Production of leucocyte inhibitory factor (LIF) and macrophage inhibitory factor (MIF) by PHA-stimulated lymphocytes.

Supernatants from human mononuclear cells cultured with PHA inhibited the migration of both human polymorphonuclear leucocytes and guinea-pig peritoneal exudate cells, but not human mononuclear cells. Using ultrafiltration it was shown that these supernatants contained two inhibiting factors, the one with a molecular weight of 15,000-50,000 inhibited only guinea-pig peritoneal exudate cells (MIF), whereas the fraction containing molecules of a size between 50,000 and 75,000 specifically inhibited the migration of polymorphonuclear leucocytes (LIF). The polymorphonuclear leucocyte inhibiting activity was heat labile. It is suggested that the leucocyte migration inhibition test is dependent upon the production of a lymphokine (LIF) which acts specifically on polymorphonuclear leucocytes causing their inhibition of migration.