Products of Activated Lymphocytes: Leukocyte Inhibitory Factor (LIF) Distinct from Migration Inhibitory Factor (MIF)

The mechanism of inhibition in the leukocyte migration system was investigated. The migration of human buffy coat cells was inhibited by a soluble product of activated lymphocytes. This factor was found to have an elution pattern in Sephadex G-100 gels similar to that of albumin (69,000 daltons), thus differentiating it from human migratory inhibitory factor (MIF) (23,000 daltons). Leukocyte inhibitory factor (LIF), like MIF, was shown to be elaborated by sensitized lymphocytes following stimulation by specific antigen. LIF selectively inhibited the migration of polymorphonuclear (PMN) leukocytes but did not affect the migration of guinea pig macrophages or human monocytes. Thus, the leukocyte migration system has been shown to be mediated by a separate factor (LIF) and different indicator cells (PMN leukocytes) than the MIF-mediated system of migration inhibition which utilizes guinea pig macrophages or human monocytes as indicator cells.