Macrophage production during murine listeriosis: colony-stimulating factor 1 (CSF-1) and CSF-1-binding cells in genetically resistant and susceptible mice

M-CSF directs myeloid and NK cell differentiation to protect from CMV after hematopoietic cell transplantation

Therapies reconstituting autologous antiviral immunocompetence may represent an important prophylaxis and treatment for immunosuppressed individuals. Following hematopoietic cell transplantation (HCT), patients are susceptible to Herpesviridae including cytomegalovirus (CMV). We show in a murine model of HCT that macrophage colony-stimulating factor (M-CSF) promoted rapid antiviral activity and protection from viremia caused by murine CMV. M-CSF given at transplantation stimulated sequential myeloid and natural killer (NK) cell differentiation culminating in increased NK cell numbers, production of granzyme B and interferon-γ. This depended upon M-CSF-induced myelopoiesis leading to IL15Rα-mediated presentation of IL-15 on monocytes, augmented by type I interferons from plasmacytoid dendritic cells. Demonstrating relevance to human HCT, M-CSF induced myelomonocytic IL15Rα expression and numbers of functional NK cells in G-CSF-mobilized hematopoietic stem and progenitor cells. Together, M-CSF-induced myelopoiesis triggered an integrated differentiation of myeloid and NK cells to protect HCT recipients from CMV. Thus, our results identify a rationale for the therapeutic use of M-CSF to rapidly reconstitute antiviral activity in immunocompromised individuals, which may provide a general paradigm to boost innate antiviral immunocompetence using host-directed therapies.

Functions of macrophage colony-stimulating factor (CSF1) in development, homeostasis, and tissue repair

Macrophage colony-stimulating factor (CSF1) is the primary growth factor required for the control of monocyte and macrophage differentiation, survival, proliferation and renewal. Although the cDNAs encoding multiple isoforms of human CSF1 were cloned in the 1980s, and recombinant proteins were available for testing in humans, CSF1 has not yet found substantial clinical application. Here we present an overview of CSF1 biology, including evolution, regulation and functions of cell surface and secreted isoforms. CSF1 is widely-expressed, primarily by cells of mesenchymal lineages, in all mouse tissues. Cell-specific deletion of a floxed Csf1 allele in mice indicates that local CSF1 production contributes to the maintenance of tissue-specific macrophage populations but is not saturating. CSF1 in the circulation is controlled primarily by receptor-mediated clearance by macrophages in liver and spleen. Administration of recombinant CSF1 to humans or animals leads to monocytosis and expansion of tissue macrophage populations and growth of the liver and spleen. In a wide variety of tissue injury models, CSF1 administration promotes monocyte infiltration, clearance of damaged cells and repair. We suggest that CSF1 has therapeutic potential in regenerative medicine.

M-CSF instructs myeloid lineage fate in single haematopoietic stem cells

Under stress conditions such as infection or inflammation the body rapidly needs to generate new blood cells that are adapted to the challenge. Haematopoietic cytokines are known to increase output of specific mature cells by affecting survival, expansion and differentiation of lineage-committed progenitors, but it has been debated whether long-term haematopoietic stem cells (HSCs) are susceptible to direct lineage-specifying effects of cytokines. Although genetic changes in transcription factor balance can sensitize HSCs to cytokine instruction, the initiation of HSC commitment is generally thought to be triggered by stochastic fluctuation in cell-intrinsic regulators such as lineage-specific transcription factors, leaving cytokines to ensure survival and proliferation of the progeny cells. Here we show that macrophage colony-stimulating factor (M-CSF, also called CSF1), a myeloid cytokine released during infection and inflammation, can directly induce the myeloid master regulator PU.1 and instruct myeloid cell-fate change in mouse HSCs, independently of selective survival or proliferation. Video imaging and single-cell gene expression analysis revealed that stimulation of highly purified HSCs with M-CSF in culture resulted in activation of the PU.1 promoter and an increased number of PU.1(+) cells with myeloid gene signature and differentiation potential. In vivo, high systemic levels of M-CSF directly stimulated M-CSF-receptor-dependent activation of endogenous PU.1 protein in single HSCs and induced a PU.1-dependent myeloid differentiation preference. Our data demonstrate that lineage-specific cytokines can act directly on HSCs in vitro and in vivo to instruct a change of cell identity. This fundamentally changes the current view of how HSCs respond to environmental challenge and implicates stress-induced cytokines as direct instructors of HSC fate.

SR-A ligand and M-CSF dynamically regulate SR-A expression and function in primary macrophages via p38 MAPK activation

BACKGROUND

Inflammation is characterized by dynamic changes in the expression of cytokines, such as M-CSF, and modifications of lipids and proteins that result in the formation of ligands for Class A Scavenger Receptors (SR-A). These changes are associated with altered SR-A expression in macrophages; however, the intracellular signal pathways involved and the extent to which SR-A ligands regulate SR-A expression are not well defined. To address these questions, SR-A expression and function were examined in resident mouse peritoneal macrophages incubated with M-CSF or the selective SR-A ligand acetylated-LDL (AcLDL).

RESULTS

M-CSF increased SR-A expression and function, and required the specific activation of p38 MAPK, but not ERK1/2 or JNK. Increased SR-A expression and function returned to basal levels 72 hours after removing M-CSF. We next determined whether prolonged incubation of macrophages with SR-A ligand alters SR-A expression. In contrast to most receptors, which are down-regulated by chronic exposure to ligand, SR-A expression was reversibly increased by incubating macrophages with AcLDL. AcLDL activated p38 in wild-type macrophages but not in SR-A-/- macrophages, and p38 activation was specifically required for AcLDL-induced SR-A expression.

CONCLUSIONS

These results demonstrate that in resident macrophages SR-A expression and function can be dynamically regulated by changes in the macrophage microenvironment that are typical of inflammatory processes. In particular, our results indicate a previously unrecognized role for ligand binding to SR-A in up-regulating SR-A expression and activating p38 MAPK. In this way, SR-A may modulate inflammatory responses by enhancing macrophage uptake of modified protein/lipid, bacteria, and cell debris; and by regulating the production of inflammatory cytokines, growth factors, and proteolytic enzymes.

Effect of bacterial endotoxins on superovulated mouse embryos in vivo: is CSF-1 involved in endotoxin-induced pregnancy loss?

Mammalian embryonic development is regulated by several cytokines and growth factors from embryonic or maternal origins. Since CSF-1 plays important role in embryonic development and implantation, we investigated its role in gram-negative bacterial LPS-induced implantation failure. The effect of LPS on normal (nonsuperovulated) and superovulated in vivo-produced embryos was assessed by signs of morphological degeneration. A significantly similar number of morphologically degenerated embryos recovered from both nonsuperovulated and superovulated LPS treated animals on day 2.5 of pregnancy onwards were morphologically and developmentally abnormal as compared to their respective controls (P < .001. Normal CSF-1 expression level and pattern were also altered through the preimplantation period in the mouse embryos and uterine horns after LPS treatment. This deviation from the normal pattern and level of CSF-1 expression in the preimplantation embryos and uterine tissues suggest a role for CSF-1 in LPS-induced implantation failure.

Uncaria tomentosa extract increases the number of myeloid progenitor cells in the bone marrow of mice infected with Listeria monocytogenes

In this study, we demonstrated that Uncaria tomentosa extract (UTE) protects mice from a lethal dose of Listeria monocytogenes when administered prophylactically at 50, 100, 150 and 200 mg/kg for 7 days, with survival rates up to 35%. These doses also prevented the myelosuppression and the splenomegaly caused by a sublethal infection with L. monocytogenes, due to increased numbers of granulocyte-macrophage progenitors (CFU-GM) in the bone marrow. Non-infected mice treated with 100 mg/kg UTE also presented higher numbers of CFU-GM in the bone marrow than the controls. Investigation of the production of colony-stimulating factors revealed increased colony-stimulating activity (CSA) in the serum of normal and infected mice pre-treated with UTE. Moreover, stimulation of myelopoiesis and CSA occurred in a dose-dependent manner, a plateaux being reached with the dose of 100 mg/kg. Further studies to investigate the levels of factors such as IL-1 and IL-6 were undertaken. We observed increases in the levels of IL-1 and IL-6 in mice infected with L. monocytogenes and treated with 100 mg/kg of UTE. White blood cells (WBC) and differential counting were also performed, and our results demonstrated no significant changes in these data, when infected mice were pre-treated with 100 mg/kg of UTE. All together, our results suggest that UTE indirectly modulates immune activity and probably disengages Listeria-induced supression of these responses by inducing a higher reserve of myeloid progenitors in the bone marrow in consequence of biologically active cytokine release (CSFs, IL-1 and IL-6).

Colony-stimulating factor-1 suppresses responses to CpG DNA and expression of toll-like receptor 9 but enhances responses to lipopolysaccharide in murine macrophages

During bacterial infections, the balance between resolution of infection and development of sepsis is dependent upon the macrophage response to bacterial products. We show that priming of murine bone marrow-derived macrophages (BMMs) with CSF-1 differentially regulates the response to two such stimuli, LPS and immunostimulatory (CpG) DNA. CSF-1 pretreatment enhanced IL-6, IL-12, and TNF-alpha production in response to LPS but suppressed the same response to CpG DNA. CSF-1 also regulated cytokine gene expression in response to CpG DNA and LPS; CpG DNA-induced IL-12 p40, IL-12 p35, and TNF-alpha mRNAs were all suppressed by CSF-1 pretreatment. CSF-1 pretreatment enhanced LPS-induced IL-12 p40 mRNA but not TNF-alpha and IL-12 p35 mRNAs, suggesting that part of the priming effect is posttranscriptional. CSF-1 pretreatment also suppressed CpG DNA-induced nuclear translocation of NF-kappaB and phosphorylation of the mitogen-activated protein kinases p38 and extracellular signal-related kinases-1/2 in BMMs, indicating that early events in CpG DNA signaling were regulated by CSF-1. Expression of Toll-like receptor (TLR)9, which is necessary for responses to CpG DNA, was markedly suppressed by CSF-1 in both BMMs and thioglycolate-elicited peritoneal macrophages. CSF-1 also down-regulated expression of TLR1, TLR2, and TLR6, but not the LPS receptor, TLR4, or TLR5. Hence, CSF-1 may regulate host responses to pathogens through modulation of TLR expression. Furthermore, these results suggest that CSF-1 and CSF-1R antagonists may enhance the efficacy of CpG DNA in vivo.

Evaluation of Caesalpinia ferrea extract on bone marrow hematopoiesis in the murine models of listeriosis and Ehrlich ascites tumor

The capacity of hematopoietic tissues to produce and mobilize phagocytes to the site of infection and tumor growth is of central importance to mediate the early immunological response. In this perspective, studies from our laboratory have defined Listeria monocytogenes infection and the Ehrlich ascites tumor (EAT) as useful models to investigate the effects of natural compounds on the growth and differentiation of granulocyte-macrophage progenitor cells (CFU-GM). As expected, a significant reduction in the number of bone marrow CFU-GM was observed in the initial stages of infection with a sublethal dose of Listeria. Similarly, the bone marrow CFU-GM decreased sharply 4 days after the EAT transplantation. Treatment of infected and tumor-bearing mice with 500 and 1,000 mg/kg of Caesalpinia ferrea aqueous extract, given 3 times orally, significantly stimulated myelopoiesis, whereas no effects were observed with the 250 mg/kg dose. Similar results were obtained in normal mice. The administration of the two higher doses of the extract also protected 15-20% of mice from a lethal dose of Listeria and significantly prolonged survival of EAT-bearing mice. In summary, these results demonstrate that C. ferrea extract acts as a positive regulator of myelopoiesis, and suggest that the therapeutic effect of C. ferrea may be partially mediated by this action.

Aberrant macrophage and neutrophil population dynamics and impaired Th1 response to Listeria monocytogenes in colony-stimulating factor 1-deficient mice

Listeria monocytogenes, a facultative intracellular bacterium, has been used extensively to study innate immune responses. Macrophages act as hosts for this bacterium as well as a major defense against it. Using mice homozygous for a null mutation (Csf1(op)) in the gene for the mononuclear phagocytic growth factor colony-stimulating factor 1 (CSF-1), we have demonstrated that CSF-1-regulated macrophages were essential to defend against a listerial infection. In the absence of CSF-1, monocytes were not recruited to the sites of infection due to the lack of synthesis of the macrophage chemoattractant chemokine MCP-1. In addition, there was no burst of interleukin-10 (IL-10) synthesis that has been shown to result in the egress of neutrophils from sites of infection. Consequently, neutrophils were not replaced by macrophages, and numerous neutrophil-filled microabscesses developed, followed by tissue destruction and death of the mice. In the CSF-1 nullizygous mice compared to wild-type mice, there was also a very low synthesis of gamma interferon (IFN-gamma), resulting in reduced macrophage activation. However, the concentrations of the IFN-gamma-inducing cytokines IL-12 and IL-18 at this bacterial load were similar in these mutant mice. In contrast, IL-6 concentrations were dramatically reduced. Administration of IL-6 to Csf1(op)/Csf1(op) mice significantly increased the synthesis of IFN-gamma and reduced the bacterial burden to a greater extent than treatment with IFN-gamma alone. These data indicate that IL-6 occupies a central role in the CSF-1-regulated macrophage response to L. monocytogenes.

Stimulation of myelopoiesis in Listeria monocytogenes-infected mice by an aggregated polymer isolated from Aspergillus oryzae

In this work, we investigated the effects of the proteic aggregated polymer of magnesium ammonium phospholinoleate-palmitoleate anhydride (MAPA) isolated from Aspergillus oryzae on the growth and differentiation of bone marrow granulocyte-macrophage progenitor cells (CFU-GM) in Listeriamonocytogenes-infected mice. A significant reduction in the CFU-GM number was observed in the initial phase of infection with a sublethal dose of Listeria. Treatment of mice with 0.5, 2.0 and 5.0 mg/kg MAPA for 7 days prior to infection significantly stimulated myelopoiesis in a dose-dependent manner. Moreover, treatment with 0.5 and 5.0 mg/kg MAPA resulted in 30% and 40% cures of mice lethally infected with Listeria, respectively. MAPA added directly to the culture dishes hardly affected colony formation by bone marrow cells, suggesting an indirect effect ofthis compound on myelopoiesis in vivo. In summary, the data show that MAPA can modulate the CFU-GM generation and antibacterial resistance in listeriosis. As the ability of hematopoietic tissues to produce phagocytes is of particular significance to mediate resistance to Listeria, the promotion of bone marrow CFU-GM by MAPA may contribute to a rapid restoration of phagocyte numbers in infected sites, thus mitigating the course of infection.

Stimulatory action of Pluchea quitoc extract on the hematopoietic response during murine listeriosis

The importance of both granulocytes and macrophages in the response to Listeria monocytogenes infection make this infection a suitable choice to investigate the effects of Pluchea quitoc on hematopoiesis. A significant depletion of bone marrow granulocyte-macrophage progenitor cells (CFU-GM) was observed at 48 and 72 h after intraperitoneal infection of mice with 1 x 10(4) L. monocytogenes. However, the treatment of infected animals with P. quitoc ethanolic extract (250, 500 or 1000 mg/kg) given orally for 3 consecutive days prior to infection produced a stimulatory effect on myelopoiesis, restoring the number of CFU-GM to normal. This same dose-schedule also increased colony formation in normal mice as compared to controls. In addition, P. quitoc significantly enhanced survival of infected mice. Thus, it is probable that the ability of P. quitoc to induce a higher reserve of granulocyte-macrophage precursors in the bone marrow is of major significance in determining early resistance to infection.

Bacterial/CpG DNA Down-Modulates Colony Stimulating Factor-1 Receptor Surface Expression on Murine Bone Marrow-Derived Macrophages with Concomitant Growth Arrest and Factor-Independent Survival

Unmethylated CpG motifs within bacterial DNA constitute a pathogen-associated molecular pattern recognized by the innate immune system. Many of the immunomodulatory functions of bacterial DNA can be ascribed to the ability to activate macrophages and dendritic cells. Here we show stimulatory DNA, like LPS, caused growth arrest of murine bone marrow-derived macrophages proliferating in CSF-1. Stimulatory DNA caused selective down-modulation of CSF-1 receptor surface expression. Flow cytometric analysis of CSF-1-deprived bone marrow-derived macrophages revealed that in contrast to the synchronous reduction of CSF-1 receptor upon CSF-1 addition, activating DNA (both bacterial DNA and CpG-containing oligonucleotide) caused rapid removal of receptor from individual cells leading to a bimodal distribution of surface expression at intermediate times or submaximal doses of stimulus. Despite causing growth arrest, both stimulatory DNA and LPS promoted factor-independent survival of bone marrow-derived macrophages, which was associated with phosphorylation of the mitogen-activated protein kinase family members, extracellular-regulated kinase 1 and 2. CSF-1 receptor down-modulation may polarize the professional APC compartment to the more immunostimulatory dendritic cell-like phenotype by suppressing terminal macrophage differentiation mediated by CSF-1.

Effects of Chlorella vulgaris on bone marrow progenitor cells of mice infected with Listeria monocytogenes

In this study we investigated the effects of the treatment with Chlorella vulgaris extract (CVE) on the hematopoietic response of granulocyte-macrophage colony-forming unit (CFU-GM) of mice infected with a sublethal dose of Listeria monocytogenes (1 x 10(4) organisms/animal). CVE was given orally as 50 mg/kg/day for 5 days. In the CVE treated/infected groups L. monocytogenes was administered at the end of CVE treatment. The colony stimulating activity of the serum (CSA) was also studied in all groups. Although no effects on CFU-GM, as compared to controls, were observed in the groups receiving CVE alone, the extract produced an increase in CSA levels as compared to controls. On the other hand, the presence of the infection led to a significant reduction in the numbers of CFU-GM as observed at 48 and 72 h after the infection, in spite of the significant increase in serum CSA activity. CVE treatment of infected animals restored the numbers of CFU-GM to control levels. In the treated/ infected group the increased serum CSA was significantly higher than that observed in the only infected group. The CVE treatment (50 and 500 mg/kg) of mice infected with a dose of 3 x 10(5) bacteria/animal, which was lethal for all the non-treated controls, produced a dose-response protection which led to a 20 and 52% survival, respectively. These results demonstrated that CVE produces a significant increase in the resistance of the animals infected with L. monocytogenes, and that this protection is due, at least in part, to increased CFU-GM in the bone marrow of infected animals.

Petiveria alliacea L. extract protects mice against Listeria monocytogenes infection--effects on bone marrow progenitor cells

In this study we have investigated the effects of Petiveria alliacea on the hematopoietic response of mice infected with Listeria monocytogenes. Our results demonstrate a protective effect of the crude extract of P. alliacea since the survival of the treated/infected was higher than that in the infected group. Moreover, the number of granulocyte/macrophage colonies (CFU-GM) and the serum colony stimulating activity levels were increased in the treated/infected mice in relation to the infected group. These results suggest an immunomodulation of Petiveria alliacea extract on hematopoiesis, which may be responsible, at least in part, for the increased resistance of mice to Listeria monocytogenes infection.

Effect of tylosin tartrate (Tylan Soluble) on cellular immune responses in chickens

Although many antimicrobial agents have been reported to cause immunosuppression in animals, macrolide antibiotics enhance immune function. Tylosin is a macrolide antibiotic approved for the control of mycoplasmosis in poultry. The purpose of this investigation was to determine the effect of tylosin on cellular immune functions in chickens. There was no significant difference in adherent splenocyte chemotaxis between tylosin-treated and untreated (control) chickens. Tylosin increased splenocyte proliferation and splenocyte conditioned medium (CM) proliferative activity above control levels. Removal of adherent splenocytes before preparation of CM caused a reduction in CM proliferative activity. Tylosin also increased antitumor activity of splenocytes. These data are the first to suggest that the macrolide antibiotic, tylosin tartrate, has a modulatory effect in chickens on the immune parameters studied.

Effect of tylosin tartrate on humoral immune responses in chickens

While many antimicrobial agents have been reported to cause immunosuppression in animals, macrolide antibiotics enhance the immune function. Tylosin tartrate is a macrolide antibiotic approved for the control of mycoplasmosis in poultry. The purpose of this investigation was to determine the effect of tylosin on the humoral immune functions in chickens. Three days after oral tylosin tartrate administration, 4- or 8-week-old chickens were immunized intravenously with carbolic acid-killed Brucella abortus bacterin or sheep red blood cells. Seven days (plasma antibodies titre) or 4 days (antibody forming cells) post-immunization, there was a significant increase in antibody production as well as in the numbers of antibody-producing cells in tylosin tartrate-administered chickens compared with the untreated controls. However, 3 days after tylosin tartrate administration, there was no difference in the distribution of T-lymphocyte subpopulations (CD4 or CD8 positive cells) or B lymphocytes (surface immunoglobulin positive cells) in either the peripheral blood or spleens or untreated control chickens.

Immune privilege in the anterior chamber of the eye is not extended to intraocular Listeria monocytogenes

Resistance to many pathogens, such as Listeria monocytogenes, is correlated with the host's capacity to generate a ThI cell-mediated immune response in which delayed-type hypersensitivity (DTH) is activated. A wide variety of antigens induce down-regulation of DTH when introduced into the anterior chamber of the eye. This immunoregulatory phenomenon has been termed anterior chamber-associated immune deviation (ACAID) and is believed to be a primary mechanism for the immune privilege of the anterior chamber. Suppression of DTH, as a result of anterior chamber priming, could carry significant risk to the host's well-being as the resistance to many pathogens relies heavily on DTH-dependent ThI responses. Studies were performed to determine if a bacterial pathogen, L. monocytogenes, introduced into the anterior chamber of the eye would induce a down-regulation of systemic DTH. Intracameral inoculation of infectious L. monocytogenes into genetically susceptible C3H and BALB/c mice did not induce suppression of DTH, but instead resulted in a significant footpad swelling response to bacterial antigens. Likewise, intracameral inoculation of L. monocytogenes into genetically resistant C57BL/6 mice also induced vibrant bacterial-specific DTH. Using an in-vitro model of ACAID, we showed that macrophage suspensions that were simultaneously exposed to L. monocytogenes and bovine serum albumin (BSA) antigens, in the presence of aqueous humor (AH), induced listerial-specific DTH responses, yet simultaneously induced suppression of BSA-specific DTH. Collectively, the results indicate that immune privilege is not extended to all foreign antigens that enter the anterior chamber of the eye, and as a result, some intraocular antigens can provoke strong systemic DTH. However, non-ACAID-inducing antigens do not prejudice the down-regulation of DTH by other antigens which normally induce ACAID.

Listeria monocytogenes in laboratory mice: a model of short-term infectious and pathogenic processes controllable by regulated protective immune responses

The mammalian immune system is an integrated network of tissue, leukocytes and effector and regulatory molecules. All these components operate i) to maintain the proper structure of and processes expressed by each tissue. and ii) to protect the hosts from those microorganisms that generally invade them as part of their life cycle. Among the invading microorganisms. Listeria monocytogenes (L. monocytogenes) can persist as a live organism independent of the host, and is, thus, able to drive short-term infectious and pathogenic processes that are controlled by integrated innate and adaptive protective immune responses driven by CD8 and CD4 type 1 T lymphocytes acting on non-T non-B leukocytes. Although the effector functions and the fine specificity of T lymphocytes have been more and more characterized, an understanding of the precise regulation of both leukocyte traffic and T-lymphocyte migration depends on knowledge of the early tissue distribution of L. monocytogenes, points that are addressed in this review.

Colony-stimulating factor 1 in the human response to neonatal listeriosis

Immunity to Listeria monocytogenes, an important pathogen in human neonatal sepsis, is mediated by mononuclear phagocytes, which are regulated by the hematopoietic growth factor colony-stimulating factor 1. Neonates with listeriosis had higher circulating colony-stimulating factor 1 levels and subsequent monocyte counts than those of both noninfected newborns and newborns infected with nonlisterial organisms.

The role of cytokines in experimental listeriosis

Listeria monocytogenes is a Gram-positive, intracytoplasmatically replicating pathogen that elicits host reactions which are very similar in man and rodents. Using murine listeriosis as a highly reproducible and convenient experimental model for studying the immune response to infections with facultative intracellular bacteria, Mackaness developed the concept of T cell-mediated macrophage activation as the pivotal mechanism in host defense against this type of infectious agents. Continued research in listeriosis itself, however, provided paradoxical findings that challenged the original dogma. In particular, the finding that T cell-mediated inflammatory events, like DTH and granuloma formation, can be dissociated from protective effector mechanisms has provided a new impetus and experimental access to characterizing the molecular mediators responsible for these diverging phenomena. This review first summarizes the cellular basis for the dichotomy of immunological phenomena outlined above and will then relate recent findings on cytokine expression in infected tissues to these dual categories of the host response to infection. The authors will focus on data obtained from in vivo experiments and draw on evidence from in vitro systems only when appropriate in vivo verification is still lacking. The data presented will cover the developments made in the field of cytokine research since our previous review in 1981 (Rev. Infect. Dis. 3: 1221-1250). Detectable numbers of listeria-specific T cells become apparent on day 4 to 5 of a primary infection. Whereas the localized and sustained release of TNF and IFN-gamma mediated by CD4+ cells seems to be the focusing event triggering mononuclear cell accumulation, the coincidental eradication of bacteria critically depends on CD8+ and/or CD4-CD8-Thy1+ cells. Their effector functions, however, remain obscure, since cytokines cannot be identified that will substitute for their presence. None of the cytokines studied thus far has been demonstrated to effectively cure an established infection. In addition, the increased production of cytokines characteristic of an anamnestic response (IL-2, IL-3, IL-4, IFN-gamma and TNF) can be dramatically reduced by depleting CD4+ T cells without any effect on the animal's ability to eradicate high lethal doses of bacteria and Listeria-specific CD8+ T cells can mediate protection even in the presence of neutralizing antibodies to IFN-gamma. In conclusion, the murine model of Listeria infection provides an interesting experimental approach for the development of immunotherapeutic strategies aimed at reducing T cell-mediated immunopathology without interfering with innate resistance and T cell-mediated cure and prevention of disease.

Expanded macrophage precursor populations in BXSB mice: possible reason for the increasing monocytosis in male mice

The BXSB mouse spontaneously develops an autoimmune disease that resembles human systemic lupus erythematosus (SLE). During their lifetime, male BXSB mice show an increasing monocytosis in the peripheral blood as opposed to their female littermates. This monocytosis is unique among autoimmune-prone mice. To test the hypothesis that alterations at the stem cell level may be responsible for this monocytosis, myeloid bone marrow precursor cells were examined in both male and female BXSB mice from 4 to 40 weeks of age. The number of M-CSF responding stem cells (CFU-M) and the number of GM-CSF responding stem cells (CFU-GM) were higher than in all other inbred mouse strains tested. In addition, male BXSB mice developed a progressive increase of CFU-M and CFU-GM in the bone marrow during their lifetime, which paralleled the peripheral blood monocytosis. The monocytosis in male BXSB mice is the result of a further expansion of the strain-specific high number of macrophage precursors by intrinsic factors, which may be attributed to the influence of the Yaa factor. The sex-specific expanded mononuclear phagocyte system may promote the autoimmune process and may be one reason for the dramatic course of murine SLE in male BXSB mice.

Murine hypersensitivity pneumonitis: production and importance of colony-stimulating factors in the course of a lung inflammatory reaction

The release of colony-stimulating factors (CSFs) and their contribution to the inflammatory response in the lungs of mice exposed by the intranasal route to the actinomycete Faeni rectivirgula (150 micrograms/day, 3 days/wk), an important thermophilic actinomycete that determines farmer's lung in humans, was examined. Bronchoalveolar lavages (BAL) and lung homogenates of normal mice or saline-instilled mice contained undetectable levels (less than 0.5 U/ml) of the cytokines interleukin-3 (IL-3), colony-stimulating factor-1 (CSF-1), and granulocyte/macrophage colony-stimulating factor (GM-CSF). Mice instilled with F. rectivirgula developed a CSF cytokine response early (24 h) after the instillation that increased and plateaued 2 wk later, and stayed high thereafter. Similarly, lung homogenates of F. rectivirgula-challenged mice contained significant levels of all three CSFs from 24 h after treatment until termination of the experiment. The offending agent itself, F. rectivirgula, was found to directly induce the secretion of IL-3 and GM-CSF from isolated mouse BAL cells and mouse splenocytes, at doses ranging from 1 to 100 micrograms/ml. This was not due to contaminating endotoxin, as inclusion of polymyxin B did not modify this release. Instillation of antibodies against the CSFs in mice challenged with F. rectivirgula did not modify the increase in BAL cell number determined by the challenge (11-fold increase in BAL cell number in F. rectivirgula-instilled mice at 3 wk, whether given anti-CSFs or not). Moreover, direct intratracheal infusion of CSFs (5,000 U of IL-3/CSF-1/GM-CSF) every week did not change the cellular response seen in challenged mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant interleukin-6 protects mice against experimental bacterial infection

Because of reports of high levels of interleukin-6 (IL-6) in patients during infection, we studied the role of IL-6 in experimental infection. Mice infected with the facultative intracellular pathogen Listeria monocytogenes displayed high levels of IL-6 in their sera and tissues, particularly the spleen, 1 to 3 days after infection. At this time, the IL-6 titers correlated with bacterial numbers in individual mice and in groups of mice given graded doses of Listeria organisms. However, the presence of IL-6 in serum declined after 4 days, even when a large initial dose of bacteria meant that bacterial numbers were still increasing at this time. Recombinant mouse IL-6 injected intraperitoneally before infection protected mice in a dose-dependent manner. It was effective when given 4 h before infection but not when administration was delayed for 24 h postinfection. It is therefore believed that IL-6 plays a role in early priming of the immune response to infection. Its exact function in this model is being investigated.

Effect of recombinant human macrophage colony-stimulating factor 1 on immunopathology of experimental brucellosis in mice

Brucella abortus injected into CBA mice replicated primarily in the spleen and liver, reaching a peak bacterial count in both organs about 7 days postinfection. The organism was eliminated from the liver but declined to a chronic phase in the spleen. The infection caused hepatosplenomegaly. An influx of macrophages into the two organs was monitored by quantitative Northern (RNA blot) analysis of the macrophage-specific marker lysozyme mRNA. Lysozyme mRNA was detectable in spleen and increased three- to fourfold during infection. In liver, lysozyme mRNA was initially undetectable, but at about the peak of infection it reached a level comparable to that in the spleen. Macrophage colony-stimulating factor 1 (CSF-1) has been reported to be elevated in the circulation of animals infected with B. abortus and is known to stimulate monocytopoiesis. To investigate the role of CSF-1 in pathogenesis, we studied the effect of further increasing the CSF-1 concentration by administration of recombinant human CSF-1. Since the infection is characterized by several distinct phases, recombinant human CSF-1 was administered at defined times relative to these phases. Pronounced effects were observed only when CSF-1 administration was begun during the developing acute phase. The consequences were decreased bacterial numbers in the spleen but an increase in the liver, reduced antibody generation, and increased hepatosplenomegaly. A feature of many chronic intracellular infections is immunosuppression. B. abortus caused a substantial diminution of responsiveness of spleen cells to T-cell mitogens, particularly concanavalin A. This action was mimicked by CSF-1 treatment of the animals prior to spleen cell isolation. The results suggest that CSF-1 plays a role in macrophage recruitment in brucellosis and that recruited macrophages contribute to the immunopathology and immunosuppression.

Prophylaxis or treatment of experimental brucellosis with interleukin-1

Intravenously injected recombinant human interleukin-1 alpha (IL-1 alpha) given to mice 4 h before infection with Brucella abortus 19 depressed the growth of bacteria in the spleen and liver. However, the same dose (10(5) U) or a 10-fold higher dose was not able to decrease numbers of bacteria when given to chronically infected mice. IL-1 injected into normal mice induced a dramatic increase 2 h later in colony-stimulating activity in serum, measured by bone marrow proliferation, and in colony-stimulating factor 1, measured by radioimmunoassay. Colony-stimulating factor levels declined but remained higher than normal for at least 12 h. The early peak stimulation was not observed in chronically infected mice, but the more prolonged elevation was. As a result of IL-1 treatment, the number of colony-forming cells, especially in the spleen, was increased in normal and acutely or chronically infected mice. Myeloperoxidase staining of newly formed monocytes and polymorphonuclear cells in the spleen revealed an increase in the number of these cells in normal and acutely infected mice as a result of IL-1 treatment, but there was no increase in the already high numbers in chronically infected mice. The relationship between these observations and the basis of chronic infection are discussed.

Anti-bacterial activity of peritoneal cells from transgenic mice producing high levels of GM-CSF

Two lines of transgenic mice carrying the gene for granulocyte-macrophage colony-stimulating factor (GM-CSF) produce vastly increased numbers of macrophages with abundant foamy cytoplasm resembling classical activated macrophages. Cells from both lines were negative for myeloperoxidase, a bactericidal enzyme found in monocytes as well as neutrophils, but not mature macrophages. Cells from the so called 'male line' produced greatly increased levels of oxygen degradation products in response to phagocytosis, compared with cells from the 'female line' or from normal littermates. The ability of the cells to phagocytose and lyse the intracellular bacterium Listeria monocytogenes was tested in vitro using radiolabelled organisms. Although the cells from transgenic mice were more highly phagocytic than cells from normal littermates, cells from either line were no more efficient than normal at lysing the bacteria they had phagocytosed. Nevertheless, because of the high phagocytic rate, more bacteria were exposed to lysis in the cells of transgenic mice, and the final outcome was a higher rate of bacteriolysis.

Distinction between 'inflammatory' and 'immune' macrophages killing Listeria monocytogenes in murine infection

Two populations of efficiently phagocytic and bacteriolytic cells have been defined in the peritoneal cavity following infection of mice with Listeria monocytogenes. One was the result of a transient inflammatory response 2 days after intraperitoneal (i.p.) infection. It consisted of a mixture of monocyte/macrophages and neurotrophils which, when separated on Percoll gradients or by adherence, were both highly bacteriolytic compared with normal resident peritoneal macrophages. It was rich in recently divided cells as evidenced by in vivo labelling with tritiated thymidine. Although having the enlarged, vacuolated appearance of 'activated' macrophages, three-quarters of the monocyte/macrophages stained positive for myeloperoxidase (MPO), characteristic of monocytes rather than mature macrophages. In contrast, intravenous (i.v.) infection, which localizes in spleen and liver, did not produce this early response in the peritoneal cavity. However, 8 days after either i.v. or i.p. infection there existed in the peritoneal cavity a highly active population of cells comprising chiefly macrophages of typical foamy appearance which did not stain for MPO+. They were actively phagocytic and bacteriolytic and, like the early inflammatory exudate, produced increased amounts of oxygen degradative products. They appear to typify the concept of macrophages activated by T cell mediated immunity. Two day peritoneal exudates induced in these previously infected mice by i.p. rechallenge with L. monocytogenes organisms comprised mostly MPO- macrophages.

Relationship between colony-stimulating activity and interferon production during infection

Normal mouse spleen, when cultured in vitro for 3 days in the presence of 10(8) heat-killed Listeria monocytogenes organisms, produced colony-stimulating factors (CSF) that were capable of supporting the production of haemopoietic colonies by bone marrow cells in semi-solid agar, or supporting bone marrow proliferation in liquid medium. In contrast, when the spleen cells were prepared from mice that had been infected with Listeria monocytogenes, colony-stimulating activity (CSA) was no longer detectable over a period from Day 3 to Day 17 post-infection. Suppression of CSA was imposed on normal spleen cells when nylon-wool filtered, T-cell enriched spleen cells from infected mice were co-cultured with normal spleen cells. Suppression largely coincided with the production of interferon by whole spleen from infected mice, and when interferon-gamma (IFN-gamma) was neutralized by antibody CSA was again detected. An early IFN-gamma-independent decrease in CSA production was also detected 2-3 days post-infection. The relevance of this system to the control of CSF production in vivo is discussed.

Stimulation of macrophage phagocytic but not bactericidal activity by colony-stimulating factor 1

The ability of mouse peritoneal cells to phagocytose and lyse Listeria monocytogenes was measured after the cells were incubated with purified murine macrophage-specific colony-stimulating factor (CSF-1). Activation of combined phagocytic and bacteriolytic ability required 24 h, with an optimal dose of 1,000 U of CSF-1 per ml. No activation was achieved with a shorter period of incubation, known to be sufficient for GM-CSF to stimulate phagocytosis by granulocytes, and there was no advantage in longer exposure. After 24 h in 1,000 U of CSF-1, macrophages showed visibly increased spreading on the plastic petri dish. Activated cells examined microscopically showed an increase in the number of phagocytic cells and in the numbers of bacteria per phagocytic cell. This increased phagocytic ability was evident also in the increase in the amount of radioactivity associated with the cells following a 30-min incubation with radiolabeled bacteria. When these cells were carefully washed, the percentage of this initial uptake released during the next 2 h was not increased by pretreatment of the cells with CSF-1, showing that the effect of this growth factor was on phagocytosis of the bacteria not on the killing mechanisms per se.