engleski

Immune aspects of liver regeneration induced in mice by partial hepatectomy

Liver regeneration that follows after partial hepatectomy (pHx) is well-defined process, which involves the concerted action of extra and intracellular factors resulting in induction of cell replication and its inhibition at time when the entire liver mass is restored. Concomitantly, the breakdown of previously maintained tolerance and/or exposure to self antigens lead to the activation of natural immune repertoire, which through cytolytic activities participate in surveillance against aberrant cells and elimination of superfluous cells. In an attempt to enlarge our previous data, showing regulatory role of activated Kupffer cells and CD4+ and CD8+ T lymphocytes in liver regeneration in this study we investigated the dynamics of liver regeneration in wild, MHC class I deficient, NKT-cell depleted, perforin knock out (PKO) and gld/gld (FasL deficient) C57Bl/6 mice, determining the cell cycle of hepatocytes, as well as the phenotype and spontaneous cytotoxic activity of intrahepatic and splenic mononuclear lymphatic cells (MNLC) against NK-sensitive (YAC-1) targets and syngeneic thymocytes. The data have shown that in early phase of regeneration (at 24h) in the liver accumulate particularly NK1.1+ /CD3intermediate cells, which co-express CD69 (57% in pHx mice versus 2.2% in sham operated mice), as well as CD4+ cells. Accumulation lasted two days and then the percentages of NK1.1+, CD8+, CD4+ and Vb8.1-8.2+ cells decreased below the control values. In the spleen predominated CD3high and CD4+ T cells. Both, hepatic and splenic MNLC after pHx became cytotoxic to YAC-1 target and syngeneic thymocytes, while cytotoxicities were completely or partially depressed when hepatic or splenic cells were derived from PKO and gld donors, suggesting that lytic pathways activated by pHx were perforin and FasL-dependent. The cytotoxicity of splenic cells was, however, in all intervals higher than that obtained by the hepatic MNLC. Moreover, the reactivity of splenic cells against YAC-1 target was expressed earlier (24h after pHx) than other types of cytotoxicity (after 48h after pHx). Furthermore, in mice defective in b2-microglobulin this dynamics was completely changed, suggesting the involvement of CD1-molecules. Cell cycle analysis of hepatocytes also showed that mice with nonfunctional MHC-class I molecules and perforin-deficient mice in comparison with wild mice had initially smaller (on 1st day) and then greater (at the 3rd and 7th day) fraction of cells in G2+M phase, suggesting that CD1-restricted NKT cells or MHC-class I restricted cytotoxic CD8+ T lymphocytes had regulatory role in these events. Moreover, in NKT cells-depleted wild mice, the increased proportion of hepatic cells in S and G2+M phase was found in early phase of liver regeneration (at the 1st day after pHx). Taken together, the data suggest that partial resection of parenchymal organs induces the extrathymic T cell generation in the liver, enabling the appearance of cytotoxic, auto reactive NKT cells, which then potentiate NK and LAK-mediated cytotoxicity in the spleen using the perforin-dependent and FasL-dependent pathways for the control of reparatory process.

liver regeneration; intrahepatic lymphocytes; cytotoxicity; perforin; FasL; cell cycle

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