Modulation of immune response in aged humans through different administration modes of thymopentin.

Thymopentin, a synthetic pentapeptide corresponding to the active site of thymopoietin, has been shown to restore antibody production in old mice. A decrease in immune response can also be observed in elderly humans, which is mainly caused by defective T cell function. The present study shows that the immunomodulating properties of thymopentin involve both specific and nonspecific responses in a population of elderly people vaccinated with keyhole limpet hemocyanin (KLH) antigen. Furthermore, it is demonstrated that these effects depend upon the mode of administration of thymopentin: The specific KLH antibodies (IgM and IgG), measured by solid-phase radioimmunoassay, reach the highest titers after subcutaneous injection. The lowest titers are produced after intravenous injections, whereas the responses to placebo are between these two ranges. The nonspecific immunoglobulin production, measured by nephelometry, does not follow the same pattern, suggesting that different regulatory mechanisms are involved. Future implications of these findings are discussed.