The importance of antibody affinity in the performance of immunoassays for antibody

Measurement of the concentration of murine IgG monoclonal antibody in hybridoma supernatants and ascites in absolute units by sensitive and reliable enzyme-linked immunosorbent assays (ELISA)

We have investigated an enzyme-linked immunosorbent assay (ELISA) for mouse IgG using affinity-purified goat anti-mouse antibodies for capture and detection. This assay was used to measure the absolute or weight/volume concentration of murine monoclonal antibody in hybridoma supernatants. Bovine or subclasses except IgG3 in the 1-20 ng/ml range. Antibody capture was essentially complete in the optimized assay. In combination with an antigen-dependent ELISA, the assay allowed estimation of the absolute concentration of specific monoclonal antibody in ascites. These rapid and relatively simple assays may be applicable in many situations in which a practical means of measuring murine monoclonal antibodies in weight/volume units is needed.

A method for the determination of antibody affinity using a direct ELISA

Antibody affinity is of major significance in immunoassays. Since affinity may be influenced by the immunoassay methodology it is important to determine this parameter under the conditions of the assay used. Here a method is described for the determination of binding constants (K) in a direct ELISA with the use of the computer program LIGAND. Five of the antibodies studied bound to their antigen with two classes of antigen binding site, while all the other antibodies studied reacted with only a single class of antigen binding site. The accuracy of the method and the implications for antigen-antibody reactions are discussed.

Recent rubella virus infection indicated by a low avidity of specific IgG

Rubella-specific IgG in acute-phase sera produces a characteristically altered zone termed "soft hemolysis" in the radial hemolysis test. Here, the soft hemolysis was shown to be a product of the purified IgG1 subclass isolated from acute-phase sera. In contrast, ordinary hemolysis was produced by IgG1 isolated from sera of previous rubella immunity, indicating that the subclass composition of IgG was not involved in the mechanism of soft hemolysis. A novel type of solid-phase immunoassay was developed for the avidity of virus-specific IgG. Acute-phase IgG (with soft hemolysis) was dissociated from rubella antigen in an enzyme immunoassay (EIA) test by hydrogen-bond disrupting agents under conditions where IgG of previous immunity (showing ordinary hemolysis) remained mostly bound. These data suggest that the mechanism of soft hemolysis is the avidity of rubella-specific IgG. The new quantitative avidity EIA was tested with sera taken from 169 subjects. Recent infection could be shown from sera taken weeks or months after primary rubella.

Passive hemagglutination test for measles immunity and serodiagnosis

A passive hemagglutination (PHA) test for measles was evaluated in comparison with hemagglutination inhibition (HI) and neutralization (NT) tests. The PHA test determines exclusively the level of antibody directed to the hemagglutinin protein of measles virus. The ratio of PHA to HI titer was 1 to 32 (geometric mean, 6.5) for the first 5 weeks of infection but declined to near unity thereafter. It gradually increased again to 4 to 32 (geometric mean, 11.7) over several years. The initial high PHA titer relative to the HI titer was most likely due to the presence of the immunoglobulin M antibody known to be efficient in agglutination, because 2-mercaptoethanol (2ME) treatment of sera reduced the PHA titer to a level similar to that of the HI titer. The PHA titer in sera obtained after the convalescent phase was insensitive to 2ME, and the relative increase in the PHA over the HI titer was presumably a result of increased antibody avidity. In some individuals, the HI titer fell to below detectable levels several years after either natural infection or vaccination, but the PHA as well as the NT titer remained positive. The PHA titer was therefore a more reliable and more sensitive indicator of immune status against measles than the HI titer. The decrease in PHA titer by 2ME treatment provided evidence of a current or very recent infection. PHA was found to be useful both for assessing immunity status and for serodiagnosis.

Somatic mutations in B lymphocytes: new perspectives in tolerance research?

This paper extends the concept of clonal anergy developed in the author's laboratory. It has been shown that the primary population of B lymphocytes induced into clonal expansion and IgM antibody formation by mitogens contains many cells capable of autoantibody synthesis, but the affinity of binding to the self constituents, or indeed to foreign antigens, is low. The creation of high affinity antibody, which will still register strongly in an ELISA as an IgG molecule, demands not only the addition of lymphokines to cause isotype switching, but also intentional immunization of the donor mice to permit mutations in V region genes and selection of higher affinity B memory cells. This process appears to begin about 6 days after in vivo immunization. It is postulated that these mutational events occur primarily in germinal centres, and that there must be mechanisms to prevent escape of cells which, by chance, mutate not to higher affinity against an immunogen, but to higher affinity against a self constituent. If such mutants were allowed to enter the long-lived, recirculating pool of B lymphocytes, they might pose a graver threat of autoimmune disease than the low-affinity anti-self cells of the primary repertoire. Therefore, it is suggested that recently mutated germinal centre B cells represent a pool of 'pre-memory' cells, which are immature in the sense of displaying the same kind of sensitivity to negative signalling by antigen that immature B cells from newborn spleen or adult bone marrow display. If so, then the earliest phases of memory generation represent a second window of opportunity for tolerance induction within the B lymphocyte compartment.

Analysis of the B lymphocyte repertoire by polyclonal activation. Hindrance by clones yielding antibodies which bind promiscuously to plastic

We here describe a form of 'noise' in the ELISA as commonly performed on antigen-coated microtiter trays that represents a major hindrance to the accurate enumeration of infrequent antibody-forming cell (AFC) precursors (AFCp) specific for epitopes on monomeric proteins. Supernatants from cultures of lipopolysaccharide-stimulated murine splenocytes, when split into aliquots and separately assayed, scored as positive in parallel on ELISA trays coated with unrelated proteins and on uncoated trays. Some properties of such coincident false positives (CFP) noted were: (1) optical density (OD) ranges for CFP and non-CFP overlapped; (2) different members of CFP triplets on differently coated assay trays usually had similar OD values; (3) CFP-generating culture supernatants did not contain unusually high immunoglobulin concentrations; and (4) numbers of CFP-forming supernatants increased with increasing input cells/culture consistent with causation by single AFCp present at an approximate mean frequency of 1 in 6600 CBA splenocytes. It is proposed that CFP are due to AFC clones that secrete antibody reactive with some epitope(s) present in the assay tray itself. Repertoire elements with such 'anti-plastic' characteristics are rarer than anti-keyhole limpet hemocyanin (KLH) AFCp, but at least as frequent as anti-bovine serum albumin (BSA) or anti-transferrin (TFN) AFCp.

Estimation of association constants of 42 monoclonal antibodies to human IgG epitopes using a fluorescent sequential-saturation assay

We measured the association constant (Ka) for 42 murine monoclonal antibodies (MAbs) to human IgG epitopes. Included are antibodies, previously evaluated in an IUIS/WHO collaborative study, to various epitopes on the four subclasses of human IgG - IgG Fc, IgG Fab, kappa, and lambda - and to selected IgG allotopes. We used a sequential-saturation immunofluorescent assay and interactive computer program to determine the Ka by Scatchard analysis. Kas ranged from unmeasurably low by this method (approximately 10(6) L/M) to 3.8 X 10(9) L/M. Some class specific MAbs had large Ka differences for different subclasses and some subclass specific MAbs had large Ka differences for molecules of the same subclass but of different light-chain types.

Estimating the relative avidity of mucosal IgA for antigen

This report concerns the application of a method to estimate the relative avidity of mucosal IgA for casein and beta-lactoglobulin. The chaotropic ion, thiocyanate, was used to disrupt antigen-antibody binding in an enzyme immunoassay. The resultant proportional decrease in optical density of the enzyme immunoassay was directly related to the proportion of IgA eluted from the solid phase-bound antigen. The relative avidity was expressed as the molarity of KSCN resulting in a particular reduction in optical density. The measurement of avidity, the avidity index, was independent of the concentration of mucosal IgA. For anti-casein IgA the interassay coefficient of variation of the index was 14-18%, and the intra-assay coefficient of variation was 6%. For anti-beta-lactoglobulin IgA the interassay coefficient of variation was 10-13% and the intra-assay coefficient of variation was 6%. The method is simple and free of complicated calculations.

The effect of divalent and univalent binding on antibody titration curves in solid-phase ELISA

This paper describes the influence of antigen coating concentration, epitope density per antigen molecule and anti-immunoglobulin reagents on antibody titration curves in solid-phase ELISA. Based on results obtained with fluorescein as the hapten and monoclonal anti-fluorescein antibody, which were confirmed in another antigen-antibody system, it is concluded that: (a) Antibody titration curves are independent of antigen-coating concentration in a limited range of concentrations only. (b) The complex between one antibody and two epitopes ('divalent binding') is more stable than the complex between one antibody and one epitope ('univalent binding). The ratio between divalent and univalent binding depends on the epitope density per antigen molecule and on the antigen-coating concentration. (c) The prozone phenomenon can be explained by an increased instability of plate bound antibodies due to a shift from divalent to univalent binding. (d) In solid-phase ELISA a correct evaluation of the antiserum specificity can be performed only if it is ascertained that all target antigens are coated under saturating conditions.

Analysis of vesicle immunolysis assays. The direct binding model

Assays based on lysis of lipid vesicles have shown high sensitivity. However, little as yet is known about the quantitative relationships among the various assay parameters, due in part to the lack of a predictive theoretical model. This paper presents the derivation of the equations that describe a simple model assay system in terms of the total fraction of vesicles with bound antibodies and the distribution of vesicles with one, two, or more antibodies bound. The equations show how the binding of antibodies to vesicles is affected by such variables as: vesicle concentration, antigen density on vesicle surfaces, antibody concentration, and antibody affinity. With the distribution functions, experiments can be designed to determine the minimum number of antibodies needed to lyse a vesicle. In addition, it is shown how estimations of the ultimate sensitivity of lipid vesicle lytic assays can be made. The model can be used to optimize vesicle lysis assay systems.

Method of analysis of non-competitive enzyme immunoassays for antibody quantification

A computerized analysis of a quantitative enzyme-linked immunoadsorbent assay (EIA) using a non-specific immunoglobulin (IgG) of known concentration as the standard has been developed for measuring specific antibody levels in serum without the need for affinity purification of the positive control antibody. The computer program utilized logit-log linear regression analysis of sigmoid serial dilution curves plus a weighted least-squares best curve fit analysis and an iterative manipulation to eliminate errant data points. The EIA was performed using serial dilutions of standard and unknown antibodies, and a double sandwich technique. A comparison of antibody levels determined by EIA using non-specific IgG as a standard relative to antibody levels determined using affinity-purified specific antibody as a standard were 1.04, 0.53, 0.48, and 0.97 for four different polyclonal antibody systems. Five monoclonal antibodies to carcinoembryonic antigen gave ratios as described above of 1.07, 1.59, 1.73, 2.32, and 2.42. The corresponding antibody affinity constants (1/mol) were 1.0 X 10(8), 3.8 X 10(8), 5.5 X 10(9), 1.8 X 10(10), and 2.6 X 10(10) respectively. This method permits accurate quantification of serum antibody levels when affinity-purified antibodies are not readily available and avoids errors due to loss of antibody activity during affinity purification.

The use of human antigen-specific monoclonal antibodies in an enzyme-linked immunosorbent assay for the determination of anti-HBsAg antibody subclasses

A human monoclonal anti-HBsAg antibody (IgG1, lambda) was used as a reference for an ELISA determination of the serum levels of anti-HBsAg antibodies in human volunteers after vaccination with H-B vax. The IgG subclass distribution of specific antibodies showed a marked dominance of IgG1 antibodies. In addition, small amounts of specific IgG4 antibodies were occasionally found, suggesting a different pattern from that found after natural disease. The novel use of a human monoclonal antibody to measure specific antibodies may give a more accurate determination of specific IgG subclass levels than previously available methods.

Pathogenetic and serological aspects of pulmonary aspergillosis

Af is an important pathogen of the bronchopulmonary system, and the clinical spectrum encompasses aspergilloma, CNPA, IPA, ABPA, bronchial asthma, and allergic alveolitis. Bronchial carriage may, however, not always be associated with pathological effects. The polymorphism of the aspergillus-related disorders seems mostly to depend upon the different responses of the hosts. This review considers the antigenic composition of Af and specific antibody responses in man in relation to the pathogenesis and diagnosis of the various forms of pulmonary aspergillosis. More than 200 macromolecular components have been listed for Af and more than 30 antigens found to react with human sera. Serum antibodies to Af are common in healthy subjects. Schønheyder and his associates (A-L) have shown that IgG, IgA and IgM antibodies in healthy subjects are directed towards antigens to which also patients with aspergillosis strongly react. With immunofluorescent staining these antigens were found to be associated with hyphal walls, and a MW 470,000 fraction from ruptured mycelium was most reactive in ELISA. The respiratory tract appears to be the major route for exposure since the humoral responses include IgA class antibodies, and sIgA antibodies are found in bronchial secretions. Moreover, IgG antibody levels to the MW 470,000 fraction correlate with occupational exposure and smoking habits. In patients with cystic fibrosis high IgG antibody levels to MW 470,000 and MW 25,000-50,000 antigen fractions were associated with the carriage of Af in the sputum. An individual patient's level of IgA antibodies to the MW 470,000 fraction was inversely related to the Af carrier rate, and this was also true for IgE dependent reactivity to Af antigens. These observations indicate that IgG antibodies to some antigens mirror the extent of antigenic exposure, whereas some IgA and IgE antibodies may play a protective role against bronchial colonization with Af. IgG antibody determinations by ELISA were found to provide a higher diagnostic efficacy in pulmonary aspergillosis than IgA antibody assays. With IgG antibodies there were statistically significant differences between patients and the controls and there was little overlap of ELISA values between the groups. The fractions of MW 250,000 with catalase activity and MW 25,000-50,000 with protease activity, were most suitable for serological diagnosis. A gel immunoelectrophoretic assay proved Af catalase to be a major diagnostic antigen in patients with aspergilloma or with an apical aspergillus lung infiltrate.(ABSTRACT TRUNCATED AT 400 WORDS)

A monoclonal-based, two-site enzyme immunoassay of human insulin

A procedure is described for the efficient production of insulin-specific monoclonal antibodies, which involves primary and secondary immunization of BALB/c mice in the hind footpads with bovine or porcine insulin and fusion of lymphocytes from popliteal lymph nodes with a P3x63 murine myeloma line. With this protocol, over 200 positive hybrids were obtained from four separate fusions. Dissociation constants of 31 purified monoclonals, cross-reacting with human insulin, were determined by two different methods and ranged between 4 X 10(-10) and 2 X 10(-6) mol/l. 24 monoclonals were biotinylated, paired in all possible combinations and tested by ELISA for their capacity to simultaneously bind to human insulin in a two-site assay. More than 40 monoclonal pairs were found which formed a sandwich with the hormone. The development of a simple and rapid one-step enzyme immunoassay is described, which involves a first monoclonal bound to the wells of a microtiter plate and a second monoclonal conjugated to alkaline phosphatase. With this assay, insulin can be determined in a range between 0.08 and 7.5 ng/ml in 3-4 h.

Clonal analysis of the anti-DNA repertoire of murine B lymphocytes

The present studies characterize at the clonal level the repertoire of lipopolysaccharide-responsive murine B lymphocytes committed to the production of antibodies reactive with denatured DNA. This repertoire is vast in normal mice as 1-5% of total mitogen-induced antibody-forming cell clones secreted denatured DNA-reactive antibodies when the splenocyte donors were CBA (Ighj), BALB/c (Igha), C57BL/6 (Ighb), CBA nu/nu, and C57BL/6 nu/nu athymic mice. The autoimmune NZB (Ighe) strain did not display elevated proportions of anti-denatured DNA antibody-forming cell precursors. Cross-reactions shown by CBA anti-denatured DNA antibodies suggest that many antibodies might derive significant binding energy from interaction with the bases or similar hydrophobic moieties. Cross-reactions with other tested polynucleotides were frequent, but cross-reactions with phospholipids and phosphocholine were undetectable. Most anti-DNA antibodies bound preferentially or exclusively to single-stranded denatured DNA as compared to double-stranded native DNA. The frequency of anti-denatured DNA antibody-forming cell precursors among CBA peritoneal cells was not elevated. Fluorescence-activated cell sorter-selected Ly-1-positive NZB splenic B cells were not enriched, and Ly-1 negative B cells were not depleted of anti-DNA antibody-forming cell precursors. These results show that antibody-forming cell precursors specific for denatured DNA are not restricted to the Ly-1 positive B-cell subset.

Modification of the ELISA for the estimation of tetanus antitoxin in human sera

The use of indirect ELISA for the quantitation of tetanus toxin neutralizing antibodies in human sera is limited by marked overestimations in low titered sera. The reasons for the discrepancy between the results obtained by ELISA and by in vivo assay and modifications of the ELISA to overcome the problem were investigated. Catching ELISA and indirect ELISA using trays coated with the contaminant proteins in toxoid preparations indicated that antibodies to contaminants were only partly responsible for the discrepancy and the introduction of these modifications did not solve the problem. In ELISA competition experiments with toxin neutralizing monoclonal antibodies, the human immunoglobulins irrelevant in toxin neutralization, but detectable in indirect ELISA, were found to be difficult to inhibit in their binding to the solid antigen phase. These might represent antitoxins bound bivalently to the solid phase but with affinities in monovalent binding insufficient for toxin neutralization or other coupled antibodies due to conformational changes of the antigen. A competition ELISA with toxin in solution was therefore developed to assess selectively the antitoxin capable of binding the antigen in solution and by this approach the in vivo activities of even low titered sera were accurately predicted. This antigen competition ELISA may be easily introduced into routine tetanus serology and the principle may also be of value for the in vitro detection of functional antibodies to other antigens.

Serum antibody and cellular responses in LEW and F344 rats after immunization with Mycoplasma pulmonis antigens

Mycoplasma pulmonis causes a chronic respiratory disease in rats which is more severe in LEW than in F344 rats. This study compared the ability of each of these rat strains to produce specific immune responses to M. pulmonis antigens. By an enzyme-linked immunosorbent assay, LEW rats were found to produce approximately 10 times lower levels of specific immunoglobulin G (IgG) after immunization with M. pulmonis antigens than F344 rats, while no significant difference was found in the levels of IgM. The difference in IgG levels was due to much greater levels of specific IgG2b (about 50 times) in F344 rats; no differences were found in other subclasses. Nonimmune LEW rats were found to have as much total IgG2b in their sera as unimmunized F344 rats by a single radial immunodiffusion test; thus, the difference was not due to the inability of LEW rats to produce IgG2b. In contrast to the antibody response to M. pulmonis antigens, anti-keyhole limpet hemocyanin IgG responses in LEW and F344 rats were similar, but F344 rats produced significantly more (about 21 times) IgG2b than was found in M. pulmonis responses. Antisera from F344 rats recognized several additional M. pulmonis antigens than antisera from LEW rats; however, this could not explain the differences in the level of IgG2b in LEW and F344 rats. In vitro stimulation of splenic lymphocytes with M. pulmonis antigens from immunized F344 rats produced much greater proliferative responses than in LEW and nonimmune F344 cells. Thus, the susceptible rat strain LEW produced lower cellular and humoral immune responses to M. pulmonis antigens than the resistant rat strain F344 after immunization.

Serologic detection of active infections with human herpes viruses (CMV, EBV, HSV, VZV): diagnostic potential of IgA class and IgG subclass-specific antibodies

In 175 sera from healthy persons as well as those suffering from primary or secondary herpes virus infections/reactivations, serum antibodies were assessed by an indirect ELISA in the immunoglobulin classes A, G and M and the subclasses G1-4, using carrier-fixed antigens (CMV, VZV, HSV) and monoclonal tracer antibodies. In a similar way EBV-specific antibodies were tested by an indirect IFT. Only IgG1 antibodies were detectable in nearly all persons. Virus-specific IgA and IgG3 may support conventional serological methods (IgM, IgG) indicating recent infection/reactivation with VZV, EBV and possibly CMV. Furthermore, differentiation of primary and secondary CMV and VZV infection was possible in some cases, when IgG3 was detectable before IgG1 in subsequent blood specimens. Recurrent herpes lesions could not be diagnosed serologically.

Influence of endotoxin-protein in immunoglobulin G isotype responses of mice to Brucella abortus lipopolysaccharide

Brucella abortus endotoxin preparations, containing approximately 5 to 6% protein, induce strong immune and adjuvant immunoglobulin G (IgG) responses as compared with Escherichia coli endotoxin preparations, with equivalent amounts of protein, which induce responses in which IgM antibody predominates. Using an enzyme-linked immunoassay with isotype-specific conjugates, we found that antibody of all four subclasses of IgG were evoked during the course of the immune responses of C3H/HeAu mice to B. abortus endotoxin. Secondary responses of endotoxin-hyporesponsive C3H/HeJ mice were similar to those seen in C3H/HeAu mice, although lower levels of antibody were produced during their primary responses. The primary responses of BALB/c athymic mice consisted almost entirely of IgG3, and IgG1 appeared following a second injection. The effects of lipopolysaccharide (LPS)-associated protein on the immunogenic properties of B. abortus endotoxin were examined by comparing responses to endotoxin with those to a purified B. abortus LPS containing less than 1% protein. The endotoxin evoked strong primary and secondary responses in which antibody directed to LPS determinants consisted mainly of IgG3 and those to the protein determinants were largely IgG1 antibody. Primary and secondary responses to purified LPS consisted mainly of IgG3 antibody. The potential mechanism of the contribution of protein to the immunogenic properties of the endotoxin as well as possible immune mechanisms involved in these responses are discussed.

Nature and reactivity of staphylococcal enterotoxin A monoclonal antibodies

Monoclonal antibodies from four clones (C5, C3, B2II, and B2I) directed against staphylococcal enterotoxin A were tested by the indirect enzyme-linked immunosorbent assay and double-gel immunodiffusion (micro-Ouchterlony) assay for the nature of heavy and light chain types. The reactivities of monoclonal antibodies were also tested by indirect enzyme-linked immunosorbent assay with various levels of purified staphylococcal enterotoxin A and various levels (dilutions) of monoclonal antibodies and saturation analysis-competitive indirect enzyme-linked immunosorbent assay. The heavy-chain isotype of monoclonal antibodies was found to be an unspecified subclass of immunoglobulin G1, and the light chain was the kappa type. Monoclonal antibodies from all of the clones exhibited high reactivity and nearly the same affinity to staphylococcal enterotoxin A in saturation analysis-competitive enzyme-linked immunosorbent assay. Purified immunoglobulin G from B2I yielded very high absorbance (1.2) at 405 nm with 1 ng of staphylococcal enterotoxin A as the coating antigen in the enzyme-linked immunosorbent assay. Monoclonal antibodies from B2I also neutralized the biological activity of staphylococcal enterotoxin A when tested by the kitten bioassay.

New experimental criteria for optimization of solid-phase antigen concentration and stability in ELISA

A peroxidase saturation technique for the determination of coating antigen concentration necessary to saturate polystyrene plates with a wide range of different antigens is described. The same technique has also been used to compare the stability of antigen-polystyrene bonds for native and denaturated antigens. Furthermore, the inappropriate selection of solid-phase antigen concentration and its influence on ELISA results is analyzed and an experimental criterion to select the optimum antigen concentration is proposed. Two different antigens, BSA-Ar and hydatid antigen, were used for ELISA determination of specific antibodies as a model system. Optimum solid-phase antigen concentration was determined by two different methods: peroxidase saturation, in which binding of peroxidase to non-antigen-occupied polystyrene surface sites was used to evaluate the degree of coating by antigen; chequer-board titration, using several immune sera of different affinity. Optimum antigen concentration selected by chequer-board titration using low affinity sera was similar to that selected with peroxidase saturation. On the other hand, lower antigen concentration would be selected by chequer-board titration using high affinity sera. For this reason, the concentrations of low affinity antibodies would be underestimated using the chequer-board titration. These results indicate that peroxidase saturation should be used to avoid avidity-dependent artifacts in ELISA.

The potency determination of human varicella-zoster immunoglobulin by enzyme-linked immunosorbent assay, complement-fixation test and indirect fluorescent antibody tests

Traditionally, plasma for the production of the human varicella-zoster immunoglobulin (VZIG) has been selected on the basis of the complement-fixing antibody (CFA) titre. Since immune individuals may lack CFA to varicella-zoster virus (VZV), non-CFA may be of importance in protection. In a search for a simple and reliable method for potency determination, 24 VZIG preparations were quantified by enzyme-linked immunosorbent assay (ELISA), the complement-fixation test (CFT), the indirect fluorescent antibody test to acetone-fixed (IF) and viable (FAMA) VZV-infected cells, respectively. The antibody titres obtained by the various methods were compared. Arranged in order of decreasing agreement, the correlation coefficients (r) of the regression equations between the variables were 0.62 for CFT and FAMA, 0.50 for CFT and ELISA and 0.26 for CFT and IF in a log2 plot. There was complete agreement between the titres obtained by the commercially available Enzygnost Varicella/Zoster kits (Behring Institute, Marburg, F.R. Germany) and the ELISA microtitre plates produced at our institute (r = 1). The regression equation lines for ELISA/CFT and FAMA/CFT titres tended to be parallel to each other, while the line for IF/CFT titres had a less steep slope. Similar titration curves were obtained for VZIGs fractionated by two different methods. Furthermore, the titration curves of serum pools from varicella and zoster convalescents, respectively, had a similar shape below delta OD = 0.4. Generally, a steeper slope was observed above delta OD = 0.4. As antibody detectable by ELISA seems to correlate with protection and the method is sensitive, specific, reproduceable, simple to carry out and easily automated, it may be suitable for the potency determination of VZIGs.

Stability of immunofluorescence reactions produced by polyclonal and monoclonal antibody conjugates for rabies virus

We investigated two consumer complaints that described fading of immunofluorescence reactions associated with the use of a commercial antirabies, fluorescein-labeled, monoclonal antibody conjugate. We compared the performance of this product with that of two polyclonal antibody antirabies conjugates and observed significant diminution of fluorescence with the monoclonal antibody conjugate only. Furthermore, the fading occurred only on tissue impressions that had been mounted but not exposed to UV light excitation, thereby essentially eliminating the photobleaching associated with fluorescence microscopy as a causative factor. Our observations suggest that mounting medium pH and the holding temperature of stained slides may be critical factors in maintaining optimal immunofluorescence reactions with this monoclonal antibody conjugate. We discuss some probable mechanisms that could produce the type of fading observed and also suggest certain precautionary measures for use with this monoclonal antibody conjugate.

ELISA for the routine determination of antitoxic immunity to tetanus

Serum samples from 727 persons with different vaccination histories were assessed for tetanus antitoxin content in an enzyme linked immunosorbent assay (ELISA) and tested for tetanus toxin neutralization activity in mice in order to compare the results obtained by the two methods. Neutralizing antibody activities in sera from individuals previously completely vaccinated correlated well with results obtained by ELISA and the accuracy increased with increasing antitoxin concentration in serum. This correlation was observed in sera from persons vaccinated recently as well as in sera from persons vaccinated many years ago. In sera from persons with an incomplete vaccination history ELISA was found to be an unreliable tool for the prediction of in vivo results. Many of these sera had antitoxin levels by ELISA far above the in vivo values, probably due to the presence of non specific or low avidity antitoxin which is detected in ELISA. The lowest ELISA value reliably predictive of protective antibody activity in serum irrespective of vaccination history was found to be 0.16 IU/ml. It was concluded that ELISA is useful for larger population studies as an initial test, but sera with an antitoxin content below 0.16 IU/ml should also be assessed in a neutralization system.

Measurement of tumour reactive antibody and antibody conjugate by competition, quantitated by flow cytofluorimetry

Binding of unlabelled monoclonal antibody preparations has been assessed by competition at saturation with fluorochrome labelled homologous antibody for binding to antigen bearing target cells. The extent of competition was measured by quantitative flow cytofluorimetry, and simple mathematical procedures have been developed to allow the interpretation of competition data in terms of antibody binding activity. In the system studied, non-specific (non-competitive) fluorescence was minimal, but an iterative method to calculate its contribution to the measured signal is given. This approach has the advantage that the antibody preparation to be tested does not need to be labelled or modified; this is particularly important when evaluating the binding activity of therapeutic antibody conjugates. Comparison with a well characterized standard antibody preparation provides a rapid, sensitive and accurate quality control procedure. This test is also simple to perform, requiring only the mixing of labelled and unlabelled antibodies with target cells, a single incubation, followed by analysis without washing of the target cells.

The influence of antibody affinity on the radioallergosorbent test (RAST) and in vitro histamine release. Studies with hapten-specific monoclonal IgE antibodies

Four murine monoclonal IgE antibodies specific for the hapten, 4-hydroxy-3-nitrophenylacetyl (NP), had been previously found to be heteroclitic in nature in that they bound the crossreacting hapten, 4-hydroxy-3-iodo-5-nitrophenylacetyl (NIP), with greater affinity than NP. The influence of antibody affinity on the results of two commonly used assays for IgE, namely the radioallergosorbent test (RAST) and histamine release from rat peritoneal mast cells, was studied using these antibodies. In general, in agreement with previous reports, it was found that affinity influences both RAST and histamine release; however, the affinity constants deduced from equilibrium dialysis measurements for the reactions with monovalent haptens were not directly related to the activities of the antibodies as reflected in assays using multivalent hapten protein conjugates.

Practical considerations of the ability of monoclonal antibodies to detect antigenic differences between closely related variants

This report describes an investigation of the abilities of different immunoassays to detect differences in affinities between related antigens for particular monoclonal antibodies. Nine different monoclonal antibodies were used and 6 strains of influenza virus represented closely related antigens. Parameters defining assay sensitivity were estimated experimentally for each antibody in 4 different immunoassays. Predicted failures of particular assays to detect differences in antigen affinities, based on these parameters, were demonstrated. One assay method failed to detect heteroclitic activity of 1 antibody which was clearly evident in the other 3 assays. As well as supporting theoretical models of assay sensitivity derived in the preceding paper the experiments demonstrated a significant effect of antibody subclass.