Intensive expansion of natural killer T cells in the early phase of hepatocyte regeneration after partial hepatectomy in mice and its association with sympathetic nerve activation

When C57BL/6 mice were partially hepatectomized (PHx), severe lymphocytosis was induced in the liver in the early phase of hepatocyte regeneration (4 to 12 hours after PHx). A major lymphocyte subset expanding in this organ w as estimated to be natural killer 1.1(+) (NK1.1(+)) intermediate CD3 (CD3(i nt)) cells (i.e., NKT cells). CD3(int) cells are extrathymic T cells genera ted in situ in the liver. These changes were suppressed when mice with PHx were pretreated with a beta-adrenergicD antagonist (i.e., beta-blocker), pr opranolol (PPL). This might have been caused by sympathetic nerve stimulati on during hepatocyte regeneration. An alpha-blocker showed a similar effect , although the magnitude of suppression was lower than that of the beta-blo cker, We previously showed that NK and NKT cells express surface beta-adren ergic receptors and are activated in number by sympathetic nerve stimulatio n. In the present study, NK cytotoxicity mediated by liver lymphocytes obta ined from mice with PHx decreased, whereas NKT cytotoxicity against syngene ic thymocytes increased. Purified CD3(int) cells were also found to be able to mediate NKT cytotoxicity against regenerating hepatocytes. These result s suggest that sympathetic nerve stimulation after PHx results in subsequen t activation of NKT cells and that these NKT cells might be associated with immunologic surveillance during hepatocyte regeneration.