Heterogeneity among macrophages cultured from mouse bone marrow. Morphologic, cytochemical and flow cytometric analyses

Spatially Resolved Immunometabolism to Understand Infectious Disease Progression

Infectious diseases, including those of viral, bacterial, fungal, and parasitic origin are often characterized by focal inflammation occurring in one or more distinct tissues. Tissue-specific outcomes of infection are also evident in many infectious diseases, suggesting that the local microenvironment may instruct complex and diverse innate and adaptive cellular responses resulting in locally distinct molecular signatures. In turn, these molecular signatures may both drive and be responsive to local metabolic changes in immune as well as non-immune cells, ultimately shaping the outcome of infection. Given the spatial complexity of immune and inflammatory responses during infection, it is evident that understanding the spatial organization of transcripts, proteins, lipids, and metabolites is pivotal to delineating the underlying regulation of local immunity. Molecular imaging techniques like mass spectrometry imaging and spatially resolved, highly multiplexed immunohistochemistry and transcriptomics can define detailed metabolic signatures at the microenvironmental level. Moreover, a successful complementation of these two imaging techniques would allow multi-omics analyses of inflammatory microenvironments to facilitate understanding of disease pathogenesis and identify novel targets for therapeutic intervention. Here, we describe strategies for downstream data analysis of spatially resolved multi-omics data and, using leishmaniasis as an exemplar, describe how such analysis can be applied in a disease-specific context.

Contribution of clonally distinct subpopulations to heterogeneous production of inducible nitric oxide synthase by LPS-stimulated mouse macrophages

Expression of the inducible nitric oxide synthase (iNOS) gene in mouse macrophages can be induced by bacterial lipopolysaccharide (LPS). iNOS (EC 1.14.13.39) catalyzes production of the reactive nitrogen intermediate, nitric oxide (NO), which is very important to macrophage-mediated host defense in species such as the mouse and rat. We have investigated production of iNOS at the level of single cells through immunocytochemical analysis of LPS-stimulated macrophages. Both bone marrow culture-derived macrophages and those of the cell line, RAW 264.7, were examined. Heterogeneous production of iNOS within macrophage populations was explained in part by the existence of clones that were high producers of iNOS and, therefore, NO, while other clones were reproducibly low producers of each. All clonally derived populations continued to demonstrate heterogeneous iNOS production, suggesting that at least one additional mechanism must be responsible for the phenomenon of heterogeneity. In contrast to iNOS, LPS-stimulated macrophages synthesized interferonβ (IFNβ) uniformly throughout the population.

Indirect induction of suppressor of cytokine signalling-1 in macrophages stimulated with bacterial lipopolysaccharide: partial role of autocrine/paracrine interferon-alpha/beta

It has previously been reported by us that a brief prior exposure of mouse bone marrow culture-derived macrophages to bacterial lipopolysaccharide (LPS) resulted in a dramatic reduction in their ability to produce NO in response to a subsequent stimulus with either interferon-gamma (IFN-gamma) or IFN-gamma plus LPS. We show here that this brief exposure to LPS results in an impaired response to subsequently added IFN-gamma. A 2--4 h pretreatment with LPS leads to a dramatic reduction in the IFN-gamma-induced DNA-binding of the transcription factor, signal transducer and activator of transcription 1 alpha (STAT1 alpha). This loss in ability to activate STAT1 alpha temporally correlates with the LPS-induced accumulation of mRNA encoding the suppressor of cytokine signalling-1 (SOCS-1). However, LPS does not directly induce the synthesis of SOCS-1. Rather, LPS induces the synthesis of autocrine/paracrine factors that are the true mediators of SOCS-1 induction. IFN-alpha/beta is one of these mediators, but plays only a partial role in the induction of SOCS-1 because neutralization of LPS-induced IFN-alpha/beta production incompletely inhibits the induction of SOCS-1. We show that mouse IFN-beta directly induces the synthesis of SOCS-1, without the need for prior protein synthesis, and does so with faster kinetics than does LPS. Our results are consistent with the non-specific nature of LPS-induced tolerance and provide a mechanistic insight into nonspecificity; LPS indirectly induces the synthesis of a protein mediator, SOCS-1, which inhibits the signalling that is induced by IFN-gamma.

Interleukin 3 enhances cytotoxic T lymphocyte development and class I major histocompatibility complex "re-presentation" of exogenous antigen by tumor-infiltrating antigen-presenting cells

We show that interleukin 3 (IL-3) enhances the generation of tumor-specific cytotoxic T lymphocytes (CTLs) through the stimulation of host antigen-presenting cells (APCs). The BALB/c (H-2d) spontaneous lung carcinoma line 1 was modified by gene transfection to express ovalbumin as a nominal "tumor antigen" and to secrete IL-3, a cytokine enhancing myeloid development. IL-3-transfected tumor cells are less tumorigenic than the parental cell line, and tumor-infiltrating lymphocytes isolated from these tumors contain increased numbers of tumor-specific CTLs. By using B3Z86/90.14 (B3Z), a unique T-cell hybridoma system restricted to ovalbumin/H-2b and implanting the tumors in (BALB/c x C57BL/6)F1 (H-2d/b) mice, we demonstrate that the IL-3-transfected tumors contain an increased number of a rare population of host cells that can process and "re-present" tumor antigen to CTLs. Electron microscopy allowed direct visualization of these host APCs, and these studies, along with surface marker phenotyping, indicate that these APCs are macrophage-like. The identification of these cells and their enhancement by IL-3 offers a new opportunity for tumor immunotherapy.

Determination of half-life for mRNA expressed in few copies and with short life

Determination of stability of mRNA expressed in low abundance and with short life requires a sensitive method for detection and an accurate measurement of mRNA level. The method described here meets both of these criteria. An uniformly labeled single-stranded probe with high specific activity was used for the increased sensitivity in detection and quantitation of mRNA. The levels of mRNA were normalized with an invariant mRNA specie with longer half-life under the same experimental conditions in the same cells. These modifications may be helpful for situations where measurement of mRNA half-life for short-lived few copies of mRNA is necessary.

A specific sequence of stimulation is required to induce synthesis of the antimicrobial molecule nitric oxide by mouse macrophages

Nitric oxide production by macrophages required either simultaneous or sequential exposure to gamma interferon and lipopolysaccharide; exposure to lipopolysaccharide followed by exposure to gamma interferon gave little response. The apparently evanescent nature of the lipopolysaccharide signal, necessitating persistent stimulation, could be essential to down-regulating nitric oxide production after bacteria are cleared in vivo.

A subpopulation of bone marrow-derived macrophage-like cells shares a unique ion channel pattern with microglia

Rat microglia share a number of antigenic, functional, and morphological similarities with macrophages from other tissues, but are characterized by a distinctly different pattern of ion channels in the cellular membrane (Kettenmann et al., J Neurosci Res 26:278-287, 1990). Macrophages typically express outward and inward K+ currents. In contrast, microglia lack outward currents and only show inwardly rectifying K+ currents, regardless of the isolation or cultivation method employed for microglia. In this study we demonstrate that a subpopulation of bone marrow-derived macrophage-like cells possesses inward rectifier K+ currents, but no outward currents and thus with regard to the electrophysiological characteristics closely resembles microglia. A second population of bone marrow-derived macrophage-like cells shows the usual channel pattern described for other body macrophages. Our results strengthen the hypothesis that in the bone marrow distinct pools of precursor cells exist, possibly reflecting an early differential lineage determination for body and brain macrophages, i.e., microglia.

Activation-associated marker proteins: peptide mapping and their expression in macrophage cell lines

The activation-associated markers, p47b and p71/73, have been recognized as minor proteins in peritoneal and bone marrow culture-derived macrophages activated for tumor cell killing. Proteins with identical characteristics of migration on 2-dimensional gels and comparable Cleveland peptide maps are described here in macrophage cell lines that could be activated for tumor cell killing (J774A.1, RAW 264, UNC-2). Macrophage cell lines that could not be activated (P388D1 and PU5-1.8) did not express the markers. The expression of these markers in activatable macrophage cell lines strengthens their association with the activation process and provides a bulk source of the proteins for purification studies.

Characterization of mouse macrophage differentiation antigens by monoclonal antibodies

Monoclonal rat antibodies to mouse macrophage antigens were prepared. For immunization phagocytic cells in the spleens of mice recovering from sublethal irradiation were used. Specificities of the monoclonal antibodies obtained were determined on cells of normal mouse cell populations as well as on cells of a panel of mouse cell lines. In an attempt to monitor expression of differentiation-related antigens two models of in vitro-induced macrophage differentiation were used: differentiation of cells of the myeloblast line Ml; CSF-1-induced differentiation of bone marrow cells. The results obtained clearly show that during maturation from undifferentiated to highly differentiated cells of the macrophage lineage expression of antigens recognized by the MIV 38, MIV 55, MV 87, and MV 114 monoclonal antibodies is enhanced. At the same time, expression of antigens recognized by the MIV 52, MIV 113, and MIV 116 monoclonal antibodies diminishes at a similar rate. The suitability of these monoclonal antibodies for the characterization of differentiation states of mouse macrophages is discussed.

A monoclonal antibody against the ligand binding site of the receptor for mouse interferon-gamma

A rat monoclonal IgG2a antibody, GR-20, has been produced against the receptor for mouse interferon-gamma (MuIFN-gamma). Comparison of competitive binding studies performed with either 125I-labeled GR-20 or recombinant (r) MuIFN-gamma, as well as a variety of other studies, suggested that the epitope recognized by the monoclonal antibody (mAb) is in the domain of the receptor that binds ligand. The binding of GR-20 to cells of the monomyelocytic line WEHI-3 was of high affinity (1-2 nM). Approximately 20,000 binding sites were found per cell, a value that is in close agreement with the number of MuIFN-gamma receptors quantified on cells of the same type by ligand binding studies. The mAb also bound to a variety of other mouse cells, suggesting that the same epitope is shared by receptors for MuIFN-gamma, regardless of cell type. The epitope was not detected on two human cell types that were tested, while cells of a rat cell line shown to be minimally responsive to rMuIFN-gamma gave equivocal binding results when they were interacted with GR-20. Binding of the mAb to the receptor did not mimic the effects of ligand. In fact, the opposite was true: binding blocked the induction of three biological effects of MuIFN-gamma, including priming of macrophages for tumor cell killing, upregulation of the expression of class II major histocompatibility antigens (Ia) on the same cell type, and induction of antiviral activity in L cells. Following intravenous injection, initial removal of GR-20 was precipitous, followed after 1 h by a phase which was more gradual, resulting in 5-10% of biologically active mAb remaining in the circulation after 24 h. Such retention should make this mAb useful in a variety of studies in vivo.

Activation of macrophages to express cytocidal activity correlates with inhibition of their responsiveness to macrophage colony-stimulating factor (CSF-1): involvement of a pertussis toxin-sensitive reaction

Bone marrow-derived murine macrophages were used to study the relationship between the proliferative response of macrophages to macrophage colony-stimulating factor (CSF-1) and their activation for cytocidal activity against tumour cells. Macrophage activation required two sequential signals. Lymphokines (gamma interferon, interleukin-4) provided the first (priming) signal; bacterial products (lipopolysaccharide, lipophilic muramyl tripeptide, lipopeptide 31362, pertussis toxin) provided the second (triggering) signal. Both priming and triggering agents inhibited [3H]-thymidine uptake by macrophages stimulated with CSF-1. The antiproliferative activity of priming and triggering stimuli was synergistic. Pretreatment with triggering stimuli at 37 degrees C caused a rapid reduction of the subsequent binding of [125I]-CSF-1 to the cell surface at 4 degrees C, whereas priming agents had relatively little effect. Growth inhibition by both priming and triggering agents was largely reversible by washing the cells, and occurred even when they were added as long as 24 h after the growth factor. The ability of pertussis toxin to both inhibit CSF-1-induced proliferation and trigger cytotoxicity in macrophages suggests the involvement of a regulatory GTP-binding protein (G protein) in both processes.

Prostaglandin and thromboxane biosynthesis in isolated platelet-free human monocytes. III. The induction of cycloxygenase by colony stimulating factor-1

Previous observations showing the presence in the serum of a component capable of regulating prostanoid biosynthesis in human cultured monocytes, have led us to suspect its presence in human platelets. We have purified this serum monocytotropic factor (SMF) and have shown its identity with a component of platelet membranes. Surprisingly its structure appeared to be very similar to that of a polypeptide growth factor never before identified in platelets: the colony stimulating factor-1 (CSF-1 or M-CSF). Here we show that SMF and CSF-1 have very similar biological properties. Thus, CSF-1 when released from human platelets is capable of triggering the differentiation pathway leading from blood monocytes to resident macrophages. It is likely that cycloxygenase induction plays a pivotal role in these events.

Regulation of bone marrow cell survival in short-term cultures: a new macrophage function

The involvement of macrophages (M phi) in the regulation of bone marrow (BM) cell survival in short-term cultures was studied. We developed a system to measure the survival of fresh BM cells in vitro, by evaluating 111indium (111In) release from prelabeled BM cells. 111In release was proportional to cell death and inversely related to the number of trypan blue excluding cells. Upon 24 hr of culture in conventional medium, more than 50% of BM cells died. In order to investigate whether BM cell death could be reduced by coculture with other cell types, 111In-labeled BM cells were incubated for 24 hr with peritoneal M phi, thymocytes (THY), or polymorphonuclear cells (PMN) and then assayed for their survival. We found that coculture of BM cells with M phi dramatically increased BM survival, whereas THY or PMN consistently failed to enhance BM survival. The ability to promote BM cell survival, here designated nurse activity, represented a novel function of M phi and was further characterized. The stage of activation of M phi did not influence their nurse activity, since M phi elicited in vivo by proteose-peptone, thioglycollate, or Bacillus Calmette-Guérin, as well as resident M phi unstimulated or activated in vitro with lipopolysaccharide, equally sustained survival of BM cells. BM-derived M phi (adherent cells from BM cultures maintained in 20% L-cell-conditioned medium for 14 days) were equally effective in exerting nurse activity. Moreover, nurse activity was also exerted across the histocompatibility barriers. Supernatants from M phi cultures or killed M phi were ineffective. We propose that the nurse effect of M phi on BM is a primitive function that may play an important role in the development of the hemopoietic system.

Lipopolysaccharide and polyribonucleotide activation of macrophages: implications for a natural triggering signal in tumor cell killing

There is evidence that activation of macrophages for tumor cell killing can involve either two signals (interferon/lipopolysaccharide, for example) or one signal (lipopolysaccharide or double-stranded RNA, for example). We investigated the apparent one-signal activation of bone marrow-derived macrophages for P815 mastocytoma killing by treatment with lipopolysaccharide (LPS) or by the synthetic double-stranded polyribonucleotide polyinosinic acid-polycytidylic acid (poly I:C). We found that "direct" activation of macrophages by either LPS or poly I:C was still a two-signal process. Based on antibody neutralizations, the first signal was probably mediated by LPS or poly I:C induced alpha/beta interferon in the macrophage cultures, and the second signal was that of a direct effect of the LPS or poly I:C on the cell. The fact that poly I:C can provide the triggering signal for macrophage activation suggests a possible role for double-stranded RNA structures in macrophage triggering. Such double-stranded RNA requirements could be met by single-stranded RNAs that possess significant double-strandedness in their structures.