Role of innate immune response in liver regeneration.

Liver regeneration following partial hepatectomy (PH) requires several steps including innate immune responses, particularly interleukin-6 (IL-6) and tumor necrosis factor-(TNF-)alpha production by Kupffer cells, although the activation processes are still unknown. Toll-like receptors (TLR) act as innate immune signal sensors and play central roles in host defense. Myeloid differentiation factor (MyD) 88 is a common adaptor molecule required for signaling mediated by TLR. When the receptors are activated, cells bearing TLR produce various pro-nflammatory cytokines in a MyD88-dependent manner. The authors investigated whether TLR/MyD88 signaling is critical for induction of innate immune responses after PH. In Myd88(-/-) mice after PH, induction of expression of immediate early genes involved in hepatocyte replication and phosphorylation of signal transducer and activators of transcription 3 (STAT3) in the liver, and production of TNF-alpha/IL-6 by and activation of NF-kappaB in the Kupffer cells were grossly subnormal and were associated with impaired liver regeneration, while TLR2, 4 and 9, which recognize Gram-negative and -positive bacterial products, are not essential for NF-kappaB activation and IL-6 production after PH. In conclusion, the TLR/MyD88 pathway is essential for liver restoration after PH, particularly its early phase.