞FOS蛋白阳性细胞的表达数量。结果①对照组始终未出现临床症状。NMDA组抱团样发作总次数较母体IgG组明显增多（336次vs109次,P〈0.05）;NMDA组致症状评分为5.67分,母体IgG组为3.53分,差异有统计学意义（P=0.012）。母体IgG组抱团样发作潜伏期≥40min的比例为80%,NMDA组为32%,差异有统计学意义（P=0.022）。②NMDA组FOS蛋白阳性细胞呈弥漫性分布,其中以皮质、梨状皮质、海马和丘脑表达最多,染色深,其中皮质Ⅰ-Ⅴ均可见大量的FOS蛋白阳性细胞。母体IgG组FOS蛋白阳性细胞在以上各个脑区表达普遍减低。结论NMDA组FOS蛋白阳性细胞呈弥漫性分布、色深,其表达是对损伤刺激的早期反应,乳鼠痉挛发作模型FOS蛋白表达和NMDA受体分布部位基本一致。皮质、丘脑和海马、梨状皮质等边缘系统可能是NMDA诱导痉挛发作的主要结构。母体IgG具有抗痉挛作用,并可脑内使FOS蛋白表达降低。     

Immunogenicity and effector functions of glutaraldehyde-treated rabbit and mouse immunoglobulin G

Rabbit and mouse IgG treated with glutaraldehyde (GA) were immunogenic in homologous species. Glutaraldehyde treatment induced in the IgG molecule two types of antigenic determinants. One of them was found on the monomeric fraction of GA-treated rabbit IgG (haptenic determinant) and the other on the polymeric fraction (structural determinant). The haptenic determinants were found also on monoaldehyde-treated rabbit IgG and GA-treated Fab and Fc fragments. It was demonstrated that rabbit and mouse antibodies are specific for GA-treated IgG and have species specificity. While GA treatment did not alter the antigen binding capacity of rabbit IgG antibody, its effector functions (except protein A binding) were much affected. Thus it was found that GA treatment enhances IgG ability to react with rheumatoid factor, reduces drastically its capacity to activate the complement system, abolishes the cytophilic properties of IgG and accelerates its catabolic rate. The possible blocking effect of GA on the amino acid residues (mainly Lys) situated in or very close to the effector sites of the IgG molecule is suggested.     

Increased central adiposity is associated with pro-inflammatory immunoglobulin G N-glycans

Background

Increased body fat may be associated with an increased risk of developing an underlying pro-inflammatory state, thus leading to greater risk of developing certain chronic conditions. Immunoglobulin G has the ability to exert both anti- and pro-inflammatory effects, and the N-glycosylation of the fragment crystallisable portion is involved in mediating this process. Body mass index, a rudimentary yet gold standard indication for body fat, has been shown to be associated with agalactosylated immunoglobulin G N-glycans.

Mutual inhibition of the binding of Clq and protein A to rabbit IgG immune complexes

A complex of rabbit IgG antibody with horseradish peroxidase covalently linked to Sepharose 4B was used as an insoluble immune complex for studying the binding of complement factor C1q protein A from Staphylococcus aureus, and its IgG-binding fragments AB and B, to rabbit IgG. It was shown that protein A (mol. wt approx. 42,000) and fragments AB and B (mol. wts approx. 14,000 and 7000, respectively) inhibited the binding of C1q to insoluble immune complex at 4 degrees C. However, at 37 degrees C fragment B did not inhibit this binding. On the other hand, C1q, when bound to an insoluble immune complex, almost completely blocked the binding of protein A and fragment B at both temps. The higher affinity of C1q for its CH2-binding site than of fragment B for its CH2-binding site may explain the displacement of the latter from the CH2 domain. The mutual inhibition of the binding of C1q and protein A (and its smaller fragments) indicates that the binding sites for C1q and protein A are closely located in the CH2 domain.     

Correlation between the structure of IgG and its Fc-fragment and their ability to interact with staphylococcal protein A

Interaction between 7S monomers of rabbit IgG, dimers of molecules of this protein, IgG with disulfide bond ruptured in the hinge region of the molecule, and various fragments of IgG molecules, on the one hand, and protein A ofStaphylococcus aureus, on the other hand, were investigated by the passive hemagglutination inhibition test. Only the Fc-fragment of the rabbit IgG molecule obtained with papain was shown to bind protein A. Activity of the Fc-fragment on a molar basis was shown to be only one-sixth of that of native IgG. After repair of the disulfide bond between the chains in the hinge region of the IgG molecule, its ability to bind protein A was reduced by two-thirds. The binding activity of IgG was increased on a molar basis twelvefold as a result of its spontaneous dimerization. It is concluded from the results that the structural organization of the Fc-fragment of the IgG molecule correlates with its ability to interact with protein A.Laboratory of Immunochemistry, N. F. Gamaleya Institute of Epidemiology and Microbiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR P. A. Vershilova.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 89, No. 3, pp. 318–320, March, 1980.     

Duration of clinical reactivity in cow's milk allergy is associated with levels of specific immunoglobulin G4 and immunoglobulin A antibodies to β‐lactoglobulin

Background The development of tolerance in IgE‐mediated allergies has been associated with lower cow's milk (CM)‐specific IgE levels, increasing levels of specific IgG4 and, more contestably, IgA. Objective We investigated whether specific antibody responses to CM proteins differ over time between patients who recovered from cow's milk allergy (CMA) by the age of 3 years and those who developed tolerance only after the age of 8 years. Methods The study population comprised of 83 patients with IgE‐mediated CMA. They belonged to a cohort of 6209 healthy, full‐term infants followed prospectively for the emergence of CMA. Serum samples were available at diagnosis (median age 7 months), 1 year later (median 19 months) and at follow‐up (median 8.5 years). Age‐matched control subjects with no history of CMA (n=76) participated in the follow‐up. Serum levels of IgE antibodies to CM were measured using UniCAP. Levels of IgA, IgG1 and IgG4 antibodies to β‐lactoglobulin and α‐casein were measured using ELISA. Results Patients with persistent CMA at the age of 8 years (n=18 at diagnosis, n=16 at later time‐points) had higher CM‐specific IgE levels at all three time‐points (P<0.001) compared with patients who became tolerant by 3 years (n=55 at diagnosis, n=54 a year later, n=40 at follow‐up). They had lower serum IgA levels to β‐lactoglobulin at diagnosis (P=0.01), and lower IgG4 levels to β‐lactoglobulin (P=0.04) and α‐casein (P=0.05) at follow‐up. Conclusion High CM‐specific IgE levels predict the persistence of CMA. Development of tolerance is associated with elevated levels of β‐lactoglobulin‐specific serum IgA at the time of diagnosis, and later increasing specific IgG4 levels to β‐lactoglobulin and α‐casein. Cite this as: E. M. Savilahti, K. M. Saarinen and E. Savilahti, Clinical & Experimental Allergy, 2010 (40) 251–256.     

High prevalence of the IVS 1 + 1 G to A/GJB2 mutation among Czech hearing impaired patients with monoallelic mutation in the coding region of GJB2

Biallelic pathogenic GJB2 gene mutations cause pre-lingual genetic hearing loss in up to 50% of individuals with bilateral sensorineural hearing loss worldwide. Sequencing of the entire GJB2 gene-coding region in Czech patients with pre-lingual bilateral hearing loss revealed that 10.3% of Czech patients carry only one monoallelic pathogenic mutation in the coding region of the GJB2 gene, which is significantly more than the population frequency of 3.4%. The 309-kb GJB6 deletion, frequent in Spain and France, is very rare in the Czech population. In order to evaluate the impact of the IVS1 + 1 G to A splice site mutation in the non-coding part of the GJB2 gene among Czech patients, we tested all available patients with pre-lingual hearing loss with only one monoallelic mutation in the coding part of GJB2. By sequencing of the exon 1 region of the GJB2 gene and HphI restriction analysis in 20 Czech patients we identified nine patients carrying IVS1 + 1 G to A. Testing for this mutation explained deafness in 45% of Czech GJB2 monoallelic patients. This mutation represents now 4% of GJB2 pathogenic mutations in Czech patients and is the third most common GJB2 mutation found in our cohort of 242 unrelated Czech patients with prelingual hearing loss. A similar frequency may also be expected in other Central European or Slavic populations.     

Interactions between Fab and Fc regions in liganded immunoglobulin G: A study employing the antigenic polymorphism and multivalency of the human red-cell membrane

Previous studies indicated that the inter-y chain disulphide bonds restrict segmental flexibility within the Fc region of human IgG; the present study suggests that there are also non-covalent hinge-region restrictions of flexibility in the liganded molecule. Staphylococcus aureas protein A-Sepharose-passed F(ab′)₂ fragments from IgG fractions of blood-group antisera were tested in parallel with the parent antibodies in haemagglutination tests. At molar-equivalence in protein, the titre of F(ab′)₂ from incomplete antibodies was 2- to 3-fold greater than the titre of the intact antibody (p < 0.001). Increased activity occurred whether enzyme or albumin techniques were used to convert the incomplete antibodies to agglutinins, and was particularly striking with Kell blood-group antibodies where F(ab′)₂ fragments were weak saline agglutinins. Antiglobulin tests, using anti-κ, revealed small differences in intrinsic antigenbinding activity between IgG and F(ab′)₂ fractions, but these differences were either of inverse relationship or insufficient to account for the increased agglutinating activity of F(ab′)₂ compared with the whole molecule. By contrast, with IgG saline agglutinins [anti-κ (anti-glycophorin A^M) and anti-B], the apparent freedom introduced by peptic removal of Fc, or by reduction of interchain disulphide bonds, was inimical to agglutination, as would be predicted from other studies (Hornick & Karush, 1972; Crothers & Metzger, 1972). These results show that the Fe region imposes limitations on full segmental flexibility of Fab regions in liganded IgG.A comparison of the intrinsic and functional antigen-binding activities of IgG anti-M and anti-B confirmed that both antibodies engage in substantial monogamous bivalency. That the relative monogamous bivalency of F(ab′)₂ and IgG anti-M was unaffected by an increased mean separation of M sites on the cell surface suggests that it is predominantly dimers of glycophorin a^M, in situ, which generate the monogamous bivalency and that, on M/N red cells, some glycophorin-A^M molecules are associated as homologous dimers. For IgG anti-A and anti-B, the known decreased affinity with A₂ and A₁B red cells can be explained by the fewer opportunities for monogamous bivalency. Using the increased flexibility in F(ab′)₂ and reduced-alkylated IgG anti-D as molecular probes for spatial relationships between D antigens, (i) a marked deviation from an average separation of antigens was found on normal red cells under conditions of agglutination, and (ii) an early effect of trypsin-treatment (< 2 min) which permits limited redistribution of D sites was detected.Mildly reduced IgG3 exhibited significantly greater flexibility than reduced IgG1, presumably reflecting the extended γ3 hinge region. Unreduced IgG3, however, did not show the increased Fab-region flexibility shown by F(ab′)₂ fragments on the IgG1 sub-class. In reduced IgG molecules, Cγ2 and Cγ3 domains retained much of their native surface topography.     

Measurements of the true affinity constant in solution of antigen-antibody complexes by enzyme-linked immunosorbent assay

A simple, general procedure is described for the determination of the dissociation constant (KD) of antigen-antibody equilibria in solution. First the monoclonal antibody is incubated in solution with the antigen until the equilibrium is reached; then the proportion of antibody which remains unsaturated at equilibrium is measured by a classical indirect ELISA. The experimental values of KD found by this ELISA procedure for 2 monoclonal antibodies are shown to be very close to those obtained by conventional methods (immunoprecipitation of the radiolabeled antigen, or fluorescence transfer). Moreover, it is shown that, provided the measurements are made under conditions where the total antigen concentration is in large excess over the total antibody concentration, the dissociation constant of antibody-antigen complexes can be determined even with crude preparations of monoclonal antibody. The sensitivity of the ELISA used permits the detection of very small concentrations of antibody and the determination of KD values as small as 10(-9) M. This method also offers the great advantage of dealing with unmodified molecules since no labeling of either the antigen or the antibody is required.     

A glycoprotein of molecular weight 85,000 on human cells of B-lineage: detection with a family of monoclonal antibodies

Immunization of BALB/c mice with glycoproteins purified from a detergent extract of human chronic lymphocytic leukemia (CLL) cells by affinity to Lens culinaris lectin led to the production of several monoclonal antibodies with similar reactivity. One of the antibodies, 50B4, was purified and the corresponding antigen was isolated from a B-lymphoblastoid cell line extract by affinity chromatography to the 50B4-IgG immunoadsorbent. Co-purification of the antigenic activities associated with five other monoclonal antibodies was achieved. Purified and radiolabelled 50B4 antigen could be specifically immunoprecipitated not only by 50B4 but also by the other five antibodies. SDS-PAGE analysis revealed that all antibodies precipitated the same component, a polypeptide chain of apparent mol. wt 85,000 under reducing conditions. Competitive-binding studies between the purified antibodies indicated the presence of two distinct epitopes on the antigen. The epitopes, each recognized by three different antibodies, were equally accessible on the cell surface of either a B-CLL (3 X 10(5) molecules/cell), a B-lymphoblastoid cell line (11 X 10(5) molecules/cell) or two acute lymphocytic leukemia (ALL) cell lines of pre-B phenotype (5 X 10(5) and 0.8 X 10(5) molecules/cell respectively). Although the antigens purified from the strongly positive ALL cell line gave a gel pattern identical to that of the B-lymphoblastoid cell line, the antigens purified from the B-CLL extract were resolved into two distinct glycosylated polypeptides of mol. wts 85,000 and 77,000 under reducing conditions. The distribution of the antigen(s) is not restricted to cells of the B-lineage as mature T-cells and a variety of non-hematopoietic cell types express both epitopes of the antigen(s).     

5-HT_(1A)受体蛋白在PC12细胞膜转运的动态变化

目的在神经元样PC12活细胞上进行实时、可视和定量研究5-羟色胺1A受体的时空分布、膜转运和信号传导机制。方法运用RT-PCR方法获得小鼠5-HT1A基因,并插入到pEGFP-N1真核表达载体中。采用阳离子脂质体方法将质粒转染至PC12细胞和HEK293细胞中,通过G418筛选出稳定表达5-HT1A-EGFP的PC12细胞系。运用激光共聚焦成像系统观察活细胞中5-HT1A-EGFP的表达情况,利用光漂白荧光恢复(FRAP)技术在PC12细胞膜局部漂白后观察5-HT1A-EGFP荧光蛋白在细胞膜上转运的情况。结果克隆所获得的小鼠5-HT1A基因是准确的。5-HT1A-EGFP蛋白清晰的分布于PC12和HKE293细胞膜上。通过FRAP技术观察到漂白区域的细胞膜在100s内有部分恢复,说明受体在细胞膜上发生转运。结论建立了稳定表达5-HT1A-EGFP融合蛋白的PC12细胞系,并利用活细胞成像和FRAP技术观察分析并证实了5-HT1A受体在PC12细胞的膜表面的表达和转运的动态变化。     

An enzyme immunoassay for the detection of staphylococcal protein A in affinity-purified products

Rabbit antiserum, specific for protein A from Staphylococcus aureus, was conjugated to alkaline phosphatase and used in a double antibody solid-phase enzyme immunoassay. The assay was developed to monitor eluate from a large-scale protein A-Sepharose affinity column used to purify monoclonal antibodies for human clinical trials. The assay detected soluble protein A in the presence of immunoglobulin at concentrations as low as 4 ng/ml. Analysis of the product purified by affinity chromatography revealed the presence of protein A at ng/ml concentrations. The assay developed here can provide a reliable and convenient method for detecting soluble protein A.