A biologic assay for IL-4.  Rapid fluorescence assay for IL-4 detection in supernatants and serum. 
Interleukin-4 (IL-4) is a lymphokine produced by activated T helper cells with effects on T cells, B cells, monocytes and mast cells.  The conventional tonsillar B cell assay used for quantification of IL-4 activity is sensitive to the presence of other cytokines and requires the acquisition of fresh cells on a regular basis.  We have evaluated the ability of IL-4 in the presence of antibody to IgM to induce CD23 on a cultured B cell line (Ramos) The requirements of measuring hundreds of samples at a single time precluded ready use of a conventional flow cytometer.  We therefore developed a rapid fluorescence assay which allows the detection of IL-4 in supernatants and serum.  The use of a particle fluorescence immunoassay reproducibly allows detection of IL-4 to 6 U in supernatants and serum.  This assay is specific for IL-4 and is not sensitive to other recombinant cytokines including IL-1, IL-2, IL-3, IL-6; interferon-alpha, -beta or -gamma, tumor necrosis factor (TNF) or GM-CSF.  Finally, in cancer patients receiving IL-4 its detection in serum using this assay reveals an alpha distribution phase of approximately 8 min and a beta clearance phase of approximately 48 min.