Ailing Lu

Pathogenic Fungus Microsporum canis Activates the NLRP3 Inflammasome

ABSTRACT Microsporum canis is a pathogenic fungus with worldwide distribution that causes tinea capitis in animals and humans. M. canis also causes invasive infection in immunocompromised patients. To defy pathogenic fungal infection, the host innate immune system is the first line of defense. As an important arm of innate immunity, the inflammasomes are intracellular multiprotein complexes that control the activation of caspase-1, which cleaves proinflammatory cytokine pro-interleukin-1β (IL-1β) into its mature form. To determine whether the inflammasome is involved in the host defense against M. canis infection, we challenged human monocytic THP-1 cells and mouse dendritic cells with a clinical strain of M. canis isolated from patients with tinea capitis. We found that M. canis infection triggered rapid secretion of IL-1β from both THP-1 cells and mouse dendritic cells. Moreover, by using gene-specific shRNA and competitive inhibitors, we determined that M. canis-induced IL-1β secretion was dependent on NLRP3. The pathways proposed for NLRP3 inflammasome activation, namely, cathepsin B activity, K+ efflux, and reactive oxygen species production, were all required for the inflammasome activation triggered by M. canis. Meanwhile, Syk, Dectin-1, and Card9 were found to be involved in M. canis-induced IL-1β secretion via regulation of pro-IL-1β transcription. More importantly, our data revealed that M. canis-induced production of IL-1β was dependent on the NLRP3 inflammasome in vivo. Together, this study unveils that the NLRP3 inflammasome exerts a critical role in host innate immune responses against M. canis infection, and our data suggest that diseases that result from M. canis infection might be controlled by regulating the activation of inflammasomes.

Biofilm from a clinical strain of Cryptococcus neoformans activates the NLRP3 inflammasome

Biofilm from a clinical strain of Cryptococcus neoformans activates the NLRP3 inflammasome

Acapsular Cryptococcus neoformans activates the NLRP3 inflammasome

Cryptococcus neoformans (C. neoformans) is an opportunistic fungal pathogen that mainly infects immunocompromised individuals such as AIDS patients. Although cell surface receptors for recognition of C. neoformans have been studies intensively, cytoplasmic recognition of this pathogen remains unclear. As an important detector of pathogen infection, inflammasome can sense and get activated by infection of various pathogens, including pathogenic fungi such as Candida albicans and Aspergillus fumigatus. Our present study showed that acapsular C. neoformans (cap59Δ) activated the NLRP3-, but not AIM2-nor NLRC4- inflammasome. During this process, viability of the fungus was required. Moreover, our in vivo results showed that during the pulmonary infection of cap59Δ, immune cell infiltration into the lung and effective clearance of the fungus were both dependent on the presence of NLRP3 inflammasome. In summary, our data suggest that the capsule of C. neoformans prevents recognition of the fungus by host NLRP3 inflammasome and indicate that manipulation of inflammasome activity maybe a novel approach to control C. neoformans infection.

Internalized Cryptococcus neoformans Activates the Canonical Caspase-1 and the Noncanonical Caspase-8 Inflammasomes

Cryptococcus neoformans is an opportunistic fungal pathogen that causes cryptococccosis in immunocompromised patients as well as immunocompetent individuals. Host cell surface receptors that recognize C. neoformans have been widely studied. However, intracellular sensing of this pathogen is still poorly understood. Our previous studies have demonstrated that both biofilm and acapsular mutant of C. neoformans are able to activate the NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome. In the current study, it was found that opsonization-mediated internalization of encapsulated C. neoformans also activated the canonical NLRP3–apoptosis-associated speck-like protein containing a CARD (ASC)–caspase-1 inflammasome. In addition, the internalized C. neoformans activated the noncanonical NLRP3–ASC–caspase-8 inflammasome as well, which resulted in robust IL-1β secretion and cell death from caspase-1–deficient primary dendritic cells. Interestingly, we found that caspase-1 was inhibitory for the activation of caspase-8 in dendritic cells upon C. neorformans challenge. Further mechanistic studies showed that both phagolysosome membrane permeabilization and potassium efflux were responsible for C. neoformans–induced activation of either the canonical NLRP3–ASC–caspase-1 inflammasome or the noncanonical NLRP3–ASC–caspase-8 inflammasome. Moreover, challenge with zymosan also led to the activation of the noncanonical NLRP3–ASC–caspase-8 inflammasome in cells absent for caspase-1. Collectively, these findings uncover a number of novel signaling pathways for the innate immune response of host cells to C. neoformans infection and suggest that manipulating NLRP3 signaling may help to control fungal challenge.

Human pathogenic fungus Trichophyton schoenleinii activates the NLRP3 inflammasome

The fungus Trichophyton schoenleinii (T. schoenleinii) is the causative agent of Trichophytosis and Tinea favosa of the scalp in certain regions of Eurasia and Africa. Human innate immune system plays an important role in combating with various pathogens including fungi. The inflammasome is one of the most critical arms of host innate immunity, which is a protein complex controlling maturation of IL-1β. To clarify whether T. schoenleinii is able to activate the inflammasome, we analyzed human monocytic cell line THP-1 for IL-1β production upon infection with T. schoenleinii strain isolated from Tinea favosa patients, and rapid IL-1β secretion from THP-1 cells was observed. Moreover, applying competitive inhibitors and gene specific silencing with shRNA, we found that T. schoenleinii induced IL-1β secretion, ASC pyroptosome formation as well as caspase-1 activation were all dependent on NLRP3. Cathepsin B activity, ROS production and K+ efflux were required for the inflammasome activation by T. schoenleinii. Our data thus reveal that the NLRP3 inflammasome plays an important role in host defense against T. schoenleinii, and suggest that manipulating NLRP3 signaling can be a novel approach for control of diseases caused by T. schoenleinii infection.

Hyperactivation of the NLRP3 Inflammasome in Myeloid Cells Leads to Severe Organ Damage in Experimental Lupus.

Systemic lupus erythematosus (SLE) is an autoimmune syndrome associated with severe organ damage resulting from the activation of immune cells. Recently, a role for caspase-1 in murine lupus was described, indicating an involvement of inflammasomes in the development of SLE. Among multiple inflammasomes identified, the NLRP3 inflammasome was connected to diverse diseases, including autoimmune encephalomyelitis. However, the function of NLRP3 in SLE development remains elusive. In this study, we explored the role of NLRP3 in the development of SLE using the pristane-induced experimental lupus model. It was discovered that more severe lupus-like syndrome developed in Nlrp3-R258W mice carrying the gain-of-function mutation. Nlrp3-R258W mutant mice exhibited significantly higher mortality upon pristane challenge. Moreover, prominent hypercellularity and interstitial nephritis were evident in the glomeruli of Nlrp3-R258W mice. In addition, hyperactivation of the NLRP3 inflammasome in this mouse line resulted in proteinuria and mesangial destruction. Importantly, all of these phenotypes were largely attributed to the Nlrp3-R258W mutation expressed in myeloid cells, because Cre recombinase–mediated depletion of this mutant from such cells rescued mice from experimental lupus. Taken together, our study demonstrates a critical role for NLRP3 in the development of SLE and suggests that modulating the inflammasome signal may help to control the inflammatory damage in autoimmune diseases, including lupus.

Remodelling of the gut microbiota by hyperactive NLRP3 induces regulatory T cells to maintain homeostasis

Inflammasomes are involved in gut homeostasis and inflammatory pathologies, but the role of NLRP3 inflammasome in these processes is not well understood. Cryopyrin-associated periodic syndrome (CAPS) patients with NLRP3 mutations have autoinflammation in skin, joints, and eyes, but not in the intestine. Here we show that the intestines of CAPS model mice carrying an Nlrp3R258W mutation maintain homeostasis in the gut. Additionally, such mice are strongly resistant to experimental colitis and colorectal cancer; this is mainly through a remodelled gut microbiota with enhanced anti-inflammatory capacity due to increased induction of regulatory T cells (Tregs). Mechanistically, NLRP3R258W functions exclusively in the lamina propria mononuclear phagocytes to directly enhance IL-1β but not IL-18 secretion. Increased IL-1β boosts local antimicrobial peptides to facilitate microbiota remodelling. Our data show that NLRP3R258W-induced remodelling of the gut microbiota, induces local Tregs to maintain homeostasis and compensate for otherwise-detrimental intestinal inflammation.Inflammasomes are involved in gut homeostasis and inflammatory pathologies. The authors show that a hyperactive NLRP3 inflammasome maintains gut homeostasis through remodelling of the gut microbiota and induction of regulatory T cells.

Detection of cutaneous antibodies in excised skin explants from grass carp, Ctenopharyngodon idella (Valenciennes), immune to Scophthalmus maximus rhabdovirus

This study determined whether cutaneous antibodies were present in excised skin explants of grass carp, Ctenopharyngodon idella, immune to Scophthalmus maximus rhabdovirus (SMRV). Culture fluid from immune skin explants were assayed by indirect enzyme-linked immunosorbent assay (iELISA), Western blot, indirect immunofluorescent assay (IFA) and flow cytometry (FCM). iELISA showed that cutaneous antibody titres were much lower (1:12) than antiserum titres (1:1458) from intraperitoneally immunized grass carp. The phosphoprotein and matrix protein antigens of purified SMRV proteins were recognized by cutaneous antibodies from skin culture fluid using Western blot. The skin culture fluid produced staining signals in viral assembly sites and cytoplasm of SMRV-infected epithelioma papulosum cyprini (EPC) cells by IFA. FCM showed that 4.39% SMRV-infected EPC cells were detected, while non-specific reaction was seen in 2% of control cells. This is the first description of cutaneous antibodies against SMRV in grass carp.

Antiviral effects of ferric ammonium citrate

Iron is an essential nutrient for cell survival and is crucial for DNA replication, mitochondrial function and erythropoiesis. However, the immunological role of iron in viral infections has not been well defined. Here we found the iron salt ferric ammonium citrate (FAC) inhibited Influenza A virus, HIV virus, Zika virus, and Enterovirus 71 (EV71) infections. Of note, both iron ion and citrate ion were required for the antiviral capability of FAC, as other iron salts and citrates did not exhibit viral inhibition. Mechanistically, FAC inhibited viral infection through inducing viral fusion and blocking endosomal viral release. These were further evidenced by the fact that FAC induced liposome aggregation and intracellular vesicle fusion, which was associated with a unique iron-dependent cell death. Our results demonstrate a novel antiviral function of FAC and suggest a therapeutic potential for iron in the control of viral infections.

Cross reactivity of S. aureus to murine cytokine assays: A source of discrepancy.

Staphylococcus aureus is one of the versatile Gram positive bacteria causing a range of diseases. Upon challenge, host immune cells recognize S. aureus and mount diverse immune responses including production of pro-inflammatory cytokines such as IL-1β and TNF-α. These cytokines are important mediators of inflammation which can be detected via various immunological methods such as enzyme linked immunosorbent assay (ELISA) and immunoblotting. In the current study, we found that a number of clinical isolates as well as laboratory strains of S. aureus exhibited cross reactivity with ELISA antibodies for murine IL-1β and TNF-α assays. This cross reactivity generates exaggerated false positive signals which can be a source of discrepancy for the understanding of real immune responses against S. aureus infection by host immune cells.