Activation and Maintenance of Intestinal Intraepithelial Lymphocytes (IELs)

The intestinal tissue is charged with a delicate immunological task. The intestinal immune system needs to be tolerant towards nutrients and microbiota present in the intestinal lumen, while simultaneously detecting and responding to dangers such as pathogens. A single-cell layer of intestinal epithelial cells (IECs) acts as a first line of defence. There is a T cell population located between the IECs that have been named intraepithelial lymphocytes (IELs). As the main lymphoid population within the intestinal barrier, IELs are thought to have an important role in intestinal homeostasis maintenance, as well as a role in intestinal inflammatory and autoimmune diseases such as inflammatory bowel disease and celiac disease. Despite extensive research on IEL biology, there are still questions remaining in terms of the development, maintenance and activation of IELs. Furthermore, IELs survive poorly in vitro, which hinders mechanistic insights. In this thesis, a co-culture system between IELs and intestinal organoids, “mini-guts”, provides an in vitro model for IELs. With this IEL-organoid co-culture system, IELs associated with the organoids survive for at least 4 days. Additional findings suggest that IELs are kept in a poised state of activation due to differences in their mitochondria compared to other T cells found in spleen, lung and skin. Upon activation or intestinal inflammation, the mitochondrial mass in IELs increases. This increase correlates with effector functions such as cytokine production and proliferation. In addition, the composition of the mitochondria-specific lipid, cardiolipins, alters drastically in IELs after activation. These data support a model of mitochondria-dependent activation of IELs. The mitochondria-dependent activation in IELs appears to have at least two pathways: one T cell receptor-dependent and one microbiota-dependent. The latter pathway suggests a model in which IELs can become activated regardless of the cause of intestinal epithelial barrier damage.National Centre of the 3Rs (NC3R) Biotechnology and Biological Sciences Research Council (BBRSC) Funds for Women Graduates (FfWG

El Tor biotype Vibrio cholerae activates the caspase-11-independent canonical Nlrp3 and Pyrin inflammasomes

Vibrio cholerae is a Gram-negative enteropathogen causing potentially life-threatening cholera disease outbreaks, for which the World Health Organization currently registers 2-4 million cases and similar to 100.000 cholera-associated deaths annually worldwide. Genomic Vibrio cholerae research revealed that the strains causing this ongoing cholera pandemic are members of the El Tor biotype, which fully replaced the Classical biotype that caused former cholera pandemics. While both of these biotypes express the characteristic Cholera Toxin (CT), the El Tor biotype additionally expresses the accessory toxins hemolysin (hlyA) and multifunctional auto-processing repeat-in-toxin (MARTX). Previous studies demonstrated that the Classical biotype of Vibrio cholerae triggers caspase-11-dependent non-canonical inflammasome activation in macrophages following CT-mediated cytosolic delivery of LPS. In contrast to the Classical biotype, we here show that El Tor Vibrio cholerae induces IL-1 beta maturation and secretion in a caspase-11- and CT-independent manner. Instead, we show that El Tor Vibrio cholerae engages the canonical Nlrp3 inflammasome for IL-1 beta secretion through its accessory hlyA toxin. We further reveal the capacity of this enteropathogen to engage the canonical Pyrin inflammasome as an accessory mechanism for IL-1 beta secretion in conditions when the pro-inflammatory hlyA-Nlrp3 axis is blocked. Thus, we show that the V. cholerae El Tor biotype does not trigger caspase-11 activation, but instead triggers parallel Nlrp3- and Pyrin-dependent pathways toward canonical inflammasome activation to induce IL-1 beta-mediated inflammatory responses. These findings further unravel the complex inflammasome activating mechanisms that can be triggered when macrophages face the full arsenal of El Tor Vibrio cholerae toxins, and as such increase our understanding of host-pathogen interactions in the context of the Vibrio cholerae biotype associated with the ongoing cholera pandemic

Candidalysin crucially contributes to Nlrp3 inflammasome activation by Candida albicans hyphae

Candida albicans is an opportunistic fungal pathogen that can cause life-threatening infections, particularly in immunocompromised patients. C. albicans induced activation of the Nlrp3 inflammasome, leading to secretion of bioactive interleukin 1β (IL-1β) is a crucial myeloid cell immune response needed for antifungal host defense. Being a pleiomorphic fungus, C. albicans can provoke Nlrp3 inflammasome responses only upon morphological transformation to its hyphal appearance. However, the specific hyphal factors that enable C. albicans to activate the Nlrp3 inflammasome in primary macrophages remain to be revealed. Here, we identify candidalysin, a peptide derived from the hypha-specific ECE1 gene, as a fungal trigger for Nlrp3 inflammasome-mediated maturation and secretion of IL-1β from primary macrophages. Direct peptide administration experiments showed that candidalysin was sufficient for inducing secretion of mature IL-1β from macrophages in an Nlrp3 inflammasome-dependent manner. Conversely, infection experiments using candidalysin-deficient C. albicans showed that candidalysin crucially contributed to the capacity of this fungus to induce maturation and secretion of IL-1β from primary macrophages. These complementary observations identify the expression of candidalysin as one of the molecular mechanisms by which hyphal transformation equips C. albicans with its proinflammatory capacity to elicit the release of bioactive IL-1β from macrophages.IMPORTANCE Candidiasis is a potentially lethal condition that is caused by systemic dissemination of Candida albicans, a common fungal commensal residing mostly on mucosal surfaces. The transition of C. albicans from an innocuous commensal to an opportunistic pathogen goes hand in hand with its morphological transformation from a fungus to a hyphal appearance. On the one hand, the latter manifestation enables C. albicans to penetrate tissues, while on the other hand, the expression of many hypha-specific genes also endows it with the capacity to trigger particular cytokine responses. The Nlrp3 inflammasome is a crucial component of the innate immune system that provokes release of the IL-1β cytokine from myeloid cells upon encountering C. albicans hyphae. Our study reveals the peptide candidalysin as one of the hypha-derived drivers of Nlrp3 inflammasome responses in primary macrophages and, thus, contributes to better understanding the fungal mechanisms that determine the pathogenicity of C. albicans

Nlrp3 inflammasome activation in macrophages suffices for inducing autoinflammation in mice

Cryopyrin-associated periodic syndromes (CAPS) are a spectrum of autoinflammatory disorders caused by gain-of-function NLRP3 mutant proteins that form hyperactive inflammasomes leading to overproduction of the pro-inflammatory cytokines IL-1 beta and IL-18. Expressing the murine gain-of-function Nlrp3(A350V) mutant selectively in neutrophils recapitulates several autoinflammatory features of human CAPS, but the potential contribution of macrophage inflammasome hyperactivation to CAPS development is poorly defined. Here, we show that expressing Nlrp3(A350V) in macrophages is sufficient for driving severe multi-organ autoinflammation leading to perinatal lethality in mice. In addition, we show that macrophages contribute to autoinflammation also in adult mice, as depleting macrophages in mice ubiquitously expressing Nlrp3(A350V) significantly diminishes splenic and hepatic IL-1 beta production. Interestingly, inflammation induced by macrophage-selective Nlrp3(A350V) expression does not provoke an influx of mature neutrophils, while neutrophil influx is still occurring in macrophage-depleted mice with body-wide Nlrp3(A350V) expression. These observations identify macrophages as important cellular drivers of CAPS in mice and support a cooperative cellular model of CAPS development in which macrophages and neutrophils act independently of each other in propagating severe autoinflammation

Candidalysin Crucially Contributes to Nlrp3 Inflammasome Activation by Candida albicans Hyphae

Candida albicans is an opportunistic fungal pathogen that can cause life-threatening infections, particularly in immunocompromised patients. C. albicans induced activation of the Nlrp3 inflammasome, leading to secretion of bioactive interleukin 1β (IL-1β) is a crucial myeloid cell immune response needed for antifungal host defense. Being a pleiomorphic fungus, C. albicans can provoke Nlrp3 inflammasome responses only upon morphological transformation to its hyphal appearance. However, the specific hyphal factors that enable C. albicans to activate the Nlrp3 inflammasome in primary macrophages remain to be revealed. Here, we identify candidalysin, a peptide derived from the hypha-specific ECE1 gene, as a fungal trigger for Nlrp3 inflammasome-mediated maturation and secretion of IL-1β from primary macrophages. Direct peptide administration experiments showed that candidalysin was sufficient for inducing secretion of mature IL-1β from macrophages in an Nlrp3 inflammasome-dependent manner. Conversely, infection experiments using candidalysin-deficient C. albicans showed that candidalysin crucially contributed to the capacity of this fungus to induce maturation and secretion of IL-1β from primary macrophages. These complementary observations identify the expression of candidalysin as one of the molecular mechanisms by which hyphal transformation equips C. albicans with its proinflammatory capacity to elicit the release of bioactive IL-1β from macrophages.IMPORTANCE Candidiasis is a potentially lethal condition that is caused by systemic dissemination of Candida albicans, a common fungal commensal residing mostly on mucosal surfaces. The transition of C. albicans from an innocuous commensal to an opportunistic pathogen goes hand in hand with its morphological transformation from a fungus to a hyphal appearance. On the one hand, the latter manifestation enables C. albicans to penetrate tissues, while on the other hand, the expression of many hypha-specific genes also endows it with the capacity to trigger particular cytokine responses. The Nlrp3 inflammasome is a crucial component of the innate immune system that provokes release of the IL-1β cytokine from myeloid cells upon encountering C. albicans hyphae. Our study reveals the peptide candidalysin as one of the hypha-derived drivers of Nlrp3 inflammasome responses in primary macrophages and, thus, contributes to better understanding the fungal mechanisms that determine the pathogenicity of C. albicans.status: publishe

Myeloid OTULIN deficiency couples RIPK3-dependent cell death to Nlrp3 inflammasome activation and IL-1\u3b2 secretion

Abstract: Loss-of-function mutations in the deubiquitinase OTULIN result in an inflammatory pathology termed \u201cOTULIN-related autoinflammatory syndrome\u201d (ORAS). Genetic mouse models revealed essential roles for OTULIN in inflammatory and cell death signaling, but the mechanisms by which OTULIN deficiency connects cell death to inflammation remain unclear. Here, we identify OTULIN deficiency as a cellular condition that licenses RIPK3-mediated cell death in murine macrophages, leading to Nlrp3 inflammasome activation and subsequent IL-1\u3b2 secretion. OTULIN deficiency uncoupled Nlrp3 inflammasome activation from gasdermin D\u2013mediated pyroptosis, instead allowing RIPK3-dependent cell death to act as an Nlrp3 inflammasome activator and mechanism for IL-1\u3b2 release. Accordingly, elevated serum IL-1\u3b2 levels in myeloid-specific OTULIN-deficient mice were diminished by deleting either Ripk3 or Nlrp3 . These findings identify OTULIN as an inhibitor of RIPK3-mediated IL-1\u3b2 release in mice