Regulation of lymphocyte transformation by components identified in ultrafiltrates prepared from leukocyte extracts

Leukocyte components which can inhibit or enhance the uptake of 3H-thymidine by peripheral lymphocytes can be prepared by ultrafiltration of leukocyte extracts followed by gel filtration on Sephadex G-10. A potent inhibitor of lymphocyte transformation is present in an ultrafiltrate fraction having a nominal molecular weight of 5,000-10,000. Three other components having inhibitory, and one component having enhancing, activity on lymphocyte transformation were found in an ultrafiltrate fraction having a molecular weight less than 5,000. The inhibitory components in the latter were principally derived from polymorphs and inhibited both T and B lymphocyte proliferation. Enhancing components were mainly derived from mononuclear cells and augmented the proliferation of T cells only.