Lipidomic scanning of self-lipids identifies headless antigens for natural killer T cells.

To broadly measure the spectrum of cellular self-antigens for natural killer T cells (NKT), we developed a sensitive lipidomics system to analyze lipids trapped between CD1d and NKT T cell receptors (TCRs). We captured diverse antigen complexes formed in cells from natural endogenous lipids, with or without inducing endoplasmic reticulum (ER) stress. After separating protein complexes with no, low, or high CD1d-TCR interaction, we eluted lipids to establish the spectrum of self-lipids that facilitate this interaction. Although this unbiased approach identified fifteen molecules, they clustered into only two related groups: previously known phospholipid antigens and unexpected neutral lipid antigens. Mass spectrometry studies identified the neutral lipids as ceramides, deoxyceramides, and diacylglycerols, which can be considered headless lipids because they lack polar headgroups that usually form the TCR epitope. The crystal structure of the TCR-ceramide-CD1d complex showed how the missing headgroup allowed the TCR to predominantly contact CD1d, supporting a model of CD1d autoreactivity. Ceramide and related headless antigens mediated physiological TCR binding affinity, weak NKT cell responses, and tetramer binding to polyclonal human and mouse NKT cells. Ceramide and sphingomyelin are oppositely regulated components of the "sphingomyelin cycle" that are altered during apoptosis, transformation, and ER stress. Thus, the unique molecular link of ceramide to NKT cell response, along with the recent identification of sphingomyelin blockers of NKT cell activation, provide two mutually reinforcing links for NKT cell response to sterile cellular stress conditions.

Distinct T cell subsets in adipose tissue are associated with obesity.

Adipose tissue inflammation is a driving factor for the development of obesity-associated metabolic disturbances, and a role of adipose tissue T cells in initiating the pro-inflammatory signaling is emerging. However, data on human adipose tissue T cells in obesity are limited, reflected by the lack of phenotypic markers to define tissue-resident T cell subsets. In this study, we performed a deep characterization of T cells in blood and adipose tissue depots using multicolor flow cytometry and RNA sequencing. We identified distinct subsets of T cells associated with obesity expressing the activation markers, CD26 and CCR5, and obesity-specific genes that are potentially engaged in activating pro-inflammatory pathway, including ceramide signaling, autophagy, and IL-6 signaling. These findings increase our knowledge on the heterogeneity of T cells in adipose tissue and on subsets that may play a role in obesity-related pathogenesis.

Implications of Serum Anti-Ceramide Antibodies and Interleukin 4 on Nerve Damage and Physical Impairments Among Leprotic Patients: A Case-Controlled Study.

BACKGROUND: Leprosy is a chronic granulomatous disease affecting skin and nerves with a range of clinical and immunological responses. OBJECTIVES: The study aimed to identify levels of IL-4 and antibodies to ceramide in the sera of leprosy patients and healthy subjects using enzyme linked immunosorbent assay (ELISA) to evaluate their possible role in disease severity and their correlation to nerve involvement and physical impairments. METHODS: This study included 25 patients with multibacillary leprosy, 25 with paucibacillary, and 25 healthy controls who were subjected to history taking, clinical examination, and identification of sites and morphology of skin lesions, nerve examination, eye examination, as well as sensory examination. Slit skin smear examination was used for diagnosing paucibacillary (PB) and multibacillary (MB) leprosy cases. Anti-ceramide antibody (ACA) and IL-4 titers were estimated and correlated with the type of leprosy, disease duration, nerve damage, and disabilities. RESULTS: Serum ACA and IL-4 levels were significantly higher in MB than its level in PB leprotic patients and controls. A significant positive correlation was established between nerve affection; physical impairments and serum levels of ACA and IL-4. CONCLUSION: Levels of ACA and IL-4 can impact nerve affection in leprotic patients and can serve as potential biomarkers of disease progression J Drugs Dermatol. 2022;21(3):284-291. doi:10.36849/JDD.5543.

Anti-ceramide single-chain variable fragment mitigates radiation GI syndrome mortality independent of DNA repair.

After 9/11, threat of nuclear attack on American urban centers prompted government agencies to develop medical radiation countermeasures to mitigate hematopoietic acute radiation syndrome (H-ARS) and higher-dose gastrointestinal acute radiation syndrome (GI-ARS) lethality. While repurposing leukemia drugs that enhance bone marrow repopulation successfully treats H-ARS in preclinical models, no mitigator potentially deliverable under mass casualty conditions preserves GI tract. Here, we report generation of an anti-ceramide 6B5 single-chain variable fragment (scFv) and show that s.c. 6B5 scFv delivery at 24 hours after a 90% lethal GI-ARS dose of 15 Gy mitigated mouse lethality, despite administration after DNA repair was complete. We defined an alternate target to DNA repair, an evolving pattern of ceramide-mediated endothelial apoptosis after radiation, which when disrupted by 6B5 scFv, initiates a durable program of tissue repair, permitting crypt, organ, and mouse survival. We posit that successful preclinical development will render anti-ceramide 6B5 scFv a candidate for inclusion in the Strategic National Stockpile for distribution after a radiation catastrophe.

Ceramide in apoptosis and oxidative stress in allergic inflammation and asthma.

BACKGROUND: Nothing is known about the mechanisms by which increased ceramide levels in the lung contribute to allergic responses and asthma severity. OBJECTIVE: We sought to investigate the functional role of ceramide in mouse models of allergic airway disease that recapitulate the cardinal clinical features of human allergic asthma. METHODS: Allergic airway disease was induced in mice by repeated intranasal administration of house dust mite or the fungal allergen Alternaria alternata. Processes that can be regulated by ceramide and are important for severity of allergic asthma were correlated with ceramide levels measured by mass spectrometry. RESULTS: Both allergens induced massive pulmonary apoptosis and also significantly increased reactive oxygen species in the lung. Prevention of increases in lung ceramide levels mitigated allergen-induced apoptosis, reactive oxygen species, and neutrophil infiltration. In contrast, dietary supplementation of the antioxidant α-tocopherol decreased reactive oxygen species but had no significant effects on elevation of ceramide level or apoptosis, indicating that the increases in lung ceramide levels in allergen-challenged mice are not mediated by oxidative stress. Moreover, specific ceramide species were altered in bronchoalveolar lavage fluid from patients with severe asthma compared with in bronchoalveolar lavage fluid from individuals without asthma. CONCLUSION: Our data suggest that elevation of ceramide level after allergen challenge contributes to the apoptosis, reactive oxygen species generation, and neutrophilic infiltrate that characterize the severe asthmatic phenotype. Ceramide might be the trigger of formation of Creola bodies found in the sputum of patients with severe asthma and could be a biomarker to optimize diagnosis and to monitor and improve clinical outcomes in this disease.

Cancer stem cells and ceramide signaling: the cutting edges of immunotherapy.

The multipotent, self renewing "cancer stem cells" (CSCs), a small population within tumor microenvironment facilitates transformed cells to grow and propagate within the body. The CSCs are discovered as resistant to the chemotherapeutic drug with distinct immunological characteristics. In recent years, immunologically targeting CSCs have emerged as an integral part of effective and successful cancer therapy. CSCs notably exhibit dysregulation in conventional sub-cellular sphingolipid metabolism. Recently, ceramide decaying enzymes have been shown to activate alternative ceramide signaling pathways leading to reduction in efficacy of the chemotherapeutic drugs. Therefore, a control over ceramide mediated modulations of CSCs offers an attractive dimension of effective cancer treatment strategy in future. In this review, we focused on the recent findings on broad spectrum of ceramide mediated signaling in CSCs within the tumor niche and their role in potential cancer immunotherapy.

CCR5 deficiency impairs CD4+ T-cell memory responses and antigenic sensitivity through increased ceramide synthesis.

CCR5 is not only a coreceptor for HIV-1 infection in CD4+ T cells, but also contributes to their functional fitness. Here, we show that by limiting transcription of specific ceramide synthases, CCR5 signaling reduces ceramide levels and thereby increases T-cell antigen receptor (TCR) nanoclustering in antigen-experienced mouse and human CD4+ T cells. This activity is CCR5-specific and independent of CCR5 co-stimulatory activity. CCR5-deficient mice showed reduced production of high-affinity class-switched antibodies, but only after antigen rechallenge, which implies an impaired memory CD4+ T-cell response. This study identifies a CCR5 function in the generation of CD4+ T-cell memory responses and establishes an antigen-independent mechanism that regulates TCR nanoclustering by altering specific lipid species.

Multiple Sclerosis: Melatonin, Orexin, and Ceramide Interact with Platelet Activation Coagulation Factors and Gut-Microbiome-Derived Butyrate in the Circadian Dysregulation of Mitochondria in Glia and Immune Cells.

Recent data highlight the important roles of the gut microbiome, gut permeability, and alterations in mitochondria functioning in the pathophysiology of multiple sclerosis (MS). This article reviews such data, indicating two important aspects of alterations in the gut in the modulation of mitochondria: (1) Gut permeability increases toll-like receptor (TLR) activators, viz circulating lipopolysaccharide (LPS), and exosomal high-mobility group box (HMGB)1. LPS and HMGB1 increase inducible nitric oxide synthase and superoxide, leading to peroxynitrite-driven acidic sphingomyelinase and ceramide. Ceramide is a major driver of MS pathophysiology via its impacts on glia mitochondria functioning; (2) Gut dysbiosis lowers production of the short-chain fatty acid, butyrate. Butyrate is a significant positive regulator of mitochondrial function, as well as suppressing the levels and effects of ceramide. Ceramide acts to suppress the circadian optimizers of mitochondria functioning, viz daytime orexin and night-time melatonin. Orexin, melatonin, and butyrate increase mitochondria oxidative phosphorylation partly via the disinhibition of the pyruvate dehydrogenase complex, leading to an increase in acetyl-coenzyme A (CoA). Acetyl-CoA is a necessary co-substrate for activation of the mitochondria melatonergic pathway, allowing melatonin to optimize mitochondrial function. Data would indicate that gut-driven alterations in ceramide and mitochondrial function, particularly in glia and immune cells, underpin MS pathophysiology. Aryl hydrocarbon receptor (AhR) activators, such as stress-induced kynurenine and air pollutants, may interact with the mitochondrial melatonergic pathway via AhR-induced cytochrome P450 (CYP)1b1, which backward converts melatonin to N-acetylserotonin (NAS). The loss of mitochnodria melatonin coupled with increased NAS has implications for altered mitochondrial function in many cell types that are relevant to MS pathophysiology. NAS is increased in secondary progressive MS, indicating a role for changes in the mitochondria melatonergic pathway in the progression of MS symptomatology. This provides a framework for the integration of diverse bodies of data on MS pathophysiology, with a number of readily applicable treatment interventions, including the utilization of sodium butyrate.

Translational Approaches Targeting Ceramide Generation From Sphingomyelin in T Cells to Modulate Immunity in Humans.

In T cells, as in all other cells of the body, sphingolipids form important structural components of membranes. Due to metabolic modifications, sphingolipids additionally play an active part in the signaling of cell surface receptors of T cells like the T cell receptor or the co-stimulatory molecule CD28. Moreover, the sphingolipid composition of their membranes crucially affects the integrity and function of subcellular compartments such as the lysosome. Previously, studying sphingolipid metabolism has been severely hampered by the limited number of analytical methods/model systems available. Besides well-established high resolution mass spectrometry new tools are now available like novel minimally modified sphingolipid subspecies for click chemistry as well as recently generated mouse mutants with deficiencies/overexpression of sphingolipid-modifying enzymes. Making use of these tools we and others discovered that the sphingolipid sphingomyelin is metabolized to ceramide to different degrees in distinct T cell subpopulations of mice and humans. This knowledge has already been translated into novel immunomodulatory approaches in mice and will in the future hopefully also be applicable to humans. In this paper we are, thus, summarizing the most recent findings on the impact of sphingolipid metabolism on T cell activation, differentiation, and effector functions. Moreover, we are discussing the therapeutic concepts arising from these insights and drugs or drug candidates which are already in clinical use or could be developed for clinical use in patients with diseases as distant as major depression and chronic viral infection.

Roles of Ceramides and Other Sphingolipids in Immune Cell Function and Inflammation.

Ceramides are bioactive sphingolipids that support the structure of the plasma membrane and mediate numerous cell-signaling events in eukaryotic cells. The finding that ceramides act as second messengers transducing cellular signals has attracted substantial attention in several fields of Biology. Since all cells contain lipid plasma membranes, the impact of various ceramides, ceramide synthases, ceramide metabolites, and other sphingolipids has been implicated in a vast range of cellular functions including, migration, proliferation, response to external stimuli, and death. The roles of lipids in these functions widely differ among the diverse cell types. Herein, we discuss the roles of ceramides and other sphingolipids in mediating the function of various immune cells; particularly dendritic cells, neutrophils, and macrophages. In addition, we highlight the main studies describing effects of ceramides in inflammation, specifically in various inflammatory settings including insulin resistance, graft-versus-host disease, immune suppression in cancer, multiple sclerosis, and inflammatory bowel disease.

The ORMDL3 asthma susceptibility gene regulates systemic ceramide levels without altering key asthma features in mice.

BACKGROUND: Genome-wide association studies in asthma have repeatedly identified single nucleotide polymorphisms in the ORM (yeast)-like protein isoform 3 (ORMDL3) gene across different populations. Although the ORM homologues in yeast are well-known inhibitors of sphingolipid synthesis, it is still unclear whether and how mammalian ORMDL3 regulates sphingolipid metabolism and whether altered sphingolipid synthesis would be causally related to asthma risk. OBJECTIVE: We sought to examine the in vivo role of ORMDL3 in sphingolipid metabolism and allergic asthma. METHODS: Ormdl3-LacZ reporter mice, gene-deficient Ormdl3-/- mice, and overexpressing Ormdl3Tg/wt mice were exposed to physiologically relevant aeroallergens, such as house dust mite (HDM) or Alternaria alternata, to induce experimental asthma. Mass spectrometry-based sphingolipidomics were performed, and airway eosinophilia, TH2 cytokine production, immunoglobulin synthesis, airway remodeling, and bronchial hyperreactivity were measured. RESULTS: HDM challenge significantly increased levels of total sphingolipids in the lungs of HDM-sensitized mice compared with those in control mice. In Ormdl3Tg/wt mice the allergen-induced increase in lung ceramide levels was significantly reduced, whereas total sphingolipid levels were not affected. Conversely, in liver and serum, levels of total sphingolipids, including ceramides, were increased in Ormdl3-/- mice, whereas they were decreased in Ormdl3Tg/wt mice. This difference was independent of allergen exposure. Despite these changes, all features of asthma were identical between wild-type, Ormdl3Tg/wt, and Ormdl3-/- mice across several models of experimental asthma. CONCLUSION: ORMDL3 regulates systemic ceramide levels, but genetically interfering with Ormdl3 expression does not result in altered experimental asthma.

The impact of recent advances in lipidomics and redox lipidomics on dermatological research.

Dermatological research is a major beneficiary of the rapidly developing advances in lipid analytic technology and of bioinformatic tools which help to decipher and interpret the accumulating big lipid data. At its interface with the environment, the epidermis develops a blend of lipids that constitutes the epidermal lipid barrier, essential for the protection from water loss and entry of dangerous noxae. Apart from their structural role in the barrier, novel intra- and inter-cellular signaling functions of lipids and their oxidation products have been uncovered in most cutaneous cell types over the last decades, and the discovery rate has been boosted by the advent of high resolution and -throughput mass spectrometric techniques. Our understanding of epidermal development has benefited from studies on fetal surface lipids, which appear to signal for adaptation to desiccation post partum, and from studies on the dynamics of epidermal lipids during adjustment to the atmosphere in the first months of life. At birth, external insults begin to challenge the skin and its lipids, and recent years have yielded ample insights into the dynamics of lipid synthesis and -oxdiation after UV exposure, and upon contact with sensitizers and irritants. Psoriasis and atopic dermatitis are the most common chronic inflammatory skin diseases, affecting at least 3% and 7% of the global population, respectively. Consequently, novel (redox-) lipidomic techniques have been applied to study systemic and topical lipid abnormalities in patient cohorts. These studies have refined the knowledge on eicosanoid signaling in both diseases, and have identified novel biomarkers and potential disease mediators, such as lipid antigens recognized by psoriatic T cells, as well as ceramide species, which specifically correlate with atopic dermatitis severity. Both biomarkers have yielded novel mechanistic insights. Finally, the technological progress has enabled studies to be performed that have monitored the consequences of diet, lifestyle, therapy and cosmetic intervention on the skin lipidome, highlighting the translational potential of (redox-) lipidomics in dermatology.

Acid Sphingomyelinase-Ceramide System in Bacterial Infections.

Acid sphingomyelinase hydrolyzes sphingomyelin to ceramide and phosphorylcholine. Ceramide molecules spontaneously interact with each other and generate ceramide-enriched membrane domains. These ceramide-enriched domains further fuse, forming large ceramideenriched platforms that participate in the organization of receptors and in the amplification of signaling molecules. Recent studies have suggested several bacteria and bacterial toxins that stimulate the activation and the translocation of acid sphingomyelinase, which leads to the release of ceramide. The acid sphingomyelinase/ceramide system also regulates the internalization of bacteria into the host cell, the subsequent cytokine release, inflammatory response, and initiation of host cell apoptosis. In addition, ceramide has been implicated in the fusion of phagosomes and lysosomes upon bacterial infection. Thus, this system modulates the reorganization of cell membrane receptors and intracellular signaling molecules during bacteria-host interactions. The acid sphingomyelinase and ceramide system may thus serve as a novel therapeutic target for treating infections.

Mycobacterial Infection is Promoted by Neutral Sphingomyelinase 2 Regulating a Signaling Cascade Leading to Activation of ß1-Integrin.

BACKGROUND/AIMS: Mycobacteria-induced diseases, especially tuberculosis, cause more than 1 million deaths each year, which is higher than any other single bacterial pathogen. Neutral sphingomyelinase 2 (Nsm2) has been implied in many physiological processes and diseases, but the role of Nsm2 in pathogen-host interactions and mycobacterial infections has barely been studied. METHODS: We investigated the role of the Nsm2/ceramide system in systemic infection of mice and murine macrophages with Mycobacterium bovis Bacillus Calmette-Guérin (BCG) as a model for mycobacterial infection. For in vitro assays we isolated bone marrow-derived macrophages from Wildtype mice or Nsm2-heterozygous and investigated the role of Nsm2 for macrophage migration/clustering as well as the involvement of p38 mitogen-activated protein kinases (p38K), c-Jun N-terminal kinase (JNK), ß1-integrin and Rac1 activity by Western blot and microscopic studies. For in vivo assays we injected mice intravenously with BCG and analyzed infected tissues for the role of Nsm2-mediated activation of ß1-integrin in granuloma formation and bacterial burden. RESULTS: Our results reveal that BCG infection of macrophages results in rapid stimulation of Nsm2. Genetic and pharmacological studies demonstrate that Nsm2 stimulates a signaling cascade via p38K and JNK to an activation of surface ß1-integrin and Rac1 that leads to the formation of granuloma-like macrophages clusters in vitro and granuloma in vivo. Heterozygosity of Nsm2 in macrophages or antibody-mediated neutralization of active b1-integrin reduced macrophage clusters in vitro and granuloma formation in vivo. Most importantly, Nsm2 heterozygosity or treatment with neutralizing antibodies against ß1-integrin protected mice from systemic BCG infections and chronic infections of the liver and spleen. CONCLUSION: The findings indicate that the Nsm2/ ceramide system plays an important role in systemic infection of mice with mycobacteria by regulating a signaling cascade via p38K, JNK, b1-integrin and Rac1.

Surfactant Protein D Deficiency Aggravates Cigarette Smoke-Induced Lung Inflammation by Upregulation of Ceramide Synthesis.

Cigarette smoke (CS) is the main cause of chronic obstructive pulmonary disease. Surfactant protein D (SP-D) is an important anti-inflammatory protein that regulates host immune defense in the lungs. Here, we investigated the role of SP-D in a murine model of CS-induced inflammation. Pulmonary SP-D localization and abundance was compared between smoker and non-smoker individuals. For in vivo studies, wildtype, and SP-D-deficient mice were exposed to CS for either 12 weeks or 3 days. Moreover, the effect of therapeutic administration of recombinant fragment of human SP-D on the acute CS-induced changes was evaluated. Pulmonary SP-D appeared with heterogenous expression in human smokers, while mouse lung SP-D was uniformly upregulated after CS exposure. We found that SP-D-deficient mice were more susceptible to CS-induced macrophage-rich airway inflammation. SP-D deficiency influenced local pro-inflammatory cytokine levels, with increased CCL3 and interleukin-6 but decreased CXCL1. Furthermore, CS exposure caused significant upregulation of pro-inflammatory ceramides and related ceramide synthase gene transcripts in SP-D-deficient mice compared to wildtype littermates. Administration of recombinant fragment of human SP-D (rfhSP-D) alleviated CS-induced macrophage infiltration and prevented induction of ceramide synthase gene expression. Finally, rfhSP-D treatment attenuated CS-induced human epithelial cell apoptosis in vitro. Our results indicate that SP-D deficiency aggravates CS-induced lung inflammation partly through regulation of ceramide synthesis and that local SP-D enrichment rescues CS-induced inflammation.

NB 06: From a simple lysosomotropic aSMase inhibitor to tools for elucidating the role of lysosomes in signaling apoptosis and LPS-induced inflammation.

Ceramide generation is involved in signal transduction of cellular stress response, in particular during stress-induced apoptosis in response to stimuli such as minimally modified Low-density lipoproteins, TNFalpha and exogenous C6-ceramide. In this paper we describe 48 diverse synthetic products and evaluate their lysosomotropic and acid sphingomyelinase inhibiting activities in macrophages. A stimuli-induced increase of C16-ceramide in macrophages can be almost completely suppressed by representative compound NB 06 providing an effective protection of macrophages against apoptosis. Compounds like NB 06 thus offer highly interesting fields of application besides prevention of apoptosis of macrophages in atherosclerotic plaques in vessel walls. Most importantly, they can be used for blocking pH-dependent lysosomal processes and enzymes in general as well as for analyzing lysosomal dependent cellular signaling. Modulation of gene expression of several prominent inflammatory messengers IL1B, IL6, IL23A, CCL4 and CCL20 further indicate potentially beneficial effects in the field of (systemic) infections involving bacterial endotoxins like LPS or infections with influenza A virus.

Anticeramide antibody and butyrylcholinesterase in peripheral neuropathies.

Ceramide is a glycosphingolipid, a component of nerve and non neuronal cell membrane and plays a role in maintaining the integrity of neuronal tissue. Butyrylcholinesterase (BChE) is a multifunctional enzyme, its involvement in neurodegenerative diseases has been well established. Anticeramide antibody (Ab-Cer) and enzyme BChE have been implicated in peripheral neuropathies. The present study investigates whether there is an association between Ab-Cer and BChE activities and peripheral neuropathies. Patients included: human immunodeficiency virus associated peripheral neuropathy (HIV-PN, n=39), paucibacillary leprosy (PB-L, n=36), multibacillary leprosy (MB-L, n=52), diabetic neuropathy (DN, n=22), demyelinating sensory motor polyneuropathy (DSMN, n=13) and chronic inflammatory demyelinating polyneuropathy (CIDP, n=10). Plasma Ab-Cer was measured by indirect enzyme linked immune assay (ELISA) and BChE activity in plasma was measured by colorimetric method. Ab-Cer levels were significantly elevated in MB-L and DN as compared to healthy subjects (HS). BChE levels were significantly higher in MB-L and DN as well as in HIV and HIV-PN. There is no significant difference in either Ab-Cer or BChE levels in DSMN and CIDP. Elevated plasma Ab-Cer and BChE levels may be considered significant in the pathogenesis of neuropathies. The variation in concurrent involvement of both the molecules in the neuropathies of the study, suggest their unique involvement in neurodegenerative pathways.

Tolerogenic versus Immunogenic Lipidomic Profiles of CD11c+ Immune Cells and Control of Immunogenic Dendritic Cell Ceramide Dynamics.

Lipids affect the membrane properties determining essential biological processes. Earlier studies have suggested a role of switch-activated protein 70 (SWAP-70) in lipid raft formation of dendritic cells. We used lipidomics combined with genetic and biochemical assays to analyze the role of SWAP-70 in lipid dynamics. TLR activation using LPS as a ligand represented a pathogenic immunogenic stimulus, physical disruption of cell-cell contacts a tolerogenic stimulus. Physical disruption, but not LPS, caused an increase of phosphatidylcholine ether and cholesteryl esters in CD11c+ immune cells. An increase of ceramide (Cer) was a hallmark for LPS activation. SWAP-70 was required for regulating the increase and localization of Cers in the cell membrane. SWAP-70 controls Cer accumulation through the regulation of pH-dependent acid-sphingomyelinase activity and of RhoA-dependent transport of endosomal contents to the plasma membrane. Poor accumulation of Cers in Swap70-/- cells caused decreased apoptosis. This shows that two different pathways of activation, immunogenic and tolerogenic, induce different changes in the lipid composition of cultured CD11c+ cells, and highlights the important role of SWAP-70 in Cer dynamics in dendritic cells.