GM-CSF regulates alveolar macrophage differentiation and innate immunity in the lung through PU.1

Modulation of Neonatal Microbial Recognition: TLR-Mediated Innate Immune Responses Are Specifically and Differentially Modulated by Human Milk

The mechanisms controlling innate microbial recognition in the neonatal gut are still to be fully understood. We have sought specific regulatory mechanisms operating in human breast milk relating to TLR-mediated microbial recognition. In this study, we report a specific and differential modulatory effect of early samples (days 1-5) of breast milk on ligand-induced cell stimulation via TLRs. Although a negative modulation was exerted on TLR2 and TLR3-mediated responses, those via TLR4 and TLR5 were enhanced. This effect was observed in human adult and fetal intestinal epithelial cell lines, monocytes, dendritic cells, and PBMC as well as neonatal blood. In the latter case, milk compensated for the low capacity of neonatal plasma to support responses to LPS. Cell stimulation via the IL-1R or TNFR was not modulated by milk. This, together with the differential effect on TLR activation, suggested that the primary effect of milk is exerted upstream of signaling proximal to TLR ligand recognition. The analysis of TLR4-mediated gene expression, used as a model system, showed that milk modulated TLR-related genes differently, including those coding for signal intermediates and regulators. A proteinaceous milk component of > or =80 kDa was found to be responsible for the effect on TLR4. Notably, infant milk formulations did not reproduce the modulatory activity of breast milk. Together, these findings reveal an unrecognized function of human milk, namely, its capacity to influence neonatal microbial recognition by modulating TLR-mediated responses specifically and differentially. This in turn suggests the existence of novel mechanisms regulating TLR activation.

A vesicular stomatitis virus recombinant expressing granulocyte-macrophage colony-stimulating factor induces enhanced T-cell responses and is highly attenuated for replication in animals

Live attenuated vectors based on recombinant vesicular stomatitis viruses (rVSVs) expressing foreign antigens are highly effective vaccines in animal models. In this study, we report that an rVSV (VSV-GMCSF1) expressing high levels of murine granulocyte-macrophage colony-stimulating factor (GM-CSF) from the first position in the viral genome is highly attenuated in terms of viral dissemination and pathogenesis after intranasal delivery to mice. However, this highly attenuated virus generated antibody and T-cell responses equivalent to those induced by a control virus expressing enhanced green fluorescent protein (EGFP) from the first position (VSV-EGFP1). The better containment and clearance of VSV-GMCSF1 may be due to enhanced recruitment of macrophages to the site of infection but is not explained by a greater induction of interferons. The primary CD8 T-cell and neutralizing antibody responses to VSV-GMCSF1 were equivalent to those generated by VSV-EGFP1, while the CD8 T-cell memory and recall responses to the vector were enhanced in mice infected with VSV-GMCSF1. It is likely that the GM-CSF produced by immunization with this virus results in an enhanced recruitment of antigen-presenting cells, leading to better acute and long-term T-cell responses. This recruitment appears to cancel out any negative effect of viral attenuation on immunogenicity.

PU.1 regulates cathepsin S expression in professional APCs

Cathepsin S (CTSS) is a cysteine protease that is constitutively expressed in APCs and mediates processing of MHC class II-associated invariant chain. CTSS and the Ets family transcription factor PU.1 are highly expressed in cells of both myeloid (macrophages and dendritic cells) and lymphoid (B lymphocytes) lineages. Therefore, we hypothesized that PU.1 participates in the transcriptional regulation of CTSS in these cells. In A549 cells (a human epithelial cell line that does not express either CTSS or PU.1), the expression of PU.1 enhances CTSS promoter activity approximately 5- to 10-fold. In RAW cells (a murine macrophage-like cell line that constitutively expresses both CTSS and PU.1), the expression of a dominant-negative PU.1 protein and a short-interfering RNA PU.1 construct attenuates basal CTSS promoter activity, mRNA levels, and protein expression. EMSAs show binding of PU.1 to oligonucleotides derived from the CTSS promoter at two different Ets consensus binding elements. Mutation of these sites decreases the baseline CTSS activity in RAW cells that constitutively express PU.1. Chromatin immunoprecipitation experiments show binding of PU.1 with the CTSS promoter in this same region. Finally, the expression of PU.1, in concert with several members of the IFN regulatory factor family, enhances CTSS promoter activity beyond that achieved by PU.1 alone. These data indicate that PU.1 participates in the regulation of CTSS transcription in APCs. Thus, manipulation of PU.1 expression may directly alter the endosomal proteolytic environment in these cells.

Role of granulocyte macrophage colony-stimulating factor during gram-negative lung infection with Pseudomonas aeruginosa

Granulocyte macrophage colony-stimulating factor (GM-CSF) stimulates survival, proliferation, differentiation, and function of myeloid cells. Recently, GM-CSF has been shown to be important for normal pulmonary homeostasis. We report that GM-CSF is induced in lung leukocytes during infection with Gram-negative bacteria. Therefore, we postulated that deficiencies in GM-CSF would increase susceptibility to Gram-negative infection in vivo. After an intratracheal inoculum with Pseudomonas aeruginosa, GM-CSF-/- mice show decreased survival compared with wild-type mice. GM-CSF-/- mice show increased lung, spleen, and blood bacterial CFU. GM-CSF-/- mice are defective in the production of cysteinyl leukotrienes, prostaglandin E2, macrophage inflammatory protein, and keratinocyte-derived chemokine in lung leukocytes postinfection. Despite these defects, inflammatory cell recruitment is not diminished at 6 or 24 h postinfection, and the functional activity of polymorphonuclear leukocytes from the lung and peritoneum against P. aeruginosa is enhanced in GM-CSF-/- mice. In contrast, alveolar macrophage (AM) phagocytosis, killing, and H2O2 production are defective in GM-CSF-/- mice. Although the absence of GM-CSF has profound effects on AMs, peritoneal macrophages seem to have normal bactericidal activities in GM-CSF-/- mice. Defects in AM function may be related to diminished levels of IFN-gamma and TNF-alpha postinfection. Thus, GM-CSF-/- mice are more susceptible to lung infection with P. aeruginosa as a result of impaired AM function.

Phenotypical and functional characterization of alveolar macrophage subpopulations in the lungs of NO2-exposed rats

Background

Alveolar macrophages (AM) are known to play an important role in the regulation of inflammatory reactions in the lung, e.g. during the development of chronic lung diseases. Exposure of rats to NO₂ has recently been shown to induce a shift in the activation type of AM that is characterized by reduced TNF-α and increased IL-10 production. So far it is unclear, whether a functional shift in the already present AM population or the occurrence of a new, phenotypically different AM population is responsible for these observations.

Methods

AM from rat and mice were analyzed by flow cytometry for surface marker expression and in vivo staining with PKH26 was applied to characterize newly recruited macrophages. Following magnetic bead separation, AM subpopulations were further analyzed for cytokine, inducible NO synthase (iNOS) and matrix metalloproteinase (MMP) mRNA expression using quantitative RT-PCR. Following in vitro stimulation, cytokines were quantitated in the culture supernatants by ELISA.

Results

In untreated rats the majority of AM showed a low expression of the surface antigen ED7 (CD11b) and a high ED9 (CD172) expression (ED7^-/ED9^high). In contrast, NO₂ exposure induced the occurrence of a subpopulation characterized by the marker combination ED7⁺/ED9^low. Comparable changes were observed in mice and by in vivo labeling of resident AM using the dye PKH26 we could demonstrate that CD11b positive cells mainly comprise newly recruited AM. Subsequent functional analyses of separated AM subpopulations of the rat revealed that ED7⁺ cells showed an increased expression and production of the antiinflammatory cytokine IL-10 whereas TNF-α production was lower compared to ED7^- AM. However, iNOS and IL-12 expression were also increased in the ED7⁺ subpopulation. In addition, these cells showed a significantly higher mRNA expression for the matrix metalloproteinases MMP-7, -8, -9, and -12.

Conclusion

NO₂ exposure induces the infiltration of an AM subpopulation that, on the one hand may exert antiinflammatory functions by the production of high amounts of IL-10 but on the other hand may contribute to the pathology of NO₂-induced lung damage by selective expression of certain matrix metalloproteinases.

Chronic ethanol ingestion in rats decreases granulocyte-macrophage colony-stimulating factor receptor expression and downstream signaling in the alveolar macrophage

Although it is well recognized that alcohol abuse impairs alveolar macrophage immune function and renders patients susceptible to pneumonia, the mechanisms are incompletely understood. Alveolar macrophage maturation and function requires priming by GM-CSF, which is produced and secreted into the alveolar space by the alveolar epithelium. In this study, we determined that although chronic ethanol ingestion (6 wk) in rats had no effect on GM-CSF expression within the alveolar space, it significantly decreased membrane expression of the GM-CSF receptor in alveolar macrophages. In parallel, ethanol ingestion decreased cellular expression and nuclear binding of PU.1, the master transcription factor that activates GM-CSF-dependent macrophage functions. Furthermore, treatment of ethanol-fed rats in vivo with rGM-CSF via the upper airway restored GM-CSF receptor membrane expression as well as PU.1 protein expression and nuclear binding in alveolar macrophages. Importantly, GM-CSF treatment also restored alveolar macrophage function in ethanol-fed rats, as reflected by endotoxin-stimulated release of TNF-alpha and bacterial phagocytosis. We conclude that ethanol ingestion dampens alveolar macrophage immune function by decreasing GM-CSF receptor expression and downstream PU.1 nuclear binding and that these chronic defects can be reversed relatively quickly with rGM-CSF treatment in vivo.

Why does the autoantibody against granulocyte-macrophage colony-stimulating factor cause lesions only in the lung?

OBJECTIVES

During the course of investigating the etiology of idiopathic pulmonary alveolar proteinosis (IPAP), the authors found that the autoantibody against granulocyte-macrophage colony-stimulating factor (GM-CSF) was consistently present in both sera and the lung tissue. The autoantibody completely blocked bioactivity by direct binding with high specificity and avidity. Because of the existence of patients with congenital PAP who lack GM-CSF receptors and the development of PAP in GM-CSF and GM-CSF receptor knock-out mice, the autoantibody is likely to be the causative agent for IPAP. However, this finding posed the question as to why the autoantibody against GM-CSF caused lesions only in the lung.

METHODOLOGY

To answer this question, the authors investigated, using immunohistochemistry, confocal laser microscopy, and immunoblotting, the expression of PU.1 in tissue macrophages. PU.1 is a critical transcription factor for terminal differentiation of alveolar macrophage (AM), as reported previously in the lung, liver, spleen, kidney, intestine and brain.

RESULTS

PU.1 was consistently expressed in the nuclei of normal AM, but faintly or not at all in IPAP-AM. Moreover, it was not expressed in the nuclei of any other normal tissue macrophages tested. Blood monocytes expressed PU.1 in the cytosol but not in the nuclei. These results suggested that the differentiation pathway is different between AM and other tissue macrophages. PU.1 was not expressed in the nuclei of newborn rat lung AM but was gradually expressed during the first 10 days.

CONCLUSIONS

The authors demonstrated that GM-CSF is crucial for terminal differentiation of AM, but not for that of other tissue macrophages.

Granulocyte-macrophage colony-stimulating factor increases L-arginine transport through the induction of CAT2 in bone marrow-derived macrophages

L-arginine transport is crucial for macrophage activation because it supplies substrate for the key enzymes nitric oxide synthase 2 and arginase I. These enzymes participate in classic and alternative activation of macrophages, respectively. Classic activation of macrophages is induced by type I cytokines, and alternative activation is induced by type II cytokines. The granulocyte macrophage colony-stimulating factor (GM-CSF), in addition to inducing proliferation and differentiation of macrophages, activates arginase I, but its action on L-arginine transport is unknown. We studied the L-arginine transporters that are active in mouse primary bone marrow-derived macrophages (BMM) and examined the effect of GM-CSF treatment on transport activities. Under basal conditions, L-arginine entered mainly through system y(+)L (>75%). The remaining transport was explained by system y(+) (<10%) and a diffusion component (10-15%). In response to GM-CSF treatment, transport activity increased mostly through system y(+) (>10-fold), accounting for about 40% of the total L-arginine transport. The increase in y(+) activity correlated with a rise in cationic amino acid transporter (CAT)-2 mRNA and protein. Furthermore, GM-CSF induced an increase in arginase activity and in the conversion of L-arginine to ornithine, citrulline, glutamate, proline, and polyamines. BMM obtained from CAT2-knockout mice responded to GM-CSF by increasing arginase activity and the expression of CAT1 mRNA, which also encodes system y(+) activity. Nonetheless, the increase in CAT1 activity only partially compensated the lack of CAT2 and L-arginine metabolism was hardly stimulated. We conclude that BMM present mainly y(+)L activity and that, in response to GM-CSF, l-arginine transport augments through CAT2, thereby increasing the availability of this amino acid to the cell.

Elevated gelatinase activity in pulmonary alveolar proteinosis: role of macrophage-colony stimulating factor

Pulmonary alveolar proteinosis (PAP) is an anti-granulocyte macrophage-colony stimulating factor (GM-CSF) autoimmune disease resulting in the accumulation of phospholipids in the alveoli. GM-CSF knockout (KO) mice exhibit a strikingly similar lung pathology to patients with PAP. The lack of functionally active GM-CSF correlates with highly elevated concentrations of M-CSF in the lungs of PAP patients and GM-CSF KO mice. M-CSF has been associated with alternative macrophage activation, and in models of pulmonary fibrosis, M-CSF also contributes to tissue resorption and fibrosis. Matrix metalloproteinase-2 (MMP-2) and MMP-9 have been implicated in extracellular matrix degradation in animal models of fibrosis and asthma. We show for the first time that the lungs of PAP patients contain highly elevated levels of MMP-2 and MMP-9. PAP broncholaveolar lavage (BAL) cells but not bronchial epithelial cells expressed increased MMP-2 and MMP-9 mRNA relative to healthy controls. Both MMPs were detectable as pro and active proteins by gelatin zymography; and by fluorometric global assay, PAP-MMP activity was elevated. BAL cells/fluids from GM-CSF KO mice also demonstrated significantly elevated MMP-2 and MMP-9 gene expression, protein, and activity. Finally, PAP patients undergoing GM-CSF therapy exhibited significantly reduced MMPs and M-CSF. These data suggest that in the absence of GM-CSF, excess M-CSF in PAP may redirect alveolar macrophage activation, thus potentially contributing to elevated MMP expression in the lung.

Identification of the surfactant protein A receptor 210 as the unconventional myosin 18A

Mass spectrometric characterization of the surfactant protein A (SP-A) receptor 210 (SP-R210) led to the identification of myosin (Myo) XVIIIA and nonmuscle myosin IIA. Antibodies generated against the unique C-terminal tail of MyoXVIIIA revealed that MyoXVIIIA, MyoIIA, and SP-R210 have overlapping tissue distribution, all being highly expressed in myeloid cells, bone marrow, spleen, lymph nodes, and lung. Western blot analysis of COS-1 cells stably transfected with either MyoXVIIIA or MyoIIA indicated that SP-R210 antibodies recognize MyoXVIIIA. Furthermore, MyoXVIIIA but not MyoIIA localized to the surface of COS-1 cells, and most importantly, expression of MyoXVIIIA in COS-1 cells conferred SP-A binding. Western analysis of recombinant MyoXVIIIA domains expressed in bacteria mapped the epitopes of previously derived SP-R210 antibodies to the neck region of MyoXVIIIA. Antibodies raised against the neck domain of MyoXVIIIA blocked the binding of SP-A to macrophages. Together, these findings indicate that MyoXVIIIA constitutes a novel receptor for SP-A.

Inducible binding of PU.1 and interacting proteins to the Toll-like receptor 4 promoter during endotoxemia

We hypothesized that PU.1 and PU.1 interacting proteins (PIP) binding to the Toll-like receptor 4 (TLR4) promoter is involved in endotoxin-induced upregulation of TLR4 gene expression. Our results employing chromatin immunoprecipitation assays indicate that PU.1 binds to the murine TLR4 promoter both in macrophage cells and, most importantly, in whole lung tissue. Treatment of RAW 264.7 cells with endotoxin induced the association of PU.1 and the TLR4 promoter in a time-dependent manner, and this was closely tied to interactions between the TLR4 promoter and the PIP interferon regulatory factors (IRF)4 and IRF8. PU.1 binding was related to increases in steady-state TLR4 mRNA and total TLR4 protein in RAW cells. Endotoxemia in animals caused the similar inducible interaction between PU.1 and IRF4 and the TLR4 promoter in lung tissue of mice that was treated with a single intraperitoneal injection of endotoxin. PU.1 binding to the TLR4 promoter was not enhanced in the lung tissue of endotoxin-resistant C3H/HeJ mice in response to endotoxemia. Transient transfection studies in RAW cells indicate that inducible binding of PU.1 to the TLR4 promoter is abrogated by a Ser148 to Ala mutation in PU.1. These data suggest that induction of PU.1/PIP binding to the TLR4 promoter is involved in endotoxin response in vivo and may mediate transcriptional changes in TLR4 gene expression.

Granulocyte-Macrophage Colony–Stimulating Factor and Lung Immunity in Pulmonary Alveolar Proteinosis

The anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) autoantibody is inferred to cause idiopathic pulmonary alveolar proteinosis (iPAP): the antibody neutralizes GM-CSF and thereby impairs differentiation of alveolar macrophages. Administration of GM-CSF improves respiratory function of patients with iPAP, as confirmed in this study using aerosolized GM-CSF. To elucidate its mechanism, we characterized bronchoalveolar lavage fluid and alveolar macrophages obtained from three patients with iPAP who were treated successfully with aerosolized GM-CSF. Cell number, expressions of surface mannose receptor and the transcription factor PU.1, and phagocytic ability of alveolar macrophages were all restored to control levels. With treatment, the neutralizing capacity of GM-CSF activity was reduced markedly, concomitant with the decreasing autoantibody levels. Interestingly, the amount of GM-CSF autoantibody complex also decreased. In one case in which the complex was analyzed, the majority of GM-CSF binding the complex was endogenous protein, suggesting that the complex is removed immediately from the lung after treatment. Our study shows that GM-CSF administration engenders a decrease in the neutralizing capacity against the protein in the lungs. Thereby, it facilitates restoration of the normal function of alveolar macrophages.

Transcriptional regulation in myelopoiesis: Hematopoietic fate choice, myeloid differentiation, and leukemogenesis

Myeloid cells (granulocytes and monocytes) are derived from multipotent hematopoietic stem cells. Gene transcription plays a critical role in hematopoietic differentiation. However, there is no single transcription factor that is expressed exclusively by myeloid cells and that, alone, acts as a "master" regulator of myeloid fate choice. Rather, myeloid gene expression is controlled by the combinatorial effects of several key transcription factors. Hematopoiesis has traditionally been viewed as linear and hierarchical, but there is increasing evidence of plasticity during blood cell development. Transcription factors strongly influence cellular lineage during hematopoiesis and expression of some transcription factors can alter the fate of developing hematopoietic progenitor cells. PU.1 and CCAAT/enhancer-binding protein alpha (C/EBPalpha) regulate expression of numerous myeloid genes, and gene disruption studies have shown that they play essential, nonredundant roles in myeloid cell development. They function in cooperation with other transcription factors, co-activators, and co-repressors to regulate genes in the context of chromatin. Because of their essential roles in regulating myeloid genes and in myeloid cell development, it has been hypothesized that abnormal expression of PU.1 and C/EBPalpha would contribute to aberrant myeloid differentiation, i.e. acute leukemia. Such a direct link has been elusive until recently. However, there is now persuasive evidence that mutations in both PU.1 and C/EBPalpha contribute directly to development of acute myelogenous leukemia. Thus, normal myeloid development and acute leukemia are now understood to represent opposite sides of the same hematopoietic coin.

Balance of MafB and PU.1 specifies alternative macrophage or dendritic cell fate

Macrophages and myeloid dendritic cells (DCs) represent alternative differentiation options of bone marrow progenitors and blood monocytes. This choice profoundly influences the immune response under normal and pathological conditions, but the underlying transcriptional events remain unresolved. Here, we show that experimental activation of the transcription factors PU.1 and MafB in transformed chicken myeloid progenitors triggered alternative DC or macrophage fate, respectively. PU.1 activation also was instructive for DC fate in the absence of cytokines in human HL-60 cell-derived myeloid progenitor and monocyte clones. Differentiation of normal human monocytes to DCs led to a rapid increase of PU.1 to high levels that preceded phenotypic changes, but no MafB expression, whereas monocyte-derived macrophages expressed MafB and only moderate levels of PU.1. DCs inducing levels of PU.1 inhibited MafB expression in monocytes, which appeared to be required for DC specification, since constitutive MafB expression inhibited DC differentiation. Consistent with this, PU.1 directly bound to MafB, inhibited its transcriptional activity in macrophages, and repressed its ability to induce macrophage differentiation in chicken myeloid progenitors. We propose that high PU.1 activity favors DCs at the expense of macrophage fate by inhibiting expression and activity of the macrophage factor MafB.

Disruption of granulocyte macrophage-colony stimulating factor production in the lungs severely affects the ability of mice to control Mycobacterium tuberculosis infection

Mice lacking expression of granulocyte macrophage-colony stimulating factor (GM-CSF KO) are unable to contain Mycobacterium tuberculosis (M. tuberculosis) growth and succumb to infection by 35 days following pulmonary challenge. GM-CSF KO mice do not express normal levels of the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha) nor the chemokines, regulated on activation, normal T expressed and secreted (RANTES), macrophage-inflammatory protein-1beta (MIP-1beta), MIP-1alpha, and lymphotactin, which are required for recruitment of lymphocytes and expression of a T helper cell type 1 (TH1) response within the lungs. In contrast, transgenic mice overexpressing GM-CSF in the lungs but with a lack of GM-CSF in other organs (GM+) are able to recruit lymphocytes and to express a TH1 response with production of TNF-alpha and interferon-gamma in the lungs. However, GM+ mice succumb to infection between 60 and 90 days post-challenge, as they are unable to develop a normal granulomatous response. Although GM+ mice are able to express the chemokine RANTES, they lack the ability to express other inflammatory chemokines such as lymphotactin and MIP-1beta. We conclude that GM-CSF is essential to the recruitment of lymphocytes and expression of a TH1 response in the lung, to the generation of a normal mononuclear granuloma, and most importantly, to the containment of M. tuberculosis bacterial growth.

Mast cells acquire monocyte-specific gene expression and monocyte-like morphology by overproduction of PU.1

PU.1 is a myeloid- and lymphoid-specific transcription factor that belongs to the Ets family. Recently, we found that overproduction of PU.1 in mouse bone marrow-derived hemopoietic progenitor cells induced monocyte-specific gene expression and caused their monocyte-like morphological change. In the present study, PU.1 was overproduced by using retrovirus expression system in differentiated bone marrow-derived mast cells. By overexpression of PU.1, cell surface expression of MHC class II, CD11b, CD11c, and F4/80 was induced, accompanied by reduced expression of c-kit, a mast cell-specific marker. Morphology of PU.1-transfected cells was altered toward monocyte-like one. PU.1-overproducing cells acquired T cell stimulatory ability and showed an increase in response to LPS stimulation, while response through FcepsilonRI was markedly reduced by overproduction of PU.1. These results suggest that the differentiated mast cells still have potential to display monocytic features. When PU.1 was overproduced in a different type of mast cell, peritoneal mast cells, similar monocyte-like morphological change, and the expression of CD11b and F4/80 were induced. However, surface level of CD11c and MHC class II was not affected. These results indicate that the potential capacity to exhibit monocytic features is different between both the mast cells.

Selective up-regulation of PDE1B2 upon monocyte-to-macrophage differentiation

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a major regulator of monocyte to macrophage differentiation. In both humans and mice, the main phenotype of decreased GM-CSF function is pulmonary proteinosis due to aberrant function of alveolar macrophages. Recently, this cytokine has been shown to up-regulate a cyclic nucleotide phosphodiesterase, PDE1B. Two PDE1B variants with unique N-terminal sequences, PDE1B1 and PDE1B2, have been identified. Here, we report that the previously uncharacterized PDE1B2 is selectively increased by GM-CSF by stimulation of transcription at a previously unknown transcriptional start site. Analysis of the exon and intron organization of the PDE1B gene reveals that PDE1B2 has a different N-terminal sequence because of a separate first exon that is located 11.5 kb downstream from the PDE1B1 first exon. By using 5'-RACE, alignment of EST sequences, and a luciferase-reporter system, we provide evidence that PDE1B2 has a separate transcriptional start site from PDE1B1 that can be activated by monocyte differentiation. Furthermore, IL-4 treatment in the presence of GM-CSF, which shifts the differentiation from a macrophage to a dendritic cell phenotype, suppresses the up-regulation of PDE1B2. Induction of PDE1B2 is also found in T cells upon activation by PHA. Therefore, PDE1B2 may have a regulatory role in multiple immune cell types. Last, characterization of the catalytic properties of recombinant PDE1B2 shows that it prefers cGMP over cAMP as a substrate and, thus, is likely to regulate cGMP in macrophages. Also, PDE1B2 has a nearly 3-fold lower EC(50) for activation by calmodulin than PDE1B1.

Impaired toll-like receptor 9 expression in alveolar macrophages with no sensitivity to CpG DNA

Unmethylated CpG motifs in bacterial DNA or synthetic oligodeoxynucleotides (ODN) potently stimulate the innate immune system, and they are recognized by Toll-like receptor 9 (TLR9), which is expressed by monocytes/macrophages, dendritic cells, and B cells. However, it is unknown whether alveolar macrophages (AMs) express functional TLR9. To clarify this, we analyzed mRNA expressions of TLRs in murine AMs by real-time polymerase chain reaction, and compared with those in other tissue macrophages and lung antigen-presenting cells. In addition, we determined the sensitivity of these cell populations to CpG-ODN. Interestingly, TLR9 mRNA was almost absent in AMs, but highly expressed in bone marrow-derived macrophages and peritoneal macrophages, whereas TLR2 and TLR4 were present in all macrophage populations. Consistent with the receptor expression, AMs showed no sensitivity to CpG-ODN, whereas other macrophage populations secreted tumor necrosis factor alpha, interleukin 12 p40, and interleukin 6, and enhanced expression of CD40, CD80, and CD86, in response to CpG-ODN. Lung dendritic cells and B cells highly expressed TLR9 mRNA and responded to CpG-ODN. These results indicate selective loss of TLR9 expression in AMs with no sensitivity to CpG-ODN, suggesting that dendritic cells and B cells play a role in the immune response against bacterial DNA in the lung.

GM-CSF mediates alveolar epithelial type II cell changes, but not emphysema-like pathology, in SP-D-deficient mice

Surfactant protein D (SP-D) is a member of the collectin subfamily of C-type lectins, pattern recognition proteins participating in the innate immune response. Gene-targeted mice deficient in SP-D develop abnormalities in surfactant homeostasis, hyperplasia of alveolar epithelial type II cells, and emphysema-like pathology. Granulocyte/macrophage colony-stimulating factor (GM-CSF) is required for terminal differentiation and subsequent activation of alveolar macrophages, including the expression of matrix metalloproteinases and reactive oxygen species, factors thought to contribute to lung remodeling. Type II cells also express the GM-CSF receptor. Thus we hypothesized GM-CSF might mediate some or all of the cellular and structural abnormalities in the lungs of SP-D-deficient mice. To test this, SP-D (D−G+) and GM-CSF (D+G−) single knockout mice as well as double knockout mice deficient for both SP-D and GM-CSF (D−G−) were analyzed by design-based stereology. Compared with wild type, D−G+ as well as D+G− mice showed decreased alveolar numbers, increased alveolar sizes, and decreased alveolar epithelial surface areas. These emphysema-like changes were present to a greater extent in D−G− mice. D−G+ mice developed type II cell hyperplasia and hypertrophy with increased intracellular surfactant pools, whereas D+G− mice had smaller type II cells with decreased intracellular surfactant pools. In contrast to the emphysematous changes, the type II cell alterations were mostly corrected in D−G− mice. These results indicate that GM-CSF-dependent macrophage activity is not necessary for emphysema development in SP-D-deficient mice, but that type II cell metabolism and proliferation are, either directly or indirectly, regulated by GM-CSF in this model.

Pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis (PAP) has been recognized for almost half a century. At least three separate pathophysiologic mechanisms may lead to the characteristic feature of PAP: the excessive accumulation of surfactant lipoprotein in pulmonary alveoli, with associated disturbance of pulmonary gas exchange. The prognosis for adult patients with PAP varies, but disease-specific survival rate exceeds 80% at 5 years. The survival rates for adult PAP patients seem to have increased progressively in the four decades since the initial clinical description of this condition. The last decade has brought new advances in laboratory and clinical research that are lifting a veil not only on PAP but also on general aspects of pulmonary surfactant biology and innate immune defense.

Serum cholestenoic acid as a potential marker of pulmonary cholesterol homeostasis: increased levels in patients with pulmonary alveolar proteinosis

The conversion of cholesterol into the more polar metabolites 27-hydroxycholesterol (27-OH) and cholestenoic acid by the cytochrome P450 sterol 27-hydroxylase is a cholesterol-removal mechanism used by almost all cells. Most of the cholestenoic acid present in the circulation originates from the lung, and it has been suggested that sterol 27-hydroxylase is of particular importance for cholesterol homeostasis in this organ. As an example of pulmonary cholesterol accumulation, a known disorder of surfactant homeostasis, pulmonary alveolar proteinosis (PAP), was studied. Analysis of bronchoalveolar lavage fluid from PAP patients revealed a significant accumulation of the cholesterol metabolites cholestenoic acid and 27-OH. This pattern was recapitulated in serum, with a significant increase in the levels of both cholestenoic acid (P=0.003) and 27-OH (P=0.017) in PAP patients compared with healthy controls. Analysis of PAP alveolar macrophages did not reveal a significant change in mRNA expression levels of either sterol 27-hydroxylase or the cholesterol-esterifying enzyme acyl-CoA:cholesterol acyltransferase-1. These results are consistent with the contention that substrate availability, rather than enzyme expression, is the key factor in regulating the production of cholestenoic acid by the lung and that serum cholestenoic acid may be a marker of pulmonary cholesterol homeostasis.

Evidence against requirement of Ser41 and Ser45 for function of PU.1 -- molecular cloning of rat PU.1

The transcription factor PU.1 plays an important role in the development of the myeloid and lymphoid lineages and regulates the transcription of several genes expressed in these cells. Ser41 is conserved in the acidic region (33-47) of PU.1 from a variety of eukaryocytes and has been reported to be one of the two important Ser residues (S41 and S45) for the function of PU.1. In the present study, however, we found that rat PU.1 has Gly at position 41. To elucidate the role of amino acid residues at 41 and 45 in functions of PU.1, we generated mutants of rat PU.1, G41S, G41A, and S45A, and analyzed their transcription-enhancing activities by using two different systems, transient reporter assay system and retroviral transfection system. The amino acid substitution at 41 of PU.1 causes no effect on both transcription-enhancing activity for M-CSF receptor promoter and the cooperative transcription-enhancing activity with GATA-1 for FcRI alpha-chain promoter. Furthermore, the substitution at 41 also had no effect on the activity to induce monocyte-specific gene expression in the bone marrow-derived hematopoietic cells. From these results, we conclude that Ser41 as well as Ser45 are not essential for the promoter-upregulating function of PU.1.

The origin of hematopoietic cell type diversity

The hematopoietic system remains robust with regards to extrinsic perturbations, in sharp contrast with the stochastic behavior of hematopoeitic stem cells (HSCs) at the single cell level, suggesting that stability may be achieved within a stem cell system that undergoes constant self-renewal, commitment to differentiation and generates cell type diversification. Converging evidence at the interface of cellular, molecular and numerical studies suggests that diversity is generated by the chaotic dynamics of transcription factor networks within a cell and of the combination of growth factors and cytokines in the environment, both involving cooperation and competition. Current evidence indicates that HSCs are primed for multilineage gene expression. A subtle shift in transcription factor dosage is sufficient to perturb this equilibrium and to drive lineage commitment that involves a resolution of complexity at the molecular level and a transition towards less chaotic behavior. This dynamical instability establishes a state of responsiveness to extrinsic signals. Evolutionary conserved environmental cues that drive pattern formation or migratory behavior during embryonic development operate in the adult to influence the decision between self-renewal and differentiation in HSCs, as exemplified by the role of Notch1, Wnt proteins, BMPs and VEGF. In contrast, a network of cytokines uniquely present in mammalians influences later developmental stages, from progenitors with more restricted potentials (tri-, bi- or unipotent) to mature functional cells. These cytokines have co-opted the ancient Jak-STAT pathway but also appear to trigger lineage-affiliated transcription factors, thus linking environmental signaling to cell fate decisions.

Cigarette Smoke Inhibits Lipopolysaccharide-Induced Production of Inflammatory Cytokines by Suppressing the Activation of Activator Protein-1 in Bronchial Epithelial Cells

Chronic smoking is characterized by immunosuppressive changes in the airways, leading to chronic colonization with bacteria, which in turn may contribute to the chronic obstructive pulmonary disease. The mechanisms causing this immunosuppression, however, are poorly characterized. This study evaluated whether cigarette smoke can inhibit endotoxin (LPS)-induced inflammatory cytokine production in bronchial epithelial cells and, if so, what the mechanisms are behind this effect. Pretreatment with cigarette smoke extract (CSE) concentration dependently inhibited the LPS-induced GM-CSF and IL-8 protein release, which was accompanied by decreased expression of mRNA in human bronchial epithelial cells (Beas-2B). The increase of neutrophil chemotaxis induced by conditioned medium from LPS-treated Beas-2B cells was also suppressed by CSE. In addition, the activity of LPS-induced transcription factor AP-1, but not NF-kappaB, was down-regulated by CSE. Notably, at the concentrations used, CSE had no effect on number or viability of Beas-2B cells. These data indicate that cigarette smoke possesses immunosuppressive properties by down-regulating the bacterial pathogen-induced neutrophil-mobilizing cytokine production via suppression of AP-1 activation in the airways. Hence, this study suggests a novel mechanism by which cigarette smoke may contribute to chronic colonization and chronic obstructive pulmonary disease in smokers.

Overproduction of PU.1 in mast cell progenitors: its effect on monocyte- and mast cell-specific gene expression

The Ets family transcription factor PU.1 is required for development of various lymphoid and myeloid cell lineages, and regulates the expression of several genes in a cell type-specific manner. Mouse bone marrow-derived hematopoietic progenitor cells are programmed to differentiate into mast cells, when the cells are maintained in the presence of pokeweed mitogen-stimulated spleen-conditioned medium. However, by retroviral introduction of PU.1 cDNA, the progenitor cells expressed MHC class II, CD11b, CD11c, and F4/80, and acquired the ability to stimulate T cells. Furthermore, PU.1-overproducing cells exhibited the morphology, in part, similar to that of monocyte. These results indicate that the mast cell progenitors still have the ability to express monocyte-specific genes by increased expression of PU.1.

Transgenic overexpression of granulocyte macrophage-colony stimulating factor in the lung prevents hyperoxic lung injury

Granulocyte macrophage-colony stimulating factor (GM-CSF) plays an important role in pulmonary homeostasis, with effects on both alveolar macrophages and alveolar epithelial cells. We hypothesized that overexpression of GM-CSF in the lung would protect mice from hyperoxic lung injury by limiting alveolar epithelial cell injury. Wild-type C57BL/6 mice and mutant mice in which GM-CSF was overexpressed in the lung under control of the SP-C promoter (SP-C-GM mice) were placed in >95% oxygen. Within 6 days, 100% of the wild-type mice had died, while 70% of the SP-C-GM mice remained alive after 10 days in hyperoxia. Histological assessment of the lungs at day 4 revealed less disruption of the alveolar wall in SP-C-GM mice compared to wild-type mice. The concentration of albumin in bronchoalveolar lavage fluid after 4 days in hyperoxia was significantly lower in SP-C-GM mice than in wild-type mice, indicating preservation of alveolar epithelial barrier properties in the SP-C-GM mice. Alveolar fluid clearance was preserved in SP-C-GM mice in hyperoxia, but decreased significantly in hyperoxia-exposed wild-type mice. Staining of lung tissue for caspase 3 demonstrated increased apoptosis in alveolar wall cells in wild-type mice in hyperoxia compared to mice in room air. In contrast, SP-C-GM mice exposed to hyperoxia demonstrated only modest increase in alveolar wall apoptosis compared to room air. Systemic treatment with GM-CSF (9 micro g/kg/day) during 4 days of hyperoxic exposure resulted in decreased apoptosis in the lungs compared to placebo. In studies using isolated murine type II alveolar epithelial cells, treatment with GM-CSF greatly reduced apoptosis in response to suspension culture. In conclusion, overexpression of GM-CSF enhances survival of mice in hyperoxia; this effect may be explained by preservation of alveolar epithelial barrier function and fluid clearance, at least in part because of reduction in hyperoxia-induced apoptosis of cells in the alveolar wall.

The use of growth factors and cytokines to treat opportunistic infections in HIV-1 disease

The success of highly active antiretroviral therapy (HAART) in reducing AIDS-related mortality means that in regions where HAART is available, HIV infection may now be regarded as a chronic disease. However the inability of HAART to eliminate HIV-1 from various anatomical and cellular reservoirs within the body means that HIV-infected individuals require life-long treatment with therapy that can have significant side effects. Management of HIV disease is therefore increasingly focused on drug-related toxicities and the improvement of current HAART regimens. Here we review the potential use of immunomodulatory cytokines to directly or indirectly stimulate the mononuclear phagocyte system as adjuncts to current HIV treatment as well as their use in the management of opportunistic infections in individuals who develop immunodeficiency. We argue that cytokines, which stimulate mononuclear phagocyte activity against opportunistic pathogens, may be useful for the treatment of individuals who develop recurrent opportunistic infections. Cytokines may act synergistically with antimicrobial agents to improve outcomes, which is of particular importance since recurrent infections frequently result in resistance to standard antimicrobial treatments. Before their use can be advocated however, given their toxicity and significant cost, the potential benefits of cytokines must be demonstrated in larger clinical trials.

Innate immune responses to LPS in mouse lung are suppressed and reversed by neutralization of GM-CSF via repression of TLR-4

The innate immune inflammatory response to lipopolysaccharide (LPS, an endotoxin) is essential for lung host defense against infection by gram-negative bacteria but is also implicated in the pathogenesis of some lung diseases. Studies on genetically altered mice implicate granulocyte-macrophage colony-stimulating factor (GM-CSF) in lung responses to LPS; however, the physiological effects of GM-CSF neutralization are poorly characterized. We performed detailed kinetic and dose-response analyses of the lung inflammation response to LPS in the presence of the specific GM-CSF-neutralizing antibody 22E9. LPS instilled into the lungs of BALB/c mice induced a dose-dependent inflammation comprised of intense neutrophilia, macrophage infiltration and proliferation, TNF-alpha and matrix metalloproteinase release, and macrophage inflammatory protein-2 induction. The neutralization of anti-GM-CSF in a dose-dependent fashion suppressed these inflammatory indexes by 85% when given before or after LPS or after repeat LPS challenges. Here we report for the first time that the physiological expression of Toll-like receptor-4 in lung is reduced by anti-GM-CSF. We observed that lower Toll-like receptor-4 expression correlated with a similar decline in peak TNF- levels in response to endotoxin. Consequently, sustained expression of key inflammatory mediators over 24 h was reduced. These data expand the understanding of the contribution of GM-CSF to innate immune responses in lung and suggest that blocking GM-CSF might benefit some lung diseases where LPS has been implicated in etiology.

Defective Phagocytosis and Clearance ofPseudomonas aeruginosain the Lung Following Bone Marrow Transplantation

Bone marrow transplantation (BMT) is an important therapeutic option for a variety of malignant and nonmalignant disorders. Unfortunately, BMT recipients are at increased risk of infection, and in particular, pulmonary complications occur frequently. Although the risk of infection is greatest during the neutropenic period immediately following transplant, patients are still vulnerable to pulmonary infections even after neutrophil engraftment. We evaluated the risk of infection in this postengraftment period by using a well-established mouse BMT model. Seven days after syngeneic BMT, B6D2F(1) mice are no longer neutropenic, and by 3 wk, they demonstrate complete reconstitution of the peripheral blood. However, these mice remain more susceptible throughout 8 wk to infection after intratracheal administration of Pseudomonas aeruginosa; increased mortality in the P. aeruginosa-infected BMT mice correlates with increased bacterial burden in the lungs as well as increased systemic dissemination. This heightened susceptibility to infection was not secondary to a defect in inflammatory cell recruitment to the lung. The inability to clear P. aeruginosa in the lung correlated with reduced phagocytosis of the bacteria by alveolar macrophages (AMs), but not neutrophils, decreased production of TNF-alpha by AMs, and decreased levels of TNF-alpha and IFN-gamma in the bronchoalveolar lavage fluid following infection. Expression of the beta(2) integrins CD11a and CD11c was reduced on AMs from BMT mice compared with wild-type mice. Thus, despite restoration of peripheral blood count, phagocytic defects in the AMs of BMT mice persist and may contribute to the increased risk of infection seen in the postengraftment period.

Regulation of macrophage and neutrophil cell fates by the PU.1:C/EBPalpha ratio and granulocyte colony-stimulating factor

Hematopoietic transcription factors are essential for specifying cell fates; however, the function of cytokines in such developmental decisions is unresolved. We demonstrate here that haploinsufficiency for the gene encoding the transcription factor PU.1 partially suppresses the neutropenia of mice deficient in granulocyte colony-stimulating factor. This suppression was due to an increase in granulocytic progenitors and a diminution of monocytic progenitors. With (PU.1+/-) ES cells as well as (PU.1-/-) hematopoietic progenitors, we show that higher expression of PU.1 is needed for macrophage than for neutrophil development. In a (PU.1-/-) progenitor cell line, in which graded activity of PU.1 regulates neutrophil versus macrophage development, granulocyte colony-stimulating factor signaling supported the neutrophil cell fate by increasing expression of the neutrophil transcription factor C/EBPalpha in relation to expression of PU.1. Collectively, these results indicate that cytokines can promote cell fate decisions by altering the relative concentrations of lineage-determining transcriptional regulators.

Dynamics of macrophage cell populations during murine pulmonary tuberculosis

The influx of macrophages into the lungs is the major component of the granulomatous response to infection with Mycobacterium tuberculosis. In this investigation we used flow cytometric analysis to define macrophage populations entering the airways and lung tissues of infected mice. We demonstrate that by the judicious use of cell surface markers, especially CD11b and CD11c, several cell populations can be distinguished, allowing cell sorting and morphological definition. Primary populations of CD11b(-)/CD11c(+/high) were defined as alveolar macrophages, CD11b(high)/CD11c(+/high) as dendritic cells, and CD11b(+/mid)/CD11c(+/mid) as small macrophages or monocytes, and changes in the activation phenotype of these populations were followed over the early course of the infection. In further studies, these cell populations were compared with cells harvested during the chronic stage of the disease. During the chronic stage of infection, Ag-presenting class II molecules and activation markers were poorly expressed on dendritic, small macrophage, and monocyte cell populations, which may have important implications for the breakdown of the lesions during reactivation disease. This analytical approach may facilitate the further characterization of macrophage populations entering into the lung tissues and their relative contributions to host resistance to tuberculosis infection.

Regulation of the class II MHC pathway in primary human monocytes by granulocyte-macrophage colony-stimulating factor

GM-CSF stimulates the growth and differentiation of hematopoietic progenitors and also affects mature cell function. These effects have led to the use of GM-CSF as a vaccine adjuvant with promising results; however, the mechanisms underlying GM-CSF-mediated immune potentiation are incompletely understood. In this study, we investigated the hypothesis that the immune stimulatory role of GM-CSF is in part due to effects on class II MHC Ag presentation. We find that, in primary human monocytes treated for 24-48 h, GM-CSF increases surface class II MHC expression and decreases the relative level of the invariant chain-derived peptide, CLIP, bound to surface class II molecules. GM-CSF also increases expression of the costimulatory molecules CD86 and CD40, but not the differentiation marker CD1a or CD16. Furthermore, GM-CSF-treated monocytes are better stimulators in a mixed leukocyte reaction. Additional analyses of the class II pathway revealed that GM-CSF increases total protein and RNA levels of HLA-DR, DM, and DOalpha. Expression of class II transactivator (CIITA) types I and III, but not IV, transcripts increases in response to GM-CSF. Furthermore, GM-CSF increases the amount of CIITA associated with the DR promoter. Thus, our data argue that the proinflammatory role of GM-CSF is mediated in part through increased expression of key molecules involved in the class II MHC pathway via induction of CIITA.

Sublethal hyperoxia impairs pulmonary innate immunity

Supplemental oxygen is often required in the treatment of critically ill patients. The impact of hyperoxia on pulmonary host defense is not well-established. We hypothesized that hyperoxia directly impairs pulmonary host defense, beyond effects on alveolar wall barrier function. C57BL/6 mice were kept in an atmosphere of >95% O(2) for 4 days followed by return to room air. This exposure does not lead to mortality in mice subsequently returned to room air. Mice kept in room air served as controls. Mice were intratracheally inoculated with Klebsiella pneumoniae and followed for survival. Alveolar macrophages (AM) were harvested by bronchoalveolar lavage after 4 days of in vivo hyperoxia for ex vivo experiments. Mortality from pneumonia increased significantly in mice exposed to hyperoxia compared with infected mice in room air. Burden of organisms in the lung and dissemination of infection were increased in the hyperoxia group whereas accumulation of inflammatory cells in the lung was impaired. Hyperoxia alone had no impact on AM numbers, viability, or ability to phagocytize latex microbeads. However, following in vivo hyperoxia, AM phagocytosis and killing of Gram-negative bacteria and production of TNF-alpha and IL-6 in response to LPS were significantly reduced. AM surface expression of Toll-like receptor-4 was significantly decreased following in vivo hyperoxia. Thus sublethal hyperoxia increases Gram-negative bacterial pneumonia mortality and has a significant adverse effect on AM host defense function. Impaired AM function due to high concentrations of supplemental oxygen may contribute to the high rate of ventilator-associated pneumonia seen in critically ill patients.

Susceptibility to tuberculosis: a locus on mouse chromosome 19 (Trl-4) regulates Mycobacterium tuberculosis replication in the lungs

The mouse DBA/2 (D2) strain is very susceptible to infection with virulent Mycobacterium tuberculosis, whereas C57BL/6 (B6) is much more resistant. Infection of D2 and B6 mice with M. tuberculosis H37Rv by the respiratory route is biphasic: during the first 3 weeks, there is rapid bacterial growth in the lung of both strains, whereas beyond this point replication stops in B6 but continues in D2, causing rapidly fatal pulmonary disease. To identify the genes regulating growth of M. tuberculosis in the lungs of these two strains, 98 informative (B6 x D2) F2 mice were infected by the respiratory route with M. tuberculosis H37Rv (2 x 102 colony-forming units), and the extent of bacterial replication in the lungs at 90 days was used as a quantitative measure of susceptibility in a whole-genome scan. Quantitative trait locus mapping identified a major locus on chromosome 19 (Tuberculosis resistance locus-4, Trl-4; logarithm of odds 5.6), which regulated pulmonary replication of M. tuberculosis and accounted for 25% of the phenotypic variance. B6 alleles at Trl-4 were inherited in an incompletely dominant fashion and associated with reduced bacterial replication. An additional effect of a locus (Trl-3), previously shown to affect survival to i.v. infection with M. tuberculosis, was also noted. F2 mice homozygous for B6 alleles at both Trl-3 and Trl-4 were as resistant as B6 parents, whereas mice homozygous for D2 alleles were as susceptible as D2 parents. These results suggest a strong genetic interaction between Trl-3 and Trl-4 in regulating pulmonary replication of M. tuberculosis.

Deficiencies of GM-CSF and interferon gamma link inflammation and cancer

Chronic inflammation contributes to carcinogenesis, but the underlying mechanisms are poorly understood. We report that aged granulocyte-macrophage colony stimulating factor (GM-CSF)-deficient mice develop a systemic lupus erythematosis (SLE)-like disorder associated with the impaired phagocytosis of apoptotic cells. Concurrent deficiency of interferon (IFN)-gamma attenuates the SLE, but promotes the formation of diverse hematologic and solid neoplasms within a background of persistent infection and inflammation. Whereas activated B cells show a resistance to fas-induced apoptosis, antimicrobial therapy prevents lymphomagenesis and solid tumor development. These findings demonstrate that the interplay of infectious agents with cytokine-mediated regulation of immune homeostasis is a critical determinant of cancer susceptibility.

Breast milk macrophages spontaneously produce granulocyte-macrophage colony-stimulating factor and differentiate into dendritic cells in the presence of exogenous interleukin-4 alone

Peripheral blood monocytes extravasate and differentiate into tissue macrophages to mediate effective local defence, but how tissue-specific stimuli and environments may influence their functions remains unknown. Here, we found that peripheral blood monocytes gained the ability to produce granulocyte-macrophage colony-stimulating factor (GM-CSF) upon exposure to breast milk and differentiated into CD1+ dendritic cells (DCs) in the presence of exogenous interleukin-4 (IL-4) alone. This in vitro observation appeared physiologically relevant since macrophages that were freshly isolated from breast milk were also found to produce GM-CSF spontaneously. Furthermore, in contrast to peripheral blood monocytes that differentiated into DCs only in the presence of both exogenous GM-CSF and IL-4, differentiation of breast milk macrophages into DCs was induced by incubation with exogenous IL-4 alone. These IL-4-stimulated breast milk macrophages were efficient in stimulating T cells, suggesting their potential role in mediating T-cell-dependent immune responses in situ. On the other hand, unexpected expression of DC-SIGN, a DC-specific receptor for human immunodeficiency virus (HIV), even in unstimulated breast milk macrophages, may favour HIV infection, resulting in an increased risk of mother-to-infant vertical transmission of the virus via breast milk. Thus, tissue-specific development of macrophages is often linked to effective local immunity, but may potentially provide an opportunity for a pathogen to spread and transmit.

Selective early production of CCL20, or macrophage inflammatory protein 3alpha, by human mast cells in response to Pseudomonas aeruginosa

Mast cells are important as sentinel cells in host defense against bacterial infection. Much of their effectiveness depends upon recruiting other immune cells; however, little is known about the mechanisms of this response. CCL20, also known as macrophage inflammatory protein-3alpha (MIP-3alpha), Exodus, and LARC, is a chemokine known to be a potent chemoattractant for immature dendritic cells and T cells. In this study, we examined the human mast cell production of both CCL20 and granulocyte-macrophage colony-stimulating factor (GM-CSF), a critical cytokine for innate immune responses in the lung, in response to Pseudomonas aeruginosa. Reverse transcription-PCR and Western blot analysis demonstrated that the human mast cells (HMC-1) express CCL20 mRNA and are able to produce a significant amount (32.4 ng/ml) of CCL20 protein following stimulation by calcium ionophore and phorbol myristate acetate. Importantly, P. aeruginosa potently stimulated CCL20 production in human cord blood-derived mast cells (CBMC), with production peaking at 6 h after stimulation. This time course of expression was distinct from that of GM-CSF, which peaked after 24 to 48 h. Significant CCL20 production did not occur following immunoglobulin E-mediated activation of CBMC under conditions which induced a substantial GM-CSF response. Interestingly, the CCL20 response of mast cells to P. aeruginosa was relatively resistant to inhibition by the corticosteroid dexamethasone, interleukin-10, or cyclosporine, while GM-CSF production was potently inhibited. However, P. aeruginosa-induced CCL20 production was blocked by the protein kinase C (PKC) inhibitor Ro 31-8220 and a PKC pseudosubstrate. These results support a role for human mast cells in the initiation of immune responses to P. aeruginosa infection.

Endocytic internalization of adenovirus, nonspecific phagocytosis, and cytoskeletal organization are coordinately regulated in alveolar macrophages by GM-CSF and PU.1

GM-CSF gene-targeted (GM(-/-)) mice have impaired pulmonary clearance of bacterial and fungal pathogens by alveolar macrophages (AMs). Because AMs also clear adenovirus from the lung, the role of GM-CSF in endocytic internalization of adenovirus by AMs was evaluated. Pulmonary clearance of adenovirus was severely impaired in GM(-/-) mice compared to wild-type (GM(+/+)) mice as determined by Southern analysis of viral DNA. Internalization of adenovirus by AMs was deficient in GM(-/-) mice in vivo and in vitro as determined by uptake of fluorescently labeled adenovirus or by PCR quantification of adenoviral DNA internalized within AMs. An AM cell line previously established from GM(-/-) mice (mAM) had impaired internalization of adenovirus and transferrin-coated 100-nm latex beads compared to MH-S, a GM(+/+) AM cell line. Phagocytosis of 4- micro m latex beads was also impaired in mAM cells as determined by confocal and fluorescence microscopy. Retroviral vector-mediated reconstitution of PU.1 expression in cultured GM(-/-) AMs restored phagocytosis of 4- micro m beads, endocytosis of adenovirus, and transferrin-coated 100-nm beads (independent of integrin alpha(V) and transferrin receptors, respectively), and restored normal cytoskeletal organization, filamentous actin distribution, and stimulated formation of filopodia. Interestingly, mRNA for the phosphoinositide 3 kinase p110gamma isoform, important in macrophage phagocytic function, was absent in GM(-/-) AMs and was restored by PU.1 expression. These data show that GM-CSF, via PU.1, regulates endocytosis of small ( approximately 100 nm) pathogens/inert particles and phagocytosis of very large inert particles and suggests regulation of cytoskeletal organization by GM-CSF/PU.1 as the molecular basis of this control.

GM-CSF, via PU.1, regulates alveolar macrophage Fcgamma R-mediated phagocytosis and the IL-18/IFN-gamma -mediated molecular connection between innate and adaptive immunity in the lung

Severely impaired pulmonary microbial clearance was observed in granulocyte-macrophage colony-stimulating factor (GM-CSF)-deficient mice. To determine mechanisms by which GM-CSF mediates lung host defense, FcgammaR-mediated phagocytosis (opsonophagocytosis) by alveolar macrophages (AMs) was assessed in GM-CSF-sufficient (GM(+/+)) and -deficient (GM(-/-)) mice and in GM(-/-) mice expressing GM-CSF only in the lungs from a surfactant protein C (SPC) promoter (SPC-GM(+/+)/GM(-/-)). Opsonophagocytosis by GM(-/-) AMs was severely impaired and was restored by pulmonary GM-CSF expression in vivo or by PU.1 expression in vitro. Defective opsonophagocytosis by GM(-/-) AMs was associated with decreased FcgammaR expression. Because interferon-gamma (IFN-gamma) augments macrophage FcgammaR levels, the role of GM-CSF/PU.1 in the regulation of AM FcgammaR expression by IFN-gamma was assessed during adenoviral lung infection. Adenoviral infection stimulated IFN-gamma production and augmented FcgammaR levels on AMs in GM-CSF-expressing but not GM(-/-) mice. However, IFN-gamma exposure ex vivo stimulated FcgammaR expression on GM(-/-) AMs. Because interleukin-18 (IL-18) and IL-12 stimulate IFN-gamma production during adenoviral infection, their role in GM-CSF/PU.1 regulation of IFN-gamma-augmented FcgammaR expression on AMs was assessed. Adenoviral infection stimulated IL-18 and IL-12 production in GM-CSF-expressing mice, but both were markedly reduced or absent in GM(-/-) mice. IL-18 expression by GM(-/-) AMs was severely impaired and was restored by pulmonary GM-CSF expression in vivo or by PU.1 expression in vitro. Pulmonary administration of IL-18 in GM(-/-) mice stimulated IFN-gamma production and restored FcgammaR expression on AMs. These results show that GM-CSF, via PU.1, regulates constitutive AM FcgammaR expression and opsonophagocytosis and is required for the IFN-gamma-dependent regulation of AM FcgammaR expression, enabling AMs to release IL-18/IL-12 during lung infection.

Granulocyte/macrophage-colony-stimulating factor (GM-CSF) regulates lung innate immunity to lipopolysaccharide through Akt/Erk activation of NFkappa B and AP-1 in vivo

The lung innate immune response to lipopolysaccharide (LPS) coordinates cellular inflammation, mediator, and protease release essential for host defense but deleterious in asthma, chronic obstructive pulmonary disease, and cystic fibrosis. In vitro, LPS signals to the transcription factors NFkappaB via TLR4, MyD88, and IL-1R-associated kinase (IRAK), to AP-1 by mitogen-activated protein (MAP) kinases, and via an alternate route in IRAK-deficient mice, but the in vivo lung signaling pathway(s) are not understood. We investigated the role of Akt and Erk1/2 as LPS intensely stimulates granulocyte/macrophage-colony-stimulating factor (GM-CSF) release, and neutralizing GM-CSF profoundly suppressed LPS-induced inflammation, suppressed expression and activity of lung proteases, significantly reduced GM-CSF and tumor necrosis factor alpha (TNFalpha) mRNA expression, and dampened nuclear localization of both NFkappaB (p50/65) and AP-1. LPS markedly activated Akt and Erk1/2, but not p38, in a GM-CSF-dependent manner in direct temporal association with NFkappaB and AP-1 activation. Pharmacological inhibition of Akt or Erk activation in LPS-treated tracheal explants ex vivo inhibited the release of GM-CSF. These data implicate GM-CSF-dependent activation of Akt in the amplification of this response and demonstrate the role of Erks rather than p38 in lung LPS inflammatory responses. Inhibition of GM-CSF may be of therapeutic benefit in inflammatory diseases in which LPS contributes to lung damage.

Constitutive activation of the SRC family kinase Hck results in spontaneous pulmonary inflammation and an enhanced innate immune response

To identify the physiological role of Hck, a functionally redundant member of the Src family of tyrosine kinases expressed in myelomonocytic cells, we generated Hck(F/F) "knock-in" mice which carry a targeted tyrosine (Y) to phenylalanine (F) substitution of the COOH-terminal, negative regulatory Y(499)-residue in the Hck protein. Unlike their Hck(-/-) "loss-of-function" counterparts, Hck(F/F) "gain-of-function" mice spontaneously acquired a lung pathology characterized by extensive eosinophilic and mononuclear cell infiltration within the lung parenchyma, alveolar airspaces, and around blood vessels, as well as marked epithelial mucus metaplasia in conducting airways. Lungs from Hck(F/F) mice showed areas of mild emphysema and pulmonary fibrosis, which together with inflammation resulted in altered lung function and respiratory distress in aging mice. When challenged transnasally with lipopolysaccharide (LPS), Hck(F/F) mice displayed an exaggerated pulmonary innate immune response, characterized by excessive release of matrix metalloproteinases and tumor necrosis factor (TNF)alpha. Similarly, Hck(F/F) mice were highly sensitive to endotoxemia after systemic administration of LPS, and macrophages and neutrophils derived from Hck(F/F) mice exhibited enhanced effector functions in vitro (e.g., nitric oxide and TNFalpha production, chemotaxis, and degranulation). Based on the demonstrated functional association of Hck with leukocyte integrins, we propose that constitutive activation of Hck may mimic adhesion-dependent priming of leukocytes. Thus, our observations collectively suggest an enhanced innate immune response in Hck(F/F) mice thereby skewing innate immunity from a reversible physiological host defense response to one causing irreversible tissue damage.

Lineage plasticity and commitment in T-cell development

The earliest stages of intrathymic T-cell development include not only the acquisition of T-cell characteristics but also programmed loss of potentials for B, natural killer, and dendritic cell development. Evidence from genetics and cell-transfer studies suggests an order and some components of the mechanisms involved in loss of these options, but some of the interpretations conflict. The conflicts can be resolved by a view that postulates overlapping windows of developmental opportunity and individual mechanisms regulating progression along each pathway. This view is consistent with molecular evidence for the expression patterns of positive regulators of non-T developmental pathways, SCL, PU.1 and Id2, in early thymocytes. To some extent, overexpression of such regulators redirects thymocyte development in vitro. Specific commitment functions may normally terminate this developmental plasticity. Both PU.1 overexpression and stimulation of ectopically expressed growth factor receptors can perturb T- and myeloid/dendritic-cell divergence, but only in permissive stages. A cell-line system that approximates DN3-stage thymocytes reveals that PU.1 can alter specification even in a homogeneous population. However, the response of the population to PU.1 is sharply discontinuous. These studies show a critical role for regulatory context in restricting plasticity, which is probably maintained by interacting transcription factor networks.

Granulocyte-macrophage colony-stimulating factor induces an expression program in neonatal microglia that primes them for antigen presentation

Neonatal microglial cells respond to GM-CSF and M-CSF by acquiring different morphologies and phenotypes. To investigate the extent and consequences of this process, a global gene expression analysis was performed, with significant changes in transcript levels confirmed by biochemical analyses. Primary murine microglial cells underwent substantial expression reprogramming after treatment with GM-CSF or M-CSF with many differentially expressed transcripts important in innate and adaptive immunity. In particular, many gene products involved in Ag presentation were induced by GM-CSF, but not M-CSF, thus potentially priming relatively quiescent microglia cells for Ag presentation. This function of GM-CSF is distinct from its primary function in cell proliferation and survival.

Pulmonary alveolar proteinosis: progress in the first 44 years

Pulmonary alveolar proteinosis is a rare clinical syndrome that was first described in 1958. Subsequently, over 240 case reports and small series have described at least 410 cases in the literature. Characterized by the alveolar accumulation of surfactant components with minimal interstitial inflammation or fibrosis, pulmonary alveolar proteinosis has a variable clinical course ranging from spontaneous resolution to death with pneumonia or respiratory failure. The most effective proven treatment--whole lung lavage--was described soon after the first recognition of this disease. In the last 8 years, there has been rapid progress toward elucidation of the molecular mechanisms underlying both the congenital and acquired forms of pulmonary alveolar proteinosis, following serendipitous discoveries in gene-targeted mice lacking granulocyte-macrophage colony-stimulating factor (GM-CSF). Impairment of surfactant clearance by alveolar macrophages as a result of inhibition of the action of GM-CSF by blocking autoantibodies may underlie many acquired cases, whereas congenital disease is most commonly attributable to mutations in surfactant protein genes but may also be caused by GM-CSF receptor defects. Therapy with GM-CSF has shown promise in approximately half of those acquired cases treated, but it is unsuccessful in congenital forms of the disease, consistent with the known differences in disease pathogenesis.

A randomized phase II trial of granulocyte-macrophage colony-stimulating factor therapy in severe sepsis with respiratory dysfunction

Granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates hemopoiesis and effector functions of granulocytes and macrophages and is involved in pulmonary surfactant homeostasis. We investigated whether GM-CSF therapy improved clinically diagnosed severe sepsis and respiratory dysfunction in critically ill patients. This randomized, double-blind, placebo-controlled phase II study added low-dose (3 mcg/kg) intravenous recombinant human GM-CSF daily for 5 days to conventional therapy in 10 patients, with a further eight patients receiving placebo. GM-CSF-treated patients showed improvement in Pa(O(2))/FI(O(2)) over 5 days (p = 0.02) and increased peripheral blood neutrophils (p = 0.08), whereas alveolar neutrophils decreased (p = 0.02). GM-CSF therapy was not associated with decreased 30-day survival or with increased acute respiratory distress syndrome or extrapulmonary organ dysfunction. GM-CSF therapy was associated with increased blood granulocyte superoxide production and restoration or preservation of blood and alveolar leukocyte phagocytic function. We conclude that low-dose GM-CSF was associated with improved gas exchange without pulmonary neutrophil infiltration, despite functional activation of both circulating neutrophils and pulmonary phagocytes. In addition, GM-CSF therapy was not associated with worsened acute respiratory distress syndrome or the multiple organ dysfunction syndrome, suggesting a homeostatic role for GM-CSF in sepsis-related pulmonary dysfunction.

Functional heterogeneity of colony-stimulating factor-induced human monocyte-derived macrophages

Macrophages have various functions and play a critical role in host defense and the maintenance of homeostasis. However, macrophages are heterogeneous and exhibit a wide range of phenotypes with regard to their morphology, cell surface antigen expression, and function. When blood monocytes are cultured in medium alone in vitro, monocytes die, and colony-stimulating factors (CSFs) such as macrophage (M)-CSF or granulocyte-macrophage (GM)-CSF are necessary for their survival and differentiation into macrophages. However, M-CSF-induced monocyte-derived macrophages (M-Mphi) and GM-CSF-induced monocyte-derived macrophages (GM-Mphi) are distinct in their morphology, cell surface antigen expression, and functions, including Fcgamma receptor mediated-phagocytosis, H2O2 production, H2O2 sensitivity, catalase activity, susceptibility to human immunodeficiency virus type 1 and Mycobacterium tuberculosis, and suppressor activity. The characteristics of GM-Mphi resemble those of human alveolar macrophages.

Gm-CSF regulates pulmonary surfactant homeostasis and alveolar macrophage-mediated innate host defense

Recent studies in transgenic mice have revealed important insights into the roles of GM-CSF in regulation of surfactant homeostasis and lung host defense. Interruption of the GM-CSF signaling pathway by targeted ablation of the GM-CSF gene or its receptor (GM(-/-) or GM Rbetac(-/-) mice, respectively) resulted in pulmonary alveolar proteinosis (PAP) but no hematologic abnormalities. Alveolar macrophages from GM(-/-) mice have reduced capacity for surfactant catabolism, cell adhesion, phagocytosis, bacterial killing, Toll-receptor signaling, and expression of various pathogen-associated molecular pattern recognition receptors, suggesting arrest at an early stage of differentiation. PAP and abnormalities of alveolar macrophage function were corrected by local expression of GM-CSF in the lung, and expression of the transcription factor PU.1 in alveolar macrophages of GM(-/-) mice rescued most defects. Recently, a strong association of auto-antibodies to GM-CSF or GM-CSF receptor gene mutations with PAP has implicated GM-CSF signaling abnormalities in the pathogenesis of PAP in humans. Together, these observations demonstrate that GM-CSF has a critical role in regulation of surfactant homeostasis and alveolar macrophage innate immune functions in the lung.