Interleukin-6 induces monocyte chemotactic protein-1 in peripheral blood mononuclear cells and in the U937 cell line

Induction of chemokine gene expression from peripheral blood mononuclear cells (PBMCs) stimulated by proinflammatory cytokines plays an important role in both wound repair and response to infectious agents. In the present study, we show that the proinflammatory cytokine interleukin-6 (IL-6) potently induced mRNA expression and secretion of the CC chemokine monocyte chemotactic protein 1 (MCP-1) in PBMCs. In addition, because human immunodeficiency virus (HIV) infection in vivo and in vitro has been shown to dysregulate the production of and/or the response to cytokines, PBMCs from both healthy uninfected and HIV-infected individuals were studied for their constitutive and IL-6-induced expression of MCP-1. No substantial differences were observed between the two groups of individuals. In addition, IL-6 upregulated MCP-1 expression in the promonocytic cell line U937 and in its chronically HIV-infected counterpart, U1. In these cell lines, IL-6 selectively induced MCP-1 and not other chemokines, including regulated upon activation normal T cells expressed and secreted (RANTES), macrophage inflammatory protein-1α (MIP-1α), MIP-1β, and IL-8. IL-6 induction of MCP- 1 was partially inhibited by hydrocortisone in U1 cells. Thus, IL-6 activates PBMCs to secrete MCP-1, a CC chemokine pivotal for monocyte recruitment in tissue and organs in which important inflammatory events occur.