LEUKEMIA INHIBITORY FACTOR AND INTERLEUKIN-11 PROMOTE MATURATION OF MURINE AND HUMAN MEGAKARYOCYTES INVITRO

The growth-promoting activities of optimally stimulating concentrations of leukemia inhibitory factor (LIF) and interleukin-11 (IL-11), a stromal cell-derived cytokine, on megakaryocytes in liquid marrow cultures were compared to interleukin-6 (IL-6), a known megakaryocytic maturation factor. Maximally stimulating concentrations of LIF (25 ng/ml), IL-11 (10 ng/ml), or IL-6 alone (10 ng/ml) promoted an 81, 157, and 153% increase, respectively, in acetylcholinesterase (AchE) activity in murine serum-free cultures compared with controls (n = 5). In combination with 25 U/ml murine interleukin-3 (IL-3), LIF, IL-6, and IL-11 showed increases, respectively, of 35%, 49%, and 174% in AchE activity compared with IL-3 alone (n = 4). Flow cytometric analysis of 4-day-old cultures showed that LIF alone had minimal effect on megakaryocytic ploidy, whereas IL-11 and IL-6 alone markedly augmented high ploidy cells. Enumeration of cells stained for AchE showed that IL-1 1 increased the numbers of Mks in comparison to LIF, IL-6 or controls by up to 59%. Moreover, a twofold increment in Mk number was noted when IL-11 was used in combination with IL-3 (compared with either IL-3 alone of IL-3 + IL-6). Flow cytometric ploidy analysis of 8-day-old human liquid marrow cultures showed that either LIF, IL-11, or IL-6 alone markedly augmented the percentage of 32N cells compared with cultures containing only human IL-3. The data suggest that LIF and IL-11 promote murine and human Mk maturation in vitro, although the effect of IL-11 exceeds that of LIF in mice. Despite the comparable influence of IL-11 and IL-6 on Mk ploidy, IL-11 has the additional characteristic of enhancing the number of Mks, particularly in combination with IL-3.