Enzyme amplification can enhance both the speed and the sensitivity of immunoassays

The year of Pasteur: from the concept of antibody and antigen by Bordet (1895) to the ELISA. What future for immunological diagnosis?

BACKGROUND

Chronological account of the increase of the sensitivity of immunological reactions and future possible improvements are presented.

RESULTS

During these 100 years, the sensitivity of immunological reactions has been increased by approximately 5 log by reference to the basic technique of quantitative immunoprecipitation.

OBJECTIVES

Future progresses can be foreseen (i) in the signal of labeled reagents, with the development of time-resolved fluoro-immunoassays; (ii) in the presentation of viral antigens on solid phase, with a larger use of polystyrene microbeads; (iii) in the antigen used for antibody detection, by promoting the characterization of antibodies to conformational structures of viruses; (iv) for antibody reagent preparations, particularly by immunomodulation for the development of antibodies to weak epitopes or to presently non-immunogenic structures and; (v) in the discrimination of detected antibodies. Characterization of the discontinuous or continuous nature of the recognized epitopes and of the affinity of antibodies could permit to date the infection. Inhibition of a monoclonal antibody reacting with a conformational epitope, and identification of an idiotope, will be more selective than the usual characterization of a large polyclonal antibody activity. Finally, the use of antibodies specific of the sole SIgA, molecule is expected to carry new informations in serological diagnosis at the entry of numerous infectious agents. ELISA techniques will become tightly complementary to PCR, which leads to an early diagnosis when the focus of infection is easily accessible, but rapidly looses its diagnosis capacity in acute infections.

Kinetic study of the enzymatic cycling reaction conducted with 3alpha-hydroxysteroid dehydrogenase in the presence of excessive thio-NAD(+) and NADH

We have established a simple kinetic model applicable to the enzyme cycling reaction for the determination of 3alpha-hydroxysteroids. This reaction was conducted under the reversible catalytic function of a single 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) with nucleotide cofactors, thio-NAD(+) (one of the NAD(+) analogues) for the oxidation of 3alpha-hydroxysteroids and NADH for the reduction of 3-oxosteroids. This model was constructed based on the reaction mechanism of 3alpha-HSD, following an ordered bi-bi mechanism with cofactor binding first, under the assumption that the respective enzyme-cofactor complexes were distributed according to the initial ratio of thio-NAD(+) to NADH by the rapid equilibrium of both enzyme-cofactor complexes. The cycling rate in the new kinetic model could be expressed with the dissociation constants of enzyme-cofactor complexes and the initial concentrations of cofactors and enzyme. The cycling rate was verified by a comparison with the experimental data using 3alpha-HSD from Pseudomonas sp. B-0831. The results showed that the experimental data corresponded well with the results obtained from the kinetic model.

Oral administration of an edible-mushroom-derived protein inhibits the development of food-allergic reactions in mice

BACKGROUND

Food allergy is a common disease without effective treatment. Since strict elimination of food allergens may be difficult, strategies for effective intervention are urgently needed.

OBJECTIVE

The aim was to investigate the prophylactic use of orally administrated FIP-fve, an immunomodulatory protein isolated from the edible mushroom Flammulina velutipes, in a murine model of food allergy.

METHODS

BALB/c mice were immunized twice intraperitoneally with ovalbumin (OVA), at an interval of 2 weeks. Before and during each period of immunization, FIP-fve (200 microg per mouse) or phosphate-buffered saline was given orally every other day with a total of five doses. Then OVA-specific antibodies and cytokine profiles were determined. Subsequently, the mice were orally challenged with OVA. Symptoms of anaphylaxis, levels of plasma histamine, and histology of intestines were examined.

RESULTS

Mice receiving oral FIP-fve treatment during sensitization to OVA had an impaired OVA-specific IgE response with a Th1-predominant cytokine profile. These mice were protected from systemic anaphylaxis-like symptoms induced by subsequent oral challenge with OVA.

CONCLUSION

Oral administration of FIP-fve has a Th1-skewing effect on the development of the allergen-specific immune response, and may serve the purpose of immunoprophylaxis for food allergy and other allergic diseases.

Development of a quantitative immuno-PCR assay and its use to detect mumps-specific IgG in serum

Determination of the immune status of individuals to vaccine-preventable diseases requires an assay that can detect antibodies that may be present at very low levels, especially when natural or vaccine exposure may have been many years previously. Immuno-PCR (iPCR) has recently been described as an ultrasensitive method for the detection of antigens and we have adapted the method for the quantification of antibodies to mumps virus. The procedure used was similar to an indirect ELISA except that the detecting antibody (anti-human IgG) was chemically conjugated to a short capture oligonucleotide rather than an enzyme. The capture oligonucleotide was then detected by the addition of target DNA, which was designed to hybridise to the capture oligonucleotide and function as a template for real-time PCR. The quantity of target DNA detected by the PCR depended upon the level of specific antibody in the test sample. We found that the sensitivity (and specificity) of the iPCR assay did not exceed that of the conventional ELISA. The sensitivity was limited by nonspecific binding of human IgG to the solid phase. Further development of reagents and assay formats is necessary to fully exploit the potential of quantitative iPCR, so that potential improvements in the sensitivity of anti-mumps IgG detection can be realised.

A simple and reliable method for the detection of the 30delG mutation of the CX26 gene

Mutations in the CX26 gene (GJB2), encoding the gap-junction protein Connexin-26, have been shown to be the major cause of non-syndromic recessive deafness. Among these mutations, the deletion of a guanine within the stretch of six G between nucleotide positions +30 and +35 of the CX26 cDNA (30delG) accounts for the majority of this kind of deafness. Molecular detection of the 30delG mutation is usually performed by direct sequencing analysis of PCR products or by SSCP. To detect this mutation we developed an easy and reliable method, based on PCR, followed by a non-radioactive sandwich hybridization on microtiter plates. We tested 188 individuals recruited from the genetic counseling service for deaf people at the Pasteur Hospital and at the Armand-Trousseau Children's Hospital, Paris, France between April 1997 and September 1998. Our screening method is simple, uses stable and safe reagents, and employs inexpensive equipment. As such, it is suitable for widespread use in genetic diagnosis.

Immunity to airborne challenge with Venezuelan equine encephalitis virus develops rapidly after immunization with the attenuated vaccine strain TC-83

Mice vaccinated subcutaneously with the attenuated vaccine strain of Venezuelan equine encephalitis virus (VEEV) rapidly develop immunity to subcutaneous or airborne challenge with virulent VEEV. The specificity of this immune response was demonstrated by challenge with a heterologous virus (St. Louis encephalitis virus). Examination of the levels of VEEV-specific antibody classes in serum and respiratory secretions suggested that the rapid development of immunity was coincident with the appearance of specific IgM and IgG (but not IgA) in the respiratory tract. In order to confirm the role of respiratory tract antibody, mice were passively immunised either intraperitoneally or intranasally with polyclonal VEEV-specific IgG. Intranasal administration of specific IgG significantly enhanced protection against airborne challenge. These results confirm the need to emphasise local antibody production in the development of improved VEEV vaccines.

TC-83 vaccine protects against airborne or subcutaneous challenge with heterologous mouse-virulent strains of Venezuelan equine encephalitis virus

Vaccination with TC-83 virus produced solid protection against subcutaneous challenge with Venezuelan equine encephalitis (VEEV) viruses from homologous and heterologous serogroups, but breakthrough infection and disease occurred after airborne challenge. Breakthrough occurred more often with time after vaccination, and was more frequent with epizootic, homologous serogroup 1A/B viruses than with enzootic, heterologous serogroup viruses. A decrease in VEEV-specific IgA levels in the respiratory tract of vaccinated mice may explain the increased frequency of breakthrough with time after vaccination. However increased breakthrough with the highly virulent homologous serogroup 1A/B viruses (compared to less virulent viruses from heterologous serogroups) may be a consequence of their greater ability to invade the brain via the olfactory neuroepithelium and olfactory nerve.

Analysis of immunoglobulin A antibodies to Helicobacter pylori in serum and gastric juice in relation to mucosal inflammation

Helicobacter pylori is a major etiologic agent in gastroduodenal disorders. In this study, immunoglobulin A (IgA) antibodies to H. pylori antigens were evaluated in serum and gastric juice specimens obtained from patients with gastritis or peptic ulcers by utilizing antibody capture enzyme-linked immunosorbent assays (ACELISAs). Urease alpha subunit (UA), urease beta subunit (UB), the 66-kDa heat shock protein (HSP), and the 25-kDa protein (25K) were used as antigens for the ACELISAs. The antibody titers of the ACELISAs reflect the ratio of H. pylori-specific IgA to total IgA. The ratio is stable, although the antibody concentration fluctuates in gastric juice. By using ACELISAs it was possible to evaluate quantitatively not only serum IgA antibodies but also gastric juice secretory IgA (S-IgA) antibodies. In both serum IgA and gastric juice S-IgA ACELISAs, the titers of antibody to HSP and 25K were remarkably correlated with the histologic grade of gastritis, whereas those to UA and UB were not strongly correlated with histologic grade. Thus, it is useful for estimating the histologic grade of gastritis to quantify serum IgA and gastric juice S-IgA antibodies to HSP and 25K.

Covalent binding of proteins to grafted plastic surfaces suitable for immunoassays. II. Picograms of IgE detected in BAL fluid in sarcoidosis

An ELISA is described for the quantitation of minute amounts of human IgE using microtiter strips which were surface modified according to a procedure previously described. This ELISA used an IgG fraction of a rabbit polyclonal anti-IgE antibody coupled to the carboxylated surface, which prior to coupling had been preactivated with a water soluble carbodiimide. A biotinylated affinity purified rabbit anti-IgE antibody was used together with streptavidin conjugated alkaline phosphatase and biotinylated enzyme for the detection of bound analyte. Sarcoidosis is a systemic disorder of as yet unknown cause with epithelioid granuloma formation in the lung as a prominent feature. With the bronchoalveolar lavage technique, epithelial lining fluid was obtained and analyzed for IgE content since differences of immunoglobulin concentration in bronchoalveolar lavage fluid (BALF) may reflect disease activity. Our modified ELISA system was used for measuring IgE in BALF from healthy controls and sarcoid patients. The assay using modified strips demonstrated a considerably improved sensitivity compared to the use of physical adsorption of first antibody to untreated strips. The detection limit of the improved assay was approximately 3 pg IgE/sample (100 microl). Quantitative recovery of IgE was demonstrated within the measuring range (51.2-12500 pg IgE/ml) and more than 40% (23/54) of the sarcoid patients showed values above the lowest standard concentration (51.2 pg/ml). In contrast, none of the healthy controls (0/22) had detectable IgE as defined by the detection limit of the assay.

Regulation of the expression of the soluble and membrane forms of the murine IL-4 receptor

The actions of interleukin-4 (IL-4) in vivo are likely to be positively influenced by the expression of membrane IL-4 receptors (mIL-4R) on target cells and negatively by the concentration of soluble IL-4 receptors (sIL-4R) in the extracellular environment. Inasmuch as the two forms of the mouse IL-4R are differentially encoded by alternatively spliced mRNA transcripts, the purpose of this work was to determine how their expression is regulated by IL-4 and T cell activation and whether there is preferential expression of one type of transcript over the other. In this study, the expression of sIL-4R and mIL-4R transcripts was analyzed by a semiquantitative RT-PCR method in resting and mitogen-activated splenic cells. Irrespectively of the state of cell activation, IL-4 up-regulated the levels of both types of mRNA with similar kinetics and dose-response curves. In contrast, ConA failed to enhance the steady-state levels of sIL-4R or mIL-4R transcripts despite increased expression at the protein level, suggesting that sIL-4R expression is also regulated at levels other than transcription. Western blot analysis of supernatants of IL-4- and ConA-stimulated spleen cells substantiated the presence of sIL-4R molecules derived by translation of sIL-4R-specific transcripts, thus confirming the importance of this mechanism for the generation of sIL-4R molecules in normal cells. These results indicate that the sIL-4R- and mIL-4R-specific transcripts are normally regulated in a parallel manner and further suggest that expression of both forms of the IL-4R is controlled at multiple levels (i.e., transcriptional and posttranscriptional).

Cloning and expression of human V-genes derived from phage display libraries as fully assembled human anti-TNF alpha monoclonal antibodies

BACKGROUND

With the advent of phage antibody libraries, access to completely human antibody fragments is feasible, either by direct selection from human antibody libraries, or by guided selection. After selection, Fabs and scFvs may need to be expressed as complete antibodies in mammalian cells for further characterisation, or if effector functions are required.

OBJECTIVES

To rebuild and express the human anti-TNF alpha antibody Fab-P3A2 (isolated as a Fab fragment from phage display libraries by guided selection) as a fully assembled, functional human antibody (gamma-1, lambda) in Sp2/0 myeloma cells, and to perform preliminary characterisation studies of the secreted IgG1 molecule. A further objective was to investigate the kinetics of human antibody production and the stability of antibody secretion in transfectomas cultured in various media formulations.

STUDY DESIGN

A tripartite strategy was employed for cloning heavy chain gene (VH)-P3 and light chain gene V lambda-A2-C lambda into mammalian cell expression vectors p alpha Lys-30 and p alpha Lys-17 respectively. The cell line P3A2.B5 was isolated after co-transfection of Sp2/0 mouse myelomas with the constructs, expanded and weaned into a protein free medium. Fully assembled Ig-P3A2 antibody was purified by Protein A affinity chromatography and characterised with respect to size of antibody chains, and affinity for human TNF alpha. Stability of secretion was investigated by extended serial sub-culture and analysis of P3A2.B5 sub-clones. Strategies of media enrichment were tested for any effect on antibody productivity by selected P3A2.B5 sub-clones.

RESULTS

The cell line P3A2.B5 secreted an assembled, human antibody Ig-P3A2, with heavy and light chains of molecular weight 55 and 28 KD respectively. Equilibrium capture studies showed Ig-P3A2 to have a dissociation constant of approximately 1.5 x 10(-8) M. The mean specific productivity of the cell line increased from 1.2 pg/cell/day to 7.8 pg/cell/day by a combination of medium enrichment and serum reduction. Prolonged serial sub-culture of P3A2.B5 showed the cell line to be unstable with respect to antibody secretion.

CONCLUSIONS

We have outlined a method for expression of human V genes as assembled antibodies in Sp2/0 myeloma cells. A cloning strategy for the stable expression of scFv or Fab genes isolated from phage display libraries as assembled human antibodies of the IgGl subclass in Sp2/0 myeloma cells has been described. For maximising specific productivity of antibody-producing cell lines, supplementation of culture media with glucose, glutamine and amino acids increases antibody yield significantly compared to that in conventional media, indicating the latter is stoichiometrically limiting for production purposes.

Generation of atypical pulmonary inflammatory responses in BALB/c mice after immunization with the native attachment (G) glycoprotein of respiratory syncytial virus

The feasibility of using the highly purified native attachment (G) protein in a subunit vaccine against respiratory syncytial virus (RSV) was examined in a murine model with or without the fusion (F) protein of RSV and the adjuvant QS-21. The studies established that QS-21 was more potent than AIOH as an adjuvant for both F and G glycoproteins. Augmented antigen-dependent killer cell activity and complement-assisted serum neutralizing and anti-F and G protein immunoglobulin G2a antibody titers were observed. Immunization with G/QS-21 generated immune responses that were characterized by low levels of antigen-dependent killer cell activity, elevated levels of interleukin-5 (IL-5) and percentages of eosinophils in the bronchoalveolar lavage fluids after challenge, and splenic immunocytes that secreted IL-5 but not gamma interferon (IFN-gamma) after in vitro stimulation with purified whole virus antigens. The pulmonary eosinophilia was similar to that induced by a facsimile of a formalin-inactivated vaccine used in previous clinical trials and was prevented by prior in vivo treatment with anti-IL-5 but not with control immunoglobulin G or anti-IFN-gamma neutralizing monoclonal antibodies. Thus the data implied that vaccination with G/QS-21 generated helper T-cell immune responses that were type 2 in nature. Alternatively, the data suggested that the helper T-cell immune responses elicited by F/QS-21 were more type 1 in character. Neither eosinophilia nor elevated levels of IL-5 were observed in the lungs of mice after challenge. Noteworthy levels of antigen-dependent killer cell activity was observed, and splenic immunocytes secreted copious quantities of IFN-gamma. Immunization with a combination vaccine composed of highly purified native F and G proteins plus QS-21 (F+G/QS-21) resulted in augmented complement-assisted serum neutralizing antibody titers compared with vaccination with either F/QS-21 or G/QS-21 alone. However, following vaccination with F+G/QS-21, the bronchoalveolar lavage fluids contained significant increases in IL-5 and percentages of eosinophils after challenge, the spleen cells appeared to secrete less IFN-gamma after in vitro stimulation, and there was no evidence of increased numbers of antigen-dependent killer cell precursors. Taken together, the data imply that native G protein influences the nature of the immune responses elicited by F/QS-21. The results therefore suggest that G, not F, protein has more potential to bias the host for atypical pulmonary inflammatory responses.

Sera from HIV-1 infected individuals in all stages of disease preferentially recognize the V3 loop of the prototypic macrophage-tropic glycoprotein gp120 ADA

The outer membrane glycoprotein gp120 and the transmembrane glycoprotein gp41 are predominant targets of the humoral immune response to infection by human immunodeficiency virus type 1. The third hypervariable region (V3 loop) is the principal neutralizing domain and is the primary target of neutralizing antibodies directed against the envelope proteins of HIV-1. The V3 loop is also the major determinant for HIV-1 cell-specific tropism. To further characterize the humoral immune response directed against the gp120 envelope proteins, we expressed two prototypic gp120 envelope proteins (LAI/HXB2 and ADA) and chimeric gp120 envelope proteins in stable transfected Drosophila melanogaster Schneider 2 cells. Sera from four infected adults over the course of infection [McNearney et al. (1992) Proc. natn. Acad. Sci. U.S.A. 89, p. 10,242] were assayed for reactivity with the respective envelope proteins. Sera obtained at early stages preferentially recognized the gp120 envelope protein ADA, whereas in later stages of infection the sera showed diminished reactivity with both gp120 LAI/HXB2 and gp120 ADA. Chimeric envelope proteins revealed that the humoral response was directed primarily against the V3 loop of gp120 ADA. Furthermore, 22 sera from HIV-1 infected individuals in different stages of the disease were tested. Reactivity of sera with the gp120 envelope protein ADA was seven-fold higher than with the gp120 envelope protein LAI/HXB2. Our results suggest that the humoral immune response is preferentially elicited against the V3 loop of the prototypic macrophage-tropic gp120 envelope protein ADA.

Linked in vivo expression of soluble interleukin-4 receptor and interleukin-4 in murine schistosomiasis

Soluble interleukin-4 receptors (sIL-4R) are truncated IL-4R molecules that are secreted into biological fluids. To gain an insight into the mechanisms that control sIL-4R synthesis in vivo and their role in the regulation of immune responses, the expression and secretion of sIL-4R in mice infected with Schistosoma mansoni was studied. Splenocytes from infected animals responded to schistosomal antigen preparations with increased production of both IL-4 and sIL-4R. The synthesis of sIL-4R by spleen cells peaked at 8 weeks following infection and coincided with maximum levels of sIL-4R in serum and sIL-4R-specific mRNA in the liver of infected mice. The expression of IL-4-specific mRNA in the liver was different from that of IL-4R, reaching its peak approximately 2 weeks earlier. A relationship between sIL-4R production and the development and activation of Th2 cells was suggested by the findings that: (a) in vivo administration of anti-IL-4 antibodies (11B11) impaired the ability of splenic cells to secrete either IL-4 or sIL-4R; and (b) splenic cells from mice vaccinated with irradiated cercariae, which tend to develop much weaker Th2 responses than mice injected with live cercariae, expressed reduced levels of sIL-4R when challenged with schistosomal antigens. Moreover, a direct role for IL-4 in regulating the expression of sIL-4R was suggested by the ability of anti-IL-4 antibodies to inhibit sIL-4R synthesis in vitro. These data provide the first evidence demonstrating that the production of sIL-4R in vivo is up-regulated during immune responses, especially during those characterized by the development and activation of Th2 cells and IL-4 secretion. The association between sIL-4R and IL-4 synthesis is consistent with a potential role for sIL-4R in the regulation of IL-4 activity in vivo.

Amplified electrochemical immunoassay for thyrotropin using thermophilic beta-NADH oxidase

The use of the highly stable, pH insensitive flavoenzyme, reduced nicotinamide adenine dinucleotide oxidase (NADH oxidase) from the thermophilic organism Thermus aquaticus in combination with alcohol dehydrogenase in an amperometric amplified immunoassay for thyrotropin (TSH) is described. NADH oxidase catalyses the oxidation of reduced nicotinamide adenine dinucleotide (NADH) with concomitant two electron reduction of di-oxygen to hydrogen peroxide. Hydrogen peroxide can be detected by oxidation at a platinum electrode poised at +650mV vs. Ag/AgCl. The enzyme amplification system described has advantages over existing amplification techniques in terms of sensitivity, specificity and operational pH dependence. The electrochemical enzyme-amplified assay for TSH was compared with a spectrophotometric enzyme-amplified system and with a non-amplified electrochemical immunoenzymometric TSH assay. The dynamic range of the electrochemical enzyme-amplified TSH immunoassay was 0.2-100 mIU/l, which was four times that of the enzyme-amplified spectrophotometric assay while the detection limits of both techniques were comparable.

Non-radioactive analysis of biomolecules

An overview on non-radioactive bioanalytical indicator systems is presented. The nature of labels being important for direct as well as indirect systems is discussed. This is followed by the description of enzymatic, photochemical and chemical methods for labeling nucleic acids, proteins and glycans. These methods can be applied either for direct labeling of these biomolecules or for labeling of respective probes (DNA, RNA, oligonucleotides, antibodies, lectins). In the second part, various optical, luminescent and fluorescent detection approaches are described. The possibility to enhance the sensitivity by coupled amplification reactions (signal amplification, target-specific signal amplification, target amplification) is shown in a separate section. Finally, the wide variety of qualitative and quantitative reaction formats related to different applications is collected.

A universally applicable diagnostic approach to filarial and other infections

Antibody-based assays for the diagnosis of filarial and other infections cannot reliably distinguish between past and current infection, nor can they be used to assess the efficacy of chemotherapy. In this article, Thomas Nutmon, Peter Zimmerman, Joseph Kubofcik and Donna Kostyu discuss how the detection of parasite-specific PCR products using on ELISA-based assay may overcome these problems.

Antigen-binding glycosylation inhibiting factor from a human T-cell hybridoma specific for bee venom phospholipase A2

We obtained human T-cell hybridomas that are specific for bee venom phospholipase A2 (PLA2) and constitutively secrete glycosylation inhibiting factor (GIF). Upon crosslinking of CD3, the hybridoma produced GIF having affinity for PLA2. When affinity-purified PLA2-binding GIF was used as an immunogen, monoclonal antibodies specific for the antigen-binding GIF were obtained. Monoclonal antibody 110BH3 bound the antigen-binding GIF but failed to bind the 13-kDa nonspecific GIF, as determined by both bioassay and ELISA. In contrast, 388F1, a monoclonal antibody against nonspecific GIF, gave ELISA signals with both the nonspecific GIF and the antigen-binding GIF. Gel filtration of affinity-purified antigen-binding GIF revealed the presence of a 72- to 80-kDa protein which gave ELISA signals with both 110BH3 and 388F1 and contained GIF bioactivity. Upon reduction and alkylation, the antigen-binding GIF dissociated into a 62- to 64-kDa protein which gave positive ELISA with antibody 110BH3 but no signal with antibody 388F1, and a 15-kDa protein, which gave ELISA signal with the 388F1 but not with 110BH3. Immunoblotting of a PLA2-binding GIF preparation revealed that under reducing conditions, the antigen-binding GIF dissociated a 13-kDa peptide which reacted with polyclonal antibodies against recombinant GIF. The results indicate that the 13-kDa nonspecific GIF is a subunit of antigen-binding GIF. The PLA2-binding GIF has affinity for an epitope, representing amino acid residues 19-28 in PLA2 which appears to be an external structure in the antigen.

Immunoassays for inhibin and its subunits. Further applications of the synthetic peptide approach

We describe the preparation of a new rat monoclonal antibody (CRC1) to the N-terminal sequence of the 43 kDa subunit of human ovarian inhibin, and its use together with other anti-peptide monoclonal antibodies, in two-site immunoassays for the detection of inhibin-related material in biological fluids. The Fab fraction of a mouse monoclonal antibody (R1) to the N-terminal portion of the 20 kDa alpha subunit, coupled to alkaline phosphatase, was used for detection, and either CRC1 or a monoclonal antibody (E4) to the beta-A subunit were used as capture antibodies. The E4/R1 combination, expected to measure dimeric bioactive inhibin, could detect less than 2 pg/ml of recombinant inhibin in diluent, gave good recovery of activity spiked into human blood, and could measure significant levels of immunoreactivity in sera from women undergoing ovulation induction, and in some normal women. Sera from post-menopausal women contained undetectable levels. Apparent inhibin levels in human follicular fluid were increased six-fold by pretreatment with 8 M urea, suggesting masking of epitopes in this fluid. Activin cross-reactivity in the assay was 0.05%. The R1/CRC1 assay, expected to measure only large molecular weight forms of inhibin or its alpha subunit, could detect immunoreactivity in human FF diluted 50,000-fold, and in all sera tested, although the levels in the hyperovulated women were higher. By contrast to the E4/R1 assay much of the immunoreactivity was labile during the clotting process, or subsequent assay, and reliable measurements on blood with this assay will require special sample collection procedures. These results demonstrate the value of anti-peptide monoclonal antibodies in the study of inhibin, and the results obtained with CRC1 show that antibodies useful for immunoassays can sometimes be obtained without the purified target molecule being available for immunization or screening.

Rapid HLA-DR oligotyping by an enzyme-linked immunosorbent assay performed in microtiter trays

A simple, sensitive ELISA that is performed in 96-well microtiter plates and that requires less than 90 minutes to complete was developed for HLA-DRB oligotyping. The second exon of HLA-DRB1 was amplified using an unlabeled forward primer and a biotinylated reverse primer and the PCR product was immobilized in avidin-coated wells. Subsequent treatment included exposure to 0.4 N NaOH to remove the nonbiotinylated sense strand, addition of a fluorescein-labeled oligonucleotide probe, one or more 5-minute stringency washes, addition of an alkaline-phosphatase-labeled anti-FL FAB, and then alkaline-phosphatase substrate and amplifier. An intense red-violet color developed within 15 minutes in positive wells and could be quantitated by OD readings at 490-495 nm. To control for stringency and to establish threshold OD values for positive reactions, biotin-labeled antisense oligos that were complementary to the probe or that differed by one or more bases were immobilized in wells in place of PCR products. The assay was sensitive to < 0.05 pmol (approximately 4 ng)/well and required only standard incubators and waterbaths and an optional microplate reader. All reagents were commercially available. The method should facilitate oligotyping of both class I and class II alleles and is adaptable for analysis of other polymorphic gene products.

Cross-protection against lymphocytic choriomeningitis virus mediated by a CD4+ T-cell clone specific for an envelope glycoprotein epitope of Lassa virus

Recombinant vaccinia virus expressing the Lassa virus (LV) envelope glycoprotein precursor, V-LSGPC, was used to study the basis of LV-induced cross-protective immunity against the closely related arenavirus lymphocytic choriomeningitis virus (LCMV). C3H/HeJ mice primed with V-LSGPC developed neither circulating antibodies nor CD8+ cytotoxic T cells specific for LCMV, yet they resisted a normally lethal LCMV challenge. Spleen cells from such mice gave a proliferative response to LCMV in vitro that was inhibitable by anti-CD4 antibody. Synthetic peptides corresponding to predicted T-cell sites common to the envelope glycoprotein precursor (GP-C) of LV and that of LCMV were used to map the specificity of the proliferative response to an epitope located between amino acids 403 and 417 of LV GP-C. Several CD4+ T-cell clones specific for the 403-417 peptide were isolated and found to produce gamma interferon in response to both the peptide and LCMV. One of these clones, C9, was selected for further study. C9 lysed I-AK-bearing target cells, and when adoptively transferred to C3H/HeJ mice, it was capable of mediating both a peptide-specific delayed hypersensitivity reaction and resistance to lethal LCMV challenge. These collective findings demonstrate, for the first time, that CD4+ T cells can play a major role in arenavirus-specific cross-protective immunity.

Anti-CD23 monoclonal antibodies: comparisons of epitope specificities and modulating capacities for IgE binding and production

A large battery of anti-CD23 mAb were compared for their epitope specificities and for their abilities to alter both IgE binding to cell-associated CD23 and IgE production in vitro in response to three sets of stimulants. The nine mAb tested can be divided into four families which define four antigenic epitopes (A-D) of CD23. Of these four families, two bind antigenic sites, (A and D) that appear to lie outside the IgE ligand binding site and two bind sites (B and C) that appear to be located within or close to this site, as determined by the abilities of appropriate mAb to alter IgE binding to CD23. The effects that these mAb had on IgE secretion by normal peripheral blood mononuclear cells (PBMNC) varied depending on the stimulant employed to induce IgE production. Interactions with epitope A, which was found to lie outside the ligand binding site and to be made more accessible by binding of mAb to other epitopes, had different effects on IgE production than interactions with the other epitopes. Indeed, mAb binding to this epitope lead to as much as a 10 fold enhancement in IgE biosynthesis induced by IL-4 alone or by IL-4 + hydrocortisone whereas interactions at the other sites resulted in almost complete inhibition of IgE production. In addition, mAb reactive with epitopes B and C had minimal effects on IgE production induced by IL-4 + anti-CD40 mAb whereas interactions at epitope A consistently enhanced IgE production. Finally, no apparent direct correlation was found between the ability of individual anti-CD23 mAb to alter IgE binding to cell-associated CD23 and their ability to modulate IgE production by PBMNC. These studies suggest that IgE binding to cell-associated CD23 does not have a major role in the de novo synthesis of IgE that involves CD23 interactions. In addition, the different effects that binding to epitope A vs B or C have on IgE synthesis suggest that molecular interactions between distinct portions of the CD23 molecule and other cell surface molecules expressed on the same B cell or adjacent communicating cells may lead to divergent cellular effects on IgE production. Finally these studies imply that only epitope A is involved in the generation of an IgE response through the CD40 pathway.

Isotypic variation in antibody responses in a community in Papua New Guinea to larval and adult antigens during infection, and following reinfection, with the hookworm Necator americanus

The natural infection of a community with the hookworm Necator americanus induces a vigorous humoral response to both larval and adult parasite antigens. This response occurs in all five human antibody isotypes, and data are presented to show that, at the population level, isotypes respond differently, following chemotherapy and during reinfection, to changes in antigen stimulation. The differential response probably reflects the fact that the parasite, during the course of its life cycle, presents different amounts of antigens at different anatomical locations. It is suggested that IgG and IgM responses against adult excretory-secretory (ES) products most accurately reflect the efficacy of chemotherapy, and the load of resident adult infection, while IgG responses against larval somatic antigens reflect continuous exposure to infection. These hypotheses should now be tested, at the level of the individual, in a longitudinal manner using more closely spaced sampling intervals. This repetitive sampling, and the inclusion of a measure of the exposure of the population to infective stages, will allow more definitive conclusions to be made about the role of the immune response in controlling worm burdens.

Experimental enzyme-linked amperometric immunosensors for the detection of salmonellas in foods

Two enzyme-linked amperometric immunosensors specific for salmonellas were developed as rapid methods for quantifying and detecting these organisms in pure cultures and foods. Both used alkaline phosphatase as the enzyme reporter molecule but one system used phenyl phosphate as the substrate followed by the electrochemical detection of phenol at a polarized platinum electrode. The other system incorporated an enzyme amplification step and relied on the electrochemical detection of a reduced mediator, ferrocyanide. Both assays were rapid (4 h) and specific and generated salmonella-dependent signals above 10(4) cfu/ml (phenyl phosphate system) or 10(5) cfu/ml (enzyme amplified system) in pure cultures and samples of several foods, although the results with beef samples showed considerable variation. Both systems were able to detect low (1-5 cfu/g or /ml) numbers of salmonellas in foods after non-selective (18 h) and selective (22 h) enrichment steps but four samples, out of 147, gave false positive results. False positive results were eliminated by reducing the enrichment steps to 6 h and 18 h respectively (90 samples).

An ultrasensitive system to detect IL-4: enzyme-linked immunosorbent assay (ELISA) combined with an avidin-biotin and enzyme amplification system

We established an ultrasensitive interleukin-4 enzyme-linked immunosorbent assay by combining ELISA with an avidin-biotin and enzyme amplification system. The resultant system (AB-EA ELISA) was 250 times more sensitive than conventional ELISA and 2.5 times more sensitive than enhanced ELISA using an enzyme amplification system alone. The ultrasensitive assay was specific to IL-4 alone; there was no cross reaction with other cytokines. Using the ultrasensitive assay, we measured IL-4 synthesis in vitro by unstimulated and stimulated peripheral blood mononuclear cells (PBMC) from patients with allergic rhinitis. PBMC from patients spontaneously produced measurable amounts of IL-4, whereas IL-4 production from PBMC of normal controls, if any, was below detectable levels. Stimulation of the cultures with LPS significantly increased IL-4 production in two of six patient PBMC cultures but in none of the control cultures; stimulation with Con A markedly increased IL-4 production in all patient PBMC cultures but in only two of seven control cultures. These results suggest that the AB-EA ELISA is a useful method to study the mechanism of IL-4 synthesis in type-I allergic diseases.

New techniques in rapid viral diagnosis

The development of new diagnostic techniques in immunology and molecular biology during the last two decades has opened up new possibilities for rapid viral diagnosis. Solid phase immunoassays for antigen and antibody detection are now widely used in diagnostic settings. Several novel techniques have been introduced and have led to commercially available tests. Diagnostic methods using nucleic acid amplification procedures are already applied in research laboratories and will be commercialized soon. Biosensor-based diagnostic techniques have the potential of generating a result nearly instantaneously and it has become possible to monitor kinetic processes. Automatization and simplified procedures are needed to allow diagnostic tests to be performed soon after the sample has been obtained from the patient. In order to evaluate the new procedures and avoid false results, rigorous quality control in diagnostic virology will have to be instituted.

A colorimetric method for detection of specific ligand binding

The binding of IL-2 and IL-3 to the factor-dependent cell lines CTB6 and 32D, respectively, was determined using biotinylated ligand detected by the addition of a streptavidin/alkaline phosphatase conjugate and amplified with a phosphatase amplification system. Binding of both ligands was detectable after incubation with as little as 20 fmol of ligand and could be inhibited with a 10-fold molar excess of nonbiotinylated ligand. No binding was observed when biotinylated ligand was incubated with a receptor negative cell line (PC-12) and IL-2 was unable to compete with biotinylated IL-3 binding to 32D cells, further demonstrating specificity. These studies indicate that biotinylated ligands can be used as a nonradioactive method to detect specific, high-affinity cell surface receptors.

Immunoenzymatic techniques applied to the specific detection of nucleic acids. A review

Numerous enzymatic and chemical methods are now available for the preparation of non-radioactive nucleic acid probes. Labels, such as enzymes, fluorophores, lumiphores can be attached to the nucleic acid probe either by covalent bonds (direct labelling) or by biospecific recognition after hybridization (indirect labelling). The principle of the latter method is based on the use of a hapten-labelled nucleic acid probe which is generally detected by an immunoenzymatic assay. Indirect labelling has several advantages: this procedure uses multienzyme complexes to increase the number of enzyme molecules associated with hybridization and hence provides an increase in detectability; moreover, haptens (biotin, dinitrophenol, acetylaminofluorene analogues, digoxigenin, brominated or sulphonylated pyrimidines) used to label nucleic acid probes are not sensitive to elevated temperatures (42-80 degrees C), extended incubation times (several hours), detergents and organic solvents currently required in hybridization techniques. The application of the immunoenzymatic and related techniques to nucleic acid probing is reviewed, focussing on the strategies of non-radioactive hybridization, hapten-labelling of nucleic acids and methods for the immunodetection of the hybrids.

Using microparticle labeling and counting for attomole-level detection in heterogeneous immunoassay

A new heterogeneous "sandwich" immunoassay utilizing microparticles as labels to realize high sensitivity is described. In this method, antibody fixed on the microparticles reacts with antigen previously trapped on a microplate surface, which makes the antigen molecules visible and countable with an inverted optical microscope. The method is highly sensitive because the reacted single microparticle, therefore single antigen molecule, can be detected. The sensitivity depends both on the reaction efficiency of the immunoreaction and on nonspecific adsorption of the microparticles on the microplate surface. Therefore, the protocol for preparing microparticle having antibody on the surface and a microplate having capture antibody was investigated to realize high sensitivity. Carboxylated microparticles of 0.76 microns in diameter were conjugated with affinity-purified antibody using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. It was determined that 1 g microparticles had 880 micrograms antibody (approximately 1100 antibody molecules per 1 microparticle). The immunoreaction efficiency reached 18% at 1 x 10(-13) mol/liter antigen concentration. The lower detection limit was 3.1 x 10(-14) mol/liter (1.6 amol) using human alpha-fetoprotein as a model antigen.

Biochemical characterization of murine glycosylation-inhibiting factor

The glycosylation-inhibiting factor (GIF) was isolated from serum-free culture supernatants of the murine T-cell hybridoma, 231F1 cells, by using an immunosorbent coupled with the monoclonal anti-lipomodulin antibody. The isolated lymphokine is a 14-kDa protein with a pI of 5.5, as determined by SDS/PAGE and two-dimensional gel electrophoresis. Fractionation of a mixture of radiolabeled GIF with culture supernatant of the 231F1 cells on ion-exchange and reverse-phase columns and by gel filtration demonstrated homogeneity of the 14-kDa GIF and confirmed that the bioactivity of GIF and the antigenic determinant recognized by the monoclonal anti-GIF antibody are associated with the 14-kDa protein. The 125I-labeled 14-kDa protein binds to the murine T-cell hybridoma 12H5 cells, which have been used for bioassay of GIF, and the murine B-cell line A20.3 cells, but the binding of the protein to resting murine splenic lymphocytes was barely detectable. Under the same experimental conditions, binding of the 125I-labeled recombinant human lipocortin I to the 12H5 cells was not detectable. In contrast, the 125I-labeled lipocortin, but not the 14-kDa GIF, bound to phosphatidylserine vesicles. The results indicate that GIF does not belong to the anexin family.

Neuroendocrine challenge studies in puerperal psychoses. Dexamethasone suppression and TRH stimulation

Subjects admitted to hospital with post-partum psychoses were compared with matched normal post-partum controls using two neuroendocrine challenge tests: dexamethasone suppression of cortisol and TRH stimulation of TSH. Post-dexamethasone cortisol levels were significantly elevated. There were less-clear hints of blunting of TSH response. In the small samples there was no obvious association of abnormalities with any particular diagnoses within the range of mania, psychotic depression and schizoaffective disorders.

The digoxigenin:anti-digoxigenin (DIG) technology--a survey on the concept and realization of a novel bioanalytical indicator system

A review is given on the novel non-radioactive digoxigenin:anti-digoxigenin (DIG) bioanalytical indicator system. After a general introduction on direct and indirect indicator systems based on previous non-radioactive indicator reactions as well as in vitro and in vivo amplification procedures the principle of the new digoxigenin:anti-digoxigenin technology is demonstrated. The novel system is based on the specific high-affinity interaction between the cardenolide digoxigenin from Digitalis plants and a digoxigenin-specific antibody coupled with a reporter group. A variety of methods for digoxigenin modification of nucleic acids, proteins and glycans are presented. In addition, various applications of the novel non-radioactive indicator system in a variety of direct or indirect detection approaches with either insoluble or soluble substrates are described. It is also shown that with these applications alternative reaction formats are used which are partly characterized by additional amplification steps.

Development of monoclonal antibodies reactive with methamphetamine raised against a new antigen

Monoclonal antibodies (McAbs) specific to methamphetamine (MA) were produced using p-amino MA coupled to bovine serum albumin (BSA) with glutaraldehyde (GA) as an immunogen and with conventional hybridoma techniques. Hybridoma clones secreting the McAbs were selected by an enzyme-linked immunosorbent assay (ELISA) system using both the above conjugate and BSA modified with GA as screening antigens. In the ELISA system were used avidin and biotinyl-alkaline phosphatase which converts nicotinamide adenine dinucleotide phosphate (NADP) into NAD. The final enzyme activity was determined using diformazan of nitroblue tetrazolium formed together with the NAD produced, alcohol dehydrogenase and phenazine methosulfate. The McAbs from 9 clones were characterized by a crossreactivity test using the ELISA. The McAbs recognized MA (100%), methoxyphenamine (8.0%), ephedrine (2.3%), but did not react with metylephedrine, amphetamine, OH-amphetamine, dimethylamphetamine, beta-phenylethylamine, norephedrine, phentermine and ranitidine. An inhibition curve for MA was obtained in the range of 0.75 to 50 ng.

In vitro regulation of B cell differentiation by interleukin-6 and soluble CD23 in systemic lupus erythematosus B cell subpopulations and antigen-induced normal B cells

Polyreactive systemic lupus erythematosus (SLE) B cells were compared with antigen-induced SLE and normal B cells for their interleukin-6 (IL-6) and soluble CD23 requirements. Unlike normal B cells, secretion of antibody by SLE B cells in serum-free medium was not enhanced by exogenous IL-6. Anti-IL-6 antibodies inhibited immunoglobulin production in cultures of normal and SLE B cells, which suggests that IL-6 is required for B cell differentiation. SLE culture supernatants had elevated levels of IL-6, which explains the poor response of the SLE cells to exogenous IL-6. Soluble CD23 enhanced the responses of cells from normal subjects and SLE patients.

Gaucher's disease: lack of antibody response in 12 patients following repeated intravenous infusions of mannose terminal glucocerebrosidase

An amplified ELISA has been employed for monitoring the safety of repeated intravenous infusions of modified human placental glucocerebrosidase. The enzyme infusions consisted of biweekly injections of macrophage targeted glucocerebrosidase over a 6 month duration. Serum samples collected throughout the study were assayed by use of an ELISA using alkaline phosphatase coupled to alcohol dehydrogenase for amplification. Using this protocol, 0.2-5 ng affinity purified immunoglobulin specific for glucocerebrosidase can be detected. Occasional false positives necessitate multiple repeat assays over time to accurately assess immunogenic response. Blinded ELISAs were performed on sera from both infused patients with Gaucher's disease and uninfused control patients and compared with apparent immunoglobulin concentration in 54 normal control sera. Although several samples showed apparently elevated immunoglobulin levels, repeat analyses failed to demonstrate high levels reproducibly. Furthermore, these sera were unable to neutralize enzyme or to precipitate radiolabelled enzyme, confirming the absence of antibody. Problems with high sensitivity ELISA formats are discussed.

Differential loss of envelope glycoprotein gp120 from virions of human immunodeficiency virus type 1 isolates: effects on infectivity and neutralization

Several parameters which may affect the infectivity of human immunodeficiency virus type 1 in tissue culture were analyzed. In particular, we used gel exclusion chromatography to investigate how the loss of the surface glycoprotein gp120 from virions of the HTLV-IIIB (IIIB), HTLV-IIIRF (RF), and SF-2 isolates modulates infectivity. In IIIB and RF cultures, a high proportion of the total gp120 was virion bound initially but was gradually lost from the virions over time. In contrast, most of the gp120 (and p24) in SF-2-infected cultures was soluble and the few particles present had a fivefold-lower level of virus-bound gp120. However, this reduced level of virion-bound gp120 was more resistant to shedding. Loss of a major proportion of gp120 from IIIB and RF virions resulted in reduced infectivities, and in addition, the resulting accumulation of soluble gp120 in the cultures could competitively inhibit viral infection, especially with SF-2. Increased shedding of virion gp120 also affected the neutralization of IIIB and RF particles. However, the high sensitivity to human serum neutralization characteristic of SF-2 was unaffected by soluble gp120 in cultures, suggesting that the epitopes responsible are not present on soluble gp120.

Corticotrophin-releasing factor-41 in the human and rat-utility of a highly sensitive enzyme amplified immunometric assay

Abstract We have developed a highly sensitive and specific immunoassay for human/rat corticotrophin-releasing factor-41 (CRF-41) to enable determination of immunoreactive CRF-41 levels in biological samples. To achieve high specificity, sensitivity and speed we have used two antisera in a sandwich enzyme immunoassay combined with enzyme amplification. The assay has a sensitivity of 0.08 fmol/well compared with radioimmunoassay sensitivities of 0.5 fmol/tube and is highly specific for the intact CRF-41 molecule. Measurement of samples is complete within 24 h compared with the 5 days required to obtain sensitive radioimmunoassay measurement. The assay has been used to measure both rat hypothalamic CRF-41 tissue content and release in vitro with good correlation when compared to radioimmunoassay measurement using antisera rC70 (0.983) or R1 (0.953). The assay only measures immunoreactive CRF-41 coeluting with human/rat CRF-41 and its oxidized form Met [O(21,38)]CRF-41 in human and rat tissue extracts separated by high-performance liquid chromatography. The ability to measure immunoreactive CRF-41 in unextracted plasma allows rapid measurement and eliminates multiple extraction steps.

Enhancement of soluble CD4-mediated HIV neutralization and gp 120 binding by CD4 autoantibodies and monoclonal antibodies

We have identified 6 sera containing autoantibodies to CD4 in 174 human immunodeficiency virus-type (HIV-1) positive sera tested in an antigen-capture enzyme-linked immunosorbent assay (ELISA) using sCD4, and none in 34 HIV type 2 sera. These autoantibodies do not bind to cellular CD4, but react with sCD4 to increase its binding in ELISA to monoclonal antibodies and the HIV surface glycoprotein gp120. The effect of CD4 autoantibodies is mimicked by monoclonal antibodies to the third and fourth domains of CD4. The enhanced sCD4 binding to gp120 in ELISA is reflected by a reduction in the concentration of sCD4 required to neutralize HIV-1 and HIV-2 infection in tissue culture when CD4 autoantibodies or the relevant monoclonal antibodies were present.