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Susceptibility of natural killer cell activity of old rats to stress.

We determined an in vivo response of NK cells in young and old rats towards the suppressive effect of stress. Stress was developed by isolating rats in separate cages, but control littermates were kept together. Animals were subjected to stress for 7 days, and alterations of NK cell activities were examined in the spleen, peripheral blood (PB) and bone marrow (BM). The results showed that old rats subjected to stress had a remarkable decrease in splenic and PB-NK activity compared to old control rats, concomitant with a highly increased level of NK cell activity in BM. Suppression of the lytic activity in the spleen of stressed old rats was correlated with a decrease in the percentage of conjugate formation between splenic NK cells and target tumour cells. In contrast, stressed young rats demonstrated relatively unchanged activity of NK cells examined in different tissues compared to age-matched controls. We concluded that old animals are more sensitive to the suppressive effect of stress compared to young ones, and the mechanism of this suppression is probably due to the migration of large granular lymphocytes (LGL) from spleen and PB to other sites such as BM.