Role of Kupffer cells in developing streptococcal cell wall granulomas. Streptococcal cell wall induction of inflammatory cytokines and mediators.

Hepatic granulomas are induced by intraperitoneal injection of streptococcal cell walls (SCW) into Lewis rats. Kupffer cells rapidly clear SCW from the blood, and the authors examined Kupffer cells further for a role in SCW-hepatic inflammation. Isolated Kupffer cells cultured with SCW secreted high levels of tumor necrosis factor alpha (TNF alpha), interleukin-1 (IL-1), transforming growth factor beta (TGF beta), and prostaglandin E2 (PGE2). SCW transiently induced increased steady-state levels of IL-1 beta and TNF alpha mRNA; in contrast, constitutive expression of TGF beta 1 mRNA in Kupffer cells was not affected by SCW. Low concentrations of SCW induced the accumulation of intracellular IL-1 and TGF beta bioactivity, with intracellular IL-1 bioactivity remaining high through at least 72 hours of culture. Kupffer cells isolated 1, 7, and 21 days after SCW injection did not express IL-1 beta or TNF alpha mRNA greater than control levels and exhibited marked hyporesponsiveness to secondary in vitro stimulation with SCW or LPS. SCW transiently induces Kupffer cells to secrete a variety of soluble mediators that contribute to hepatic inflammation by inducing leukocyte recruitment and activation and fibroproliferation. The transient nature of the Kupffer cell response and the hyporesponsiveness to secondary stimulation may be a mechanism by which the hepatic inflammation is negatively regulated.