Cell proliferation, cytokine bioassays

Incubation periods in excess of 2 h were required before this activity was detected in cell-free supernatants. More recently, the use of cDNA probing of Northern transfers (to detect specific mRNA levels), the use of ELISA techniques (to detect protein levels immunologically) and the development of more specific bioassays (culture techniques in which a biomolecule stimulates proliferation in a particular cell line) have resulted in a more thorough analysis of IL-1 production by neutrophils. IL-1 is only poorly expressed in blood neutrophils because mRNA for this cytokine is detectable only at very low levels (if at all), and protein production is usually below the level of detection of most assays. However, exposure of neutrophils to lipopolysaccharide (LPS), or to cytokines such as GM-CSF, TNF or IL-1 itself, results in a rapid but transient increase in IL-1 expression. 

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... 

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. ... 

The multiple actions of individual cytokines mean that cell lines rarely respond only to one cytokine. This is well illustrated by the efforts to develop specific bioassays for lL-1. Although the original mouse thymocyte proliferation assay was thought to be IL-1 specific, it is now clear that many cytokines influence the assay. IL-6 and TNF can replace IL-1 (G7, U4), and IL-2 and IL-4 can sygerize with... 

---