Normal immunosuppressive protein purification and quantitative estimation experiments.

An improved method for the preparation and purification of normal immunosuppressive protein (NIP) is described. The purified material has a molecular weight between 10,000 and 25,000. Its biological and serological activity is approximately 10--20 times higher than that of the crude fraction. An antibody to normal immunosuppressive protein prepared in rabbits made the quantitative estimation of NIP by a haemaggluination inhibition test possible. Similarly, a very sensitive assay for the quantitative determination of NIP by its inhibitory effect on the proliferation of EL-4 tumor cells is also described. Eluates prepared from polyacrylamide gels were active in inhibiting EL-4 tumor cell proliferation and neutralized the anti-NIP activity in the haemagglutination inhibition test.