Antiserum to lymphocytes: interactions with chemical immunosuppressants.

An injection of rabbit antiserum to mouse lymphocytes causes temporary lymphopenia and prolonged survival of A-strain skin grafts on CBA mice. Cortisone or amethopterin without further antilymphocytic serum prolongs lymphopenia and immunosupression. When cortisone or amethopterin precedes the administration of the antiserum, the immunosuppressant action of the combination is less than that of the antiserum given alone. Whether the serum or the drug is given first does not affect the induction of lymphopenia by the serum. Thus, immunosuppressant action of antilymphocytic serum can be distinguished from its ability to induce lymphopenia. The results suggest that this serum may act as a mitogenic agent redirecting the proliferation of lymphocytes into immunologically incompetent pathways.