There is developing evidence that certain thymosin peptides and lymphokines produce a transient increase in steroid hormones when introduced systemically. Conversely, the repressive effect of adrenocortical steroids on the immune system is well documented. In the present study, the direct effect of certain components of the immune system on steroid output by rat adrenal fasciculata cells was tested. With this system, there was no direct steroidogenic effect of either the partially purified thymosin fraction 5, or any of the purified peptide components tested (thymosin alpha 1, alpha 7, or beta 4). These peptides also did not synergize the cellular response to ACTH, nor did they induce cAMP production by a ACTH- and NaF-responsive adrenal membrane preparation. Supernatants from Con A-stimulated spleen cells, which were demonstrated to contain lymphokine activity, and partially purified mouse interferon were also without a significant direct or synergistic effect on steroidogenesis by adrenocortical cells. These results suggest that the steroidogenic response to these peptides observed in vivo may be mediated by the central nervous system.
Leukotrienes are vasoactive arachidonic acid metabolites which are released by mast cells during hypersensitivity reactions.The mechanisms for regulating leukotriene biosynthesis are not well understood.A murine mast/basophil cell line (FT-18) was used to investigate this problem.Exogenously supplied ["C] arachidonic acid is not appreciably converted to leukotrienes by untreated FT-18 cells.However, when the cells were preincubated with the lymphocyte product 15-hydroxyeicosatetraenoic acid (WHETE), addition of ['4C]arachidonic acid consistently resulted in a dosedependent synthesis of large amounts of both ['4C]leukotriene B4 and ['4C]5-HETE.These metabolites were isolated by high pressure liquid chromatography, converted to the methyl ester trimethylsilyl ether derivatives, and the structures confirmed by gas chromatography-mass spectrometry.These findings indicate that 15-HETE induces a direct activation of a cryptic 5lipoxygenase in these cells.The closely related 12-HETE was ineffective.The activation phenomenon occurs rapidly and is reversible.Furthermore, the activation appears to be highly cell-and enzyme-specific, since lipoxygenases in three primary cell types including one that contains a 5-lipoxygenase and six other cell lines did not show this specific induction of leukotriene biosynthesis by 15-HETE.This report is the first evidence that 15-HETE, a major arachidonate metabolite in lymphocytes, can act as a signal to activate leukotriene production by susceptible mast cells.Immunological activation of mast cells is essential for the proper functioning of the immune response and results in the release of a number of mediators of immediate hypersensitivity (1).One of these mediators exhibits spasmogenic and vasocontrictive activities and is c d e d slow reacting substance of anaphylaxis or SRS-A.'Recently, the active components of SRS-A were identified as leukotrienes C4, D4, and E4 (2).These leukotrienes are arachidonic acid metabolites containing glutathione or amino acid moieties derived from glutathione and are formed via the 5-lipoxygenase pathway.Another biologically active product of this pathway is leukotriene B4, which is chemotactic for neutrophils and contracts smooth muscle (3-6).Various other cells including basophils, eosinophils, lymphocytes, macrophages, mastocytoma cells, and neu- AI 17551, CA 24974, CA 29943, and HL 24838.
The hematopoietic growth factor granulocyte colony-stimulating factor (G-CSF) has been in the clinic since 1986, when the clinical development of bacterially synthesized recombinant filgrastim began (1). A glycosylated form of G-CSF (lenograstim) has been approved for use in Europe and a bacterial recombinant mutein (nartograstim) has been approved in Japan. All forms of G-CSF are now commonly used for many types of neutropenia, including that resulting from anticancer therapies.
Human rIL-1 alpha was shown to be a potent stimulus of granulopoiesis in mice that have been myelosuppressed with cyclophosphamide. Stimulation of granulopoiesis was demonstrated in IL-1-treated mice by an accelerated recovery of granulocyte-macrophage colony-forming cells, bone marrow and splenic granulocytic hyperplasia, and a profound granulocytosis. Granulopoiesis was stimulated by IL-1 in a dose-dependent manner at doses ranging from 0.5 to 50 micrograms/kg. Maximal increases in granulocytes were observed after 4 days of IL-1 treatment. Mice treated with IL-1 also exhibited increased splenic megakaryopoiesis with a resultant increase in the number of peripheral blood platelets. In contrast to these positive effects on hemopoiesis, bone marrow, but not splenic, erythropoiesis was depressed in IL-1-treated mice. IL-1 effects were observed in mice treated with a wide dose range (50 to 300 mg/kg) of cyclophosphamide, with optimal effects occurring at a dose of 200 mg/kg. The doses of IL-1 leading to enhanced granulopoiesis caused only minor and transient changes in selected clinical chemistry parameters and caused no toxicities that were evident by histologic examination of tissues. The stimulation of granulopoiesis in the absence of overt toxicity suggests that IL-1 may be useful clinically to enhance the recovery of granulocytes in myelosuppressed patients.
Although IL-12 has been reported to synergize with c-kit ligand (KL) in promoting hematopoietic stem cell proliferation in vitro, administration of recombinant mouse IL-12 (rIL-12) to normal mice caused a dose- and time-dependent anemia, leukopenia, and thrombocytopenia in vivo. Decreased numbers of bone marrow cells were recovered from the tibiae of IL-12-treated mice, and histologic examination of the marrow revealed a loss of mature neutrophils and red blood cell precursors. However, simultaneously with the suppression of hematopoiesis in the bone marrow, the IL-12-treated mice developed splenomegaly, which was largely caused by a marked enhancement of splenic extramedullary hematopoiesis of the erythroid, myeloid, and megakaryocytic lineages. These histologic observations were confirmed by colony-forming cell assays in which administration of IL-12 was shown to cause a time-dependent decrease in bone marrow CFU-GM, CFU-E, and BFU-E hematopoietic colony-forming cells while causing an increase in splenic CFU-GM and BFU-E colony-forming cells. All these effects were reversible upon cessation of IL-12 treatment. The observation that in IL-12-treated mice hematopoiesis was suppressed in the marrow but enhanced in the spleen suggests that myelosuppression was not caused by a direct effect of IL-12 on hematopoietic progenitors. It seems likely that myelosuppression was caused instead by an IL-12-induced alteration in the local environment of the marrow.
