Measuring circulating cytokines.

Cytokines, i.e., regulatory proteins derived primarily (but not exclusively) from cells of the immune system, are receiving increasing attention for their influences on physiological processes. This paper outlines several of the unique characteristics of cytokines and discusses the pitfalls encountered when measuring them in biological fluids. At present, each available assay has a combination of advantages and drawbacks; therefore, investigators must be aware of the trade-offs and choose the assay that best addresses their needs. The factors that affect cytokine measurement also influence cytokine activity in vivo; thus they are important from a physiological as well as methodological standpoint. Moreover, the absolute concentration of a single cytokine is probably less important than the balance between that cytokine and its natural antagonists.