Haemopoietic stimulators and inhibitors in aplastic anaemia serum.

Normal serum and serum from four patients with severe aplastic anaemia was fractionated by Sephadex G-150 gel filtration. Fractions were tested for direct haemopoietic activity on colony forming cells in methylcellulose cultures, and for their indirect influence on haemopoiesis via CSA- and BPA-producing cells. All aplastic anaemia sera contained abnormal inhibitors and stimulators. An inhibitor acting on both haemopoietic and factor producing cells, eluting with the IgM fraction was found in all, variable inhibitors of lower molecular weight in single patients. Stimulatory activity of 10 000-50 000 MW acting on factor producing cells, but not on colony forming cells directly, was found in all, a variable stimulator eluting with the very high MW fraction in single patients. In two patients who achieved complete autologous bone marrow remission after treatment with high dose immunosuppression, Sephadex fractions of serum before treatment and remission serum were simultaneously tested on autologous bone marrow in remission. Inhibitors were detected before treatment and disappeared in remission, stimulators were not detectable before treatment but became strong in remission. It is concluded that the effect of aplastic anaemia serum on haemopoiesis in culture is determined by the balance of inhibitors and stimulators on both haemopoietic and CSA/BPA producing cells.