We have examined the effects of a stromal cell-derived cytokine designated interleukin 11 (IL-11) on the proliferation of murine hemopoietic progenitors in methylcellulose culture. COS cell-conditioned medium containing IL-11 supported formation of granulocyte/macrophage colonies and a small number of multilineage colonies including blast cell colonies in cultures of marrow cells from normal mice. When tested with marrow cells harvested 2 days after injection of 5-fluorouracil at 150 mg/kg, IL-11 enhanced interleukin 3-dependent colony formation, whereas IL-11 alone supported only scant colony formation. Serial observations (mapping studies) of cultures of post-5-fluorouracil spleen cells indicated that the mechanism of the synergistic effect of IL-11 is to shorten the dormant period of stem cells, an effect very similar to that of interleukin 6. When pooled blast cells were plated into medium containing IL-11 and erythropoietin, only macrophage colonies were observed. Thus, IL-11 can directly support the proliferation of committed macrophage progenitors and, like interleukin 6 and granulocyte colony-stimulating factor, act synergistically with interleukin 3 to shorten the Go period of early progenitors.
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.
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