Activation of monocytes--more than one process. Differential effect of cytokines on monocytes.

Monocytes and macrophages respond to a number of exogenous agents by alterations in metabolism and gene expression in a process loosely called 'activation'. The question arises whether these alterations in cellular activity are the pleiotropic effects of one programmed activation process or result from separately programmed activation pathways. We report that certain cytokines (interleukin 1 (IL-1 alpha, IL-1 beta) and interleukin 2 (IL-2] which all activate monocytes, induce the synthesis of thromboplastin (TPL) and (IL-1 beta only) factor VII. Interferon-gamma (IFN-gamma) and tumour necrosis factor alpha (TNF alpha) do not induce monocyte procoagulant activity, although they both activate monocytes in several respects. Our data thus show that different states of activation are induced. Similar observations have been made by others using different systems.