Augmented local immunity in the liver by a streptococcal preparation, OK432, related to antitumor activity of hepatic macrophages

The aim of this study was to investigate the augmentative effect of a streptoccal preparation, OK432, on the immunological competence of hepatic macrophages. We found that OK432 was distributed predominantly to hepatic macrophages after intravenous injection, and Northern blot analysis revealed that OK432 induced the gene expression of IL-1α, β, and TNFα in the liver. The induction of mRNAs was evident 1 h after the intravenous injection of OK432 and their accumulation reached a maximal level at 3 h. TNF production of hepatic macrophages was also increased by the intravenous injection of OK432. Furthermore, OK432 significantly increased the proportion of IL-2 receptor-positive hepatic macrophages. As for antitumor activity in the liver being augmented by OK432, the cytotoxic and cytostatic activity of hepatic macrophages from OK432-treated rats against tumor cells was significantly increased and OK432 markedly reduced the number of tumor nodules in the liver after the inoculation of tumor cells via the portal vein. These findings, which indicated that OK432 has various immuno-stimulating actions on hepatic macrophages, leading to the augmentation of antitumor activity in the liver, suggest that OK432 may be of some benefit in helping to prevent hepatic metastasis, at least in part, via its activation of hepatic macrophages.