Protection by human serum from the immunosuppression induced by spermine in vitro

The in vitro suppressive activity of spermine to PHA-induced proliferation of human T lymphocytes is shown to be abolished by normal human serum. This protection acts within the first 4 hr of culture and is due to a protein of 67 kDa, showing an isoelectric charge of pH 4.9. This protein does not bind, or modify, spermine and does not inhibit spermine oxidase activity, an enzyme required for the in vitro suppression. Results with acrolein confirm that this eventual cleavage product is probably not involved in the spermine-induced suppression. Nevertheless, since serum also reduces acrolein-induced suppression, it is probable that both these protective mechanisms are related. Such a protection of T lymphocytes by a serum factor may play an important role by preventing diffusion, outside the genital tract area, of a potential spermine-induced immunosuppression.