Principles of Cytokine Assays

Principles of Cytokine Assays Bioassay and immunoassay are the analytical techniques of choice to measure cytokines. However, newer instrumental techniques are also beginning to be used to measure cytokines and CKs. These techniques are used to quantify their (1) concentration and activity in biological fluids, (2) production by whole blood cells,(3) concentration of receptors, and (4) intracellular levels. 

Historically the functions of cytokines have been elucidated first with bioassays preceding immunoassays for cytokine quantification. The bioassay of a given cytokine is based on its bioactivity in a defined biological model, normally based on a certain cell line. Various approaches have been reported (1) proliferation tests— induction of cell growth (e.g., B9 cell line for IL-6) (2) tests for cytotoxicity— TNFa on WEHI164 

The major drawback of these techniques is their lack of specificity, poor precision (CV = 15% to 100%), and long analysis time (1 to 4 days). Their main advantages are that they measure biologically active molecules and detect as little as O.lpg/mL. 

A standard method for the quantitation of cytokines is to perform a bioassay in which aliquots of samples are com-pared with known concentrations of a cytokine in supporting the proliferation of a cytoldne-dependent cell line. In most instances, however, these cell lines are dependent on the cytokine not only for proliferation, but also for survival.  

Currently, immunoassay is the practical method of choice for measuring cytokines and their receptors. As cytolanes are proteins, specific antibodies can be raised against recombinant cytokines and have also been measured as an indicator of cytokine presence, The general characteristics of cytokine immunoassays are comparable with the classical immunoassays, with monoclonal, oligoclonal, or polyclonal antibodies all being used (see Chapter 9). The most popular formats are immunoradiometric assay (IRMA) and ELISA, which use a first monoclonal antibody for the capture and a second antibody labeled with a radioisotope or an enzyme. 

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