IL-3, GM-CSF and CSF-1 modulate c-fms mRNA more rapidly in human early monocytic progenitors than in mature or transformed monocytic cells

Granulocyte macrophage-colony stimulating factor: A key modulator of renal mononuclear phagocyte plasticity

Macrophage-colony stimulating factor (M-CSF) and granulocyte macrophage-colony stimulating factor (GM-CSF) play key roles in the differentiation of macrophages and dendritic cells (DCs). We examined the effect of treatment with M-CSF-containing macrophage medium or GM-CSF-containing DC medium upon the phenotype of murine bone marrow-derived macrophages and DCs. Culture of macrophages for 5 days in DC medium reduced F4/80 expression and increased CD11c expression with cells effectively stimulating T cell proliferation in a mixed lymphocyte reaction. DC medium treatment of macrophages significantly reduced phagocytosis of both apoptotic cells and latex beads and strongly induced the expression of the chemokine receptor CCR7 known to be involved in DC trafficking to lymph nodes. Lysates of obstructed murine kidneys expressed both M-CSF and GM-CSF though M-CSF expression was dominant (M-CSF:GM-CSF ratio ∼30:1). However, combination treatment with both M-CSF and GM-CSF (ratio 30:1) indicated that small amounts of GM-CSF skewed macrophages towards a DC-like phenotype. To determine whether macrophage phenotype might be modulated in vivo we tracked CD45.1⁺ bone marrow-derived macrophages intravenously administered to CD45.2⁺ mice with unilateral ureteric obstruction. Flow cytometry of enzyme dissociated kidneys harvested 3 days later indicated CD11c and MHC Class II upregulation by adoptively transferred CD45.1⁺ cells with CD45.1⁺ cells evident in draining renal lymph nodes. Our data suggests that GM-CSF modulates mononuclear phagocyte plasticity, which likely promotes resolution of injury and healing in the injured kidney.

IL-3 inhibits human osteoclastogenesis and bone resorption through downregulation of c-Fms and diverts the cells to dendritic cell lineage

IL-3 is an important cytokine that regulates hematopoiesis and functions as a link between the immune and the hematopoietic system. In this study, we investigated the role and mechanism of IL-3 action on human osteoclast formation and bone resorption using PBMCs. PBMCs differentiate into functional osteoclasts in the presence of M-CSF and receptor activator of NF-kappaB ligand as evaluated by 23c6 expression and bone resorption. We found that IL-3 dose-dependently inhibited formation of 23c6-positive osteoclasts, bone resorption and C-terminal telopeptide of type I collagen, a collagen degradation product. The inhibitory effect of IL-3 on bone resorption was irreversible. To investigate the mechanism of IL-3 action, we analyzed the effect of IL-3 on the receptor activator of NF-kappaB and c-Fms receptors and c-Fos, PU.1, NFAT cytoplasmic 1, and RelB transcription factors essential for osteoclastogenesis. IL-3 significantly inhibited c-Fms and downregulated both PU.1 and c-Fos at both mRNA and protein level. Furthermore, IL-3-treated cells showed increased expression of dendritic cell markers CD1a and CD80 and decreased expression of monocyte/macrophage marker CD14. Interestingly, IL-3 inhibited formation of human osteoclasts derived from blood monocytes and bone marrow cells of osteoporotic individuals. Thus, IL-3 may have therapeutic potential as an antiosteolytic agent in treatment of osteoporosis.

Severe Listeria monocytogenes infection induces development of monocytes with distinct phenotypic and functional features

Monocytes perform diverse roles during infection with the facultative intracellular bacterium Listeria monocytogenes. They are essential as bactericidal cells in host defense but can also become Trojan horses transporting bacteria into the brain. To explain these contrasting roles, we characterized bone marrow (BM) monocytes in steady state and generated during lethal and sublethal L. monocytogenes infection. Ly-6C(high)CD11b(+) BM monocytes expressed high amounts of M-CSFR/CD115 in steady state and 72 h following sublethal infection. However, infection with increasing numbers of bacteria resulted in progressive loss of CD115 and strongly decreased CD115-encoding c-fms mRNA expression. Conversely, analysis of regulatory molecules showed de novo expression of the nonsignaling IL-1RII, CD121b, under the same conditions. Ly-6C(high)CD11b(+) monocytes in circulation also acquired a CD115(neg/low)CD121b(high) phenotype during lethal infection. These BM monocytes showed upregulation of suppressor of cytokine signaling 1 and 3 and IL-1R-"associated kinase-M to a greater extent and/or earlier compared with cells from sublethal infection and showed decreased LPS-induced IL-6 production despite similar levels of surface TLR4 expression. BM monocytes from uninfected or sublethally infected mice bound and internalized very few L. monocytogenes in vitro. However, both functions were significantly increased in monocytes developing during lethal infection. Nonetheless, these cells did not produce reactive oxygen intermediates, suggesting an inability to kill L. monocytogenes. Together, these data show that systemic infections with lethal and sublethal amounts of bacteria differentially shape developing BM monocytes. This results in distinct phenotypic and functional properties consistent with being Trojan horses rather than bactericidal effector cells.

Erythropoietin down-regulates stem cell factor receptor (Kit) expression in the leukemic proerythroblast: role of Lyn kinase

Overexpression of the transcription factor Spi-1/PU.1 by transgenesis in mice induces a maturation arrest at the proerythroblastic stage of differentiation. We have previously isolated a panel of spi-1 transgenic erythroleukemic cell lines that proliferated in the presence of either erythropoietin (Epo) or stem cell factor (SCF). Using these cell lines, we observed that EpoR stimulation by Epo down-regulated expression of the SCF receptor Kit and induced expression of the Src kinase Lyn. Furthermore, enforced expression of Lyn in the cell lines increased cell proliferation in response to Epo, but reduced cell growth in response to SCF in accordance with Lyn ability to down-regulate Kit expression. Together, the data suggest that Epo-R/Lyn signaling pathway is essential for extinction of SCF signaling leading the proerythroblast to strict Epo dependency. These results highlight a new role for Lyn as an effector of EpoR in controlling Kit expression. They suggest that Lyn may play a central role in during erythroid differentiation at the switch between proliferation and maturation.

The Colony-Stimulating Factor 1 Receptor Is Expressed on Dendritic Cells during Differentiation and Regulates Their Expansion

The lineage of dendritic cells (DC), and in particular their relationship to monocytes and macrophages, remains obscure. Furthermore, the requirement for the macrophage growth factor CSF-1 during DC homeostasis is unclear. Using a transgenic mouse in which the promoter for the CSF-1R (c-fms) directs the expression of enhanced GFP in cells of the myeloid lineage, we determined that although the c-fms promoter is inactive in DC precursors, it is up-regulated in all DC subsets during differentiation. Furthermore, plasmacytoid DC and all CD11c(high) DC subsets are reduced by 50-70% in CSF-1-deficient osteopetrotic mice, confirming that CSF-1 signaling is required for the optimal differentiation of DC in vivo. These data provide additional evidence that the majority of tissue DC is of myeloid origin during steady state and supports a close relationship between DC and macrophage biology in vivo.

Intracellular glutathione status regulates mouse bone marrow monocyte-derived macrophage differentiation and phagocytic activity

Although a redox shift can regulate the development of cells, including proliferation, differentiation, and survival, the role of the glutathione (GSH) redox status in macrophage differentiation remains unclear. In order to elucidate the role of a redox shift, macrophage-like cells were differentiated from the bone marrow-derived monocytes that were treated with a macrophage colony stimulating factor (M-CSF or CSF-1) for 3 days. The macrophagic cells were characterized by a time-dependent increase in three major symptoms: the number of phagocytic cells, the number of adherent cells, and the mRNA expression of c-fms, a M-CSF receptor that is one of the macrophage-specific markers and mediates development signals. Upon M-CSF-driven macrophage differentiation, the GSH/GSSG ratio was significantly lower on day 1 than that observed on day 0 but was constant on days 1-3. To assess the effect of the GSH-depleted and -repleted status on the differentiation and phagocytosis of the macrophages, GSH depletion by BSO, a specific inhibitor of the de novo GSH synthesis, inhibited the formation of the adherent macrophagic cells by the down-regulation of c-fms, but did not affect the phagocytic activity of the macrophages. To the contrary, GSH repletion by the addition of NAC, which is a GSH precursor, or reduced GSH in media had no effect on macrophage differentiation, and led to a decrease in the phagocytic activity. Furthermore, we observed that there is checkpoint that is capable of releasing from the inhibition of the formation of the adherent macrophagic cells according to GSH depletion by BSO. Summarizing, these results indicate that the intracellular GSH status plays an important role in the differentiation and phagocytosis of macrophages.

The high proliferative potential-quiescent (HPP-Q) cell assay allows an optimized evaluation of gene transfer efficiency into primitive hematopoietic stem/progenitor cells

Various protocols have been described to optimize gene transfer into hematopoietic cells. However, most of these methods do not specify whether they are associated with an improved transduction of the more primitive stem/progenitor cells, the best candidates for long-term engraftment. The majority of these primitive cells remains in quiescence because of the negative control of TGF-beta1, effective on these cells at low concentrations (10 pg/ml). In this study, CD34- cells were activated by a 10 h pretreatment with anti-TGF-beta1 followed by four successive retroviral supernatant incubations of 6 h each. After 12 h (two incubations), a significant increase in TGF-beta1 mRNA in CD34+ cells was observed. We wondered whether neo-synthesized autocrine TGF-beta1 could induce reversion to quiescence of the more primitive CD34+ cells transduced after one cell cycle. This would prevent their subsequent detection in a classic clonal assay. Using the HPP-Q assay comparing a rapid mixed colony assay with or without anti-TGF-beta1, we indeed observed, that in clonal growth conditions the more primitive transduced cells were activated and detectable only with anti-TGF-beta1. Therefore, this assay represents not only a rapid means to detect quiescent multipotent stem/progenitor cells but also a necessary step for the detection of the more primitive transduced cells which have returned to quiescence after retroviral induction of TGF-beta1 secretion.