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

Detection of antibodies to myelin basic protein by solid-phase radioimmunoassay with [125I]protein A

A solid phase radioimmunoassay (RIA) for the detection of antibodies to myelin basic protein (MBP) in sera has been developed employing MBP-coated flexible polyvinylchloride microtiter trays and [125I]protein-A as the radiolabel. [125I]Protein-A directly binds to the Fc region of serum IgG from several animal species and serves as an excellent reagent for detecting antibody. It can also be used to bind to a second antibody ligand, thereby making it useful even when it does not bind directly to the primary antibody Fc region. The use of one preparation of [125I]protein-A label allows sera from several species to be tested for antibodies to MBP simultaneously, thereby making this RIA technically simple, rapid and economical. This assay has been particularly useful in examining serum samples from animals with experimental autoimmune encephalomyelitis and hypomyelinogenisis congenita. In patients with multiple sclerosis low levels of antibody to MBP can be detected in cerebrospinal fluid (CSF) and acid-eluted extracts from brain plaque material; detection of low levels of antibody in human serum has not been possible due to non-specific binding of human serum Ig in this RIA.

Detection of IgG antibodies against Bordetella pertussis with 125I-protein A

A method for the detection of IgG antibodies against Bordetella pertussis is described, based on the principle of 'sandwich' radioimmunoassay. 125I protein A is used as radioactive tracer. The influence of amounts of antigen, antibody, radioactive tracer, incubation time and temperature were tested and the optimal conditions for the assay are described. The procedure offers a simple, quick, and sensitive method for detecting antibodies against B. pertussis. Application and limitation of the test are discussed.

Preparation of protein A-peroxidase monoconjugate using a heterobifunctional reagent, and its use in enzyme immunoassays

Protein A-peroxidase monoconjugate was prepared in solution using a heterobifunctional reagent, N-succinimidyl-3-(2-pyridyldithio)-propionate. The yield of the monoconjugate was much higher than that obtained with current methods. An immunoassay method was developed in which protein A-peroxidase monoconjugate served as a universal tool. Protein A-peroxidase monoconjugate was taken up by IgG molecules immobilized on an excess of solid phase antigen. The ability of free antigen to inhibit the binding of antibody, measured as inhibition of conjugate up take, served as the basis for quantification in the assay. The method was applied to human chorionic gonadotropin (HCG) and human IgG. Optimal assay conditions were developed and it was found that as little as 1 ng of HCG/ml and 2 ng of IgG/ml could be detected. The method is of comparable sensitivity to other available immunoassay methods and gives accurate, reproducible results.

Rapid and efficient immobilization of soluble and small particulate antigens for solid phase radioimmunoassays

A rapid method of antigen immobilization (10 min.) was developed using soluble antigens (bovine serum albumin, epidermal growth factor, and goat IgG) and small particulate antigens (Keyhole limpet hemocynanine and E. coli) by drying them on filter paper discs. This technique results in a high % of the soluble antigen remaining firmly bound, goat IgG (89%), bovine serum albumin (73%). All the antigens we tested retained their antigenicity after drying as detected by [125I] labeled staphylococcal protein A radioimmunoassay. This method of antigen immobilization was compared to adsorption to plastic wells and was found to be much faster (10 min vs 18 hrs) and was 5 times more efficient than adsorption to plastic wells. Using this technique, we were able to detect as little as 40 ng of bovine serum albumin. These characteristics suggest that this technique of soluble antigen immobilization may be useful in rapid detection of antibodies to many different antigens, as well as detecting ng amounts of the antigens directly.

Detection of antibodies to central nervous system antigens by solid phase radioimmunoassay

A solid phase radioimmunoassay is described which employs 125I-protein-A to detect the presence of antibodies against a panel of cellular and soluble central nervous system (CNS) specific antigens coated onto polyvinylchloride Microtiter plates. Serum antibodies from rabbits immunized against myelin, myelin basic protein (MBP), glial acidic fibrillary protein (GFAP), astroglioma cells, and cerebellar cells were easily detected, and high specificity for each antiserum and antigen was also demonstrable. The assay is applicable to cerebrospinal fluid (CSF) from patients with neurological diseases to detect antibodies against CNS-specific antigens. The assay should be useful for examining cell lines derived from CNS tissue for the presence of brain proteins.

Monoclonal antibodies against mouse nerve growth factor produced by somatic cell hybrids

Spleen leukocytes from rats and mice immunized against mouse 2.5S nerve growth factor (NGF) and peripheral blood leukocytes from rabbits hyper-immunized against the same antigen were fused with the mouse plasmacytoma P3X63Ag8. Hybridomas were screened by immunological assays (micro-complement fixation test and solid phase radioimmunoassay) for production of antibodies that reacted with NGF. Significant variations were seen between culture fluids from different hybrid cells. In addition, most but not all hybridoma antibodies that reacted immunologically with NGF prevented neurite outgrowth from 8-day chick embryo sensory ganglia explants after binding to NGF. These results suggest that the hybridoma antibodies produced by the different clones react with different antigenic sites on the NGF molecule.

The development of a radioimmunoassay for 12-L-hydroxyeicosatetraenoic acid

Antibodies directed toward 12-L-hydroxyeicosatetraenoic acid (12-L-HETE) were generated in rabbits by immunization with conjugates of 12-L-HETE and human serum albumin. The concentration of antibodies was determined by incubating immune plasma with 12-L-HETE that had been covalently linked to a solid support, washing the 12-L-HETE support, and measuring the quantity of bound antibodies by reaction with [125I]Protein A. The addition of 0.5 ng-10 ng of fluid-phase 12-L-HETE to the standard mixture of solid-phase 12-L-HETE and anti-12-L-HETE plasma inhibited by 21-80% the binding of antibodies and consequently of [125I]Protein A to the solid support. The 12-OH function positioned between two double bonds was the immunodominant determinant of this antigen-antibody reaction, but the carboxyl function also was recognized. This radioimmunoassay was used to detect and quantitate 12-L-HETE resolved by high pressure liquid chromatography.

Solid-phase immune electron microscopy (SPIEM) for rapid viral diagnosis

Immune electron microscopy (IEM) is one of the fastest and most sensitive methods for the detection and diagnosis of viruses. This technique is based on formation of immune complexes of the virus with its corresponding antibody. In IEM optimal precipitation depends on a correct ratio, and there is a prozone effect. These problems can be overcome by using the solid-phase immune electron microscopic (SPIEM) technique. In this technique the antibody is attached to a particle which is used for 'fishing' the virus to be examined out of the suspension. After low speed centrifugation the preparation is treated either for observation in the transmission electron microscope or in the scanning electron microscope. In 'positive' samples the virus is seen attached to the surface of the particle. We report here results with S. aureus as the solid phase for the detection of Sindbis virus. The anti-Sindbis gamma globulins are attached to the bacteria by means of protein A present on their surface.

Interaction of human polyclonal IgE and IgG from different species with protein A from Staphylococcus aureus: demonstration of protein-A-reactive sites located in the Fab'2 fragment of human IgG

The peptic fragments F(ab')2 and Fc" of human polyclonal IgE were tested by the SpA-IgE radioimmunoassay for interaction with protein A from Staphylococcus aureus. The Fab'2 epsilon fragment but not the Fc" epsilon fragment retained the ability to react with protein A. IgG preparations from different species were tested for ther capacity to inhibit the reaction between 125I-IgE and protein A. IgG preparations from man and the dog, pig, guinea-pig and rhesus monkey were all potent inhibitors whereas those from the rabbit, rat, sheep, horse, cow, goat and mouse were very poor inhibitors. The inhibition of the binding of 125I-IgE to protein A by Fab'2 gamma fragments, but not by Fc gamma fragments, suggests a novel type of interaction of protein A with immunoglobulins.

Detection of antibodies against foot-and-mouth disease virus using purified Staphylococcus A protein conjugated with alkaline phosphatase

Purified protein A (PA) from Staphylococcus aureus was conjugated with the enzyme alkaline phosphatase. This reagent reacted well with pig, rabbit and guinea pig IgG and less well with mouse and bovine IgG. Radioactive 125I-labelled PA showed a similar affinity for the IgGs examined. Antibodies against foot-and-mouth disease virus contained in guinea pig, rabbit and pig serum were detected, using the enzyme-conjugated PA in indirect tests, which were of similar sensitivity to those using enzyme-conjugated anti-species antibody as tracer.

125I-labeled protein A as a general tracer in immunoassay: suitability of goat and sheep antibodies

The immunoassay method in which 125I-labeled staphylococcal Protein A ([125I]PA) serves as a general tracer has been extended to include goat and sheep IgG antibodies. Goat and sheep IgG normally do not react significantly with PA. However, once IgG antibody is bound to immobilized antigen or hapten, binding of [125I]PA is enhanced markedly. Binding efficiencies of [125I]PA to immune complexed goat anti-human IgM, human IgE, methotrexate and sheep anti-IgE were determined and compared quantitatively to rabbit IgG with the corresponding specificity. Immunoassays were developed based on the inhibition of [125I]PA binding as a measure of antibody inhibition by fluid-phase homologous ligand. In terms of sensitivity and specificity, assays using goat and sheep antibodies were comparable to assays developed using rabbit IgG. Goat antibody to the monovalent hapten methotrexate behaved anomalously: for each concentration of IgG tested, there was an optimal amount of methotrexate beads that gave maximum binding of [125I]PA. In the other immune systems, for each antibody concentration maximum binding of tracer was a function only of the amount of immobilized antigen added. In contrast to the results obtained with solid-phase antigen, solutions containing antibody and amounts of antigen ranging from large antigen excess to antibody excess to antibody excess failed to react significantly with PA or [125I]PA.

Antigenic and immunogenic characteristics of nuclear and membrane-associated simian virus 40 tumor antigen

Antisera were prepared in syngeneic hosts against subcellular fractions of simian virus 40 (SV40)-transformed cells (MoalphaPM, MoalphaNuc), glutaraldehydefixed SV40-transformed cells (HaalphaH-50-G, MoalphaVLM-G), and electrophoretically purified denatured SV40 tumor antigen (T-ag) (RaalphaT). Immune sera were also collected from animals bearing tumors induced by SV40-transformed cells (HaalphaT, MoalphaT, HAF) and from SV40-immunized animals that had rejected a transplant of SV40-transformed cells (HaalphaS, MoalphaS). Immunological reagents prepared against cell surface (MoalphaPM, HaalphaS, MoalphaS, HaalphaH-50-G, MoalphaVLM-G) reacted exclusively with the surface of SV40-transformed cells by indirect immunofluorescence or protein A surface antigen radioimmunoassay. Immunological reagents prepared against the nuclear fraction (MoalphaNuc) or whole-cell determinants (HaalphaT, MoalphaT, HAF, RaalphaT) reacted with both the nuclei and surface of SV40-transformed or -infected cells. All reagents were capable of immunoprecipitating 96,000-molecular weight large T-ag from solubilized whole cell extracts of SV40-transformed cells. The exclusive surface reactivity of HaalphaS exhibited in immunofluorescence tests was abolished by solubilization of subcellular fractions, which then allowed immunoprecipitation of T-ag by HaalphaS from both nuclear and plasma membrane preparations. Specificity was established by the fact that all T-reactive reagents failed to react in serological tests against chemically transformed mouse cells, and sera from mice bearing transplants chemically transformed mouse cells (MoalphaDMBA-2) failed to react with SV40-transformed mouse or hamster cells. Reagents demonstrating positive surface immunofluorescence and protein A radioimmunoassay reactions against SV40-transformed cells were capable of blocking the surface binding of RaalphaT to SV40-transformed cells in a double-antibody surface antigen radioimmunoassay. This blocking ability demonstrated directly that a component specificity of each surface-reactive reagent is directed against SV40 T-ag. A model is presented which postulates that the differential detection of T-ag by the various serological reagents is a reflection of immunogenic and antigenic differences between T-ag polypeptides localized in nuclei and plasma membranes.

Protein-A antibody-binding TPAAB) technique for detection of tumor-associated membrane antigen (TAMA) of Lewis lung carcinoma

Xenoantisera were prepared in rabbits against intact paraformaldehyde-fixed Lewis lung carcinoma (LLCa) cells and membrane solubilized proteins extracted with Triton X-100 and 3M KCI. The antisera were analyzed for antibodies to tumor-associated membrane antigens (TAMA) by means of a solid-phase radioimmunoassay (RIA). THe immunoassay employed 125-labelled Staphylococcus aureus protein A (SPA) to detect specific antibody binding to glutaraldehyde-fixed Lewis lung tumor target cells. The protein-A antibody-binding (PAAB) method is rapid, sensitive and reproducible. The PAAB revealed a possible LLCa-TAMA as evidenced by the reactivity of xenoantisera raised to LL paraformaldehyde tumor cell vaccine (TCV) and LL tumor Triton X-100 (TTri) and 3M KCI (TKCI) extracts of membrane preparations. The reactivity of our antisera followed linear dose-response kinetics but the degree of reactivity decreased from anti-TCV to anti-TTri to anti-TKCI respectively. The LL-TAMA demonstrated specificity since our antisera did not significantly cross-react with normal C56BL/6 cellular antigens or other known murine tumor-associated surface antigens of virally and chemically-induced tumor systems.

Indirect 125I-labeled protein A assay for monoclonal antibodies to cell surface antigens

An assay for detection of monoclonal hybridoma antibodies against cell surface antigens is described. Samples of spent medium from the hybridoma cultures are incubated in microtest wells with cells, either as adherent monolayers or in suspension. Antibodies bound to surface antigens are detected by successive incubations with rabbit anti-immunoglobulin serum and 125I-labeled protein A from Staphylococcus aureus, followed by autoradiography of the microtest plate or scintillation counting of the individual wells. Particular advantages of this assay for screening hybridomas are: (1) commerically available reagents are used, (2) antibodies of any species and of any immunoglobulin class or subclass can be detected, and (3) large numbers of samples can be screened rapidly and inexpensively. We have used the assay to select hybridomas producing monoclonal antibodies to surface antigens of human melanomas and mouse sarcomas.

Immobilization of viral antigens on filter paper for a [125I]staphylococcal protein A immunoassay: a rapid and sensitive technique for detection of herpes simplex virus antigens and antiviral antibodies

A new technique is described for the rapid detection and quantitation of herpes simplex virus (HSV) antigens and antiviral antibodies. It involves immobilization of HSV antigens on filter paper discs and subsequent analysis by 125I-labeled staphylococcal protein A (SPA) radioimmunoassay. A specially designed 96-well filtration device is employed which serves both as an incubation chamber and as a filtration manifold. It is rapid, simple, sensitive and specific, and requires only small volumes of antiserum and few target cells. The results may be readily and objectively quantitated. This technique permits the simultaneous assay of a large number of specimens in less than 1 h. Its sensitivity is considerably greater than that of other currently used immunologic techniques, and it is amenable to automation. These characteristics suggest that this [125I]SPA immunofiltration technique may be applicable to the rapid diagnosis of viral infections.

Immunoassay of indomethacin: the use of [125I] protein A to detect specific serologic binding

The sera of rabbits that were injected with indomethacin covalently linked to human albumin bound increasing amounts of [14C] indomethacin during the course of immunization. The serum-binding components chromatographed with the gamma-globulin fraction and were precipitated with goat-anti-rabbit-gamma-globulin. When measured by radioimmunoassay with [14C] indomethacin under optimal conditions, 34 ng (95 pmoles) of unlabeled indomethacin inhibited [14C] indomethacin binding 50%. The antibodies reacted most effectively with indomethacin and the desmethylated analogue, 1-(p-chlorobenzoyl)-2-methyl-5-hydroxyindole-3-acetic acid, but not 2-methyl-5-methoxy-indole-3-acetic acid. An immunoassay based on the use of [125I] Protein A as tracer for IgG antibody was developed for quantitative determination of indomethacin at the picogram level. Indomethacin, immobilized by covalent linkaae to a solid support, bound the rabbit anti-indomethacin. Protein A, labeled with [125I], measured the levels of the bound IgG antibody. Fluid phase indomethacin competed with solid-phase indomethacin for the anti-indomethacin, which resulted in decreased anti-indomethacin and consequently decreased [125I] Protein A on the immobilized indomethacin-anti-indomethacin complex. The serologic specificity with the immobilized ligand immunoassay was the same as that found with the [14C] indomethacin radioimmunoassay, but the sensitivity for detection of indomethacin was increased over 300-fold.

The use of immobilized ligands and [125I]protein a for immunoassays of thromboxane B2, prostaglandin D2, 13,14-dihydro-prostaglandin E2, 5,6-dihydro-prostaglandin I2, 6-keto-prostaglandin F1 alpha, 15-hydroxy-9 alpha, 11 alpha(epoxymethano)prosta-5,13-dienoic acid and 15-hydroxy-11 alpha,9 alpha(epoxymethano)prosta-5,13-dienoic acid

Immunoassays were developed for quantitative determination of thromboxane B2, prostaglandin D2, 13,14-dihydro-prostaglandin E2, 5,6-dihydro-prostaglandin I2, 6-keto-prostaglandin F1 alpha, 15-hydroxy-9 alpha, 11 alpha (epoxymethano) prosta-5, 13-dienoic acid and 15-hydroxy-11 alpha, 9 alpha (epoxymethano) prosta-5,13-dienoic acid. Ligands immobilized by covalent linkage to a solid support, bound homologous rabbit antibodies. [125I] Protein A was used to measure the bound IgG antibody. Increments of homologous and heterologous fluid-phase ligand completed with solid-phase ligand for antibody and resulted in decreasing amounts of bound [125I]-Protein A. The serologic specificity for each immune system was determined. Immunoassays for thromboxane B2, 6-keto-prostaglandin F1 alpha, and 5,6-dihydro-prostaglandin I2 were used to identify their respective homologous ligands that were separated by normal phase and reversed phase high pressure liquid chromatography.