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 ß-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.

PPARα/γ signaling pathways are involved in Chlamydia pneumoniae-induced foam cell formation via upregulation of SR-A1 and ACAT1 and downregulation of ABCA1/G1.

Chlamydia pneumoniae (Cpn) has been reported to be involved in the pathogenesis of early atherosclerosis by inducing macrophage-derived foam cell formation in the presence of low-density lipoprotein (LDL). However, the biochemical mechanisms underlying Cpn-induced foam cell formation are still not fully elucidated. The present study showed that in LDL-treated THP-1-derived macrophages, Cpn not only upregulated the expression of scavenger receptor A1 (SR-A1) and acyl-coenzyme A: cholesterol acyltransferase 1 (ACAT1), but it also downregulated the expression of ATP binding cassette transporters (ABCA1 and ABCG1) at both the mRNA and protein levels. These processes facilitated cholesterol accumulation and promoted macrophage-derived foam cell formation. Treatment with the peroxisome proliferator-activated receptor (PPAR)-γ agonist rosiglitazone or the PPARα agonist fenofibrate decreased the number of foam cells induced by Cpn, while the PPARγ antagonist GW9662, the PPARα antagonist MK886, or PPARα/γ siRNAs enhanced the effect of Cpn on foam cell formation and gene expression of SR-A1, ACAT1, and ABCA1/G1. Moreover, the PPARγ agonist rosiglitazone reversed the downregulation of CD36 by Cpn, while PPARγ siRNA and the PPARγ inhibitor GW9662 further suppressed CD36 expression. However, the PPARα agonist, inhibitor, and siRNA all showed no effect on CD36 expression. In conclusion, the PPARα and PPARγ pathways are both involved in Cpn-induced macrophage-derived foam cell formation by upregulating SR-A1 and ACAT1 and downregulating ABCA1/G1 expression.

Helicobacter pylori Infection Acts Synergistically with a High-Fat Diet in the Development of a Proinflammatory and Potentially Proatherogenic Endothelial Cell Environment in an Experimental Model.

Classic atherosclerosis risk factors do not explain all cases of chronic heart disease. There is significant evidence that gut microbiota may influence the development of atherosclerosis. The widespread prevalence of chronic Helicobacter pylori (H. pylori, HP) infections suggests that HP can be the source of components that stimulate local and systemic inflammatory responses. Elevated production of reactive oxygen species during HP infection leads to cholesterol oxidation, which drives atherogenesis. The aim of this study is to explore the link between persistent HP infection and a high-fat diet in the development of proinflammatory conditions that are potentially proatherogenic. An in vivo model of Caviae porcellus infected with HP and exposed to an experimental diet was investigated for the occurrence of a proinflammatory and proatherogenic endothelial environment. Vascular endothelial primary cells exposed to HP components were tested in vitro for oxidative stress, cell activation and apoptosis. The infiltration of inflammatory cells into the vascular endothelium of animals infected with HP and exposed to a high-fat diet was observed in conjunction with an increased level of inflammatory markers systemically. The arteries of such animals were the least elastic, suggesting the role of HP in arterial stiffness. Soluble HP components induced transformation of macrophages to foam cells in vitro and influenced the endothelial life span, which was correlated with Collagen I upregulation. These preliminary results support the hypothesis that HP antigens act synergistically with a high-fat diet in the development of proatherogenic conditions.

Mycobacterial antigens accumulation in foamy macrophages in murine pulmonary tuberculosis lesions: Association with necrosis and making of cavities.

Understanding mechanisms of cavitation in tuberculosis (TB) is the missing link that could advance the field towards better control of the infection. Descriptions of human TB suggest that postprimary TB begins as lipid pneumonia of foamy macrophages that undergoes caseating necrosis and fragmentation to produce cavities. This study aimed to investigate the various mycobacterial antigens accumulating in foamy macrophages and their relation to tissue destruction and necrosis. Pulmonary tissues from mice with slowly progressive TB were studied for histopathology, acid-fast bacilli (AFB) and presence of mycobacterial antigens. Digital quantification using Aperio ImageScope was done. Until week 12 postinfection, mice were healthy, and lesions were small with scarce AFB and mycobacterial antigens. Colony-forming units (CFUs) increased exponentially. At week 16-33, mice were sick, macrophages attained foamy appearance with an increase in antigens (P < .05), 1.5 log increase in CFUs and an approximately onefold increase in AFB. At week 37-41, mice started dying with a shift in morphology towards necrosis. A >20-fold increase in mycobacterial antigens was observed with only less than one log increase in CFUs and sevenfold increase in AFB. Secreted antigens were significantly (P < .05) higher compared to cell-wall antigens throughout infection. Focal areas of necrosis were associated with an approximately 40-fold increase in antigen MPT46, functionally active thioredoxin, and a significant increase in all secreted antigens. In conclusion, mycobacterial antigens accumulate in the foamy macrophages in TB lesions during slowly progressive murine pulmonary TB. Secreted antigens and MPT46 correlated with necrosis, thereby implying that they might trigger the formation of cavities.

Exosomal CagA derived from Helicobacter pylori-infected gastric epithelial cells induces macrophage foam cell formation and promotes atherosclerosis.

BACKGROUND: Seroepidemiological studies have highlighted a positive relation between CagA-positive Helicobacter pylori (H. pylori), atherosclerosis and related clinic events. However, this link has not been well validated. The present study was designed to explore the role of H. pylori PMSS1 (a CagA-positive strain that can translocate CagA into host cells) and exosomal CagA in the progression of atherosclerosis. METHODS: To evaluate whether H. pylori accelerates or even induces atherosclerosis, H. pylori-infected C57/BL6 mice and ApoE-/- mice were maintained under different dietary conditions. To identify the role of H. pylori-infected gastric epithelial cells-derived exosomes (Hp-GES-EVs) and exosomal CagA in atherosclerosis, ApoE-/- mice were given intravenous or intraperitoneal injections of saline, GES-EVs, Hp-GES-EVs, and recombinant CagA protein (rCagA). FINDINGS: CagA-positive H. pylori PMSS1 infection does not induce but promotes macrophage-derived foam cell formation and augments atherosclerotic plaque growth and instability in two animal models. Meanwhile, circulating Hp-GES-EVs are taken up in aortic plaque, and CagA is secreted in Hp-GES-EVs. Furthermore, the CagA-containing EVs and rCagA exacerbates macrophage-derived foam cell formation and lesion development in vitro and in vivo, recapitulating the pro-atherogenic effects of CagA-positive H. pylori. Mechanistically, CagA suppresses the transcription of cholesterol efflux transporters by downregulating the expression of transcriptional factors PPARγ and LXRα and thus enhances foam cell formation. INTERPRETATION: These results may provide new insights into the role of exosomal CagA in the pathogenesis of CagA-positive H. pylori infection-related atherosclerosis. It is suggested that preventing and eradicating CagA-positive H. pylori infection could reduce the incidence of atherosclerosis and related events.

Characterization of a secretory hydrolase from Mycobacterium tuberculosis sheds critical insight into host lipid utilization by M. tuberculosis.

Mycobacterium tuberculosis causes tuberculosis in humans and predominantly infects alveolar macrophages. To survive inside host lesions and to evade immune surveillance, this pathogen has developed many strategies. For example, M. tuberculosis uses host-derived lipids/fatty acids as nutrients for prolonged persistence within hypoxic host microenvironments. M. tuberculosis imports these metabolites through its respective transporters, and in the case of host fatty acids, a pertinent question arises: does M. tuberculosis have the enzyme(s) for cleavage of fatty acids from host lipids? We show herein that a previously uncharacterized membrane-associated M. tuberculosis protein encoded by Rv2672 is conserved exclusively in actinomycetes, exhibits both lipase and protease activities, is secreted into macrophages, and catalyzes host lipid hydrolysis. In light of these functions, we annotated Rv2672 as mycobacterial secreted hydrolase 1 (Msh1). Furthermore, we found that this enzyme is up-regulated both in an in vitro model of hypoxic stress and in a mouse model of M. tuberculosis infection, suggesting that the pathogen requires Msh1 under hypoxic conditions. Silencing Msh1 expression compromised the ability of M. tuberculosis to proliferate inside lipid-rich foamy macrophages but not under regular culture conditions in vitro, underscoring Msh1's importance for M. tuberculosis persistence in lipid-rich microenvironments. Of note, this is the first report providing insight into the mechanism of host lipid catabolism by an M. tuberculosis enzyme, augmenting our current understanding of how M. tuberculosis meets its nutrient requirements under hypoxic conditions.

MAPK-PPARα/γ signal transduction pathways are involved in Chlamydia pneumoniae-induced macrophage-derived foam cell formation.

Chlamydia pneumoniae (C. pneumoniae) is now widely accepted as an independent risk of atherosclerosis development. In this paper, our results showed that C. pneumoniae infection significantly increased the number of foam cells in LDL-treated THP-1 macrophages. C-Jun NH2 terminal kinase (JNK1/2) inhibitor SP600125 and extracellular signal-regulated kinase (ERK1/2) inhibitor PD98059 strongly inhibited C. pneumoniae-induced accumulation of lipid droplet, whereas p38 inhibitor SB203580 had no obvious effect on lipid accumulation. Furthermore, we found that C. pneumoniae not only stimulated the phosphorylation of Mitogen-activated protein kinase (MAPK) including JNK1/2, ERK1/2 and p38 but also down-regulated the expression of peroxisome proliferator-activated receptors (PPARγ and PPARα) at mRNA and protein levels. However, the phosphorylation of JNK1/2, ERK1/2 and p38 MAPK by C. pneumoniae was substantially reversed after PPARγ agonist (rosiglitazone) or PPARα agonist (fenofibrate) treatment while PPARγ inhibitor (GW9662) and PPARα antagonist (MK886) enhanced C. pneumoniae-induced phosphorylation of JNK1/2, ERK1/2 and p38. In addition, we demonstrated that C. pneumoniae-induced PPARγ and PPARα down-regulation were significantly suppressed by JNK1/2 inhibitor (SP600125) and ERK1/2 inhibitor (PD98059), but not p38 inhibitor (SB203580). These results first declare that MAPK-PPARα/γ reciprocal signal pathways are involved in C. pneumoniae, which induces foam cell formation, thus facilitating atherogenesis.

Mycobacterium tuberculosis modulates macrophage lipid-sensing nuclear receptors PPARγ and TR4 for survival.

Mycobacterium tuberculosis-macrophage interactions are key to pathogenesis and clearance of these bacteria. Although interactions between M. tuberculosis-associated lipids and TLRs, non-TLRs, and opsonic receptors have been investigated, interactions of these lipids and infected macrophage lipid repertoire with lipid-sensing nuclear receptors expressed in macrophages have not been addressed. In this study, we report that M. tuberculosis-macrophage lipids can interact with host peroxisome proliferator-activated receptor γ and testicular receptor 4 to ensure survival of the pathogen by modulating macrophage function. These two lipid-sensing nuclear receptors create a foamy niche within macrophage by modulating oxidized low-density lipoprotein receptor CD36, phagolysosomal maturation block by induction of IL-10, and a blunted innate response by alternative polarization of the macrophages, which leads to survival of M. tuberculosis. These results also suggest possible heterologous ligands for peroxisome proliferator-activated receptor γ and testicular receptor 4 and are suggestive of adaptive or coevolution of the host and pathogen. Relative mRNA expression levels of these receptors in PBMCs derived from clinical samples convincingly implicate them in tuberculosis susceptibility. These observations expose a novel paradigm in the pathogenesis of M. tuberculosis amenable for pharmacological modulation.

Foamy macrophages from tuberculous patients' granulomas constitute a nutrient-rich reservoir for M. tuberculosis persistence.

Tuberculosis (TB) is characterized by a tight interplay between Mycobacterium tuberculosis and host cells within granulomas. These cellular aggregates restrict bacterial spreading, but do not kill all the bacilli, which can persist for years. In-depth investigation of M. tuberculosis interactions with granuloma-specific cell populations are needed to gain insight into mycobacterial persistence, and to better understand the physiopathology of the disease. We have analyzed the formation of foamy macrophages (FMs), a granuloma-specific cell population characterized by its high lipid content, and studied their interaction with the tubercle bacillus. Within our in vitro human granuloma model, M. tuberculosis long chain fatty acids, namely oxygenated mycolic acids (MA), triggered the differentiation of human monocyte-derived macrophages into FMs. In these cells, mycobacteria no longer replicated and switched to a dormant non-replicative state. Electron microscopy observation of M. tuberculosis-infected FMs showed that the mycobacteria-containing phagosomes migrate towards host cell lipid bodies (LB), a process which culminates with the engulfment of the bacillus into the lipid droplets and with the accumulation of lipids within the microbe. Altogether, our results suggest that oxygenated mycolic acids from M. tuberculosis play a crucial role in the differentiation of macrophages into FMs. These cells might constitute a reservoir used by the tubercle bacillus for long-term persistence within its human host, and could provide a relevant model for the screening of new antimicrobials against non-replicating persistent mycobacteria.

Chlamydia pneumoniae-induced foam cell formation requires MyD88-dependent and -independent signaling and is reciprocally modulated by liver X receptor activation.

Chlamydia pneumoniae is detected by macrophages and other APCs via TLRs and can exacerbate developing atherosclerotic lesions, but how that occurs is not known. Liver X receptors (LXRs) centrally control reverse cholesterol transport, but also negatively modulate TLR-mediated inflammatory pathways. We isolated peritoneal macrophages from wild-type, TLR2, TLR3, TLR4, TLR2/4, MyD88, TRIF, MyD88/TRIF, and IFN regulatory factor 3 (IRF3) KO mice, treated them with live or UV-killed C. pneumoniae in the presence or absence of oxidized LDL, then measured foam cell formation. In some experiments, the synthetic LXR agonist GW3965 was added to macrophages infected with C. pneumoniae in the presence of oxidized LDL. Both live and UV-killed C. pneumoniae induced IRF3 activation and promoted foam cell formation in wild-type macrophages, whereas the genetic absence of TLR2, TLR4, MyD88, TRIF, or IRF3, but not TLR3, significantly reduced foam cell formation. C. pneumoniae-induced foam cell formation was significantly reduced by the LXR agonist GW3965, which in turn inhibited C. pneumoniae-induced IRF3 activation, suggesting a bidirectional cross-talk. We conclude that C. pneumoniae facilitates foam cell formation via activation of both MyD88-dependent and MyD88-independent (i.e., TRIF-dependent and IRF3-dependent) pathways downstream of TLR2 and TLR4 signaling and that TLR3 is not involved in this process. This mechanism could at least partly explain why infection with C. pneumoniae accelerates the development of atherosclerotic plaque and lends support to the proposal that LXR agonists might prove clinically useful in suppressing atherogenesis.

Mycobacterium tuberculosis Infection-Driven Foamy Macrophages and Their Implications in Tuberculosis Control as Targets for Host-Directed Therapy.

Tuberculosis (TB) is a leading cause of death worldwide following infection with Mycobacterium tuberculosis (Mtb), with 1.5 million deaths from this disease reported in 2018. Once the bacilli are inhaled, alveolar and interstitial macrophages become infected with Mtb and differentiate into lipid-laden foamy macrophages leading to lung inflammation. Thus, the presence of lipid-laden foamy macrophages is the hallmark of TB granuloma; these Mtb-infected foamy macrophages are the major niche for Mtb survival. The fate of TB pathogenesis is likely determined by the altered function of Mtb-infected macrophages, which initiate and mediate TB-related lung inflammation. As Mtb-infected foamy macrophages play central roles in the pathogenesis of Mtb, they may be important in the development of host-directed therapy against TB. Here, we summarize and discuss the current understanding of the alterations in alveolar and interstitial macrophages in the regulation of Mtb infection-induced immune responses. Metabolic reprogramming of lipid-laden foamy macrophages following Mtb infection or virulence factors are also summarized. Furthermore, we review the therapeutic interventions targeting immune responses and metabolic pathways, from in vitro, in vivo, and clinical studies. This review will further our understanding of the Mtb-infected foamy macrophages, which are both the major Mtb niche and therapeutic targets against TB.

The function of peroxisome proliferator-activated receptors PPAR-γ and PPAR-δ in Mycobacterium leprae-induced foam cell formation in host macrophages.

Leprosy is a chronic infectious disease caused by Mycobacterium leprae (M. leprae). In lepromatous leprosy (LL), skin macrophages, harboring extensive bacterial multiplication, gain a distinctive foamy appearance due to increased intracellular lipid load. To determine the mechanism by which M. leprae modifies the lipid homeostasis in host cells, an in vitro M. leprae infection system, using human macrophage precursor THP-1 cells and M. leprae prepared from the footpads of nude mice, was employed. RNA extracted from skin smear samples of patients was used to investigate host gene expressions before and after multidrug therapy (MDT). We found that a cluster of peroxisome proliferator-activated receptor (PPAR) target genes associated with adipocyte differentiation were strongly induced in M. leprae-infected THP-1 cells, with increased intracellular lipid accumulation. PPAR-δ and PPAR-γ expressions were induced by M. leprae infection in a bacterial load-dependent manner, and their proteins underwent nuclear translocalization after infection, indicating activation of PPAR signaling in host cells. Either PPAR-δ or PPAR-γ antagonist abolished the effect of M. leprae to modify host gene expressions and inhibited intracellular lipid accumulation in host cells. M. leprae-specific gene expressions were detected in the skin smear samples both before and after MDT, whereas PPAR target gene expressions were dramatically diminished after MDT. These results suggest that M. leprae infection activates host PPAR signaling to induce an array of adipocyte differentiation-associated genes, leading to accumulation of intracellular lipids to accommodate M. leprae parasitization. Certain PPAR target genes in skin lesions may serve as biomarkers for monitoring treatment efficacy.

Chlamydia pneumoniae induces macrophage-derived foam cell formation via PPAR alpha and PPAR gamma-dependent pathways.

In the presence of low density lipoprotein (LDL), Chlamydia pneumoniae induces macrophage-derived foam cell formation, a typical pathological feature of early atherosclerosis. However, its mechanism has not been fully understood. Peroxisome proliferator-activated receptors (PPARs) are key regulators of macrophage lipid metabolism. This study therefore investigated the role that PPAR alpha and PPAR gamma may play a role in C. pneumoniae-induced foam cell formation. Oil Red O staining and Lipid mass quantification showed that LDL-treated THP-1 macrophages infected with high doses of C. pneumoniae (5x10(5) and 1x10(6)IFU) resulted in the large accumulation of lipid droplets and markedly increased the ratio of intracellular cholesteryl ester (CE) to total cholesterol (TC) (>50%). The results of RT-PCR and Western blot indicated that C. pneumoniae infection dose-dependently suppressed the expression of PPAR alpha and PPAR gamma at mRNA and protein levels in LDL-treated THP-1 macrophages. PPAR alpha (fenofibrate) and PPAR gamma (rosiglitazone) agonists, inhibited the accumulation of intracellular CE by C. pneumoniae in a dose-dependent manner. Furthermore, C. pneumoniae-induced foam cell formation was significantly suppressed by higher doses of fenofibrate (20 and 50microM) and rosiglitazone (10 and 20microM). These results first reveal that C. pneumoniae induces foam cell formation via PPAR alpha and PPAR gamma-dependent pathway, which may contribute to its pro-atherogenic properties.

Transcriptome Profiling of Bovine Macrophages Infected by Mycobacterium avium spp. paratuberculosis Depicts Foam Cell and Innate Immune Tolerance Phenotypes.

Mycobacterium avium spp. paratuberculosis (MAP) is the causative agent of Johne's disease (JD), also known as paratuberculosis, in ruminants. The mechanisms of JD pathogenesis are not fully understood, but it is known that MAP subverts the host immune system by using macrophages as its primary reservoir. MAP infection in macrophages is often studied in healthy cows or experimentally infected calves, but reports on macrophages from naturally infected cows are lacking. In our study, primary monocyte-derived macrophages (MDMs) from cows diagnosed as positive (+) or negative (-) for JD were challenged in vitro with live MAP. Analysis using next-generation RNA sequencing revealed that macrophages from JD(+) cows did not present a definite pattern of response to MAP infection. Interestingly, a considerable number of genes, up to 1436, were differentially expressed in JD(-) macrophages. The signatures of the infection time course of 1, 4, 8, and 24 h revealed differential expression of ARG2, COL1A1, CCL2, CSF3, IL1A, IL6, IL10, PTGS2, PTX3, SOCS3, TNF, and TNFAIP6 among other genes, with major effects on host signaling pathways. While several immune pathways were affected by MAP, other pathways related to hepatic fibrosis/hepatic stellate cell activation, lipid homeostasis, such as LXR/RXR (liver X receptor/retinoid X receptor) activation pathways, and autoimmune diseases (rheumatoid arthritis or atherosclerosis) also responded to the presence of live MAP. Comparison of the profiles of the unchallenged MDMs from JD(+) vs. JD(-) cows showed that 868 genes were differentially expressed, suggesting that these genes were already affected before monocytes differentiated into macrophages. The downregulated genes predominantly modified the general cell metabolism by downregulating amino acid synthesis and affecting cholesterol biosynthesis and other energy production pathways while introducing a pro-fibrotic pattern associated with foam cells. The upregulated genes indicated that lipid homeostasis was already supporting fat storage in uninfected JD(+) MDMs. For JD(+) MDMs, differential gene expression expounds long-term mechanisms established during disease progression of paratuberculosis. Therefore, MAP could further promote disease persistence by influencing long-term macrophage behavior by using both tolerance and fat-storage states. This report contributes to a better understanding of MAP's controls over the immune cell response and mechanisms of MAP survival.

Giant cells lepromatous leprosy. Diffuse dermatitis with exuberant foreign body giant cells in treated lepromatous leprosy / Células gigantes en lepra lepromatosa. Dermatitis difusa con células gigantes tipo cuerpo extraño exuberantes en lepra lepromatosa tratada

Patients with lepromatous leprosy that have received treatment for many years usually get follow up biopsies for persistent skin lesions or positive bacilloscopy even if the values are lower than in the initial bacilloscopy. We report the case of a 48-year old woman with long-standing lepromatous leprosy of 15 years of evolution, with a bacterial index of 4 in the direct smear and the initial skin biopsy. The patient was treated with multidrug therapy for 32 months although the treatment recommended by the World Health Organization (WHO) is only for 12 months. A skin biopsy was taken to determine if there was an active disease. We observed a diffuse dermal inflammation with numerous foreign body giant cells and vacuolated macrophages (Virchow´s cells). These cells contained granular acid-fast material that was also positive with immunohistochemistry for BCG. There were fragmented bacilli and the BI was 2. These cells were also strongly positive for CD68. The biopsy was interpreted as a residual form of lepromatous leprosy that did not require further multidrug therapy. We have observed similar histological profiles in several cases. The lack of clinical data makes it a histological challenge. The accumulation of lipids in these giant cells is due to bacillary destruction and fusion of vacuolated macrophages. We discuss here the role of bacillary and host lipids in the pathogenesis of lepromatous leprosy. We concluded that there was no need to extend the 12-month multidrug therapy recommended by WHO.

Los pacientes con lepra lepromatosa (LL) que han recibido tratamiento durante años, usualmente tienen seguimiento con biopsias de piel para lesiones persistentes o con baciloscopia positiva, con valores menores a los iniciales. Presentamos una mujer de 48 años con LL de 15 años de evolución, con índice bacilar (IB) 4 en el extendido directo y en la biopsia, que recibió terapia multidroga durante 32 meses, aunque el tratamiento recomendado por la Organización mundial de la salud (OMS) es de 12 meses. Se tomó una biopsia de piel para determinar si la enfermedad estaba activa. Se observó inflamación dérmica difusa con numerosas células gigantes tipo cuerpo extraño y macrófagos vacuolados (células de Virchow). Estas células, CD68 positivas, contenían material granular ácido-alcohol resistente, positivo con inmunohistoquímica para BCG. Se encontraron bacilos fragmentados y el IB fue de 2. Se interpretó como una forma residual de LL y que la paciente no requería MDT adicional. Este perfil histológico lo hemos observado en casos similares. Sin datos clínicos estas biopsias son un reto diagnóstico. La acumulación de lípidos en estas células gigantes se debe a la destrucción bacilar y a la fusión de macrófagos vacuolados. Revisamos el papel de los lípidos del bacilo y del huésped en la patogénesis de la LL. En estos casos no es necesario extender los 12 meses de MDT recomendados por la OMS. En el seguimiento de los pacientes se recomienda contar con los hallazgos clínicos, la baciloscopia, la biopsia anual de piel y los títulos IgM anti-glicolípido fenólico.

Amalgamation of Chlamydia pneumoniae inclusions with lipid droplets in foam cells in human atherosclerotic plaque.

Chlamydia pneumoniae (Chlamydophila pneumoniae) infect macrophages and accelerates foam cell formation in in vitro experiments, but whether this might occur in human atherosclerosis is unknown. In the present study, we examined 17 carotid artery segments, obtained by endarterectomy, in which the presence of C. pneumoniae was confirmed by both polymerase chain reaction and immunohistochemistry. Electron microscopy demonstrated the presence of structures with the appearance of elementary, reticulate and aberrant bodies of C. pneumoniae in the cytoplasm of macrophage foam cells. The volume of the cytoplasm that was free from vacuoles and lipid droplets in C. pneumoniae-infected foam cells was dramatically reduced, and a phenomenon of the amalgamation of C. pneumoniae inclusions with lipid droplets was detected. Double immunohistochemistry showed that C. pneumoniae-infected foam cells contained a large number of oxidized low-density lipoproteins. The observations provide support to the hypothesis that C. pneumoniae could affect foam cell formation in human atherosclerosis.

Chewing the fat: lipid metabolism and homeostasis during M. tuberculosis infection.

The interplay between Mycobacterium tuberculosis lipid metabolism, the immune response and lipid homeostasis in the host creates a complex and dynamic pathogen-host interaction. Advances in imaging and metabolic analysis techniques indicate that M. tuberculosis preferentially associates with foamy cells and employs multiple physiological systems to utilize exogenously derived fatty-acids and cholesterol. Moreover, novel insights into specific host pathways that control lipid accumulation during infection, such as the PPARγ and LXR transcriptional regulators, have begun to reveal mechanisms by which host immunity alters the bacterial micro-environment. As bacterial lipid metabolism and host lipid regulatory pathways are both important, yet inherently complex, components of active tuberculosis, delineating the heterogeneity in lipid trafficking within disease states remains a major challenge for therapeutic design.

Signaling events in pathogen-induced macrophage foam cell formation.

Macrophage foam cell formation is a key event in atherosclerosis. Several triggers induce low-density lipoprotein (LDL) uptake by macrophages to create foam cells, including infections with Porphyromonas gingivalis and Chlamydia pneumoniae, two pathogens that have been linked to atherosclerosis. While gene regulation during foam cell formation has been examined, comparative investigations to identify shared and specific pathogen-elicited molecular events relevant to foam cell formation are not well documented. We infected mouse bone marrow-derived macrophages with P. gingivalis or C. pneumoniae in the presence of LDL to induce foam cell formation, and examined gene expression using an atherosclerosis pathway targeted plate array. We found over 30 genes were significantly induced in response to both pathogens, including PPAR family members that are broadly important in atherosclerosis and matrix remodeling genes that may play a role in plaque development and stability. Six genes mainly involved in lipid transport were significantly downregulated. The response overall was remarkably similar and few genes were regulated in a pathogen-specific manner. Despite very divergent lifestyles, P. gingivalis and C. pneumoniae activate similar gene expression profiles during foam cell formation that may ultimately serve as targets for modulating infection-elicited foam cell burden, and progression of atherosclerosis.

Porphyromonas gingivalis infected macrophages upregulate CD36 expression via ERK/NF-κB pathway.

CD36, a scavenger receptor, plays an important role in the progression of atherosclerosis through its interaction with oxidized low-density lipoprotein (ox-LDL). Porphyromonas gingivalis (P. gingivalis, Pg) has been shown to promote macrophage-derived foam cell formation by affecting the expression of CD36. However, the regulatory role of CD36 in macrophages infected with Pg remains largely unknown. Therefore, the aim of the present study was to explore the molecular mechanism of Pg induced CD36 expression in macrophages. Our results showed that Pg promoted ox-LDL uptake by macrophages and the formation of foam cells. Pg infection increased CD36 mRNA and protein levels in ox-LDL-untreated macrophages. Moreover, small interferon RNA (siRNA) targeting CD36 significantly reduced foam cell formation induced by Pg. Additionally, Pg stimulated nuclear translocation of p65, which directly bound to the promoters of CD36 to facilitate its transcription. Inhibition of p65, NF-κB or ERK1/2 blocked Pg-induced CD36 production; whereas, overexpression of NF-κB subunits p65 and p50 upregulated CD36. Furthermore, Ras inhibitors significantly attenuated ERK1/2 activation and CD36 expression. Taken together, the data indicated that stimulation of the ERK/NF-κB pathway by Pg led to transactivation of the CD36 promoters, thereby upregulating CD36 expression in the infected macrophages. These findings may help design new treatment strategies in atherosclerosis.

Foam cell formation inhibits growth of Chlamydia pneumoniae but does not attenuate Chlamydia pneumoniae-induced secretion of proinflammatory cytokines.

BACKGROUND: It has not yet been determined whether lipid-loaded macrophages (foam cells), a major cellular component of atherosclerotic lesions, have the capacity to support growth of Chlamydia pneumoniae and be activated to secrete proinflammatory cytokines in response to C pneumoniae infection. METHODS AND RESULTS: Lipid loading of RAW 264.7 cells and mouse peritoneal macrophages with either oxidized or acetylated LDL significantly inhibits the growth of C pneumoniae. Modified forms of LDL are not directly toxic to C pneumoniae and do not inhibit either the initial binding or internalization of C pneumoniae by macrophages. Lipid loading does not reduce infection of macrophages with Chlamydia trachomatis. Treatment of lipid-loaded macrophages with live, heat-killed, or UV-inactivated C pneumoniae stimulates secretion of cytokines. C pneumoniae also induces expression of the mRNA for tumor necrosis factor-alpha in foam cells despite inhibition of nuclear factor-kappaB binding to DNA by prior treatment with oxidized LDL. CONCLUSIONS: Foam cell formation is not conducive to growth of C pneumoniae but does not inhibit the C pneumoniae-induced secretion of proinflammatory cytokines.