Lipid body accumulation within leukocytes is a common feature in both clinical and experimental infectious, neoplasic and other inflammatory conditions. Here, we will review the contemporary evidence related to the biogenesis and structure of leukocyte lipid bodies (also known as lipid droplets) as inflammatory organelles. Studies of leukocyte lipid bodies are providing functional, ultrastructural and protein compositional evidences that lipid bodies are not solely storage depots of neutral lipid. Over the past years substantial progresses have been made to demonstrate that lipid body biogenesis is a highly regulated process, that culminate in the compartmentalization of a specific set of proteins and lipids, that place leukocyte lipid bodies as inducible cytoplasmic organelles with roles in cell signaling and activation, regulation of lipid metabolism, membrane trafficking and control of the synthesis and secretion of inflammatory mediators. Pertinent to the roles of lipid bodies in inflammation and cell signaling, enzymes involved in eicosanoid synthesis are localized at lipid bodies and lipid bodies are sites for eicosanoid generation. Collectively, lipid bodies in leukocytes are emerging as critical regulators of different inflammatory diseases, key markers of leukocyte activation and attractive targets for novel anti-inflammatory therapies.

Macrophages have important roles in both lipid metabolism and inflammation and are central to immunity to intracellular pathogens. Foam-like, lipid-laden macrophages are present during the course of mycobacterial infection and have recently been implicated in mycobacterial pathogenesis. In this study, we analyzed the molecular mechanisms underlying the formation of macrophage lipid bodies (lipid droplets) during Mycobacterium bovis bacillus Calmette-Guérin (BCG) infection, focusing on the role of the lipid-activated nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ). We found that BCG infection induced increased expression of PPARγ that paralleled the augmented lipid body formation and PGE2 synthesis in mouse peritoneal macrophages. BCG-induced PPARγ expression and lipid body formation were diminished in macrophages from TLR2-deficient mice, suggesting a key role for TLR2. The function of PPARγ in modulating BCG infection was demonstrated by the capacity of the PPARγ agonist BRL49653 to potentiate lipid body formation and PGE2 production; furthermore, pretreatment with the PPARγ antagonist GW9662 inhibited BCG-induced lipid body formation and PGE2 production. BCG-induced MIP-1α, IL12p70, TNF-α, and IL6 production was not inhibited by GW9662 treatment. Nonpathogenic Mycobacterium smegmatis failed to induce PPARγ expression or lipid body formation. Moreover, inhibition of PPARγ by GW9662 enhanced the mycobacterial killing capacity of macrophages. Our findings show that PPARγ is involved in lipid body biogenesis, unravels a cross-talk between the innate immune receptor TLR2 and the lipid-activated nuclear receptor PPARγ that coordinates lipid metabolism and inflammation in BCG-infected macrophages, thereby potentially affecting mycobacterial pathogenesis.

The implication of inflammation in pathophysiology of several type of cancers has been under intense investigation. Omega-3 fatty acids can modulate inflammation and present anticancer effects, promoting cancer cell death. Pyroptosis is an inflammation related cell death and so far, the function of docosahexaenoic acid (DHA) in pyroptosis cell death has not been described. This study investigated the role of DHA in triggering pyroptosis activation in breast cancer cells. MDA-MB-231 breast cancer cells were supplemented with DHA and inflammation cell death was analyzed. DHA-treated breast cancer cells triggered increased caspase-1and gasdermin D activation, enhanced IL-1β secretion, translocated HMGB1 towards the cytoplasm, and membrane pore formation when compared to untreated cells, suggesting DHA induces pyroptosis programmed cell death in breast cancer cells. Moreover, caspase-1 inhibitor (YVAD) could protect breast cancer cells from DHA-induced pyroptotic cell death. In addition, membrane pore formation showed to be a lysosomal damage and ROS formation-depended event in breast cancer cells. DHA triggered pyroptosis cell death in MDA-MB-231by activating several pyroptosis markers in these cells. This is the first study that shows the effect of DHA triggering pyroptosis programmed cell death in breast cancer cells and it could improve the understanding of the omega-3 supplementation during breast cancer treatment.

COVID-19, caused by SARS-CoV-2, is characterized by pneumonia, lymphopenia, exhausted lymphocytes and a cytokine storm. Several reports from around the world have identified obesity and severe obesity as one of the strongest risk factors for COVID-19 hospitalization and mechanical ventilation. Moreover, countries with greater obesity prevalence have a higher morbidity and mortality risk of developing serious outcomes from COVID-19. The understanding of how this increased susceptibility of the people with obesity to develop severe forms of the SARS-CoV-2 infection occurs is crucial for implementing appropriate public health and therapeutic strategies to avoid COVID-19 severe symptoms and complications in people living with obesity. We hypothesize here that increased ACE2 expression in adipose tissue displayed by people with obesity may increase SARS-CoV-2 infection and accessibility to this tissue. Individuals with obesity have increased white adipose tissue, which may act as a reservoir for a more extensive viral spread with increased shedding, immune activation and pro-inflammatory cytokine amplification. Here we discuss how obesity is related to a pro-inflammatory and metabolic dysregulation, increased SARS-CoV-2 host cell entry in adipose tissue and induction of hypercoagulopathy, leading people with obesity to develop severe forms of COVID-19 and also death. Taken together, it may be crucial to better explore the role of visceral adipose tissue in the inflammatory response to SARS-CoV-2 infection and investigate the potential therapeutic effect of using specific target anti-inflammatories (canakinumab or anakinra for IL-1β inhibition; anti-IL-6 antibodies for IL-6 inhibition), anticoagulant or anti-diabetic drugs in COVID-19 treatment of people with obesity. Defining the immunopathological changes in COVID-19 patients with obesity can provide prominent targets for drug discovery and clinical management improvement.

Prostaglandin (PG)D2 is a key mediator of allergic inflammatory diseases that is mainly synthesized by mast cells, which constitutively express high levels of the terminal enzyme involved in PGD2 synthesis, the hematopoietic PGD synthase (H-PGDS). Here, we investigated whether eosinophils are also able to synthesize, and therefore, supply biologically active PGD2. PGD2 synthesis was evaluated within human blood eosinophils, in vitro-differentiated mouse eosinophils, and eosinophils infiltrating inflammatory site of mouse allergic reaction. Biological function of eosinophil-derived PGD2 was studied by employing inhibitors of synthesis and activity. Constitutive expression of H-PGDS was found within non-stimulated human circulating eosinophils. Acute stimulation of human eosinophils with A23187 (0.1 – 5 μM) evoked PGD2 synthesis, which was located at the nuclear envelope and was inhibited by pre-treatment with HQL-79 (10 μM), a specific H-PGDS inhibitor. Pre-stimulation of human eosinophils with arachidonic acid (AA; 10 μM) or human eotaxin (6 nM) also enhanced HQL-79-sensitive PGD2 synthesis, which, by acting on membrane-expressed specific receptors (DP1 and DP2), displayed an autocrine/paracrine ability to trigger leukotriene (LT)C4 synthesis and lipid body biogenesis, hallmark events of eosinophil activation. In vitro-differentiated mouse eosinophils also synthesized paracrine/autocrine active PGD2 in response to AA stimulation. In vivo, at late time point of the allergic reaction, infiltrating eosinophils found at the inflammatory site appeared as an auxiliary PGD2-synthesizing cell population. Our findings reveal that eosinophils are indeed able to synthesize and secrete PGD2, hence representing during allergic inflammation an extra cell source of PGD2, which functions as an autocrine signal for eosinophil activation.

BackgroundThe interest in the mechanisms involved in Toxoplasma gondii lipid acquisition has steadily increased during the past few decades, but it remains not completely understood. Here, we investigated the biogenesis and the fate of lipid droplets (LD) of skeletal muscle cells (SkMC) during their interaction with T. gondii by confocal and electron microscopy. We also evaluated whether infected SkMC modulates the production of prostaglandin E2 (PGE2), cytokines interleukin-12 (IL-12) and interferon-gamma (INF-g), and also the cyclooxygenase-2 (COX-2) gene induction.MethodsPrimary culture of skeletal muscle cells were infected with tachyzoites of T. gondii and analysed by confocal microscopy for observation of LD. Ultrastructural cytochemistry was also used for lipid and sarcoplasmatic reticulum (SR) detection. Dosage of cytokines (IL-12 and INF-g) by ELISA technique and enzyme-linked immunoassay (EIA) for PGE2 measurement were employed. The COX-2 gene expression analysis was performed by real time reverse transcriptase polymerase chain reaction (qRT-PCR).ResultsWe demonstrated that T. gondii infection of SkMC leads to increase in LD number and area in a time course dependent manner. Moreover, the ultrastructural analysis demonstrated that SR and LD are in direct contact with parasitophorous vacuole membrane (PVM), within the vacuolar matrix, around it and interacting directly with the membrane of parasite, indicating that LD are recruited and deliver their content inside the parasitophorous vacuole (PV) in T. gondii-infected SkMC. We also observed a positive modulation of the production of IL-12 and IFN-g, increase of COX-2 mRNA levels in the first hour of T. gondii-SkMC interaction and an increase of prostaglandin E2 (PGE2) synthesis from 6 h up to 48 h of infection.ConclusionsTaken together, the close association between SR and LD with PV could represent a source of lipids as well as other nutrients for the parasite survival, and together with the increased levels of IL-12, INF-g and inflammatory indicators PGE2 and COX-2 might contribute to the establishment and maintenance of chronic phase of the T. gondii infection in muscle cell.

Paracoccidioides brasiliensis is the etiologic agent of paracoccidioidomycosis (PCM), the most prevalent systemic mycosis that is geographically confined to Latin America. The pro-inflammatory cytokine IL-1β that is mainly derived from the activation of the cytoplasmic multiprotein complex inflammasome is an essential host factor against opportunistic fungal infections; however, its role in infection with a primary fungal pathogen, such as P. brasiliensis, is not well understood. In this study, we found that murine bone marrow-derived dendritic cells responded to P. brasiliensis yeast cells infection by releasing IL-1β in a spleen tyrosine kinase (Syk), caspase-1 and NOD-like receptor (NLR) family member NLRP3 dependent manner. In addition, P. brasiliensis-induced NLRP3 inflammasome activation was dependent on potassium (K+) efflux, reactive oxygen species production, phagolysosomal acidification and cathepsin B release. Finally, using mice lacking the IL-1 receptor, we demonstrated that IL-1β signaling has an important role in killing P. brasiliensis by murine macrophages. Altogether, our results demonstrate that the NLRP3 inflammasome senses and responds to P. brasiliensis yeast cells infection and plays an important role in host defense against this fungus.

Human CD1a mediates foreign antigen recognition by a T cell clone, but the nature of possible T cell receptor interactions with CD1a-lipid are unknown. After incubating CD1a with a mycobacterial lipopeptide antigen, dideoxymycobactin (DDM), we identified and measured binding to a recombinant TCR (TRAV3/ TRBV3-1, KD ≈ 100µM). Detection of ternary CD1a-lipid-TCR interactions enabled development of CD1a tetramers and CD1a multimers with carbohydrate backbones (dextramers), which specifically stained T cells using a mechanism that was dependent on the precise stereochemistry of the peptide backbone and was blocked with a soluble TCR. Further, sorting of human T cells from unrelated tuberculosis patients for bright DDM-dextramer staining allowed recovery of T cells that were activated by CD1a and DDM. These studies demonstrate that the mechanism of T cell activation by lipopeptides occurs via ternary interactions of CD1a-antigen-TCR. Further, these studies demonstrate the existence of lipopeptide specific T cells in humans ex vivo.