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A recently developed alternative to the more traditional techniques for studying antigen-antibody interactions has been examined. This method involves the use of an optical biosensor employing surface plasmon resonance detection. In this system one of the reactants is immobilized on the sensor surface and other reactants are passed over the sensor surface sequentially at a constant flow rate. Binding phenomena are detected in real time from changes in the angle at which surface plasmon resonance occurs. This is dependent, among other things, on changes in the refractive index (which is directly proportional to the mass) at or near to the sensor surface. Applications of this biosensor technique for comparing the binding of related neuraminidases, purified from escape mutants of influenza virus NWS/G70C/75 (N9), to two antibody Fab fragments, are described. These results were compared with those obtained from ELISA and slot blot assays on the same neuraminidases interacting with the same two monoclonal antibodies. The biosensor method was shown to be highly specific, permitting rapid screening of binding in such antigen-antibody systems.

A rapid, sensitive, solid-phase immunoassay, using horseradish peroxidase and 3,3',5,5'-tetramethylbenzidine, was found to be more sensitive and the colour developed was more stable compared with HRPO using 4-chloro-1-naphthol or diaminobenzidine. Assay sensitivity was equal to or greater than that obtained with the alkaline phosphatase reaction. The essential step was to incubate filters in 1% dextran sulphate for 10 min in a pH 5 (10 mM citrate-EDTA) buffer before reacting with TMB (0.05 mg/ml in the same buffer).

A simple two-step method involving ammonium sulfate precipitation followed by hydrophobic chromatography is described for the separation of T cell growth factor (TCGF) from a number of other factors contained in medium conditioned by concanavalin A-stimulated spleen cells. Thus, granulocyte-macrophage colony-stimulating factor, P cell-stimulating activity, pluripotential stem cell-supporting activity and interferon activity were not detected in TCGF partially purified by these steps. T cell-replacing factor co-purified with TCGF. Macrophage activity factor (MAF) co-purified with TCGF, but the ratio of MAF to TCGF activities was reduced more than 20-fold relative to that in crude conditioned medium. All of the factors were present in the 50-80% saturated ammonium sulfate fraction, however, levels of concanavalin A were reduced by 98% in this step. TCGF, separated in this way from these other regulatory factors will be useful in experiments analyzing the actions of TCGF on mixed populations of cells.

The conditions required for storing and recovering IL-2-dependent T cell clones from liquid nitrogen were investigated. For maximum cell recovery, cultured T lymphocytes were precooled at 4 degrees C for 15 min in medium containing 10% DMSO and 20% FCS before storage in liquid nitrogen. This method allowed adequate time for DMSO to penetrate the cells before freezing.