Effects of recombinant human interleukin-11 on hematopoietic reconstitution in transplant mice: acceleration of recovery of peripheral blood neutrophils and platelets

We have examined the effects of recombinant human interleukin-11 (rhIL-11) on the recovery of peripheral blood cell counts and proliferation of progenitors and hematopoietic stem cells (day 12 colony-forming units-spleen-CFU-S12) in vivo using a mouse bone marrow (BM) and spleen cell transplantation model. Recovery of leukocytes was accelerated in animals receiving daily administration of rhIL-11 (100 micrograms/kg/d) and reached normal levels by day 14 posttransplantation. This increased total leukocyte count reflected mainly an increase in neutrophils. Neutropenia (absolute neutrophil count [ANC] < 1,500) was present in control transplant mice for 14 to 15 days, while in the rhIL-11-treated group, neutrophils recovered to normal by days 8 to 10 and continued to increase until day 19. Animals treated with rhIL-11 had only 1 day with ANC demonstrated < 500. Correspondingly, rhIL-11 treatment increased granulocyte-macrophage progenitors (CFU-GM) derived from both spleen and BM cells. Higher doses of IL-11 increased CFU-GM nearly threefold and CFU-Mix fourfold to fivefold, while increasing burst-forming units-erythroid to a lesser degree. BM and spleen cellularity were both increased in IL-11-treated mice, but no increase in CFU-S12 was noted. In addition, in vivo daily administration of IL-11 increased peripheral platelet counts by threefold over control transplant mice at day 10 posttransplantation during the post-irradiation platelet nadir. Further treatment led to platelet counts higher than normal 18 days posttransplantation when control animals had just attained normal platelet counts. IL-11 can accelerate the recovery of the peripheral blood leukocytes, mainly neutrophils, and platelets in transplant mice, effects that may be clinically useful in future applications for BM transplantation and chemotherapy-related cytopenias.

Interleukin-11 promotes accessory cell-dependent B-cell differentiation in humans

Interleukin-11 (IL-11) is a recently described stromal-derived cytokine that supports the growth of an IL-6-dependent murine plasmacytoma line in the presence of antibody to IL-6 and appears to act in a manner similar to IL-6 on hematopoietic stem cells. Because IL-6 is known to promote differentiation of normal human B cells, the role of IL-11 on B-cell differentiation in vitro was characterized. IL-11 does not result in significantly increased DNA synthesis or Ig secretion by purified B cells alone or B cells cultured with Staphylococcus Cowan I, a T-cell-independent B-cell mitogen. In contrast, purified B cells cultured in the presence of pokeweed mitogen (PWM), irradiated T cells, and monocytes show increased DNA synthesis at day 3 and increased IgG and IgM secretion at day 7 of culture; addition of IL-11 further augments Ig secretion without change in DNA synthesis, an effect that can only be partially blocked by monoclonal antibody to IL-6. Similar experiments confirmed that increased IgG secretion was demonstrable when either IL-11 or IL-6 was added to B cells + CD4+/45RA- T cells + monocytes + PWM; in contrast, Ig secretion was low and equivalent when CD4+/45RA+ T cells were cultured with B cells+monocytes+PWM with or without IL-6 or IL-11. Neither IL-6 nor IL-11 could significantly increase phytohemagglutinin (PHA)-induced DNA synthesis by CD4+/45RA- or CD4+/45RA+ T cells. Although PWM or IL-11 induced IL-6 mRNA expression in both CD4+/45RA- T cells and monocytes, in neither cell did IL-11 increase IL-6 mRNA expression over that noted to PWM alone. These observations support the view that IL-11 promotes differentiation of human B lymphocytes only in the presence of accessory T cells and monocytes and that a minor component of this effect may be through stimulation of IL-6 production by CD4+/45RA- T cells and monocytes.

Leukemia inhibitory factor and interleukin-11 promote maturation of murine and human megakaryocytes in vitro

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 megakaryocytes 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-11 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.