[125I]protein A: a tracer for general use in immunoassay

Facile Purification and Use of Tobamoviral Nanocarriers for Antibody-Mediated Display of a Two-Enzyme System

Immunosorbent turnip vein clearing virus (TVCV) particles displaying the IgG-binding domains D and E of Staphylococcus aureus protein A (PA) on every coat protein (CP) subunit (TVCVPA) were purified from plants via optimized and new protocols. The latter used polyethylene glycol (PEG) raw precipitates, from which virions were selectively re-solubilized in reverse PEG concentration gradients. This procedure improved the integrity of both TVCVPA and the wild-type subgroup 3 tobamovirus. TVCVPA could be loaded with more than 500 IgGs per virion, which mediated the immunocapture of fluorescent dyes, GFP, and active enzymes. Bi-enzyme ensembles of cooperating glucose oxidase and horseradish peroxidase were tethered together on the TVCVPA carriers via a single antibody type, with one enzyme conjugated chemically to its Fc region, and the other one bound as a target, yielding synthetic multi-enzyme complexes. In microtiter plates, the TVCVPA-displayed sugar-sensing system possessed a considerably increased reusability upon repeated testing, compared to the IgG-bound enzyme pair in the absence of the virus. A high coverage of the viral adapters was also achieved on Ta2O5 sensor chip surfaces coated with a polyelectrolyte interlayer, as a prerequisite for durable TVCVPA-assisted electrochemical biosensing via modularly IgG-assembled sensor enzymes.

Protein A superantigen: structure, engineering and molecular basis of antibody recognition

Staphylococcus aureus interacts with the human immune system through the production of secreted factors. Key among these is protein A, a B-cell superantigen capable of interacting with both antibody Fc and VH regions. Here, we review structural and molecular features of this important example of naturally occurring bacterial superantigens, as well as engineered variants and their application in biotechnology.

Western blotting: remembrance of things past

Western blotting sprung from the need to develop a sensitive visual assay for the antigen specificity of monoclonal antibodies. The technique employed SDS-PAGE of protein antigens, electrophoretic replica transfer of gel-resolved proteins to unmodified nitrocellulose sheets, probing the immobilized antigens with hybridomas, and detection of antibody-antigen complexes with radiolabeled staphylococcal protein A and autoradiography. The simplicity and relevance of the method have led to its expansive application as an immunodiagnostic and a ubiquitous research tool in biology and medicine.

The gene for staphylococcal protein A

Protein A from Staphylococcus aureus has become an important tool in immunology and molecular biology due to its specific binding to the constant region of immunoglobulins (Igs) from most mammalian species(1). Many qualitative and quantitative techniques have been developed which take advantage of this 'pseudo-immune' reaction(2). In addition, solid state protein A has recently been introduced in medical therapy to decrease the amount of circulating immune complexes in sera(3). In this article Mathias Uhlén, Martin Lindberg and Lennart Philipson describe the structure of the protein A molecule and its gene. They also discuss the possibilities for fusing the protein A gene to other genes.

Western blotting : remembrance of past things

Western blotting sprung from the need to develop a sensitive visual assay for the antigen specificity of monoclonal antibodies. The technique employed SDS-PAGE of protein antigens, electrophoretic replica transfer of gel-resolved proteins to unmodified nitrocellulose sheets, probing the immobilized antigens with hybridomas, and detection of antibody-antigen complexes with radiolabeled staphylococcal protein A and autoradiography. The simplicity and relevance of the method has led to its expansive application as an immunodiagnostic and a ubiquitous research tool in biology and medicine.

A genome level survey of Burkholderia pseudomallei immunome expressed during human infection

Burkholderia pseudomallei is the etiological agent of melioidosis, a severe infectious disease of humans and animals. The role of the bacterium's proteins expressed in vivo during human melioidosis continues to remain an enigma. This study's aim was to identify B. pseudomallei target proteins that elicit the humoral immune response in infected humans. A small insert genomic expression library was constructed and immunoscreened to identify peptides that reacted exclusively with melioidosis patients' sera. Sero-positive clones expressing immunogenic peptides were sequenced and annotated, and shown to represent 109 proteins involved in bacterial cell envelope biogenesis, cell motility and secretion, transcription, amino acid, ion and protein metabolism, energy production, DNA repair and unknown hypothetical proteins. Western blot analysis of three randomly selected full-length immunogenic polypeptides with patients' sera verified the findings of the immunome screening. The patients' humoral immune response to the 109 proteins suggests the induction or significant upregulation of these proteins in vivo during human infection and thus may play a role in the pathogenesis of B. pseudomallei. Identification of B. pseudomallei immunogens has shed new light on the elucidation of the bacterium's pathogenesis mechanism and disease severity. These immunogens can be further evaluated as prophylactic and serodiagnostic candidates as well as drug targets.

Use of protein chip mass spectrometry to monitor biotinylation reactions

Surface-enhanced laser desorption/ionization time-of-flight analysis was used to monitor both the kinetics and heterogeneity of product formation during the biotinylation of a number of model proteins and peptide targets. The selected molecules were the IgG-binding protein, protein A, human serum albumin, and a synthetic peptide corresponding to the N terminus of a streptococcal M1 protein. The extent of biotinylation was determined by kinetic analysis of the shift in molecular mass from the native material. Each residue modified by reaction with N-hydroxysuccinimide biotin resulted in an addition of approximately 341 amu to the native protein or polypeptide. The novelty of the method was in the ability to determine the molecular mass shift, without first separating the targeted molecule from the biotinylating reagent. The analysis was rapid, simple, and provided information on the average number of biotin molecules added and the homogeneity of the resulting product.

Demonstration of labeless detection of food pathogens using electrochemical redox probe and screen printed gold electrodes

The demonstration of a labeless immunosensor for the detection of pathogenic bacteria using screen printed gold electrodes (SPGEs) and a potassium hexacyanoferrate(II) redox probe is reported. Gold electrodes were produced using screen printing and the gold surfaces were modified by a thiol based self assembled monolayer (SAM) to facilitate antibody immobilisation. SAMs based on the use of thioctic acid (TA), mercaptopropionic acid (MPA) and mercaptoundecanoic acid (MUA) were evaluated. Following antibody immobilisation via the optimum SAM, the redox behaviour and diffusion co-efficient (D) of the potassium hexacyanoferrate(II) probe was monitored in the absence and presence of analyte. In the presence of analyte, a change in the apparent diffusion co-efficient of the redox probe was observed, attributable to impedance of the diffusion of redox electrons to the electrode surface due to the formation of the antibody-bacteria immunocomplex. No change in the diffusion co-efficient was observed when a non-specific antibody (mouse IgG) was immobilised and antigen added. The system has been demonstrated with Listeria monocytogenes and Bacillus cereus.

Presentation of antigen in immune complexes is boosted by soluble bacterial immunoglobulin binding proteins

Using a snake toxin as a proteic antigen (Ag), two murine toxin-specific monoclonal antibodies (mAbs), splenocytes, and two murine Ag-specific T cell hybridomas, we showed that soluble protein A (SpA) from Staphylococcus aureus and protein G from Streptococcus subspecies, two Ig binding proteins (IBPs), not only abolish the capacity of the mAbs to decrease Ag presentation but also increase Ag presentation 20-100-fold. Five lines of evidence suggest that this phenomenon results from binding of an IBP-Ab-Ag complex to B cells possessing IBP receptors. First, we showed that SpA is likely to boost presentation of a free mAb, suggesting that the IBP-boosted presentation of an Ag in an immune complex results from the binding of IBP to the mAb. Second, FACS analyses showed that an Ag-Ab complex is preferentially targeted by SpA to a subpopulation of splenocytes mainly composed of B cells. Third, SpA-dependent boosted presentation of an Ag-Ab complex is further enhanced when splenocytes are enriched in cells containing SpA receptors. Fourth, the boosting effect largely diminishes when splenocytes are depleted of cells containing SpA receptors. Fifth, the boosting effect occurs only when IBP simultaneously contains a Fab and an Fc binding site. Altogether, our data suggest that soluble IBPs can bridge immune complexes to APCs containing IBP receptors, raising the possibility that during an infection process by bacteria secreting these IBPs, Ag-specific T cells may activate IBP receptor-containing B cells by a mechanism of intermolecular help, thus leading to a nonspecific immune response.

Receptins: a novel term for an expanding spectrum of natural and engineered microbial proteins with binding properties for mammalian proteins

A new term 'receptin', derived from recipere (lat.), is proposed to denote microbial binding proteins that interact with mammalian target proteins. An example of such a 'receptin' is staphyloccocal protein A which binds to the Fc part of many mammalian immunoglobulins. Several other types of 'receptins' are listed. This term may easily be distinguished from the similar term 'receptor', describing a binding site on a cell surface, mostly eukaryotic, where a secondary effect is induced inside the cell upon binding to a ligand. A receptin, however, does not necessarily have to induce a secondary event. Receptins include so called MSCRAMMs, adhesins, and also engineered receptins, affibodies, and engineered ligands. It denotes any protein of microbial origin, cell-bound or soluble, which can bind to a mammalian protein. It fulfills the need for an umbrella terminology for a large group of binding structures. In contrast, the term 'lectin' represents a group of proteins with affinity for carbohydrate structures. The new term 'receptin' includes a number of key microbial proteins involved in host-parasite interactions and in virulence. Some receptins are promising vaccine candidates.

Clearance properties of liposomes involving conjugated proteins for targeting

This review examines methods of protein conjugation onto liposomes and the effects of surface bound protein on the liposomes' biological behavior. It is evident that the presence of a conjugated protein significantly alters the attributes of targeted liposomes. Specifically, protein conjugation can result in dramatic increases in liposome size, enhanced immunogenicity, and increased plasma elimination. Techniques are discussed for preventing some of the physical (size) and biological (immunogenic) alterations involving the use of PEG-lipids and drug loaded liposomes. In addition, the advantages of conjugating antibodies via carbohydrate moieties, to minimize changes in antibody binding and tertiary structure as well as effectively decreasing plasma elimination, are also discussed. It is, however, apparent that the accessibility of targeted liposomes to extravascular sites is a key step that will require further study and it is, therefore, anticipated that with the development of novel ligands and novel ligand-liposome interactions, the therapeutic utility of targeting strategies will likely be realized.

Purification of mouse antibodies and Fab fragments

Although monoclonal antibodies can have different properties, it should still be possible to purify any antibody to homogeneity. Often, by utilizing these differences, the purification procedure can be improved. All of the methods discussed are fairly simple and fast. With 1 week of work, over 50 mg of purified antibody can be realized. These methods can also yield material of sufficient quality for structural studies.

Direct time-resolved fluoroimmunoassay of estriol in serum

A rapid, direct, solid-phase, time-resolved fluoroimmunoassay for free estriol in serum, using Europium-chelate-protein A as a label, is described. The coefficient of correlation with the results of RIA was 0.983.

Isolation and partial characterization of a type IV bacterial immunoglobulin binding protein

A series of bovine G streptococcal isolates were screened for expression of type IV Fc binding proteins. An isolate expressing high levels of type IV binding proteins was selected and expanded by use of a colony selection technique. A variety of different extraction procedures were compared and the optimal solubilization procedure was found to be hot acid extraction of the bacteria. The extracted protein could be affinity purified on a column of immobilized rabbit IgG. The type IV Fc binding protein was found to be antigenically unrelated to the type I, II or III bacterial Fc binding proteins and displayed the lowest affinity and most limited range of species and subclass reactivity of any bacterial Fc binding protein thus far characterized.

Optimization of binding capacity and specificity of protein G on various solid matrices for immunoglobulins

Streptococcal protein G is a more versatile and efficient alternative to staphylococcal protein A in purifying immunoglobin G (IgG) isotypes from various animal species. Optimizations are most dramatic with goat IgG, which binds protein G 55 times better than protein A. Using GammaBind G (a recombinant form of protein G (Genex Corp.)), we optimized binding capacity and specificity for IgG. Protein G was covalently coupled to three different matrices (CNBr-Sepharose, Tresyl-Sepharose, and Affigel-10) and compared with protein A-CNBr-Sepharose. Equal volumes of human, mouse, and goat serum samples were equilibrated into Hepes/NaOH buffers with various ionic strengths (i.e., concentrations of NaCl) and pH values and allowed to bind to affinity columns of proteins G and A. Bound ligands were eluted with 8.0 M urea, 0.05-M Tris/HCl, pH 8.00. Bound fractions were assayed for protein concentration and analyzed by sodium dodecyl sulfate polyacrylamide electrophoresis. The optimal conditions for binding IgG to protein G are 1.0 M NaCl and pH 8.0 for human, mouse, and goat.

One- and two-step non-competitive avidin-biotin immunoassays for monomeric and heterodimeric antigen

In this study of one-step and two different two-step non-competitive avidin-biotin assays (NABAs) were developed for the measurement of a monomeric antigen (lactoferrin, LF) using polyclonal antibodies and the detection of a heterodimeric antigen (lutropin. LH) using monoclonal antibodies. The assays were based on the use of performed complexes of biotinylated antibody and avidin-peroxidase conjugate. The detection limits and intra-assay CVs of the one- and two-step NABAs were 0.1-0.5 mg/ml and 2.6-5.1% for LF, and 0.1-0.2 IU/l and 2.3-3.7% for LH, respectively. The working range was 1-100 ng/ml for the LF assay and 1-100 IU/l for the LH assay. A linear relationship with high correlation coefficients (0.979-0.992 for LF-NABAs: 0.949-0.990 for LH-NABAs) and good agreement was observed between the one- and two-step assays and the corresponding three-step NABAs used as reference methods. However, under stringent conditions the one-step assay for heterodimeric antigen was found to be sensitive to interference. The results indicate that it is possible to perform the multistep NABAs using convenient one- and two-step protocols. The one- and two-step assays also retained the advantages of the avidin-biotin system: rapidity and good sensitivity.

Time-resolved fluoroimmunoassay of progesterone in milk

A direct, solid-phase, time-resolved fluoroimmunoassay for progesterone in cow's and goat's milk, using europium-chelate-protein A as a label, is described. The coefficients of correlation with the results by RIA were 0.987 and 0.989.

Immunological applications of type III Fc binding proteins. Comparison of different sources of protein G

Protein G, a type III bacterial IgG Fc receptor isolated from certain group C or G streptococci, shows a wider range of species and subclass immunoglobulin reactivity than staphylococcal protein A and has been shown to be more useful than protein A for many immunochemical applications. Recently, two forms of wild type protein G and three forms of recombinant protein G have become commercially available. Each form of protein G was tested for reactivity with a variety of species of immunoglobulin and albumin. Additionally, one form of wild type protein G and two forms of the recombinant protein G were examined for their ability to stimulate in vitro proliferation of human peripheral blood leukocytes (PBL). Similar IgG species reactivity was observed for all forms of unlabeled protein G. By contrast, considerable variability in the relative IgG binding potentials of different protein G preparations was observed following radioiodination. Binding to human serum albumin was observed with one of the wild type protein G samples, however, the IgG binding activity of this protein was not affected by the presence of excess human serum albumin. In the human PBL proliferation assays, wild type protein G was weakly mitogenic and one form of recombinant protein G was shown to be a potent mitogen, while another form of recombinant protein G displayed no mitogenic potential. Differences in both functional and biological reactivities were observed among the various sources of protein G. These differences may lead to confusion if investigators consider all sources of protein G as a single entity with common properties.

Idiotype-anti-idiotype hapten immunoassays: assay for cotinine

Practical application of the idiotype-anti-idiotype reaction to hapten immunoassays has been demonstrated with cotinine as an example. The assay relies on the ability of cotinine, a major nicotine metabolite, to inhibit binding between a monoclonal anti-cotinine antibody (the idiotype) and a second monoclonal antibody (the anti-idiotype) specific for the antigen combining region on the idiotype. A solid phase enzyme-linked immunoadsorbent assay (ELISA) format was adopted in which fluid phase anti-cotinine and cotinine present either as a standard or in a test sample were incubated in microtiter plate wells coated with F(ab')2 fragments of the anti-idiotype. Horseradish peroxidase-labeled protein A and o-phenylenediamine were used to detect idiotype-anti-idiotype binding. Under optimal assay conditions, 0.9 ng cotinine inhibited immune binding by 50% and as little as 0.04 ng could be detected. In contrast, nearly 70 times more trans-3'-hydroxycotinine, a major urinary metabolite, and over 1000-fold more nicotine were required for 50% inhibition. Several other metabolites and structurally related compounds also were poor competitors. Assay reliability was good over a range of cotinine concentrations from 5 to 500 ng/ml saliva with intraassay coefficients of variation between 6 and 10% and interassay values between 6 and 13%. Also, there was a strong correlation (R2 = 0.994) between the cotinine levels found in saliva from 35 cigarette smokers with the idiotype-anti-idiotype assay and a cotinine-anti-cotinine ELISA. Because only monoclonal antibodies and antigen are required, the idiotype-anti-idiotype immunoassay offers a high degree of standardization without the need to prepare labeled hapten derivatives or macromolecular conjugates for solid phase assays.

Binding of immunoglobulin G and albumin to Streptococcus dysgalactiae

All 24 cultures of Streptococcus dysgalactiae investigated bound 125I-IgG, 13 cultures additionally interacted with 125I-albumin. Inhibition experiments with unlabelled IgG and albumin preparations from humans and various animal species indicated the specificity of the binding sites which showed characteristics of IgG Fc-receptors of type III and albumin-receptors of type c. IgG and albumin-binding proteins could be removed from the streptococcal surface by solubilization and subsequently isolated by affinity chromatography. The isolated binding proteins of S. dysgalactiae strains C 12 and C 8 obtained from IgG and albumin sepharose precipitated with IgG in immunodiffusion reactions, and in immunoelectrophoretic studies, and they reacted, after transfer onto nitrocellulose, with 125I-IgG or 125I-albumin and vice versa. Antisera produced against IgG-binding proteins of S. dysgalactiae C 12 inhibited binding of 125I-IgG and 125I-albumin. Solubilization of binding proteins by trypsinization yielded low molecular weight fragments with 125I-IgG but not with 125I-albumin binding activities. IgG-binding proteins isolated from S. dysgalactiae C 26 reacted with 125I-IgG but not with 125I-albumin, indicating the presence of 2 groups of type III Fc-receptors among S. dysgalactiae strains.

Evaluation of time-resolved fluoroimmunoassay with Eu-labelled protein-A for serum progesterone

Progesterone has been assayed in several serum samples by a time-resolved fluoroimmunoassay (TR-FIA). The solid phase was 11 alpha-hydroxyprogesterone hemisuccinate bound covalently to ovalbumin and adsorbed on wells of polystyrene. The assay was based on competitive reaction of solid phase-bound hormone and samples with specific antibody labelled in situ with protein-A prelabelled with europium. The bound Eu was dissociated from the solid phase by an enhancement solution and measured by time-resolved fluorometry. The coefficient of correlation between TR-FIA and RIA was 0.97.

Immunometric assay for lutropin (hLH) based on the use of universal reagents for enzymatic labelling and magnetic separation and monitored by enhanced chemiluminescence

A solid-phase immunometric assay of human lutropin (hLH) is described. Two different anti-hLH antibodies were utilized as capture antibodies, and anti-IgG antibodies covalently coupled to magnetic particles and horseradish peroxidase, respectively, served as 'universal' detection reagents. An anti-hLH antibody raised in rabbits was incubated with a goat anti-rabbit IgG covalently bound to magnetic particles. The resulting complex was added to a separately incubated mixture of hLH and monoclonal anti-hLH antibody. Following incubation, the immunocomplex was sedimented in a magnetic field and the supernatant discarded. Finally a sheep anti-mouse antibody (F(ab')2 fragment) conjugated to horseradish peroxidase as label was added. Following a further incubation, the particles were sedimented in the magnetic field and washed. The hLH content of the sample was quantitated by measuring 'enhanced chemiluminescence'. The sensitivity of the assay was 2.5 +/- 0.9 IU/l (mean +/- SD), the within-run variation ranged from 7.9 to 11%, the between-run variation from 12.9 to 19.8%. Cross-reaction with hFSH or hTSH could not be detected, but was approximately 0.1% with hCG. The results correlated well with those obtained by radioimmunoassay (r = 0.84).

A two-site immunoradiometric assay of proatrial natriuretic factor. Application to tissue extracts

A "two-site" immunoradiometric assay (IRMA) was developed to specifically measure ANF (1-126), the precursor of ANF. This assay is based on the simultaneous use of antibodies against two different antigenic determinants: murine monoclonal antibody (2H2), which recognizes positions 101 through 103 of ANF, is linked to Immunobeads and employed to extract any ANF C-terminal; a second antibody, which is directed against positions 11 through 37, is radioiodinated and allows binding to any C-terminal-2H2-Immunobead material which bears the N-terminal antigenic site. A curvilinear relationship was obtained between radioactivity and the amount of proANF (1.5 to 400 fmol) added. Optimisation of IRMA was determined by the amount of 2H2-Immunobeads and labeled antibody used, incubation time as well as possible interference by both ANF (99-126) and ANF (1-98). Tissue extracts were used to validate the assay. proANF was detected in decreasing amounts in heart atria, heart ventricles, lungs, kidneys and adrenal glands. Its presence was further confirmed by reverse-phase HPLC followed by radioimmunoassay. IRMA is a simple and rapid method for the direct measurement of proANF in tissue extracts and chromatographic fractions. The presence of proANF in tissues strongly suggests local synthesis.

Isolation and characterization of Fc receptors from Haemophilus somnus

Receptors that bind the Fc region of bovine immunoglobulin (Ig) have been isolated from the culture supernatant of Haemophilus somnus by chromatography on a Sepharose 4B column. One receptor with a relative molecular weight of 41,000 weakly binds both bovine IgG subclasses, IgA and IgM, while three high molecular weight receptors (350,000, 270,000, and 120,000) strongly bind bovine IgG2, IgA, and IgM. All four Fc receptors are antigenically related and the 41,000 receptor appears to be a subunit of the high molecular weight receptors. In addition to bovine Ig, the purified 270,000 Fc receptor strongly binds horse IgG, rabbit IgG, pig IgG, cat IgG, dog IgG, and sheep IgG. The receptor also reacts weakly with mouse, rat, chicken, human, and guinea pig IgG and does not bind goat IgG. Fc receptors from 19 H. somnus isolates were compared. Variations in the molecular weight of the 41,000 protein were demonstrated among preputial isolates from asymptomatic carriers, but all other isolates appeared to have identically migrating proteins.

Recognition of Mycoplasma arthritidis membrane antigens by rats and rabbits: comparison by immunoblotting and radioimmunoprecipitation

Sera from rats convalescing from infection with Mycoplasma arthritidis were tested for their ability to react with M. arthritidis membrane antigens by immunoblotting and radioimmunoprecipitation. The absence of metabolism-inhibition (MI) antibody activity in these sera suggested that rats might fail to recognize those membrane antigens involved in eliciting MI antibodies therefore rabbit antisera, which are strongly MI positive for M. arthritidis, were used for comparison. Antigenic recognition patterns of M. arthritidis surface and membrane antigens were not identical for rats and rabbits. The most striking and reproducible difference was the failure of rats to produce IgG antibodies against a surface antigen migrating in the 47,000-50,000 molecular weight range on SDS-polyacrylamide gels. However, rats recognized at least 2 antigens which we had previously shown to be "MI antigens", therefore the inability to express MI antibodies probably cannot be explained by their inability to recognize M. arthritidis "MI antigens".

Bronchial leukocyte proteinase inhibitor levels in bronchial washings in asthma patients

To evaluate whether epithelial damage of airways in asthma could be related to diminished levels of the low molecular weight bronchial leukocyte proteinase inhibitor (BLPI) in airways, we determined BLPI in bronchial washings of 13 asthma patients and 13 healthy subjects, using a sensitive enzyme-linked immunoassay. The patients had asthma due to western red cedar and had bronchial washings done 24 to 48 hours after a mild to moderate asthmatic reaction induced by inhalation challenge. We did not find significant differences in BLPI concentrations in lavage fluid of asthma patients and healthy control subjects. The ratios of BLPI to albumin levels in bronchial washings appeared to be lower among asthmatic patients, but this difference was mainly due to an increase in albumin levels in lavage fluid in asthma. In addition, there were no significant differences in BLPI levels in washings obtained from main and segmental bronchi in both control subjects and asthma patients.

Rapid protein A assay for intrinsic factor and its binding antibody

A simple and rapid method for the measurement of cobalamin bound intrinsic factor (Cbl-IF) complex and intrinsic factor binding antibody is described. The method is based on the principle of affinity chromatography and adapted to a batch separation technique. A specific ligand staphylococcal protein A was coupled to Sepharose to form a convenient solid phase matrix. The intrinsic factor binding antibody in patients with pernicious anaemia was used to form an immune complex with Cbl-IF. This complex was adsorbed on to staphylococcal protein A. Gastric juice from control subjects and patients with pernicious anaemia was assayed for intrinsic factor activity and the results correlated very closely with two other established methods. Sera from 30 control subjects were assayed for binding intrinsic factor antibody and all were found to be negative; of 15 patients with pernicious anaemia, six were positive. These patients were selected with blocking antibody. The method does not require technologically advanced protein separation techniques and could therefore be applied in any clinical laboratory using radioisotopes. It could also be adapted to assay cobalamin in body fluids or in food.

Enzyme-labeled type III bacterial Fc receptors. A versatile tracer for immunoassay

The type III bacterial Fc receptor isolated form a group C streptococcus has been conjugated to alkaline phosphatase and used as a tracer in a variety of direct and indirect immunoassays. These immunoassays have utilized specific antibodies prepared in species whose immunoglobulins are poorly reactive with the type I Fc receptor, staphylococcal protein A. The value of the type III Fc receptor as a tracer for immunoassays utilizing antibodies produced in sheep and goats is documented.

Polyclonal B-cell activation by influenza A/Texas virus-specific human T-cell clones

A previously described proliferating class-II-restricted CD4+ human T-cell clone (TA4) specific for the N2 neuraminidase of the influenza A/Texas virus was tested for its ability to induce B cells to polyclonal immunoglobulin (Ig) production. The data reported in the present study show that, when stimulated by T-depleted autologous peripheral blood mononuclear cells (E-) and A/T virus, the TA4 clone was able to induce B cells to polyclonal Ig production. This effect was also seen using another class II-restricted human T-cell clone specific for the H3 haemagglutinin of the A/Texas virus and autologous polyclonal T cells. This Ig production was MHC-restricted at the inductive level, i.e., the stimulating-virus-treated E- population and the clones or the T cells had to share the same HLA-DR determinants. However, the responding B cells could be allogeneic provided the helper T cells were activated in the presence of autologous irradiated virus-infected E- cells.

Correlation of antispermatozoal antibody with infertility in immunized female rabbits using 14C-protein A in a filter radioassay

The meaningful detection of antisperm antibody in immunologically infertile females has been confounded by the many methods of assay that exist. With many of these methods there is poor correlation of assay results with infertility. In this report, female rabbits were rendered partially or completely infertile by immunization with sperm fractions. A filter radioassay for antisperm antibody was developed that consists of incubating 10(7) sperm with sperm from immunized rabbits and 14C-Protein A, a long-lived and versatile indirect radiolabel for many antibodies of the IgG class. The spermatozoa are washed by rapid vacuum filtration on polycarbonate membrane filters instead of by time-consuming centrifugation. The filters with the collected spermatozoa are then counted in a liquid scintillation counter. Sera from female rabbits isoimmunized with sperm antigens show a highly significant correlation (r = -0.904; p less than 0.001) between assay results and infertility as measured by the percentage of eggs that underwent cleavage after artificial insemination.

Production of Brucella abortus-specific protein A-reactive antibodies (IgG2) in infected and vaccinated cattle

The IgG2 anti-Brucella antibody response of cattle to Brucella vaccination and infection was measured. Three groups of animals were studied; Group 1 contained 11 non-vaccinated cows, Group 2, 17 cows vaccinated with a low dose of Strain 19 vaccine and Group 3, 17 cows vaccinated with a high dose of Strain 19 vaccine. All animals were challenged at Week 33 with an infectious isolate of B. abortus (Strain 2308). Studies of the IgG2 antibodies response indicated an absolute correlation between anti-Brucella IgG2 levels and infection of the animal. All animals showing reciprocal titers of greater than or equal to 3000 (16 of 45 tested) were found to be positive for the challenge organism at slaughter. Animals with reciprocal IgG2 titers less than or equal to 1000 (29 of 45 tested) were found to be negative for the challenge organism at the time of slaughter. The predictive value of IgG2 antibody levels for infection held for animals in all three groups and consequently this suggests that monitoring of specific IgG2 anti-Brucella antibody levels may be of value in detection of Brucella-infected cattle.

A protein A-binding, polyethylene glycol precipitation-based immunoradiometric assay. Application to the detection of immune complexes and C3 in human sera and of private antigens in cross-reacting parasite extracts

An immunoradiometric assay, based on the precipitation of antigen-antibody complexes by polyethylene glycol (PEG) and on the subsequent binding of PEG-soluble radiolabelled staphylococcal protein A to the PEG-insoluble complexes, is described. The assay can be applied to the detection of naturally occurring, circulating immune complexes, and of complexes artificially created by mixing antigen and antibody solutions, which makes it of potential use for the detection of either antigen or antibody in several situations. Pre-treatment of the antibody-containing sera with 3% PEG greatly reduced the background values and increased the sensitivity of the assay. The assay was also applied to the detection and isolation of Leishmania donovani antigens that did not cross-react with antigens of the related parasite Trypanosoma cruzi (private antigens) and private antigens of insect-derived metacyclic trypomastigotes of T. cruzi in relation to culture-derived metacyclic trypomastigotes of T. cruzi. A simple and extremely effective procedure for washing precipitates with just one centrifugation is also described.

Antibodies to blood-brain barrier bind selectively to brain capillary endothelial lateral membranes and to a 46K protein

To begin elucidating the biochemical basis of the polarized membrane features of the blood-brain barrier (BBB), a series of immunochemical and immunoperoxidase studies were initiated with bovine brain microvessels that make up the BBB in vivo. A rabbit antiserum was prepared against isolated bovine brain BBB plasma membranes. The bovine microvessel plasma membranes were radioiodinated with chloramine-T, and the antiserum selectively immunoprecipitated a 46K protein. The antibodies directed against the 46K protein were quantitatively absorbed with bovine brain capillaries but not with rat kidney or liver powder. Only the capillaries of brain reacted with the rat kidney-absorbed antiserum in immunoperoxidase studies of ethanol-fixed, 8-micron sections of bovine brain cortex, whereas the capillaries in heart, liver, and kidney did not react. This antiserum also strongly illuminated the lateral membranes of isolated bovine brain capillary endothelial cells grown in primary tissue culture. These studies provide evidence for a polarized distribution of a surface antigen in bovine brain capillary endothelial cells that is not present in capillary endothelia of liver, heart, or kidney. The correlation of the immunoperoxidase and immunoprecipitation techniques suggests that a candidate for the asymmetrically distributed surface antigen in the BBB is the 46K protein. The relationship between the 46K protein and the composition of BBB tight junctions remains to be determined.

Anti-actin antibodies. Chemical modification allows the selective production of antibodies to the N-terminal region

The specific properties of sera elicited by various native, unfolded or chemically modified actins were compared to provide a means of obtaining high titres of antibodies directed against the N-terminal (1-39) or the central regions of the actin sequence. The antigenic structure of the N-terminal region of actin was analyzed. It has at least 2 discrete epitopes, one of which appears to be species-specific and is composed of the hydrophilic N-terminal heptapeptide sequence.

Use of chicken and rabbit antibodies in a solid phase protein A radioimmunossay for virus detection

A new rapid indirect solid phase radioimmunoassay was developed for the detection of Sindbis virus. Chicken antibodies were adsorbed onto wells in microplates to serve as 'capture antibodies' and rabbit antibodies were used as the second antibody. 125I-labelled protein A that does not bind to chicken antibodies, but binds firmly to rabbit antibodies was used as the tracer. All the steps necessary for the development of the assay are described. The minimal amount of Sindbis virus detectable was around 3 x 10(5) PFU/ml and the interassay reproducibility was about +/- 30%.

Immobilization of microorganisms for detection by solid-phase immunoassays

Several cultures of gram-negative and gram-positive bacteria were successfully immobilized with titanous hydroxide. The immobilization efficiency for the microorganisms investigated in saline and broth media ranged from 80.2 to 99.9%. The immobilization of salmonellae was effective over a wide pH range. The presence of buffers, particularly phosphate buffer, drastically reduced the immobilization rate. However, buffers may be added to immunoassay systems after immobilization of microorganisms. The immobilization process involved only one step, i.e., shaking 100 microliter of culture with 50 microliter of titanous hydroxide suspension in polystyrene tubes for only 10 min. The immobilized cells were so tenaciously bound that vigorous agitation for 24 h did not result in cell dissociation. The nonspecific binding of 125I-labeled antibody from rabbits and 125I-labeled protein A by titanous hydroxide was inhibited in the presence of 2% gelatin and amounted to only 5.6 and 3.9%, respectively. We conclude that this immobilization procedure is a potentially powerful tool which could be utilized in solid-phase immunoassays concerned with the diagnosis of microorganisms.

Islet cell surface antibodies in genetically obese hyperglycaemic (ob/ob) mice

A quantitative method for circulating islet cell surface antibodies (ICSA), based on the binding of 125I-protein A to insulin-producing RINm5F cells, was used to evaluate ICSA in plasma of 4- to 40-week-old Aston obese hyperglycaemic (ob/ob) mice and normal control (+/+) mice. RINm5F cells bound 2502 +/- 1196 c.p.m. 125I-protein A per 10(5) cells (mean +/- S.D., n = 54) after incubation with +/+ plasma. ICSA positive plasma (defined as 125I-protein A binding, mean +/- 2 S.D. of +/+ plasma) was detected in 3 out of 54 +/+ mice and 3 out of 54 ob/ob mice. ICSA were not observed in ob/ob mice before the onset of diabetes (7 weeks of age), but were detected at 9, 20 and 40 weeks. At 20 weeks 125I-protein A binding produced by ob/ob plasma was 35% greater than +/+ plasma (P less than 0.05). The low occurrence of ICSA in ob/ob mice (6%) suggests that factors other than ICSA are responsible for B-cell dysfunction and eventual islet degeneration observed in Aston ob/ob mice.

Production and characterization of [14C]protein A, a long-lived immunological reagent

A procedure for the production of [14C]protein A is described which involves reductive methylation of lysine residues with [14C]formaldehyde and NaCNBH3. The binding of [14C]protein A to IgG is apparently unaltered, as determined by competitive binding studies. The use of [14C]protein A may be preferred to that of 125I-protein A when a radioactive label with a long half-life is desirable.

Radioimmunoassay of progesterone and estriol in plasma using antibodies immobilized onto protein A-Sepharose CL-4B

Protein A-Sepharose CL-4B was used as a solid phase for antibodies in the radioimmunoassay of progesterone and estriol. The method was fast and easily standardizable. Immobilized antibodies had the same binding capacity as free antibodies and gave good correlation curves (r = 0.996 for progesterone and r = 0.989 for estriol). Sensitivity was 12.5 pg/tube for progesterone and 8.0 pg/tube for estriol. Comparison of progesterone radioimmunoassay with chemically immobilized antibody onto Sepharose CL-4B was also carried out.

Labelling of colloidal gold with protein A. A quantitative study

Colloidal gold complexes with protein A are extensively used in immunocytochemistry as secondary reagents for the localization of antigens. However detailed information on the process and extent of adsorption of protein A onto gold particles, the optimal condition of preparation and the stability of such complexes are lacking. The adsorption isotherm of 125I-protein A onto gold particles (11.2 nm in diameter) was studied quantitatively with gold sols buffered at pH 4-7. At low coverage of the particles, the isotherm was independent of pH. However in the presence of a large excess of protein A, the highest coverage was obtained with a gold sol buffered at pH 5.1, the isoelectric point of the protein. The association constant was decreased at high coverage of the particles. Maximum binding of the complex to immobilized IgG occurred with particles labelled with at least 9 molecules of protein A. The complex was stable under storage with up to 12 molecules adsorbed per particle. At high coverage (26 molecules per particle), a progressive loss of protein A was observed. The optimum condition for preparing the complex are reported.

Galactosyltransferases: physical, chemical, and biological aspects

Galactosyltransferases (GTs) are one of the members of a family of enzymes called glycosyltransferases involved in the biosynthesis of complex carbohydrates. These enzymes catalyze the transfer of galactose from UDP-galactose to an acceptor (glycoprotein, glycolipid) containing terminal N-acetylglucosamine or N-acetylgalactosamine residue. GTs occur in soluble (milk, serum, effusions, etc.) and insoluble (membrane) forms. The GT activities on the outer surface of the cells have been correlated with a host of cellular interactions, including fertilization, cell migration, embryonic induction, chondrogenesis, contact inhibition of growth, cell adhesion, hemostasis, intestinal cell differentiation, and immune recognition. GTs have been purified to homogeneity using affinity chromatography. Most GTs are found active in the pH range 6 to 8 and at temperatures between 35 to 40 degrees C. Manganese is an essential co-factor for GT activity. Isoenzymes of GT have been recognized, especially in tumor tissues, malignant effusions, and sera of cancer patients using polyacrylamide gel electrophoresis in the presence and absence of SDS. Depending on the source of the enzyme, the molecular weights of GTs range between 40,000 to 80,000 daltons. Carcinoma-associated GT isoenzyme has been reported to have a higher molecular weight than the normal GT isoenzyme. Development of monoclonal antibody against the cancer-specific GT isoenzyme will provide help in the development of an immunoassay for the measurement of this isoenzyme in the sera and an aid in the radioimmunolocalization of the tumors in cancer patients.