Principle: This IL-4 enzyme linked immunosorbent assay (ELISA) applies a technique called a quantitative sandwich immunoassay. The microtiter plate provided in this kit has been pre-coated with a polyclonal antibody specific to IL-4. Standards or samples are then added to the appropriate microtiter plate wells with a biotin-conjugated monoclonal antibody preparation specific for IL-4 and incubated. IL-4 if present, will bind and become immobilized by the antibody pre-coated on the wells and then be sandwiched by biotin conjugate. The microtiter plate wells are thoroughly washed to remove unbound IL-4 and other components of the sample. In order to quantitate the amount of IL-4 present in the sample, Avidin conjugated to Horseradish Peroxidase (HRP) is added to each microplate well and incubated. Avidin is a tetramer containing four identical subunits that each have a high affinity binding site for biotin. The wells are thoroughly washed to remove all unbound HRP-conjugated Avidin and