Activation of extrathymic T cells in the liver during liver regeneration following partial hepatectomy.

Partial hepatectomy was performed in C57BL/6 mice to investigate whether extrathymic T cells in the liver are activated during liver regeneration. This study is based on the finding that in mice with malignant tumours, extrathymic T cells in the liver are activated and yet the intrathymic pathway is suppressed (i.e. thymic atrophy). Attention was therefore focused on whether a similar phenomenon is induced during benign cell regeneration. Extrathymic T cells were identified using the two-colour immunofluorescence test for CD3 and interleukin-2 receptor beta-chain (IL-2R beta) [or lymphocyte function-associated antigen-1 (LFA-1)] antigens. They were estimated to be intermediate CD3+ [or T-cell receptor (TcR)] cells with high expressions of IL-2R beta and LFA-1. It was demonstrated that the proportion and number of intermediate CD3+ cells increased in the early phase (days 2-4 after partial hepatectomy), and that the thymus was inversely atrophic at the same time. This raised the possibility that extrathymic T cells may also be responsible for regulation of normal cell regeneration.