Role of Kupffer cells in development of streptococcal cell wall-induced hepatic granuloma in Lewis rats.

Abstract

Bacterial cell wall fragments play important roles in various inflammatory diseases. Little is known regarding the interaction of streptococcal cell walls (SCW) with Kupffer cells in SCW-induced hepatic granuloma in Lewis rats. To investigate this, in vitro functional assays were used to determine the extent of Kupffer cell involvement in this process. Isolated Kupffer cells cultured with various concentrations of SCW were found to exhibit normal phagocytic function. Kupffer cells were found to have reduced chemotactic activity and which was suppressed by SCW. However, SCW did suppress the secondary stimulus of oxidative burst in the Kupffer cells, but not in peritoneal macrophages. Kupffer cells cultured with SCW remained in an activated state over 24 hours as measured by MTT. In comparison, LPS treated cells were activated early, but this activation was lost by 24h. Activation by SCW induced a different cytokine profile than that seen with other bacterial components. Kupffer cells from non-sensitized rats cultured with SCW were found to produce high levels of TNF-α and IL-6. In addition, low concentrations of SCW (0.4μg/ml) induced expression of IL-1β and IL-6 mRNA. In ex vivo experiments, Kupffer cells isolated from SCW injected animals were found to secrete TNF-α and IL-6. Induction of TNF was best seen at 48-72 hours post SCW injection. The IL-6 production was transient until 72 hours post SCW injection. Cell surface expression of class II MHC (Ia) and macrophage marker (ED2) on isolated Kupffer cells was significantly increased in SCW injected rats as measured by flow cytometry. These studies show that Kupffer cells maintain their overall phagocytic function but exhibit reduced respiratory burst activity in response to SCW. Upon activation by SCW they express and release proinflammatory monokines and exhibit upregulated surface markers, all of which are important in the development of hepatic granuloma. These wide range of effects emphasize the multifunctional involvement of Kupffer cells and a need to understand the triggering mechanisms they use to respond against poorly degradable antigens.