Abstract
Several common metabolites and drugs in the serum in of patients with inflammatory, infectious, autoimmune, immunodeficient, neoplastic, and toxicant-induced diseases can produce artifactual suppression of the [methyl-3H]-thymidine assay, which is widely used to evaluate lymphocyte responsiveness. We have developed a sensitive, semiautomated, fluorescence-enhancement assay in which true immunosuppressors are measured in the presence of absence of such interfering substances. Peripheral blood lymphocytes are activated with mitogens in standard microtiter culture trays. Changes in lymphocyte DNA content are quantified with a reagent formulation containing mithramycin, the fluorescence of which is enhanced on binding to DNA in the presence of MgCl2. We solubilize cells within the intact microtiter tray by using an automated, inverted "Array Sonicator," and measure fluorescence with an automated, photon-counting fluorometer. With this system, immune response modulation can be accurately assessed in the presence of patients' sera and other complex test substances (e.g., supernates from hybridomas, fermentation vats, viral preparations, and macrophage cultures.