Resistance of extrathymic T cells to stress and the role of endogenous glucocorticoids in stress associated immuno suppression

When mice were exposed to restraint stress for 12 or 24 h, severe lymphopen ia was induced in all immune system organs, including the liver and the thy mus. However, in adrenalectomized mice, this response was completely absent . Phenotypic characterization revealed that interleukin (IL)-2R beta(+)CD3( int) cells (i.e. extrathymic T cells) with CD4(+) phenotype and the NK1.1() subset of CD3(int) cells (i.e. NKT cells) in the liver as well as the mat ure conventional T cells in the thymus were resistant to such stress. In ad renalectomized mice, there was no significant change in the distribution of lymphocyte subsets in all tested organs before stress. Interestingly, the number of lymphocytes in the liver and spleen and the proportion of NKT cel ls in the liver rather increased after stress in these adrenalectomized mic e. Therefore, endogenous steroid hormones were indicated to be important in the induction of immunosuppressive states after stress. Among stress assoc iated cytokines, the secretion of tumour necrosis factor (TNF)-alpha was co mpletely suppressed while that of IL-6 was partially suppressed in adrenale ctomized mice. These results suggest that endogenous steroid hormones are i mportant for the induction of the stress associated immunosuppression and t hat NKT cells are resistant to stress, namely, resistant to exposure to end ogenous steroid hormones.