Fatty acid oxidation of alternatively activated macrophages prevents foam cell formation, but Mycobacterium tuberculosis counteracts this process via HIF-1α activation

The ability of Mycobacterium tuberculosis (Mtb) to persist inside host cells relies on metabolic adaptation, like the accumulation of lipid bodies (LBs) in the so-called foamy macrophages (FM), which are favorable to Mtb. The activation state of macrophages is tightly associated to different metabolic pathways, such as lipid metabolism, but whether differentiation towards FM differs between the macrophage activation profiles remains unclear. Here, we aimed to elucidate whether distinct macrophage activation states exposed to a tuberculosis-associated microenvironment or directly infected with Mtb can form FM. We showed that the triggering of signal transducer and activator of transcription 6 (STAT6) in interleukin (IL)-4-activated human macrophages (M(IL-4)) prevents FM formation induced by pleural effusion from patients with tuberculosis. In these cells, LBs are disrupted by lipolysis, and the released fatty acids enter the β-oxidation (FAO) pathway fueling the generation of ATP in mitochondria. Accordingly, murine alveolar macrophages, which exhibit a predominant FAO metabolism, are less prone to become FM than bone marrow derived-macrophages. Interestingly, direct infection of M(IL-4) macrophages with Mtb results in the establishment of aerobic glycolytic pathway and FM formation, which could be prevented by FAO activation or inhibition of the hypoxia-inducible factor 1-alpha (HIF-1α)-induced glycolytic pathway. In conclusion, our results demonstrate that Mtb has a remarkable capacity to induce FM formation through the rewiring of metabolic pathways in human macrophages, including the STAT6-driven alternatively activated program. This study provides key insights into macrophage metabolism and pathogen subversion strategies.Fil: Genoula, Melanie. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentina. Centre National de la Recherche Scientifique; Francia. International Associated Laboratory; ArgentinaFil: Marin Franco, Jose Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentina. Centre National de la Recherche Scientifique; Francia. International Associated Laboratory; ArgentinaFil: Maio, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Dolotowicz, Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Ferreyra Compagnucci, Malena María. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Milillo, María Ayelén. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Mascarau, Rémi. Université de Toulouse; Francia. Centre National de la Recherche Scientifique; FranciaFil: Moraña, Eduardo José. Gobierno de la Ciudad de Buenos Aires. Hospital de Infecciosas "Dr. Francisco Javier Muñiz"; ArgentinaFil: Palmero, Domingo Juan. Gobierno de la Ciudad de Buenos Aires. Hospital de Infecciosas "Dr. Francisco Javier Muñiz"; ArgentinaFil: Matteo, Mario José. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Tisioneumonología "raúl F. Vaccarezza".; ArgentinaFil: Fuentes, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: López, Beatriz. Dirección Nacional de Instituto de Investigación. Administración Nacional de Laboratorio e Instituto de Salud "Dr. C. G. Malbrán"; ArgentinaFil: Barrionuevo, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Neyrolles, Olivier. International Associated Laboratory; Argentina. Université de Toulouse; Francia. Centre National de la Recherche Scientifique; FranciaFil: Cougoule, Céline. Centre National de la Recherche Scientifique; Francia. Université de Toulouse; Francia. International Associated Laboratory; ArgentinaFil: Lugo Villarino, Geanncarlo. Centre National de la Recherche Scientifique; Francia. Université de Toulouse; Francia. International Associated Laboratory; ArgentinaFil: Vérollet, Christel. Centre National de la Recherche Scientifique; Francia. International Associated Laboratory; Argentina. Université de Toulouse; FranciaFil: Sasiain, María del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentina. Centre National de la Recherche Scientifique; Francia. International Associated Laboratory; ArgentinaFil: Balboa, Luciana. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentina. Centre National de la Recherche Scientifique; Francia. International Associated Laboratory; Argentin

Estudio de los mecanismos y componentes de Brucella abortus involucrados en la disminución de MHC-I y la respuesta T CD8+ citotóxica

La brucelosis es una enfermedad infectocontagiosa de distribución mundial ocasionada por microorganismos del género Brucella. Dichas bacterias se comportan como patógenos intracelulares facultativos capaces de sobrevivir y multiplicarse dentro de las células del sistema mononuclear fagocítico y los tejidos asociados. Esta enfermedad es zoonótica y endémica en varios países en vías de desarrollo generando un problema serio para la salud pública y para la ganadería. La infección con B. abortus activa tanto el sistema inmune innato como adaptativo generando una respuesta pro-inflamatoria que favorece la diferenciación de células T hacia un perfil Th1, con la consecuente inducción de LT CD8+ citotóxicos. A pesar de esta respuesta inmune, dicha bacteria puede persistir dentro de los macrófagos que infecta, estableciendo una infección crónica.Resultados previos de nuestro laboratorio demuestran que la infección de monocitos/macrófagos humanos con B. abortus disminuye la expresión inducida por IFN-γ de las MHC-I en superficie. Como consecuencia, los macrófagos infectados presentan disminuida capacidad de presentación antigénica a los linfocitos T CD8+. Concretamente, observamos que la disminución de MHC-I reside en la capacidad de B. abortus para retener dichas moléculas dentro del aparato de Golgi. Sin embargo, aún desconocíamos varios aspectos relevantes de dicho fenómeno, a saber: los componentes de la bacteria involucrados, los mecanismos y las posibles vías de señalización gatilladas. En este trabajo, en primer lugar, observamos que la disminución de MHC-I depende de que las bacterias estén metabólicamente activas y no así de los factores de virulencia más relevantes de las bacterias. En concordancia con esto, recientemente se describió una nueva clase de PAMPs asociados a viabilidad bacteriana, llamados vita-PAMPs, siendo el ARN procariota uno de ellos, ya que los mismos se encuentran exclusivamente en bacterias vivas y se expresan activamente durante las fases tempranas de la infección. En este trabajo de tesis demostramos que un componente responsable de la disminución de MHC-I es el ARN de B. abortus. Aún más, los productos de la digestión del ARN con una ARNasa procariota fueron también capaces de reproducir este fenómeno. Asimismo, demostramos que el receptor a partir del cual se disparan los eventos que conducen a la disminución de MHC-I es el TLR8 humano/TLR7 murino. En cuanto a la vía de señalización involucrada, demostramos que el fenómeno es disparado de manera temprana (8 horas post infección), manteniéndose incluso a las 24 y 48 horas. Asimismo, el bloqueo del receptor del factor de crecimiento epidérmico (EGFR), ErbB2 (HER2) o la6inhibición de la enzima convertidora de TNF-α (TACE), involucrada en la generación de ligandos solubles tipo EGF, resultaron en una reversión parcial de la expresión en superficie de MHC-I. Por otro lado, EGF y TGF-α recombinantes fueron capaces de reproducir la disminución de MHC-I mediada por B. abortus y su ARN, siendo este efecto sinérgico. Finalmente, cuando se realizó la infección con la bacteria en presencia de un inhibidor de la vía de las MAPK ERK (Erk1/2) se revirtió significativamente la disminución de la expresión de MHC-I. Aún más, la neutralización de EGFR en las células estimuladas con ARN o ligandos sintéticos, revirtió la disminución de la expresión de MHC-I, sugiriendo también una conexión entre TLR8 y la vía de EGFR. Respecto al mecanismo de retención de MHC-I, los resultados con un inhibidor de la acidificación de las cisternas del aparato de Golgi, monensina, sugieren que una incorrecta acidificación del aparato de Golgi mediada por B. abortus podría conducir al transporte impedido de estas moléculas a la superficie. Por último, observamos que estos fenómenos tienen relevancia biológica, dado que la reducida expresión de MHC-I provoca una disminución en la funcionalidad de los LT CD8+.En conjunto, nuestros resultados establecen que el vita-PAMP ARN es un componente utilizado por B. abortus para disminuir la expresión de MHC-I, mecanismo por el cual este patógeno podría evadir el reconocimiento y la eliminación por parte de los linfocitos T citotóxicos, persistiendo en el hospedador y estableciendo una infección crónica.Fil: Milillo, María Ayelén. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentin

Bacterial RNA Contributes to the Down-Modulation of MHC-II Expression on Monocytes/Macrophages Diminishing CD4+ T Cell Responses

Brucella abortus, the causative agent of brucellosis, displays many resources to evade T cell responses conducive to persist inside the host. Our laboratory has previously showed that infection of human monocytes with B. abortus down-modulates the IFN-γ-induced MHC-II expression. Brucella outer membrane lipoproteins are structural components involved in this phenomenon. Moreover, IL-6 is the soluble factor that mediated MHC-II down-regulation. Yet, the MHC-II down-regulation exerted by lipoproteins was less marked than the one observed as consequence of infection. This led us to postulate that there should be other components associated with viable bacteria that may act together with lipoproteins in order to diminish MHC-II. Our group has recently demonstrated that B. abortus RNA (PAMP related to pathogens' viability or vita-PAMP) is involved in MHC-I down-regulation. Therefore, in this study we investigated if B. abortus RNA could be contributing to the down-regulation of MHC-II. This PAMP significantly down-modulated the IFN-γ-induced MHC-II surface expression on THP-1 cells as well as in primary human monocytes and murine bone marrow macrophages. The expression of other molecules up-regulated by IFN-γ (such as co-stimulatory molecules) was stimulated on monocytes treated with B. abortus RNA. This result shows that this PAMP does not alter all IFN-γ-induced molecules globally. We also showed that other bacterial and parasitic RNAs caused MHC-II surface expression down-modulation indicating that this phenomenon is not restricted to B. abortus. Moreover, completely degraded RNA was also able to reproduce the phenomenon. MHC-II down-regulation on monocytes treated with RNA and L-Omp19 (a prototypical lipoprotein of B. abortus) was more pronounced than in monocytes stimulated with both components separately. We also demonstrated that B. abortus RNA along with its lipoproteins decrease MHC-II surface expression predominantly by a mechanism of inhibition of MHC-II expression. Regarding the signaling pathway, we demonstrated that IL-6 is a soluble factor implicated in B. abortus RNA and lipoproteins-triggered MHC-II surface down-regulation. Finally, CD4+ T cells functionality was affected as macrophages treated with these components showed lower antigen presentation capacity. Therefore, B. abortus RNA and lipoproteins are two PAMPs that contribute to MHC-II down-regulation on monocytes/macrophages diminishing CD4+ T cell responses.Fil: Milillo, María Ayelén. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Trotta, Aldana. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Serafino, Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Marin Franco, Jose Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Marinho, Fábio A. V.. Universidade Federal de Minas Gerais; BrasilFil: Alcain, Julieta María. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Genoula, Melanie. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Balboa, Luciana. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Costa Oliveira, Sergio. Universidade Federal de Minas Gerais; BrasilFil: Giambartolomei, Guillermo Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Inmunología, Genética y Metabolismo. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Inmunología, Genética y Metabolismo; ArgentinaFil: Barrionuevo, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentin

Prokaryotic RNA associated to bacterial viability induces Polymorphonuclear neutrophil activation

Polymorphonuclear neutrophils (PMN) are the first cellular line of antibacterial host defense. They sense pathogens through recognition of pathogen-associated molecular patterns (PAMPs) by innate pattern recognition receptors, such as Toll-like receptors (TLR). The aim of this study was to investigate whether PMN sense bacterial viability and explore which viability factor could be involved in this phenomenon. For this purpose, different functions were evaluated in isolated human PMN using live Escherichia coli (Ec) and heat-killed Ec (HK-Ec). We found that bacterial viability was indispensable to induce PMN activation, as measured by forward-scatter (FSC) increase, CD11b surface expression, chemotaxis, reactive oxygen species (ROS) generation and neutrophil extracellular trap (NET) formation. As uncapped non-polyadenylated prokaryotic mRNA has been recognized as a PAMP associated to bacterial viability by macrophages and dendritic cells, total prokaryotic RNA (pRNA) from live Ec was purified and used as a stimulus for PMN. pRNA triggered similar responses to those observed with live bacteria. No RNA could be isolated from HK-Ec, explaining the lack of effect of dead bacteria. Moreover, the supernatant of dead bacteria was able to induce PMN activation, and this was associated with the presence of pRNA in this supernatant, which is released in the killing process. The induction of bactericidal functions (ROS and NETosis) by pRNA were abolished when the supernatant of dead bacteria or isolated pRNA were treated with RNAse. Moreover, endocytosis was necessary for pRNA-induced ROS generation and NETosis, and priming was required for the induction of pRNA-induced ROS in whole blood. However, responses related to movement and degranulation (FSC increase, CD11b up-regulation, and chemotaxis) were still triggered when pRNA was digested with RNase, and were not dependent on pRNA endocytosis or PMN priming. In conclusion, our results indicate that PMN sense live bacteria through recognition of pRNA, and this sensing triggers potent bactericidal mechanisms.Fil: Rodriguez Rodrigues, Nahuel Emiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Castillo Montañez, Luis Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Landoni, Verónica Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Martire Greco, Daiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Milillo, María Ayelén. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Barrionuevo, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Fernández, Gabriela Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentin

Prokaryotic RNA activates endothelial cells promoting neutrophil transmigration

Endothelial cell (EC)–neutrophil (PMN) interactions are crucial in the resolution of bacterial infections. Prokaryotic RNA (pRNA) has been reported as a pathogen‐associated molecular pattern that is released from bacteria upon death and is able to activate PMN. In this work, we studied the effects of pRNA on EC and investigated whether these effects could modulate EC–PMN interaction. For this purpose, we purified total pRNA from Escherichia coli and used it as a stimulus for Human Umbilical Vein Endothelial Cells (HUVEC). We found that the incubation of pRNA with HUVEC caused the increase of surface intercellular adhesion molecule 1 (ICAM‐1 or CD54) expression on HUVEC, and the secretion of IL‐8 and von Willebrand factor, characteristics consistent with HUVEC activation, without causing toxic effects. Moreover, pRNA‐treated HUVEC also induced PMN adhesion and the conditioned medium obtained from treated‐HUVEC was chemotactic for PMN and caused their activation, as determined by CD11b upregulation. As reported previously, the degradation products of pRNA induced similar biological effects. The treatment of HUVEC with endocytosis inhibitors revealed that the entry of pRNA partially relied on a clathrin‐dependent mechanism, whereas the effects of degradation products could not be inhibited by any of the inhibitors tested. Using a transwell system, we found that pRNA or degraded pRNA were also able to stimulate HUVEC when recognized from the basolateral side. Our results indicate that pRNA activates EC, resulting in the modulation of EC–PMN interaction by inducing PMN chemotaxis, adhesion and activation. In the context of infection, pRNA sensed by EC and PMN could favor bacterial clearance.Fil: Castillo Montañez, Luis Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Birnberg Weiss, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Rodriguez Rodrigues, Nahuel Emiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Pittaluga, José R.. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Martire Greco, Daiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Milillo, María Ayelén. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Grinstein, Sebastián. Ministerio de Defensa. Ejército Argentino. Hospital Militar Central Cirujano Mayor "Dr. Cosme Argerich"; ArgentinaFil: Camelli, María R.. Ministerio de Defensa. Ejército Argentino. Hospital Militar Central Cirujano Mayor "Dr. Cosme Argerich"; ArgentinaFil: Mena Aybar, Ana J.. Ministerio de Defensa. Ejército Argentino. Hospital Militar Central Cirujano Mayor "Dr. Cosme Argerich"; ArgentinaFil: Landoni, Verónica I. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; ArgentinaFil: Fernández, Gabriela Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentin

Formation of Foamy Macrophages by Tuberculous Pleural Effusions Is Triggered by the Interleukin-10/Signal Transducer and Activator of Transcription 3 Axis through ACAT Upregulation

The ability of Mycobacterium tuberculosis (Mtb) to persist in its human host relies on numerous immune evasion strategies, such as the deregulation of the lipid metabolism leading to the formation of foamy macrophages (FM). Yet, the specific host factors leading to the foamy phenotype of Mtb-infected macrophages remain unknown. Herein, we aimed to address whether host cytokines contribute to FM formation in the context of Mtb infection. Our approach is based on the use of an acellular fraction of tuberculous pleural effusions (TB-PE) as a physiological source of local factors released during Mtb infection. We found that TB-PE induced FM differentiation as observed by the increase in lipid bodies, intracellular cholesterol, and expression of the scavenger receptor CD36, as well as the enzyme acyl CoA:cholesterol acyl transferase (ACAT). Importantly, interleukin-10 (IL-10) depletion from TB-PE prevented the augmentation of all these parameters. Moreover, we observed a positive correlation between the levels of IL-10 and the number of lipid-laden CD14+ cells among the pleural cells in TB patients, demonstrating that FM differentiation occurs within the pleural environment. Downstream of IL-10 signaling, we noticed that the transcription factor signal transducer and activator of transcription 3 was activated by TB-PE, and its chemical inhibition prevented the accumulation of lipid bodies and ACAT expression in macrophages. In terms of the host immune response, TB-PE-treated macrophages displayed immunosuppressive properties and bore higher bacillary loads. Finally, we confirmed our results using bone marrow-derived macrophage from IL-10−/− mice demonstrating that IL-10 deficiency partially prevented foamy phenotype induction after Mtb lipids exposure. In conclusion, our results evidence a role of IL-10 in promoting the differentiation of FM in the context of Mtb infection, contributing to our understanding of how alterations of the host metabolic factors may favor pathogen persistence

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<p>The ability of Mycobacterium tuberculosis (Mtb) to persist in its human host relies on numerous immune evasion strategies, such as the deregulation of the lipid metabolism leading to the formation of foamy macrophages (FM). Yet, the specific host factors leading to the foamy phenotype of Mtb-infected macrophages remain unknown. Herein, we aimed to address whether host cytokines contribute to FM formation in the context of Mtb infection. Our approach is based on the use of an acellular fraction of tuberculous pleural effusions (TB-PE) as a physiological source of local factors released during Mtb infection. We found that TB-PE induced FM differentiation as observed by the increase in lipid bodies, intracellular cholesterol, and expression of the scavenger receptor CD36, as well as the enzyme acyl CoA:cholesterol acyl transferase (ACAT). Importantly, interleukin-10 (IL-10) depletion from TB-PE prevented the augmentation of all these parameters. Moreover, we observed a positive correlation between the levels of IL-10 and the number of lipid-laden CD14⁺ cells among the pleural cells in TB patients, demonstrating that FM differentiation occurs within the pleural environment. Downstream of IL-10 signaling, we noticed that the transcription factor signal transducer and activator of transcription 3 was activated by TB-PE, and its chemical inhibition prevented the accumulation of lipid bodies and ACAT expression in macrophages. In terms of the host immune response, TB-PE-treated macrophages displayed immunosuppressive properties and bore higher bacillary loads. Finally, we confirmed our results using bone marrow-derived macrophage from IL-10^−/− mice demonstrating that IL-10 deficiency partially prevented foamy phenotype induction after Mtb lipids exposure. In conclusion, our results evidence a role of IL-10 in promoting the differentiation of FM in the context of Mtb infection, contributing to our understanding of how alterations of the host metabolic factors may favor pathogen persistence.</p

image_1.tif

<p>The ability of Mycobacterium tuberculosis (Mtb) to persist in its human host relies on numerous immune evasion strategies, such as the deregulation of the lipid metabolism leading to the formation of foamy macrophages (FM). Yet, the specific host factors leading to the foamy phenotype of Mtb-infected macrophages remain unknown. Herein, we aimed to address whether host cytokines contribute to FM formation in the context of Mtb infection. Our approach is based on the use of an acellular fraction of tuberculous pleural effusions (TB-PE) as a physiological source of local factors released during Mtb infection. We found that TB-PE induced FM differentiation as observed by the increase in lipid bodies, intracellular cholesterol, and expression of the scavenger receptor CD36, as well as the enzyme acyl CoA:cholesterol acyl transferase (ACAT). Importantly, interleukin-10 (IL-10) depletion from TB-PE prevented the augmentation of all these parameters. Moreover, we observed a positive correlation between the levels of IL-10 and the number of lipid-laden CD14⁺ cells among the pleural cells in TB patients, demonstrating that FM differentiation occurs within the pleural environment. Downstream of IL-10 signaling, we noticed that the transcription factor signal transducer and activator of transcription 3 was activated by TB-PE, and its chemical inhibition prevented the accumulation of lipid bodies and ACAT expression in macrophages. In terms of the host immune response, TB-PE-treated macrophages displayed immunosuppressive properties and bore higher bacillary loads. Finally, we confirmed our results using bone marrow-derived macrophage from IL-10^−/− mice demonstrating that IL-10 deficiency partially prevented foamy phenotype induction after Mtb lipids exposure. In conclusion, our results evidence a role of IL-10 in promoting the differentiation of FM in the context of Mtb infection, contributing to our understanding of how alterations of the host metabolic factors may favor pathogen persistence.</p