Abstract

The fungus metabolite cyclosporin A is a small cyclic peptide acting as a novel antilymphocytic agent. It is effective following either parenteral or oral administration in mice, rats and guinea-pigs. The suppressive effect after short and prolonged treatment on plaque-forming cells, the inhibition of the secondary humoral response and the reversibility of its effect on haemagglutinin formation is demonstrated. Cyclosporin A inhibits delayed hypersensitivity skin reaction to oxazolone (primary and secondary responses) in mice and to tuberculin in guinea-pigs. Its failure to suppress antibody synthesis to lipopolysaccharide antigens in nude mice suggests a selective effect on T cells. High doses of the compound affect the haemopoietic tissues very weakly as shown by the bone marrow and stem cell numbers in mice, which finding markedly contrasts with most other immunosuppressive and cytostatic drugs.