A standardized human T-lymphocyte proliferation assay for detecting soluble accessory factors from monocytes. II....

Conditions for production and detection of a monocyte-derived interleukin-1 like accessory factor were investigated. The production of the accessory factor was not increased quantitatively by changes in monocyte concentration or incubation times. Lipopolysaccharides stimulated monocytes to accessory factor production in a broad range of concentrations, and it was active even in concentrations below the often registered endotoxin contamination of commercial culture media. Thus, to avoid unintended monocyte stimulation culture conditions should be endotoxin-free. The accessory factor was heat-labile, had a MW between 10 and 40 K, was co-mitogenic to PHA-stimulated monocyte depleted cells and it did not support the growth of an interleukin-2 dependent cell-line. Thus the factor shares characteristics with and might be identical to interleukin-1. The conditions previously defined for the demonstration of accessory effect of monocytes were also optimal for demonstration of interleukin-1 in supernatants from lipopolysaccharide stimulated monocyte cultures.