Pro-inflammatory response resulting from sindbis virus infection of human macrophages: implications for the pathogenesis of viral arthritis.

Several viruses cause acute and chronic joint inflammation in humans, and among them, the alphaviruses are of special interest due to the increasing number of outbreaks in which they are the etiological factor. Sindbis virus (SinV), a member of the Alphavirus genus, is the most widely distributed of all known arboviruses. Although SinV causes arthritis in humans, the molecular and cellular factors that contribute to the pathogenesis of this disease are almost completely unknown. Despite the crucial role of macrophages in the development of arthritis, these cells have not been recognized as potential targets for viruses causing arthritis. In this study, replication of SinV in human macrophages was demonstrated. The infection promoted macrophage activation, leading to the release of macrophage migration inhibitor factor (MIF) from intracellular stores and inducing the expression and secretion of TNF-alpha, IL-1beta, and IL-6. Production of these cytokines was followed by the expression of matrix metalloproteinases (MMPs) 1 and 3, which could be involved in the articular damage that has been observed in disease induced by SinV. The use of different strategies to block MIF action, including an anti-MIF antibody, the MIF inhibitor ISO-1 and knockout mice for the MIF gene, showed that cytokine secretion and MMP expression during infection were regulated by MIF, suggesting that this cytokine acts in autocrine and paracrine manner upstream in the macrophage activation cascade. Thus, these are remarkable similarities between macrophage responses induced by SinV infection and those observed in rheumatoid arthritis, despite the different etiologies of infectious and autoimmune arthritides. (c) 2009 Wiley-Liss, Inc.