We describe a time-resolved fluoroimmunoassay (TRFIA) for recombinant human interleukin-3 (IL-3). The assay design uses two different monoclonal anti-IL-3 antibodies, giving a two-site immunometric assay. The TRFIA for IL-3 is a direct adaptation from our existing ELISA for IL-3. By using the same assay configuration and exchanging a europium-streptavidin conjugate for alkaline phosphatase-streptavidin, we were able to minimize the time required to develop a TRFIA, but still increase the working range of the TRFIA over the ELISA by 20-fold. The limit of detection is 5 ng/L, with the limits of quantification set at 5 and 30 000 ng/L human plasma.
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