The amplified ELISA: principles of and applications for the comparative quantitation of class and subclass antibodies and the distribution of antibodies and antigens in biochemical separates

Application of immunochemical assays to food analysis

Immunochemical assays are powerful bioanalytical techniques with application to several areas in food science, including food analysis, microbiology, nutrition, food safety, food quality, and process control. In principle, immunochemical techniques can be applied to the analysis of any compound, with only one specific antibody needed that can be obtained either from laboratory animals or, when available, from commercial sources. A well-designed immunochemical assay can detect targeted compounds at levels as low as 10(-12) M. Immunochemical techniques require little or no sample pretreatment, making these analytical procedures relatively rapid. The initial cost of developing an immunoanalytical assay may be high, but when the procedure is well established, the cost per test is often a fraction of that for other analytical methods. For these reasons, immunoanalytical assays provide an attractive alternative for the food analyst who requires either inexpensive qualitative screening tests or reliable quantitative methods with a high degree of sensitivity. This review concentrates on the use of enzyme immunoassay to address analytical problems in food chemistry and the analysis of various food components.

Isolation of a specific membrane protein by immunoaffinity chromatography with biotinylated antibodies immobilized on avidin-coated glass beads

Avidin-coated, solid glass beads have been used as an immobilization support for attaching biotinylated antibodies. These beads have been packed into analytical, semi-preparative and preparative columns and used to isolate the B27 histocompatibility anigen (HLA) from human lymphocytes. The beads provided a suitable column material for all three chromatographic procedures and, depending on the size of the immunoaffinity column, B27 antigen could be isolated in nanogram to microgram quantities. Polyacrylamide gel electrophoresis demonstrated the presence of only a single band in the immunoaffinity peaks isolated by all three procedures. Enzyme-linked immunosorbent assay analysis of these immunoaffinity-isolated materials revealed that they were biologically active and could be used to determine the levels of anti-B27 antibodies in clinical studies.

The immunochemistry of sandwich ELISAs--III. The stoichiometry and efficacy of the protein-avidin-biotin capture (PABC) system

The protein-avidin-biotin capture (PABC) system was developed to decrease the adsorption-induced loss of antigen capture capacity (AgCC) of capture antibodies (CAb) used in sandwich ELISAs. This system involves immobilization of biotinylated CAbs through linkage by streptavidin (SA) to biotinylated carrier proteins adsorbed on polystyrene. Studies reported here describe the stoichiometry of the system and the influence of biotinylation of different carrier proteins and CAbs on the reaction stoichiometry and the AgCC of CAbs. Because of the widespread use of sandwich ELISAs to measure the concn of multivalent protein antigens, the AgCCs of monoclonal and polyclonal CAbs to pig IgG in the PABC system were compared with the AgCCs of these Abs immobilized on the plastic by direct adsorption. Optimal assay conditions for the carrier were obtained when 1 microgram/ml of the biotinylated protein was added to the polystyrene solid phase. An increasing degree of biotin substitution in three carrier proteins was paralleled by an increasing AgCC until a constant maximum was reached. Under conditions of maximal AgCC, 120 ng of the carrier rabbit gamma globulin (RGG; i.e. RGG25biot) was bound to polystyrene, which in turn yielded the maximum amount (i.e. 100 ng) of bound streptavidin (SA; Bdngmax) when 20 micrograms/ml of SA was added. Under conditions giving the Bdngmax for SA, CAb12biot yielded a higher Bdngmax than did CAb25biot or CAb2biot. When the AgCC of equal amounts of differentially biotinylated CAbs were compared, the following order of AgCC was observed: CAb12biot greater than CAb12biot greater than CAb25biot. Hence, while the maximal amount of CAb is immobilized on SA when CAb12biot is used, optimal AgCC is achieved with CAb2biot. The carrier:SA:CAb2biot ratio was 1:2:1 while that for carrier:SA:CAb12biot was 1:2:2. The same ratio was obtained using IgG2biot from four different species. Monoclonal antibodies to swine IgG showed a 5-6-fold increase in Bd%max when immobilized as CAbs using the PABC system versus when adsorbed on polystyrene. Plots of these data suggest that the differences result from a loss of functional affinity. On the contrary, no significant differences in Bd%max and hence functional affinity were observed when a polyclonal antibody to pig IgG was compared using the two assay configurations. Furthermore, when the globulin fraction of the anti-pig polyclonal was adsorbed on plastic, it behaved nearly as well as its affinity-purified counterpart immobilized by the PABC system. The PABC system appears to offer significant advantages for sandwich ELISAs utilizing monoclonal antibodies as the CAb, and may offer some advantages in other s

Renal membrane-bound carbonic anhydrase. Purification and properties

Microsomes from perfused human donor kidneys were separated by differential centrifugation in sucrose, and thoroughly washed before solubilization by the nonionic detergent nonyl-beta-D-glucoside. The solubilized material was first applied onto an affinity chromatographic column of acetazolamide-oxirane-SepharoseR-CL-4B to remove contaminating cytoplasmic carbonic anhydrase isozymes CA I and CA II. It was then added onto an affinity column of p-aminomethylbenzene sulfonamide coupled to CM Bio-gel AR to purify the membrane-bound carbonic anhydrase activity. This resulted in a 50% pure enzyme. It was then concentrated and fractionated on an anion-exchange column, and desalted and purified to homogeneity (SDS-PAGE and isoelectric focusing) by gel filtration. The enzyme was now purified 411-fold from extractable membrane protein. Its molecular weight was 34.4 kDa from gel filtration and SDS-PAGE, and 36.7 kDa from amino acid analysis. The amino acid composition differed from that of the cytoplasmic isozymes CA I, II, and III. Antisera, produced in rabbits against the purified SDS-treated enzyme, reacted with native nondenatured membrane enzyme protein but only weakly with CA II. Kinetically the enzyme was similar to CA II with respect to hydrase and esterase activities and to inhibition by various sulfonamides. Considered together, the data suggest that the human kidney contains a membrane-bound carbonic anhydrase protein that differs from the cytoplasmic isozymes CA I, II, and III and the secretory form (CA VI) in the saliva.

Terasaki-ELISA for murine IgE antibodies. II. Quantitation of absolute concentration of antigen-specific and total IgE

A Terasaki tray-based ELISA system was developed for the quantitative measurement of antigen-specific and total IgE antibodies in 5 microliter samples of mouse serum dilutions. The assay was based upon non-competitive binding of mouse IgE antibodies between the immobilized appropriate antigen or capture antibodies and the detecting rabbit antibodies. A conjugate of protein A-labelled beta-galactosidase and the fluorigenic substrate methylumbelliferyl-beta-D-galactoside were used as a detecting system. The resulted fluorescence could be measured rapidly and automatically using an inverted micro-fluorimeter. These measurements were automatically transformed into absolute concentrations by a microprocessor-based program using a four-parameter logistic function and an absolute IgE standard. The assay was shown to have a detection limit of 0.04 ng/ml and a range of linearity of 0.04-20 ng/ml, which is sufficient to measure IgE concentrations in mouse serum.

A review of enzyme immunoassay for detection of antibody to Brucella abortus in cattle

Enzyme immunoassay has gained wide acceptance for serological diagnosis of bovine brucellosis because of its ability to detect antibody of all isotypes unlike the conventional tests. The indirect enzyme immunoassay, however, presents several parameters that require careful analysis. These parameters include the choice of antigen and antiglobulin-enzyme conjugate reagents for use in the assay, dealing with the large amount of data the semi-automatic or automatic assay can generate and the inter- and intralaboratory standardization and quality control. This review considers the various methods described in the literature and, briefly, how some of the problems have been overcome or how they might be dealt with.

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.

Altered recognition of surface-adsorbed compared to antigen-bound antibodies in the ELISA

We found in preliminary studies using 125I-labelled antibodies that an antibody bound to a solid-phase antigen was recognized more efficiently than an antibody adsorbed directly to the solid phase. The present study was designed therefore to quantitate the differential recognition of an antibody adsorbed directly to the solid phase and an antibody bound to antigen on the solid phase using the amplified enzyme-linked immunosorbent assay (a-ELISA), and to compare results with the amounts of specific antibody determined by quantitative immunoprecipitation. The degree of differential recognition was quantitated for rabbit IgG and SIgA anti-ovalbumin (anti-OA) and anti-fluorescein, and was found to be dependent upon the isotype of the antibody and not its specificity. The ratio describing the differential recognition of SIgA antibodies (1.8) was much less than for IgG antibodies (greater than 30) and remained constant over the titration range analyzed while the ratios obtained for IgG varied substantially (25-60) over the same range. These ratios of differential recognition were used to estimate rabbit IgG antibody levels to OA, bovine serum albumin, ferritin and alpha-lactalbumin. The estimates obtained were consistently much less than total antibody levels measured by quantitative precipitation. The use of glutaraldehyde-aggregated OA in the ELISA, however, increased the amount of IgG anti-OA and SIgA anti-OA capable of recognizing OA adsorbed on plastic from 12 to 50 and from 30 to 80%, respectively.

The relationship between the binding of primary antibody to solid-phase antigen in microtiter plates and its detection by the ELISA

Radioiodinated monomeric and dimeric M315 (mM315 and dM315) prepared from BALB/c ascites fluid by gel filtration and affinity chromatography were used to study the relationship between primary antibody binding to solid-phase dinitrophenylated gelatin in microtiter ELISAs and its indirect detection by enzyme-antibody conjugates and complexes. The relationship between the amount of mM315 or dM315 which binds to dinitrophenylated gelatin to the amount added is linear over a nearly 3-log range with a slope of 1; the amount of M315 which binds in this linear range after 24 h represents all of the active antibody in the system. On a binding site basis, mM315 was inhibited by a significantly lower amount of dinitrophenyl-(DNP)glycine than was dM315. The indirect detection of bound M315 over the same 3-log range using ELISA yielded a sigmoidal titration curve which encompassed a short linear region that had a slope of 0.9 or less. Plateauing of the titration plots at high input of both mM315 and dM315 was shown to be progressively exaggerated in direct relationship to the size of the enzyme-antibody conjugate used for their detection. The data show that the upper region of the sigmoidal ELISA titration plot is the result of steric hindrance of the detection system. Through the combined use of an 131I-enzyme-antibody immune complex (EIC) detection system and 125I-M315, it was shown that the deviation from the linear binding of 125I-M315 observed during its indirect detection in the so-called linear region of the ELISA titration curve was the result of changing ratios of bound EIC: bound primary antibody, not altered enzymic activity.

The subclass nature and clinical significance of the IgG antibody response in patients undergoing allergen-specific immunotherapy

The purpose of this paper is to discuss the methodological difficulties in quantitation of human IgG subclass antibodies to allergens, to describe the subclass nature of the IgG antibody response in patients undergoing allergen-specific immunotherapy, and to discuss the possible immunological functions and clinical significance of allergen-specific IgG antibodies of different subclasses. Based on results obtained by use of assays with documented specificity it is concluded that the IgG antibody response during allergen-specific immunotherapy is IgG1 and IgG4 restricted, although low levels of IgG2 and IgG3 antibodies to some allergens may occur. In most patients the early IgG antibody response is IgG1 dominated and the late IgG4 dominated. A too early or too pronounced IgG4 dominated antibody response seems to indicate a poor clinical outcome of immunotherapy with inhalant allergens, whereas a pronounced early IgG1 antibody production has been found to be associated with a decrease in synthesis of IgE antibodies to an insect venom. It is therefore proposed that an early IgG1 dominated response is necessary to induce suppression of the ongoing IgE antibody production, which in its turn may be a prerequisite for long-lasting clinical effect. The possibility of induction of an early IgG1 dominated response in every patient by use of alternative immunotherapy procedures is discussed.

Antibody to human rotavirus in cow's milk

Rotavirus infection is an important cause of gastroenteritis in infants and young children. Since the virus replicates in the intestinal lumen, we investigated the presence and effectiveness of rotavirus antibody in three forms of milk: raw milk, pasteurized milk, and commercially available infant formulas. Both raw and pasteurized milk contained detectable levels of IgG1 antibody directed at rotavirus. On the other hand, little or no anti-rotavirus antibody was detected in commercially available infant formulas or other sterile milk preparations. The milk samples with rotavirus antibody were capable of inhibiting the replication of simian, bovine, and human rotaviruses in tissue culture. In addition, they were capable of protecting mice from infection and disease in a murine model of rotavirus infection. On the other hand, the formula preparations were incapable of modifying the in vitro replication of rotavirus strains in tissue culture and did not prevent symptomatic gastroenteritis in the mouse model. We conclude that the alteration of milk-processing procedures or the addition of effective antibodies to milk preparations commonly used in the nutrition of young children may alter the clinical course of rotavirus infection or decrease the transmission of rotavirus throughout susceptible populations.

Quantification of two cytochrome P-450 isoenzymes by an enzyme-linked immunosorbent assay (ELISA)

An enzyme linked immunosorbent assay (ELISA) using monoclonal and polyclonal antibodies has been developed to quantify individual cytochrome P-450 isoenzymes in microsomal preparations, namely UT-A and PB-B. This very sensitive method can be used for the rapid processing of large quantities of determinations and requires only limited amounts of antibodies.

Determination of nonspecific lipid transfer protein in rat tissues and Morris hepatomas by enzyme immunoassay

Rat tissues contain a nonspecific transfer protein which in vitro mediates the transfer of diacylphospholipids as well as cholesterol between membranes. This protein appears identical to sterol carrier protein. A specific enzyme immunoassay for this protein was developed using antibodies raised in rabbits, against a homogeneous protein from rat liver. This assay was based on the very high affinity of the nonspecific lipid transfer protein for polyvinyl surfaces. A reproducible adsorption was achieved by presenting the protein to the surface in the presence of a large excess of bovine serum albumin. The adsorbed protein was detected with specific immunoglobulin (IgG) isolated by antigen-linked affinity chromatography and a goat anti-rabbit IgG-enzyme conjugate. Adsorption was proportional to the amount of protein present, giving rise to a linear standard curve. The enzyme immunoassay measured transfer protein levels in the range 0.2-2 ng. The highest concentrations of transfer protein were found in liver and intestinal mucosa. Levels in other tissues including brain, lung, kidney, spleen, heart, adrenals, ovary and testis were 5-10-fold lower than in liver. In the fast-growing Morris hepatoma 7777 the concentration of nonspecific lipid transfer protein was approximately one-tenth of that measured in the host liver, whereas a reduction of 65% was observed in the slow-growing Morris hepatomas 7787 and 9633. Subcellular distribution studies showed that approx. 70% of the transfer protein was present in the soluble supernatant fraction.

A three-layer immunoradiometric assay for determination of IgG subclass antibodies in human sera ("IgG subclass RAST"). Validation of the subclass specificity, and establishment of equipotency

We report the development of a three-layer immunoradiometric assay (TIRA) for measurement of IgG antibodies of all four subclasses in human sera. The first layer consists of diluted human serum, the second layer is monoclonal mouse antibodies to human IgG subclasses, and the third layer is 125I-labelled rabbit anti-mouse IgG. Monoclonal anti-IgG1, anti-IgG3 and anti-IgG4 reacted only with their complementary IgG subclass, whereas the anti-IgG2 showed slight cross-reactivity to immunoglobins of other subclasses and classes and to light chain proteins. The observed cross-reactivity was found to be without importance, when the TIRA was applied to measurement of IgG subclass antibodies. Equipotency was established by use of appropriate dilutions of the monoclonal antibodies, and the assay was calibrated by use of human reference serum. The TIRA therefore permits reliable inter-individual and intra-individual comparisons of the IgG antibody response in all four subclasses. Non-specific binding obtained with pooled normal human serum was below 0.33%. Inter-assay coefficient of variation was between 18 and 27%. The TIRA was applied to measurement of IgG subclass antibodies to timothy grass pollen in sera from grass pollen allergics undergoing immunotherapy.

Computer-based virus sensitivity assay and neutralization method. Applications for herpesviruses

A method for computerized analysis of the antiviral efficiency of drugs and immunoglobulins was developed. The sensitivities of herpes simplex virus (HSV), cytomegalovirus (CMV) and varicella-zoster virus (VZV) to antiviral drugs were determined. A new type of neutralization assay could be performed rapidly and accurately with HSV and CMV. Combining immunological methods for herpesvirus antigen detection with a computerized analysis permitted rapid, sensitive measurement of drug sensitivities, comparison of antiviral activities at various virus concentrations and selection of potent neutralizing antisera.

Principles, problems, and strategies in the use of antigenic mixtures for the enzyme-linked immunosorbent assay

Competition between proteins and other macromolecules for adsorption sites on plastic was studied with the enzyme-linked immunosorbent assay (ELISA) to determine effects of the use of antigenic mixtures or extracts of organisms on assays of antibodies and antigens by ELISA. A comparison of a number of different polystyrene microplates with bovine albumin and human immunoglobulin G (IgG) as antigens showed two major classes of plates; those which adsorbed albumin poorly and those which adsorbed albumin well. IgG adsorbed well on all plates, but plates which adsorbed albumin best also gave significant background levels of nonspecific binding of conjugate. When mixtures of IgG and bovine serum albumin were used as coating antigens, significant competition was observed; the component present at 1% or less in the mixture was essentially undetectable unless excessive amounts of conjugate were used. The important factor was the ratio of competitor to antigen, not the absolute amount. Other proteins (ovalbumin, rabbit albumin, human albumin, and gelatin) were equally effective competitors for adsorption sites on plastic. Nonionic detergents (Tween 20, and Triton X-100) were strong competitors even at 10:1 competitor-to-antigen ratios. In antigen capture assays, normal serum components blocked attachment of antigen-specific IgG, but this competition could be lessened to a degree by the use of strongly binding polystyrene plates. In indirect ELISA for measurement of serum antibody, the use of antigenic mixtures gave significantly lower antibody titers when the desired antigen was less than 1% of the total protein coated. Therefore, the use of mixed or crude antigens in ELISA presents significant problems concerning the sensitivity and specificity of tests.