Application of the MAST Immunodiagnostic System to the determination of allergen-specific IgE.

The MAST Immunodiagnostic Test System was developed to provide a comprehensive, simple means for the in vitro measurement of multiple antigens or antibodies. The first commercial application of the MAST system incorporates several novel features for cost-effective diagnosis of IgE-mediated allergy in a clinical laboratory or a physician's office. The basis of the MAST system is a unique analytical test chamber, which contains cellulose thread as the solid-phase matrix and allows multiple test results from a single assay. This test chamber incorporates both positive and negative controls and requires no volume-dependent pipetting steps. Immunographic exposure onto high-speed Polaroid instant film allows for quantifying results with an automatic recording infrared-transmittance densitometer. Test results are easily interpreted by using a patient test record provided with the system. The MAST system greatly simplifies testing for allergen-specific IgE, while retaining specificity and sensitivity. Currently, with the MAST system one can simultaneously measure picomoles of allergen-specific IgE in up to 35 different allergen classes. In addition to allergy testing, the MAST technology is applicable to other immunodiagnostic profiles.

Antigens of Streptococcus mutans: cellular localization of the serotype-specific polysaccharide of strain AHT and release during exponential growth.

The serotype-specific polysaccharide of Streptococcus mutans AHT (serotype a) was shown to be loosely associated with the cell surface of this organism. The antigen was extracted from whole cells by boiling in sodium acetate buffer, pH 4.0, for 10 min. The purified product was found to be a diheteroglycan of galactose and glucose (3.6:1, molar ratio). The antigen possessed serological characteristics similar to the a antigen previously extracted from purified cell walls with hot formamide. Its physicochemical structure was identical to the previously studied wall antigen. Electron micrographs, developed after immunocytological labeling of this antigen on whole cells, revealed it to compose a dense microcapsule surrounding the microbe. Analyses of spent culture fluids indicated that the antigen was released during exponential growth at a rate directly proportional to the increase in culture biomass. It is concluded that the serotype-specific antigen may be a prime immunogen due to its surface localization at both capsule and wall sites.

A systems approach to fluorescent immunoassay: general principles and representative applications.

We have developed an automated system for the immunoassay of subnanogram quantities of clinically interesting compounds by molecular fluorescence. The system includes all the necessary reagents and an automated fluorometer. The microprocessor-based instrument consists of a measurement and data-processing module and an automated sampling unit. With use of 10 pmol/L amounts of fluorescent dyes such as fluorescein, measurements with precision and accuracy of 1--3% are attained. In a competitive-binding fluorescence immunoassay, antigen labeled with a fluorescent dye competes with antigen in the sample or standard for a limited amount of antibody immobilized on a polyacrylamide bead 2--5 micrometers in diameter. After separating antibody-bound from free tracer, we measure the amount of fluorescence bound to the beads. In representative example assays, correlation of fluorescence immunoassay (y) with a reference radioimmunoassay (x) of thyroxine was y = 1.01x + 13 nmol/L, r = 0.98. Correlation of fluorescence immunoassay (y) with a reference radioimmunoassay (x) of triiodothyronine was y = 0.99x + 0.004 nmol/L, r = 0.96.