Modulating effects of the synthetic thymic dipeptide pidotimod on the immune system in the aging rat.

We have investigated the in vivo and in vitro effect of pidotimod, a synthetic thymic-derived drug, on the immune response in young (2 month-old), and aging (24 month-old) Sprague-Dawley rats. We studied the effect of different doses of pidotimod on the responsiveness of both cultured peripheral blood lymphocytes and splenocytes to mitogenic stimuli, as well as on interleukin-2 production by peripheral blood lymphocytes after stimulation with interleukin-1 and phytohemagglutinin. Treatment with pidotimod in vivo as well as in vitro resulted in an increase of tritiated thymidine incorporation in both mitogen-stimulated lymphocytes and splenocytes from 24 month-old rats. Production of IL-2 from lymphocytes of 24 month-old rats was significantly increased in groups of animals treated with pidotimod. On the other hand, treatment with pidotimod did not influence the responsiveness of 2 month-old rat lymphocytes to mitogens, nor affected IL-2 production. Our results suggest a possible specific modulatory activity of pidotimod on the aging immune system.