Serum-derived immunosuppressive substances. I. Partial purification and range of action.

Two alpha-globulin fractions which had in vivo and in vitro immunosuppressive activity were prepared from human serum. The larger fraction eluted from a molecular sieving gel in the albumin fraction and was heat labile whereas the smaller one was present in the elute fraction containing materials of 8,000-25,000 daltons and was heat stable. It is believed that the smaller of the two fractions is the immunoregulatory alpha-globulin described by several other investigators. The comparative activities of various starting materials and of partially purified derivatives in several systems (in vivo and in vitro) were examined. The possibility that these substances are lymphocytic chalones is considered.