Analysis of a solid-phase radioimmunoassay for antibodies to cytoplasmic antigen fractions of Candida albicans

The serodiagnosis of tuberculosis: a comparison of an enzyme-linked immunosorbent assay and a solid-phase radioimmunoassay

Antibodies to a cytosolic fraction of Mycobacterium tuberculosis in sera from 104 patients with pulmonary tuberculosis and 141 age-matched healthy control subjects were quantitated by solid-phase radioimmunoassay (SPRIA) and an enzyme-linked immunosorbent assay (ELISA) technique. The SPRIA gave a greater discrimination than ELISA: in the former test 92% of patients had antibody levels in excess of those occurring in 97% of controls, while the corresponding figure with the latter was only 73%.

Interaction of human leukocytes and Entamoeba histolytica. Killing of virulent amebae by the activated macrophage

Capable effector mechanisms in the human immune response against the cytolytic, protozoan parasite Entamoeba histolytica have not been described. To identify a competent human effector cell, we studied the in vitro interactions of normal human polymorphonuclear neutrophils, peripheral blood mononuclear cells (PBMC), monocytes (MC), and MC-derived macrophages with virulent axenic amebae (strain HMI-IMSS). Amebae killed neutrophils, PBMC, MC, and MC-derived macrophages (P less than 0.001), without loss of parasite viability. The addition of heat-inactivated immune serum did not enable leukocytes to kill amebae, nor did it protect these host cells from amebae. MC-derived macrophages, activated with lymphokine elicited by the mitogens conconavalin A, phytohemagglutinin, or an amebic soluble protein preparation (strain HK9), killed 55% of amebae by 3 h in a trypan blue exclusion assay (P less than 0.001); during this time, 40% of the activated macrophages died. Lysis of amebae was confirmed using 111Indium oxine radiolabeled parasites and was antibody independent. Macrophage death appeared to be due to the deleterious effect of lysed amebae rather than the contact-dependent effector mechanisms of E. histolytica. Adherence between activated macrophages and amebae was greater than that between other leukocytes and amebae (P less than 0.001). Microscopic observations, kinetic analysis of the killing of amebae by activated macrophages, and suspension of amebae with adherent activated macrophages in a 10% dextran solution indicated that contact by activated macrophages was necessary to initiate the killing of amebae. Catalase but not superoxide dismutase inhibited the amebicidal capacity of activated macrophages (P less than 0.001). However, activated macrophages from an individual with chronic granulomatous disease were able to kill amebae, but not as effectively as normal cells (P less than 0.01). In summary, activated MC-derived macrophages killed virulent E. histolytica trophozoites through a contact-dependent, antibody-independent mechanism involving oxidative-dependent and -independent processes.

Identification and molecular weight characterization of antigens from Candida albicans that are recognized by human sera

Antigenic components in the cytoplasmic extract of Candida albicans were examined after fractionation by concanavalin A-Sepharose and DEAE-Sephacel ion-exchange chromatography. Fractions from the DEAE column were tested by fused rocket immunoelectrophoresis for their reactivity with antibodies in the sera of 20 patients with disseminated candidiasis. Three groups of fractions (regions A, B, and C) from the DEAE column were defined by their reactivity with these sera. Immunoblot analysis with 20 human sera identified 18 antigenic components in regions A, B, and C. Region A contained nine antigens, region B contained four antigens, and region C contained five antigens. Region A contained an antigen with an apparent molecular weight of 48,000 that was recognized by 7 of 10 sera from patients with disseminated candidiasis. Immunoprecipitation experiments with labeled proteins from region A and 51 human sera also demonstrated the presence of a major antigen whose apparent molecular weight is 48,000 to 52,000. The 48- to 52-kilodalton protein is an abundant protein in region A and is the most frequently recognized protein by antibodies in the sera of patients with disseminated candidiasis. Patients with disseminated candidiasis had significantly higher levels of antibody (immunoglobulin G) (P less than 0.001) directed against the 48- to 52-kilodalton protein than did patients with noninvasive forms of candidiasis, patients with other fungal infections, or normal, healthy persons.

Antigen and antibody attachment in ELISA for Aspergillus fumigatus IgG antibodies

Four commercial antigen extracts of Aspergillus fumigatus were evaluated for use in a rapid enzyme-linked immunosorbent assay (ELISA) for anti-A. fumigatus IgG. Initial binding of both somatic and culture filtrate preparations to a polyvinyl chloride solid phase was concentration dependent and increased with incubation time. Antigen binding to the solid phase was reproducible. Binding of A. fumigatus precipitin-positive serum to bound antigen was rapid. All four A. fumigatus antigens demonstrated similar dose-response curves when tested against pooled sera containing a high titre of A. fumigatus antibodies. Detectable activity in precipitin test-negative sera decreased rapidly with dilution. All the antigen preparations were found to be suitable for ELISA procedures and permit the rapid determination of IgG antibodies to A. fumigatus.

Comparison of immunoradiometric assays of Bacillus anthracis spores immobilised on multispot slides and on microtitre plates

Indirect immunoradiometric assays (IRMA) for Bacillus anthracis spores are described in which the spores were heat fixed either on multispot microscope slides or on polyvinyl or polystyrene microtitre plates. Assays on plastic plates sometimes suffered from poor intra-experiment reproducibility. Signals were higher in assays in flat-bottomed microtitre wells than in assays in slides, but assay noise, due to non-specific absorption of antibody, was higher also, giving an overall disadvantage in signal-to-noise ratio. Elution of antibody with acid gave up to a doubling in signal-to-noise ratio. When small volumes of antibody reagents were used in assays in round-bottomed plastic wells, signal and noise characteristics were similar to those of the slide assay. While the assays on plastic wells tended to be less sensitive in terms of anti-spore antibody concentration or the number of spores detectable, the larger volume of antigen suspension that could be used in plastic wells gave them an advantage in terms of the minimum antigen concentration detectable.

Further evaluation of factors affecting a rapid ELISA procedure for detection of IgG antibodies to Candida albicans

A rapid enzyme-linked immunosorbent assay (ELISA) was developed to detect IgG antibodies against a cytoplasmic antigen of Candida albicans. The optimum conditions and time required for each step were investigated. Pre-equilibration at 37 degrees C and constant agitation of immunoreactants resulted in a total test time of 1 h for examination of single serum dilutions. Initial binding of the antigen at 37 degrees C to the solid phase occurred within 4-6 min and was dependent on concentration. A serum dilution of 100-fold resulted in adequate discrimination between precipitin test-positive and -negative sera. Interaction of antibody and the bound antigen was maximal after 6 min incubation at 37 degrees C and was dependent upon the precipitin titre of the serum. Ten minutes was selected as the optimal incubation time for each of the stages, by which time maximal binding had occurred, irrespective of antibody affinity for antigen. The ELISA was completed by incubation at 37 degrees C for 10 min with alkaline phosphatase-conjugated anti-human IgG. Discrimination between positive and negative test sera was achieved by incorporating in each test run precipitin test-positive and -negative reference sera from groups of persons with or without C. albicans colonization or infection. Closest agreement between sera positive for C. albicans precipitins by counter-immunoelectrophoresis and the rapid ELISA was seen when reference negative sera were selected from non-colonized individuals.

Epitopic analysis of detergent-solubilized HLA molecules by solid-phase radioimmunoassay

A solid-phase radioimmunoanalysis of plasma membrane molecules solubilized in the presence of detergent was developed. From a crude cell lysate, membrane molecules were specifically immobilized by solid-phase adsorbed monoclonal antibodies. Analysis of these molecules was easily performed with radiolabeled monoclonal antibodies of different specificities. This technique was used to analyze the HLA-DR and HLA-A,B,C molecules expressed by RAJI cells. It was possible (a) to determine which epitopes are expressed on the same molecules; (b) to define subsets of HLA molecules according to the epitopes which they express, and (c) to perform quantitative analysis of HLA molecules on a crude cell lysate.