Normal immunosuppressive protein. Isolation of a glycoprotein active fraction.

Experiments to determine the nature of the active moiety of Normal immunosuppressive protein (Nip) were performed using Sepharose Con A fractionation. Nip was found to be a glycoprotein or a glycopeptide. The fraction eluted by 0.2 M mannose was found to be as active as the crude Nip preparation in inhibiting EL4 tumour cell proliferation in vitro. It also gave a positive haemagglutination inhibition test when added to a rabbit anti-Nip antibody system. The resistance of Nip to boiling as well as the positive PAS staining also confirmed the glycoprotein or glycopeptide nature of Nip.