Macrophage development: IV. Effects of blood factors on macrophages from prenatal rat lung cultures

A Novel in vitro Human Macrophage Model to Study the Persistence of Mycobacterium tuberculosis Using Vitamin D(3) and Retinoic Acid Activated THP-1 Macrophages

Mycobacterium tuberculosis (Mtb) replicates within the human macrophages and we investigated the activating effects of retinoic acid (RA) and vitamin D(3) (VD) on macrophages in relation to the viability of intracellular Mtb. A combination of these vitamins (RAVD) enhanced the levels of DC-SIGN and mannose receptors on THP-1 macrophages that increased mycobacterial uptake but inhibited the subsequent intracellular growth of Mtb by inducing reactive oxygen species and autophagy. RAVD also enhanced antigen presenting and chemotactic receptors on THPs suggesting an activated phenotype for RAVD activated THPs. RAVD mediated activation was also associated with a marked phenotypic change in Mtb infected THPs that fused with adjacent THPs to form multinucleated giant cells (MNGCs). Typically, MNGCs occurred over 30 days of in vitro culture and contained non-replicating persisting Mtb for more than 60 days in culture. Latent tuberculosis occurs in over a third of mankind and we propose that RAVD mediated induction of persistent Mtb within human macrophages provides a novel model to develop therapeutic approaches and investigate pathogenesis of latency.

Multinucleate cells (MNC) as sensitive semiquantitative biomarkers of the toxic effect after experimental fibrous dust and cigarette smoke inhalation by rats

Changes in the counts of binucleate (BNC) and multinucleate cells (MNC) in cell mixtures from lung tissue and bronchoalveolar lavage fluid (BALF) as well as in proportions of four types of BALF cells: Alveolar macrophages (AM), lymphocytes, polymorphonuclears (PMN), BNC and in total BALF protein were followed in a study comparing the toxicity of wollastonite with that of amosite asbestos in Fischer 344 rats. Both of the fibrous dusts were inhaled every second day at 30 or 60 mg/m3 air combined with daily exposure to cigarette smoke at 30 mg of total particulate matter (TPM)/m3 air for 1 h. The exposures lasted 175 days. Both, proportions of BNC as well as of MNC in lung cell mixtures rose significantly after exposure to cigarette smoke only. After inhalation of wollastonite the BNC proportions in all except the lower dust exposure group compared to controls showed a significant rise with the maximal factor value of 2.1 in the higher dust plus smoke exposure group. Wollastonite caused only marginal changes in MNC and other inflammation parameters. After inhalation of amosite at comparing to controls the proportion of BNC rose 8 times in the 30 mg/m3 and 11 times in the 60 mg/m3 exposure group, respectively. The effect of smoking was additive. The proportions of MNC were 39 times higher in the 30 mg/m3 and 41 times higher in the 60 mg/m3 amosite exposure group than in controls. In the higher exposure group the effect of smoking was synergic in that the MNC proportion rose about 58 times over control values from 0.05% up to about 3.0% (99% confidence interval--CI = 2.7-3.3%). The other followed inflammation parameters showed the presence of inflammation in the lung. It could be concluded that wollastonite at the same inhalation exposure concentration caused in rats less toxic effects than amosite, and, that the number of MNC, as well as BNC in lung cell mixtures and in BALF may serve as an important semiquantitative biomarker of inflammation.

The relation between serum cytokine levels and common laboratory tests in healthy Japanese males

OBJECTIVES

Cytokines are critical regulatory molecules that circulate in blood at measurable levels. However, the epidemiology of serum cytokine levels in healthy populations is still limited, particularly for Japanese populations. The objective of this study was to examine the relation between serum cytokine levels and common laboratory tests in a healthy Japanese population.

METHODS

We studied serum levels of six cytokines (interleukin-4 (IL-4), IL-5, IL-6, IL-10, interferon-γ (IFN-γ), granulocyte-macrophage colony-stimulating factor (GM-CSF)) in a healthy Japanese population using a sensitive chemiluminescence ELISA (CL-ELISA). We examined the relations between serum cytokine levels and common laboratory tests using multiple regression analysis. We were particularly interested in potential relations between serum cytokine levels and C-reactive protein (CRP) in light of its relation to the risk of cardiovascular events. We also investigated the relation between cytokine levels, alcohol consumption and smoking.

RESULTS

After adjusting for the influence of other cytokines and laboratory tests, the serum level of IL-4 was associated with IL-5 and GM-CSF. In addition to IL-4, IL-5 was also associated with IL-10 and IFN-γ. IL-6 was associated with IL-10 and IFN-γ, and IL-10 and IFN-γ were associated with GM-CSF. CRP was significantly negatively associated with serum IL-4 level. IL-6 was weakly correlated with alcohol consumption level in this population. IL-5 among smokers tended to be lower than that among nonsmokers.

CONCLUSIONS

Close relations among serum cytokine levels were observed in a healthy population. It is interesting that the level of IL-4, an anti-inflammatory cytokine, was inversely related to CRP level, suggested to be a marker of inflammation.

Factors influencing fetal macrophage development: I. Reactions of the tumor necrosis factor-alpha cascade and their inhibitors

BACKGROUND

When fetal rat lungs are explanted to organ culture, precursor angular cells soon convert to nascent macrophages that multiply rapidly as they mature into efficient phagocytes. The present study examines the influence of proinflammatory early cytokines of the tumor necrosis factor-alpha (TNF alpha) cascade on this initial expression of the macrophage phenotype.

METHODS

Fourteen- and 15-day fetal rat lungs were grown for varying periods on an agar-solidified medium with and without test factors added singly or in combination. Growth of the macrophage population was followed daily by light microscopy and quantified by measuring the area of coronas formed as cells emerged from explants.

RESULTS

TNF alpha interleukin-1 beta (IL-1 beta) stimulated growth of the macrophage population, as had macrophage- and granulocyte-macrophage colony-stimulating factors (M- and GM-CSFs) in prior studies. Inhibition was obtained by exposure to IL-1 receptor antagonist and antibodies neutralizing the CSFs. Only the effects of TNF alpha were sufficiently delayed to discount possible influence on conversion and growth of nascent macrophages. Two transcription blockers, dexamethasone and pyrrolidine dithiocarbamate (PDTC), an inhibitor of nuclear factor NF-kappa B, both profoundly suppressed macrophage growth without preventing conversion of precursors. Effects of dexamethasone were significantly ameliorated by IL-1 beta alone and combined with GM-CSF; those of PDTC were mitigated by M-CSF and a combination of IL-1 beta and TNF alpha but not by GM-CSF.

CONCLUSIONS

IL-1 beta, M-CSF, and GM-CSF all promote growth of the young macrophage population. TNF alpha is effective only later on, likely because early-stage cells lack its receptors which normally use intracellular signalling pathways similar to those for IL-1. The severity of PDTC inhibition to population growth indicates that NF-kappa B is important for transmitting proliferative signals in these cells.

Factors influencing fetal macrophage development: II. Effects of the PDGF subfamily of protein-tyrosine kinase receptor ligands as studied in organ-cultured rat lungs

BACKGROUND

Macrophage precursors in pseudoglandular rat lungs rapidly differentiate into phagocytes in organ culture, although this occurs only gradually in vivo. Macrophage colony-stimulating factor is vital for the process, but the possible importance of other ligands in the platelet-derived growth factor (PDGF) subfamily is scarcely appreciated.

METHODS

Macrophage development was compared in 15-day fetal rat lungs cultured on solid, serum-containing media with and without added stem cell factor (SCF) (100 ng/mL) or antibodies to PDGF-AA and -BB (10-15 micrograms/mL each). In addition, organ cultures and intact lungs were immunostained for PDGF-AA and -BB to confirm their presence in the tissues. Macrophage population growth was measured by coronal area assay.

RESULTS

SCF initially stimulated macrophage production. Thereafter, results varied depending on baseline production by control cultures: where this was vigorous, SCF-exposed explants performed similarly; where this was moderate, the SCF explants outperformed them 1.5-2.6 times over (P < 0.01-0.001). Inhibition of macrophage production by pyrrolidine dithiocarbamate (100 microM) was not significantly diminished in the presence of SCF (10 ng/mL). Immunoreactivity for PDGF-AA and -BB was prevalent in cells of the airway epithelium and stroma during the period macrophage precursors were converting, and both isoforms were detected in differentiating macrophages as early as 2 days in vitro. Nonetheless, exposure of cultures to anti-PDGFs had no significant effect on macrophage population growth.

CONCLUSIONS

Ligands of the PDGF subfamily differ greatly in their influence over development of fetal macrophages. Whereas the PDGFs are ineffective, SCF stimulates growth of macrophage precursors and early differentiating forms and enhances survival of older cells. It appears to act mainly in synergy with other growth factors present in fetal lungs. Furthermore, in the hierarchy of hematopoietic progenitors, the macrophage precursors may be ranked on a par with burst-forming units in the red cell lineage.

Precursors of macrophages in embryonic rat lungs fail to exhibit granulocyte-forming potential

BACKGROUND

Mesenchyme-like macrophage (M) precursors called angular cells are present in rat lungs on the thirteenth day of gestation and by then can differentiate into outright macrophages. Based on studies of bone marrow-derived cells, it is widely believed that the macrophage line necessarily proceeds from a colony-forming unit with dual granulocyte-macrophage potential (CFU-GM). In embryos this seems doubtful since macrophages are already scattered throughout the body before the first granulocytes appear. We examined the question in organ cultured 14 day prenatal rat lungs after having shown earlier that the macrophage population developed in explants is increased by exposure to M- and GM-colony-stimulating factors (CSFs) but is unaffected by multi (IL-3)- or granulocyte (G)-CSF. Reportedly retinoic acid (RA) shifts CFU-GM strongly towards granulocytic differentiation and inhibits mitosis of unipotential macrophage precursors but not differentiated cells. Transforming growth factor beta 1 (TGF) inhibits multipotential blood progenitors but allows proliferation of committed precursors, and TGF together with GM-CSF induces granulocytopoiesis from CFU-GM.

METHODS

Lung pairs were grown on a serum-containing medium or one supplemented either by RA, TGF, or TGF/GM-CSF to form a control and three experimental groups. A fourth experiment compared responses to M-CSF exposure and M-CSF/TGF. Macrophage population growth was estimated by measuring the areas of coronas formed by macrophages emerged from the explants. F-actin was stained with fluorescein-labeled phalloidin.

RESULTS

In all experiments macrophages were produced unmixed with granulocytes. By +8 days they had largely emerged to form coronas about the lungs. In cultures exposed to RA, macrophages were less intensely stained for actin and slower to emerge than controls. At +8 days, however, coronal areas were not significantly different from controls, as was also true for the TGF group. In contrast, coronal areas of cultures grown with TGF/GM-CSF were much larger. At +17 days, mean coronal area of TGF cultures was about half that of controls (P < 0.05), whereas mean coronal area of the TGF/GM-CSF group was 5.4 times greater (P < 0.001). Macrophages from control and TGF-exposed cultures responded to M-CSF by an increase in coronal area which was greater among cultures given M-CSF alone than those given TGF + M-CSF (both P < 0.005).

CONCLUSIONS

Macrophage precursors in embryonic lungs are distinct from CFU-GM.

Exogenous cytokines enhance survival of macrophages from organ cultured embryonic rat tissues

BACKGROUND

Macrophage precursors are present in embryonic rats shortly after the onset of hematopoiesis. During organogenesis they soon establish residency in many parts of the body and become convertible into phagocytes, at first gaining morphological characteristics of macrophages and later a range of surface antigens used to characterize subpopulations in adults. Nonetheless, it is uncertain whether representatives of this fetal lineage continue to exist past birth. We investigated the question indirectly by seeing if such cells can be made to survive in vitro to an age equivalent to adulthood and by examining underlying conditions that favor this outcome.

METHODS

Fourteen-day embryonic lungs, hearts, and limb buds were organ cultured on a firm serum-containing medium. Fetal macrophages developed within all explants and then migrated out to form a corona of cells surrounding each explant. The lung cultures were selected for subsequent work which mainly used coronal area as the measure of macrophage population size in experimental and control groups. Baseline growth and survival of macrophages were established for cultures grown on standard medium, then effects of the following were examined: indomethacin (10(-6) M) as it influences initial production of macrophages from precursors and later survival of differentiated cells; and macrophage colony-stimulating factor (M-CSF), used alone at moderate dosage (50-100 U), and combined with granulocyte-macrophage CSF (both 200 U), for its importance to long-term survival of the population. Mitogenic influence of M-CSF on differentiated macrophages was demonstrated by uptake of 5-bromo-2'-deoxyuridine.

RESULTS

Indomethacin inhibited the formation of macrophages from precursors but enhanced the survival of differentiated cells. M-CSF increased BrdU uptake of differentiated macrophages and permitted coronal growth to continue long past the approximately 30 day limit of controls. Beyond this interval, M-CSF was essential for macrophage survival, since coronas quickly shrank after the cytokine was withdrawn. Administration of the M-CSF/GM-CSF mixture to the 2 oldest M-CSF-exposed cultures between 98 and 127 days in vitro resulted in an increase in the number of coronal macrophages (P < 0.001); withdrawal between 129 and 140 days led to a decrease (P < 0.005). Ultimately a few cells were still surviving at 183 days.

CONCLUSIONS

Intrinsic factors promote early formation of macrophages within the explants, but the availability of factors is lessened by the anti-inflammatory action of indomethacin. Its later promotion of macrophage survival may be based on suppression of autogenous prostaglandin (PGE2) synthesis. M-CSF greatly promotes macrophage survival; in context this is sufficient to show that the fetal macrophage line has a clear potential to survive well into adulthood.

Early development of macrophages in intact and organ cultured hearts of rat embryos

BACKGROUND

Macrophage precursors are present early in embryonic life, being demonstrable in placental and embryonic connective tissues of rats at the neurula stage and as potential macrophages in the brain, liver, and lungs near the onset of organogenesis. We examined the development of macrophages in the heart and the possibility that they initially appear at sites of programmed cell death (apoptosis).

METHODS

Precursors were recognized by the binding of peroxidase-coupled Griffonia simplicifolia isolectin B4 (GSA) on the cell membrane. Their capacity for conversion into macrophages was assayed in organ cultures; confirmation of the progeny as bona fide macrophages was obtained from their responses to particle exposure and macrophage colony-stimulating factor (M-CSF).

RESULTS

GSA+cells were first seen on gestational day 12 (4 mm embryos) as 2-3 cycling, nonvacuolated cells located in cardiac tissue outside the blood vessels. This population increased to approximately 12 cells by day 14 (9 mm embryos). Two-thirds were distributed along the bulbus cordis in the jellylike endocardium and a more densely cellular connective tissue closer to the aortic arches where apoptotic sites are expected to develop. Such sites were not found in serial glycol methacrylate sections through our 14-day specimens, although in whole heart explants of this age an area of necrosis developed along the prospective line of bulbar endocardial fusion on the second day of organ culturing, and by then macrophages were fairly abundant. Organ culturing of 13-day embryonic hearts also yielded large, highly vacuolated, GSA+mononuclear phagocytes. After a few days in culture most of the macrophages migrated onto the medium where they formed a tight corona of cells about the explants. They readily ingested iron oxide particles and concentrated supravitally administered neutral red in their vacuoles. Macrophages from 14-day cultures exposed to M-CSF developed significantly larger coronas than macrophages from explants grown in serum-rich control medium (p < 0.001). In the presence of cytokines, moreover, these cardiac macrophages survived as many as 100 (92 "postnatal") days.

CONCLUSIONS

Macrophage precursors first appear in embryonic rat hearts well before they are needed to clear debris generated by programmed cell death and are capable of rapid conversion into outright phagocytic cells as early as the 13th prenatal day.