Reduction in non-specific binding in enzyme immunoassays using casein hydrolysate in serum diluents

Stages in ELISA

This chapter gives general information on essential practical features of ELISAs. These can be summarized as follows: 1. Adsorption of antigen or antibody to the plastic solid phase. 2. Addition of the test sample and subsequent reagents. 3. Incubation of reactants. 4. Separation of bound and free reactants by washing. 5. Addition of enzyme-labeled reagent. 6. Addition of enzyme detection system (color development). 7. Visual or spectrophotometric reading of the assay.

Interleukin-1 receptor antagonist modulates the progression of a spontaneously occurring IgA nephropathy in mice

Cytokines, such as interleukin-1 (IL-1), may play a key role in the pathogenesis of IgA nephropathy (IgAN). This study was conducted to evaluate the effects of IL-1 receptor antagonist (IL-1ra) in the treatment of a spontaneously occurring experimental IgAN in established phase. ddY mice (12/group) were injected twice daily with 3 mg/kg of IL-1ra, intraperitoneally, for 8 consecutive weeks. The placebo mice were injected with saline only. As normal controls, ddY mice, which were not treated with IL-1ra or saline, were killed at 6 weeks of age. Results showed a significant reduction of proteinuria in the IL-1ra-treated mice, compared with saline-treated mice (urinary albumin/creatinine, 0.24 +/- 0.04 v 0.39 +/- 0.03, P < 0.001). A significant improvement of renal 51Cr-EDTA (ethylenediaminetetra-acetic acid) clearance was observed in the IL-1ra-treated mice (t1/2, 12 +/- 2.7 minutes, compared with saline-treated mice 25 +/- 2.0 minutes, P < 0.001). Similarly, serum levels of creatinine (1.0 +/- 0.4 v 2.4 +/- 0.3 mg/dL, P < 0.001) and urea nitrogen (46 +/- 6 v 58 +/- 2 mg/dL, P < 0.01) were significantly lower in IL-1ra-treated mice than in saline-treated mice. In renal tissue studies, the IL-1ra-treated mice exhibited significantly decreased mesangial cell proliferation, compared with saline-treated mice (P < 0.001), as shown by light and electron microscopy. In addition, the IL-1ra-treated mice showed significantly lower glomerular expression of collagen type IV, fibronectin, laminin, and IL-6 (P < 0.001) than saline-treated mice, although they still showed higher glomerular expression of collagen type IV (P < 0.01), fibronectin (P < 0.01), laminin (P < 0.001), IL-1 (P < 0.001), and IL-6 (P < 0.01) than did normal control mice. Meanwhile, glomerular C3 deposition was significantly lower in IL-1ra-treated mice than in saline-treated mice (P < 0.001). These findings indicate that IL-1ra partially prevented the progression of spontaneously occurring IgAN in this experimental model. Data from these experiments also confirm the pathogenic effects of IL-1 in the established phase of IgAN in ddY mice.

Group-reactive ELISAs for detecting antibodies to African horsesickness and equine encephalosis viruses in horse, donkey, and zebra sera

Group-reactive enzyme-linked immunosorbent assays (ELISAs) were developed to selectively detect antibodies to African horsesickness virus (AHSV) and equine encephalosis virus (EEV), 2 orbiviruses that infect equids. In indirect ELISA, guinea pig antisera to all known AHSV or EEV serotypes recognized immobilized AHSV serotype 3 or EEV Cascara, respectively. Antisera from naturally infected animals did not cross-react with their respective heterologous viruses. The ELISA was used in parallel with the complement fixation (CF) and agar gel immunodiffusion tests to detect antibodies in sera from animals in the field. The ELISA distinguished among those that contained antibodies to AHSV, EEV, or both viruses and was useful with sera that did not yield results in CF tests because of anticomplementary activity. Zebra and donkeys, both potential subclinical carrier animals in Africa, contained AHSV or EEV antibodies. Some sera reacted with 1 of the 2 orbiviruses, whereas others reacted with both. The ELISA can be used in projected epidemiological studies in which many serum samples must be assayed.

The occurrence and sources of natural antibody in human bile and serum against the O antigens of two Escherichia coli serotypes

Paired serum and bile samples from normal subjects as well as patients with biliary disease were tested for natural antibody to two individual Escherichia coli O antigens by ELISA. Serum antibody was most commonly of IgM and IgG class. Antibody was less frequently detected in bile and was more commonly IgM than IgA, with IgG activity detected infrequently. Little relation was apparent between antibody in paired samples; activity could be present in both serum and bile or in either fluid alone. Titres in paired samples also did not correspond when 'normalized' with respect to the concentrations of relevant isotypes; bile was frequently enriched for natural antibody as a proportion of total immunoglobulin compared with serum. Secretory component-bound antibody was detectable in some biles that contained IgA and/or IgM activity and in the serum of 33% of subjects with biliary disorders but not in normal sera. A series of paired samples taken from three individuals was also examined for antibody against each subject's own intestinal commensal E. coli. Serum IgM and IgG activity was present in all samples, but antibody in bile was less frequent and was of IgM or IgA class. These results suggest that natural antibody in human bile occurs independently of antibody in serum and that it is substantially derived from local sources.

Blocking enzyme-linked immunosorbent assay for detection of antibodies against bovine enterovirus

A blocking enzyme-linked immunosorbent assay (ELISA) was developed for detecting antibodies against bovine enterovirus (BEV) in bovine sera. In this ELISA, bovine serum samples were allowed to react with captured viral antigens (by specific chicken IgG), before the addition of specific mouse IgG for measuring non-occupied viral epitopes. The ELISA was slightly more sensitive and required a shorter time period than traditional serum neutralisation (SN). Among the 871 bovine serum samples tested so far, the titres produced by this assay had a significant correlation with those recorded by SN. The ELISA could be used as an alternative assay for SN in a large-scale BEV antibody investigation.

Rapid diagnosis of acute Epstein-Barr virus infection by an indirect enzyme-linked immunosorbent assay for specific immunoglobulin M (IgM) antibody without rheumatoid factor and specific IgG interference

An indirect enzyme-linked immunosorbent assay (ELISA) for detection of Epstein-Barr virus-specific immunoglobulin M (IgM) antibody was developed with commercial reagents. Sera containing rheumatoid factor (RF) (as little as 0.5 IU/ml) coupled with specific IgG resulted in false-positives in the ELISA. This interference was eliminated by the use of anti-human IgG antibodies to remove RF and IgG. Thus, pathogen-specific IgG complexes to which IgM-RF could be bound during the subsequent test were inhibited, and competition between specific IgG and IgM was also prevented. Of the 1,672 serum specimens tested, 353 were found to be Epstein-Barr virus IgM antibody positive by indirect immunofluorescence (IF). Compared with the IF test, the ELISA showed 96.6% sensitivity, 99.7% specificity, and 99% accuracy. Further evidence indicated that most of the 12 ELISA false-negatives were IF false-positives. There was a linear correlation between mean ELISA values and increasing IF titers (r = 0.96). However, the IF test has the disadvantages that it lacks automated reading and requires considerable technical expertise, both of which restrict the range of laboratories performing the test. The indirect ELISA has the advantages that it is simple and rapid and can be automated. All the reagents used in this assay are commercially available, have been prestandardized, and are stable.

A capture antibody ELISA for detection of antibodies against bovine enterovirus

A capture antibody ELISA was developed for detecting antibodies against bovine enterovirus. Chicken IgG F(ab')2 fragments against strain J2129 captured virus effectively. The captured virus was used to detect specific antibodies against the virus in bovine sera. The specificity of the ELISA is high. The factors affecting the specificity are discussed. The assay is more sensitive and economic than traditional serum neutralisation.

Antibodies to HIV are produced within the central nervous system of all subjects with all categories of HIV infection

Anti-HIV antibodies were found in the cerebrospinal fluid of all 41 subjects tested whose serum contained these antibodies. To ensure that locally produced antibody was being detected, a sensitive assay was used to demonstrate the integrity of the blood-brain barrier. Antibodies to ubiquitous adenovirus group antigens were sought, simultaneously, in CSF and serum. A lack of adenovirus antibodies in CSF of subjects seropositive for adenovirus was required before CSF anti-HIV antibodies could be considered to be produced within the central nervous system. Of the 41 subjects tested eight were asymptomatic, eight were clinically well but had persistent lymphadenopathy, 14 were immunodeficient and had constitutional symptoms (AIDS-related complex or ARC) and 11 had AIDS. Oligoclonal banding was detected in the CSF of 16 subjects and a pleocytosis was present in 24. Neither finding clustered with a particular stage of infection. It appears that HIV infection of T lymphocytes and the central nervous system occurs simultaneously, early in the course of the infection. All HIV infected subjects are at risk of developing primary neurological as well as immunological sequelae. Currently poorly understood resistance factors must protect both lymphocytes and nervous system tissue from damage by the HIV virus, as to date, the majority of infected subjects have not become immunodeficient or developed neurological disease.

A synthetic vaccine protects humans against challenge with asexual blood stages of Plasmodium falciparum malaria

We have previously shown that a mixture of three synthetic peptides (83.1, 55.1, 35.1), corresponding to fragments of the relative molecular mass 83,000 (83K), 55K and 35K Plasmodium falciparum merozoite-specific proteins, induces protection in Aotus triviroatus monkeys experimentally infected with P. falciparum. Here we describe two polymeric synthetic hybrid proteins based on these peptides that delay or suppress the development of parasitaemia in immunized human volunteers.

An enzyme-linked lectin-binding assay on cells (CELLBA) for the comparison of lectin receptor expression on cell surfaces

Lectins can be used to specifically detect some cell surface glycans. Their expression on different cells or on cells of a given lineage throughout differentiation or following treatment with drugs can be compared using lectins labelled with radioactive, fluorescent or enzymatic probes. We describe a new method which, by analogy with CELISA (ELISA on cells), is called CELLBA (or ELLBA on cells) for cellular, enzyme-linked lectin-binding assay. It permits the comparison of the expression of specific glycans in a large number of different cell samples. As an example, it was able to detect alterations of cell surface glycan expression caused by inhibitors of N-linked oligosaccharide trimming.

Bordetella pertussis infection: a cause of persistent cough in adults

An enzyme-linked immunosorbent assay (ELISA) for Bordetella pertussis-specific immunoglobulin (Ig)A antibody in serum was used to demonstrate B. pertussis infection. The upper limit of normal for the assay (mean + 3 SD) was established by testing sera that had been collected from a group of healthy blood donors. All 13 patients with clinical whooping cough from whom B. pertussis was isolated and 25.7% of 218 adults, who were aged 18-81 years, who were referred to a consultant physician for the investigation of a persistent cough, had elevated levels of IgA to B. pertussis. The study confirms the B. pertussis IgA ELISA as a sensitive test for the diagnosis of B. pertussis infections and that these infections cause respiratory illness, in particular, persistent cough in adults.

An enzyme immunoassay for quantitation of a type 2 pneumocyte-specific surfactant-associated antigen in bronchoalveolar lavage fluid

A sensitive, specific and reproducible assay for quantitation of a surfactant-associated antigen in mouse bronchoalveolar lavage fluid is described. The procedure employed was a non-equilibrium competitive enzyme immunoassay in which detection of unreacted antibody was significantly enhanced by the use of a second antibody and peroxidase-antiperoxidase as the reporter label. The sensitivity of the assay was such that bronchoalveolar lavage fluid had to be diluted 15 to 30-fold prior to assay. No interference by serum proteins or soluble tissue proteins was observed. This assay may provide in vitro quantitative assessment of the functional status of type 2 pneumocytes.