Increased expression of osteopontin in activated Kupffer cells and hepaticmacrophages during macrophage migration in Propionibacterium acnes-treatedrat liver

Osteopontin is an extracellular matrix component that can act as a chemokin e to induce macrophage migration. The significance of osteopontin in macrop hage infiltration into the liver was examined in rats given heat-killed Pro pionibacterium acnes. In normal rats, osteopontin mRNA expression in the li ver was minimal, determined by quantitative-competitive reverse transcripti on-polymerase chain reaction (RT-PCR) assay. Northern blot analysis reveale d that osteopontin mRNA was not expressed in Kupffer cells isolated from no rmal rats. When rats received heat-killed P. acnes intravenously, marked ma crophage accumulation, forming granulomas, developed in the liver later tha n 3 days after the injection and its extent became maximal between 5 and 7 days. In these rats, osteopontin mRNA expression was increased in the liver later than 1 day (with its peak at 3 days after the injection), and the mR NA expression was increased markedly in Kupffer cells and hepatic macrophag es isolated at 7 days. The mRNA expression of monocyte chemotactic protein- 1 (MCP-1) and macrophage inflammatory protein-1 alpha (MIP-1 alpha), chemok ines for monocytes and macrophages: was also increased in the liver of P. a cnes-treated rats, with peak expression at 3 days. We conclude that osteopo ntin derived from Kupffer cells and hepatic macrophages may contribute to t he infiltration of monocytes and macrophages into the liver cooperatively w ith the actions of MCP-1 and MIP-1 alpha in P. acnes-treated rats.