Interferon-γ inhibits expression of the long pentraxin PTX3 in human monocytes

PTX3 is a prototypic long pentraxin expressed by various cell types, most prominently monocytes and endothelial cells, in response to interleukin-1 (IL-1), tumor necrosis factor (TNF) and bacterial products. In the present report, we show that interferon-γ (IFN-γ) inhibits the expression of the PTX3 gene induced by exposure to IL-1, TNF or lipopolysaccharide in human monocytes. This effect is dose dependent and observable when IFN-γ is added from 24 h before up to 3 h after the addition of IL-1. While the time course of the IL-1-induced PTX3 mRNA expression is not affected, IFN-γ reduces the stability of the PTX3 mRNA as well as its transcription. The inhibition of PTX3 expression is restricted to monocytes in that no inhibition occurs in cytokine-stimulated fibroblasts and endothelial cells. Under the same conditions, as expected, IFN-γ augmented monocyte chemotactic protein-1 expression in the same cell preparations. PTX3 protein secretion by activated monocytes is also suppressed by exposure to IFN-γ. Altogether, these data identify a negative pathway of regulation mediated by IFN-γ, which may occur under inflammatory conditions.