Immuno-suppressive lymphocyte factors—III. Complete purification and partial characterization of human inhibitor of DNA synthesis

Inhibitor of DNA synthesis (IDS) is an immunoregulatory T lymphocyte factor first characterized in the rat. It appears to cause the non-specific immune suppression seen in certain tolerant disease states. We have produced IDS from human peripheral blood lymphocytes, purified it to homogeneity and partiallycharacterized it. Human IDS has an isoelectric point of 3.40 and a molecular weight of 20,000. However, in the supernatants containing IDS activity, it usually exists in an aggregated tetrameric form which is also biologically active. IDS is not cytotoxic and is glycoprotein in nature. The activity depends on an intact carbohydrate moiety. Human IDS is identical to rat IDS except for a slightly higher isoelectric point. The biologic role is undetermined at present, but might be similar to that of rat IDS.