Hematopoietic progenitors and interleukin-3-dependent cell lines synthesize histamine in response to calcium ionophore

The calcium ionophore A23187 promotes histamine synthesis in murine bone marrow cells by increasing the expression of mRNA encoding histidine decarboxylase (HDC), the histamine-forming enzyme. The cells responsible for this biological activity copurify with hematopoietic progenitors in terms of density, light scatter characteristics, and rhodamine retention, similar to interleukin (IL) 3-induced histamine-producing cells. Yet, the effect of calcium ionophore is not mediated by IL-3. The most purified rhodamine-bright bone marrow subset contains 80% cells that respond to calcium ionophore by increased HDC mRNA expression. This high frequency makes the involvement of one particular progenitor subset in histamine synthesis unlikely. The finding that all IL-3-dependent cell lines tested so far exhibit increased histamine production and HDC mRNA expression in response to calcium influx lends further support to this notion. Cell lines requiring other growth factors or proliferating spontaneously lack this ability. Finally, it should be noted that IL-3-dependent cell lines do not produce histamine in response to their growth factor. It might, therefore, be suggested that the pathway transducing the signal for increased histamine synthesis after IL-3 receptor binding in normal hematopoietic progenitors is modified in these cell lines.

Endogenous granulocyte-macrophage colony-stimulating factor is involved in IL-1- and IL-7-induced murine thymocyte proliferation

We have reported previously that IL-1 induces murine thymocyte proliferation in the absence of artificial comitogens, provided that the cells are cultured at high densities. In the present study, we show that, in these conditions, TdR uptake in response to IL-1 is diminished significantly by anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) Abs. Indeed, a substantial production of this growth factor occurs when thymocytes are cultured in the presence of IL-1. Maximal GM-CSF levels are attained within 3 days of culture, and mRNA expression is detected after a 48-h stimulation. Both GM-CSF production and IL-1-induced thymocyte proliferation are decreased considerably by the depletion of I-A+ Mac-1+ accessory cells. Yet, addition of exogenous GM-CSF to accessory cell-depleted thymocytes does not restore the proliferative response to IL-1 alone, suggesting the implication of another accessory cell-derived mediator. Our data design IL-7 as the endogenous factor required in our culture system because: 1) GM-CSF can reverse the decrease in the proliferation after accessory cell depletion when IL-7 is provided together with IL-1, and 2) the proliferative response to IL-1 plus IL-7 is diminished as much by neutralization of GM-CSF by its specific Abs as by accessory cell removal (approximately 30%). Finally, the cells responding to IL-1 + IL-7 were identified as mature CD4-CD8-TCR+ thymocytes by the use of bromodeoxyuridine (BrdUrd), suggesting that the GM-CSF produced by thymic accessory cells in response to IL-1 participates in IL-7-dependent, intrathymic expansion of the CD4-CD8-TCR+ compartment.

Endogenous granulocyte-macrophage colony-stimulating factor is involved in IL-1- and IL-7-induced murine thymocyte proliferation

We have reported previously that IL-1 induces murine thymocyte proliferation in the absence of artificial comitogens, provided that the cells are cultured at high densities. In the present study, we show that, in these conditions, TdR uptake in response to IL-1 is diminished significantly by anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) Abs. Indeed, a substantial production of this growth factor occurs when thymocytes are cultured in the presence of IL-1. Maximal GM-CSF levels are attained within 3 days of culture, and mRNA expression is detected after a 48-h stimulation. Both GM-CSF production and IL-1-induced thymocyte proliferation are decreased considerably by the depletion of I-A+ Mac-1+ accessory cells. Yet, addition of exogenous GM-CSF to accessory cell-depleted thymocytes does not restore the proliferative response to IL-1 alone, suggesting the implication of another accessory cell-derived mediator. Our data design IL-7 as the endogenous factor required in our culture system because: 1) GM-CSF can reverse the decrease in the proliferation after accessory cell depletion when IL-7 is provided together with IL-1, and 2) the proliferative response to IL-1 plus IL-7 is diminished as much by neutralization of GM-CSF by its specific Abs as by accessory cell removal (approximately 30%). Finally, the cells responding to IL-1 + IL-7 were identified as mature CD4-CD8-TCR+ thymocytes by the use of bromodeoxyuridine (BrdUrd), suggesting that the GM-CSF produced by thymic accessory cells in response to IL-1 participates in IL-7-dependent, intrathymic expansion of the CD4-CD8-TCR+ compartment.

Aggregated IgE mimic interleukin-3-induced histamine synthesis by murine hematopoietic progenitors

Similar to interleukin-3 (IL-3), IgE acts on murine bone marrow cells by inducing histamine production. This effect does not result from degranulation of histamine-containing cells, but from histamine synthesis, as assessed by the following findings. (1) The histamine content of freshly isolated bone marrow cells is too low to account for the increase in extracellular histamine levels. (2) Neither IL-3 nor IgE induced histamine production in the presence of the specific inhibitor of histidine decarboxylase (HDC), the histamine-forming enzyme. (3) Both the enzymatic activity and the mRNA expression of HDC were enhanced in response to IL-3 or IgE. Artificial aggregation or formation of IgE immune complexes augmented ther effect on histamine synthesis, indicating that the aggregated form is responsible for this biologic activity. Yet, it is apparently not mediated by Fc epsilon RI because their cross-linkage by dinitrophenyl bovine serum albumin after presensitization with IgE did not induce histamine production by hematopoietic progenitors. Among other aggregated isotypes tested, only IgG2a and, to a lesser extent, IgG1 had a consistent but lower effect, whereas IgM and IgA were completely inactive. The target cells of IL-3 and IgE in terms of histamine synthesis do not belong to mature bone marrow populations, especially mast cells. They copurify with hematopoietic progenitors in the low-density layers of a discontinuous Ficoll gradient where they represent around 5% of the cells, as determined by in situ hybridization. This percentage remained the same, regardless of whether the cells were stimulated by IgE or IL-3 alone or by a combination of both, suggesting a common responder cell. In accordance with this notion, histamine-producing cells could not be distinguished from each other on the basis of density, size and internal structure, or rhodamine (Rh) retention. Finally, the effect of IgE is not caused by the induction of IL-3 because anti-IL-3 antibodies did not abrogate the effect of IgE.

Structure-function analysis of the C-terminal segment of human interleukin-6

It has been hypothesized that interleukin-6 (IL-6) and granulocyte-colony-stimulating factor (G-CSF) may fold as four-alpha-helix bundle proteins. To probe the functional role of the putative fourth helical segment of IL-6 (D-helix), a chimeric IL-6/G-CSF analog containing the predicted D-helix of G-CSF as well as a panel of IL-6 D-helix point mutants were analyzed for their respective secondary structure, antigenicity, and receptor binding and biological activities. The putative D-helix of IL-6 could not be replaced by its G-CSF counterpart in spite of their high degree of similarity and thus is indispensable for the antigenic and functional integrity of the IL-6 receptor binding site. Conversely, the grafting of the G-CSF D-helix did not confer any G-CSF activity to IL-6. A synthetic helical peptide containing the IL-6 D-helix was inactive, even when mixed with or linked to a peptide from the A-helix known to be involved in the active site. However, the conserved residues F173, R179, and R182 found in the D-helices of both IL-6 and G-CSF critically contribute to the architecture of the IL-6 active site. Indeed, mutation of F173 or R179 markedly affected IL-6 receptor binding and biological activities, but not the conformation of a major neutralization epitope. Furthermore, substitution of R182 resulted in a significant unfolding of the D-helix accompanied by a drastic loss in IL-6 antigenicity and functional activities. Nevertheless, residues other than F173, R179, and R182 also contribute to IL-6 specificity.

Macrophage activation by interferon-gamma from host-protective T cells is inhibited by interleukin (IL)3 and IL4 produced by disease-promoting T cells in leishmaniasis

BALB/c mice are highly susceptible to Leishmania major infection. They develop a progressive fatal disseminating disease even with a minimum infecting dose. However, these mice are able to contain the disease if they are exposed to sublethal gamma-irradiation shortly before infection. Earlier studies demonstrated that CD4+ T cells from mice which had recovered from infection (Tr) can adoptively transfer resistance. In contrast, CD4+ cells from mice with progressive disease (Ts) not only failed to protect, but can reverse the protective effect of the Tr cells. Spleen cells from BALB/c mice which had recovered from L. major infection or which had progressive disease were cultured with leishmanial antigens in vitro. The culture supernatant from spleen cells of recovered mice (TrSN) contains high levels of macrophage-activating factor (MAF) activity which can activate peritoneal macrophages to kill 51Cr-labeled P815 cells and to eliminate intracellular parasites as measured by the reduction in [3H]thymidine uptake by residual parasites released from macrophages following sodium dodecyl sulfate treatment. The MAF activity of TrSN parallels that of recombinant interferon-gamma (IFN-gamma). In contrast, culture supernatant of spleen cells from mice with progressive disease (TsSN) contains no detectable MAF but it is able to neutralize the MAF activity of TrSN. The MAF-inhibiting function of TsSN appears to be mediated by interleukin (IL)3 and IL4, since the MAF activity of TrSN and rIFN-gamma also can be inhibited by the addition of rIL3 and rIL4 but not by rIL1 or rIL2. Furthermore, the MAF-inhibiting activity of TsSN can be partially reversed by the addition of specific anti-IL3 or anti-IL4, but completely reversed by the combination of the two antibodies in vitro. These findings provide a mechanism for the immune regulation in leishmaniasis and a means by which the two subsets of CD4+ T cells influence each other through their modulation of macrophage function.

Automated chemical synthesis of a protein growth factor for hemopoietic cells, interleukin-3

Interleukin-3 (IL-3), a protein of 140 amino acids, was chemically synthesized by means of an automated peptide synthesizer and was shown to have the biological activities attributed to native IL-3. Assays of synthetic analogues established that an amino terminal fragment has detectable IL-3 activity, but that the stable tertiary structure of the complete molecule was required for full activity. The results demonstrate that automated peptide synthesis can be applied to the study of the structure and function of proteins.