Development and application of a sandwich enzyme immunoassay for Glycyrrhizae Radix protein (GRP) using monoclonal antibodies

We have developed mouse monoclonal antibodies (anti-GRP mAb-1-5, all IgG1 sub-isotype mAbs) against Glycyrrhizae Radix protein (GRP), which was recently determined to be a marker protein of Glycyrrhizae Radix (GR). Among these, anti-GRP mAb-1 and 2 were found to recognize different epitopes on the GRP molecule, as demonstrated by ELISA analysis, and were used for the development of a sandwich enzyme immunoassay (SEIA) for GRP in traditional Chinese medicines (TCMs). The SEIA was based on the principle of binding an analyte to anti-GRP mAb2 coated on polystyrene microtiter wells, followed by immunoreaction with biotinylated anti-GRP mAb1 and horseradish peroxidase-streptavidin. The SEIA was specific to GRP in GRs, and showed no cross-reaction with any Leguminosae crude drugs other than GRs. This SEIA detected GRP with excellent reproducibility (coefficient of variation=5.9%), an EC50 of 11.5 ng/well and a detection limit of 0.1 ng/well. The present SEIA was about 10-times more sensitive in detecting GRP than the selected antibody enzyme immunoassay (SAEIA) for GRP previously developed using an antiserum to GR itself. Also, the SEIA has such a low assay background that it allowed us to detect a low concentration of GRP in Kyuki-tyoketsu-in-daiichi-kagen (KTIDK), a TCM consisting of only 2.7% GR. The GRP SEIA was simple, accurate, reproducible and may provide a general analytical method for the quality control of GR-based TCMs.

Simple and sensitive enzyme-linked immunosorbent assay for ivermectin

A sensitive and reproducible enzyme-linked immunosorbent assay (ELISA) for the determination of the concentration of ivermectin (IVM) in biological fluids was developed. A conjugate of IVM on bovine serum albumin and poly-L-lysine was used to produce antibodies in rabbits and served as a solid-phase marker for titration of antibodies, respectively. The competitive ELISA was conducted by simultaneously incubating IVM and IVM-biotin conjugate with anti-IVM antiserum over goat anti-rabbit IgG (Fc) and then determining the amount of bound IVM-biotin with avidin-peroxidase conjugate as a tracer. The coefficient of variation for the assay was less than 10% in the range of 0.3-10 ng/ml. The limit of detection was 0.1 ng/ml. The cross-reactivities of anti-IVM antiserum with some anthelmintic drugs were negligible. Using this ELISA, serum levels of IVM were easily determined in Mongolian jirds (Meriones unguiculatus) up to 72 hr following a single oral dose of 500 microgram/kg of body weight.

Determination of urinary acetylpolyamines by a monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA)

A monoclonal antibody (mAb), ASPM-2, produced against N-(gamma-maleimidobutyryloxy)-succinimide (GMBS)-conjugated polyamine spermine [Spm; Fujiwara et al. (1994) Histochemistry 102, 397-404] was used for the development of an enzyme-linked immunosorbent assay (ELISA) for acetylpolyamines (Ac-PAs) in human urine. The ELISA is based on the principle of competition between an analyte and Spm-glutaraldehyde-bovine serum albumin conjugate-coated polystyrene microtiter wells for the mAb, followed by immunoreaction with biotinylated anti-mouse immunoglobulin and horseradish peroxidase-streptavidin. The ASPM-2 mAb showed strong immunoreaction with N1,N12-diacetylspermine (2Ac-Spm), N-monoacetylspermine (Ac-Spm), and N1-acetylspermidine (N1-Ac-Spd), the EC50 values being 29, 50, and 51 microM, respectively, but no cross-reaction with other PA-related compounds or amino acids. The method was used to measure urinary Ac-PA levels in healthy subjects and cancer patients, without pretreatment of the specimens, mean concentrations of 3.25 and 2.80 mumol per 24-h urine, respectively (as N1-Ac-Spd), being found. The ASPM-2 ELISA for N1-Ac-Spd, which is the PA most relevant to the analysis of human urine among the three Ac-PAs mentioned above, is specific and accurate, and can easily be used to analyze large numbers of specimens in parallel. It should thus have potential for studying the relationship between urinary N1-Ac-Spd levels and cancer.

Detection and quantitative assessment of a Vibrio cholerae O1 species in several foods by a novel enzyme immunoassay

A selected antibody enzyme immunoassay (SAEIA) for the general detection of Vibrio cholerae O1 species has been developed using the immunological reagents of a rabbit antiserum specific for V. cholerae O1 classical Inaba 569B and immobilized cell fragments of V. cholerae O1 El Tor 85P6, and beta-D-galactosidase-labeled goat anti-rabbit immunoglobulin G as tracer. The SAEIA was specific for V. cholerae O1 species and showed low cross-reaction values to other microorganism species tested including Vibrio parahaemolyticus. The detection limit of the SAEIA was 4,500 cells per assay for all the 13 strains of V. cholerae O1 examined. Quantitative comparison on the growth of the El Tor 85P4 in several foods cultured for 24 hr were studied using the SAEIA. Preceding the experiments, little inhibition of every food homogenate for the measurement of the SAEIA was first demonstrated and then the homogenate was directly used for an assay sample. The interaction of the growth of Escherichia coli to that of V. cholerae O1 in a food was also found to be little under the mixed culturing of both bacteria using the SAEIA.

A new enzyme immunoassay for a solid Chinese crude drug, pinellia tuber

A new immunoassay for a solid Chinese crude drug was studied. An antiserum specific for Pinellia tuber was elicited in two rabbits. Using the antiserum and powdered Pinellia tuber-coated microtiter plate as the immunological reagents, and beta-D-galactosidase-labeled goat anti-rabbit immunoglobulin G (IgG) as the tracer, a new enzyme immunoassay for a solid Pinellia tuber with a working range between 0.1 and 1000 micrograms/ml was developed. The assay was specific for a solid Pinellia tuber and showed low cross-reaction values on other Chinese crude drugs and the extract of Pinellia tuber. The specificity of the assay was compared with the selected antibody enzyme immunoassay (SAEIA) for the extract of Pinellia tuber recently developed. Both methods utilized the same immunological reagents such as the serum and the enzyme-labeled goat anti-rabbit IgG, and the only difference between them was the solid-phase antigen used. The assay results of several antigens determined by them were quite different, showing that selective measurements of different antigens, either solid or the extract of Pinellia tuber, were possible using the same antiserum, when the tracing reaction in the immunoassay was adequately selected.

A new liquid-phase enzyme immunoassay for rabbit IgM antibodies and its application for comparing the specificity of IgM and IgG antibodies contained in the same antiserum

A new liquid-phase enzyme immunoassay (EIA) has been developed to compare the specificities of IgM and IgG antibodies when they are both present in the same serum sample and directed towards a simple hapten. The hapten viomycin (VM) was used as the model antigen and antibodies to VM were raised in rabbits. In the immunoassay VM, labelled with the enzyme galactosidase as marker (VM-GAL), was mixed with rabbit anti-VM serum. First IgM anti-VM antibodies bound to VM-GAL were precipitated with a guinea pig anti-rabbit IgM serum and galactosidase activity was measured in the precipitate. Then IgG anti-VM antibodies bound to VM-GAL were precipitated from the supernatant with a goat anti-rabbit IgG serum and enzyme activity was measured in this precipitate. The guinea pig anti-rabbit IgM and goat anti-rabbit IgG were specific for IgM and IgG respectively and did not appear to cross-react. Nine analogues of VM were used as inhibitors in this immunoassay to compare the specificities of IgM and IgG antibodies for determinants on VM. The results suggest that recognition of the fine structure of VM by IgM is less strict than recognition by IgG.

Comparative study of complete and incomplete Freund's adjuvants for immunization of a drug immunogen using enzyme immunoassay methods

Highly sensitive and accurate enzyme immunoassays (EIAs), a sandwich EIA for mouse immunoglobulin G (IgG) and an enzyme linked immunosorbent assay for mouse antibody specific to viomycin (VM), were developed. Accuracy and specificity of the assay results were confirmed before their application. The changes of total IgG and antibody specific to VM in mice, immunized with a VM-immunogen with or without two types of Freund's adjuvants under various conditions, were assessed by means of the newly developed EIA methods. Both methods were very useful tools to follow the immunization processes of mice, and complete and incomplete Freund's adjuvant were found to have similar adjuvant activities for production of antibody specific to VM, judging from the amounts of anti-VM antibody formed. It seems to be important that too many booster injections should be avoided in the immunization of mice with a hapten immunogen.

Analyses of specific and total antibody responses of rabbits to four kinds of immunogens

As a basic study to investigate suitable conditions to immunize rabbits with drug-immunogens, two highly sensitive and accurate enzyme immunoassays (EIAs) for specific antibody to viomycin (VM) and blasticidin S (BLS) were developed using the corresponding standard antibody, the solid-phase antigens, and enzyme-labeled goat anti-rabbit immunoglobulin G (IgG) antibody as immunological reagents. The accuracy of the assay results with these newly developed EIAs was demonstrated. The new EIAs as well as two previously developed EIAs, EIA for antibody specific to neocarzinostatin (NCS) and a sandwich EIA for rabbit IgG, were applied for analyses of the changes in contents of total and specific antibodies in rabbit antisera samples collected during immunizations with four antigens. Total IgG levels increased from 7.0-9.9 mg/ml to 30-50 mg/ml in all rabbits immunized under the same immunizing schedule, despite the use of four kinds of antigens. The highest level of specific antibodies, anti-BLS, anti-VM and anti-NCS, was 0.5 mg/ml in each case.

Sandwich enzyme immunoassay of tumor-associated antigen sialosylated Lewisx using beta-D-galactosidase coupled to a monoclonal antibody of IgM isotype

Enzyme conjugates with antibody of IgG type have been used extensively in immunohistochemistry, but conjugates with antibody of IgM type have not been reported. This paper describes the beta-D-galactosidase (Gal) labeling of a monoclonal IgM antibody designated CSLEX1 (for cytotoxic sialosylated Lewisx), which is directed against a tumor-associated antigen sialosylated Lewisx (S-Lex). The antibody was first acylated with a heterobifunctional agent N-(gamma-maleimidobutyryloxy)succinimide (GMBS) to introduce the maleimide groups into the molecule; excess reagent was removed by gel filtration and then the activated antibodies were crosslinked to the thiol groups of Gal. The conjugates were partially purified of free Gal by DEAE-Toyopearl column chromatography with an increasing linear concentration of NaCl. The conjugates thus prepared retained almost full enzyme activity and were demonstrated to be free of CSLEX1 by affinity chromatography using anti-galactosidase antibody bound to Sepharose 4B. The conjugates were used as a label in a sandwich enzyme immunoassay (SEIA) to detect the antigen at concentrations as low as 0.2 U/well. The SEIA was used to measure serum S-Lex levels in both healthy subjects and lung cancer patients and mean concentrations of 70 U/ml and 198.6 U/ml were detected respectively.

A novel enzyme immunoassay commonly applied for ten strains of Pyricularia oryzae

Antiserum against a strain of the rice blast fungus Pyricularia oryzae was elicited in rabbits immunized with its cell fragments emulsified with incomplete Freund's adjuvant. The fragments were also used as solid-phase antigens. A highly sensitive, competitive type enzyme-linked immunosorbent assay for P. oryzae was developed by using these two preparations as the immune reagents together with the use of beta-D-galactosidase-labeled anti-rabbit IgG as the tracer. Cross-reactivity of nine different strains of P. oryzae were measured by the assay. Sensitivity and accuracy of the assay was improved by choosing the cell fragments of the least cross-reactive strain as the solid-phase antigen. The improved method was successfully applied for sensitive and accurate assay of all ten strains of P. oryzae with the common measuring range between 1 and 100 ng per tube. Other species of microorganisms had little reactivity in this immunoassay indicating that the assay is specific to P. oryzae group microorganisms.

Determination of an antibody-antigen binding constant by enzyme immunoassay and a theory for analysis of competitive binding of two ligands to heterogeneous receptor

A method for determining antigen-antibody binding constants by using enzyme-labeled antigens has been developed. In the measurement, enzyme-labeled and unlabeled antigens (Ag* and Ag) were allowed to compete in binding to the antibody (Ab) under conditions where Ag* much less than Ab much less than Ag. The data were analyzed according to a new theory developed for the analysis of competitive binding of two ligands to a heterogeneous receptor. The theory indicates that the binding degree of a labeled ligand measured at various concentrations of the receptor can be used to prepare a standard curve relating the binding degree of the labeled ligand and the average of the concentrations of the free receptor components which are in binding equilibrium with another unlabeled ligand. For homogeneous receptors, the method gives usual binding constants for the unlabeled ligand, but for heterogeneous receptors, it gives a new type of average binding constant for the unlabeled ligand in which the contribution of each receptor component is amplified in proportion to its affinity against the labeled ligand. This average binding constant was named the "affinity-average binding constant." A rabbit anti-blasticidin S (BLS) antiserum analyzed by the present method using beta-galactosidase-labeled BLS as the labeled ligand was found to be fairly homogeneous with respect to the affinity and to have a binding constant of 1.48 +/- 0.24 (S.D.) X 10(8) M-1 for unlabeled BLS.

A new solid support for sandwich enzyme immunoassays of human immunoglobulin G

Two antibodies were prepared for use in a sandwich enzyme immunoassay of human IgG. Completely purified guinea pig anti-human IgG was labelled with beta-D-galactosidase (EC 3.2.1.23), using a heterobifunctional cross-linker named GMBS. Partially purified anti-human IgG was immobilized on a new solid support: Amino-Dylark balls. Optimal conditions for immobilizing the antibody, using glutaraldehyde as the coupling reagent, were studied in detail. With the enzyme-labelled antibody and the solid-phase anti-human IgG, a sandwich enzyme immunoassay of human IgG with a lower limit of detection at 10.5 pM (0.3 ng/tube) was developed. A comparative study of the EIA method and a laser nephelometric method showed a good correlation. The specificity of the assay was excellent: all 4 types of IgG tested showed the maximum 0.0001%; human IgA, IgM and albumin possessed the maximum 0.54% in their cross-reactivity values with human IgG.

Enzyme immunoassay with high sensitivity and accuracy for specific antibody to neocarzinostatin

A quantitative enzyme immunoassay (EIA) for specific antibody to neocarzinostatin (NCS) is described which uses enzyme-labeled anti-rabbit IgG antibody, solid-phase NCS and standard purified specific antibody to NCS. The dose of the standard was determined by sandwich EIA for rabbit IgG. The lower detection limit was 3 ng of the specific antibody per tube. The accuracy of the assay was excellent and a comparative study with the sandwich EIA for rabbit IgG showed good correlation. The antiserum to NCS of the highest titer was found to contain 0.6 mg and 40 mg per ml of specific antibody to NCS and of normal IgG, respectively. The accuracy of the assay results and the purity of the standard was established by 2 recovery tests for anti-NCS antibody.

A sandwich enzyme immunoassay of rabbit immunoglobulin G with an enzyme labeling method and a new solid support

A method was devised for enzyme labeling goat antibody to rabbit immunoglobulin G with beta-D-galactosidase (EC 3.2.1.23) using a heterobifunctional cross-linker, N-(gamma-maleimidobutyryloxy)-succinimide. Labeling of the purified antibody was by a continuous 2-step process and including a chromatographic purification procedure could be completed within one day. The partially purified anti-rabbit IgG was coated on Amino-Dylark cylinders, a new solid support, using glutaraldehyde as the coupling reagent. With enzyme-labeled antibody and the solid-phase anti-rabbit IgG, a sandwich enzyme immunoassay for rabbit IgG was developed with a lower limit of detection at 3.5 pM (0.1 ng/tube). The specificity of the assay was excellent and all 4 types of IgG tested showed 0.0001% or less cross-reactivity with rabbit IgG.

High dimensional structure of the antigen-binding site of anti-viomycin immunoglobulin analyzed by enzyme immunoassay

Precise immunological recognition of anti-viomycin antiserum at detailed parts in the structure of viomycin was studied by cross reactivities of the antiserum to viomycin and its ten analogs using an enzyme immunoassay of viomycin. The antiserum clearly recognized all minor modifications in the sixteen membered ring of viomycin, indicating that the antiserum clearly recognizes the whole structure of the sixteen membered ring. Recognition of the antiserum on the beta-lysine terminus was also examined showing that the antiserum was also recognized on this part. Thus, the anti-viomycin antiserum was deduced to recognize the whole structure of viomycin, from which the deduction was made that the anti-viomycin antibodies in the antiserum must possess cavities fitting the whole structure of viomycin. The crystal dimensions of viomycin are 13 A in length, 8 A in width, and 7 A in depth. Thus, the high dimensional structure of the binding sites of the anti-viomycin antibodies was deduced to possess cavities of a similar size to that of viomycin.

Enzyme immunoassay of neocarzinostatin using beta-galactosidase as label

A novel convenient procedure was introduced for enzyme labelling of neocarzinostatin (NCS) with beta-D-galactosidase using a new hetero-bifunctional reagent N-(gamma-maleimidobutyryloxy) succinimide (GMBS). With the enzyme labelled NCS and a rabbit anti-NCS serum which was elicited in a rabbit immunized with NCS in complete Freund's adjuvant, a highly sensitive enzyme immunoassay which can quantify a femto mol order NCS was developed. Accuracy and precision of the assay as well as a comparison with the immunodiffussion method were studied with satisfactory results. This enzyme immunoassay of NCS was applicable to monitoring serum NCS levels of patients in clinical treatment of the antitumor agent.