Cryptococcal meningitis in a daily cannabis smoker without evidence of immunodeficiency.

Cryptococcal meningitis is a life-threatening condition most commonly observed in immunocompromised individuals. We describe a daily cannabis smoker without evidence of immunodeficiency presenting with confirmed Cryptococcus neoformans meningitis. An investigation of cannabis samples from the patient's preferred dispensary demonstrated contamination with several varieties of Cryptococcus, including C. neoformans, and other opportunistic fungi. These findings raise concern regarding the safety of dispensary-grade cannabis, even in immunocompetent users.

Activation of the innate immune receptor Dectin-1 upon formation of a 'phagocytic synapse'.

Innate immune cells must be able to distinguish between direct binding to microbes and detection of components shed from the surface of microbes located at a distance. Dectin-1 (also known as CLEC7A) is a pattern-recognition receptor expressed by myeloid phagocytes (macrophages, dendritic cells and neutrophils) that detects ß-glucans in fungal cell walls and triggers direct cellular antimicrobial activity, including phagocytosis and production of reactive oxygen species (ROS). In contrast to inflammatory responses stimulated upon detection of soluble ligands by other pattern-recognition receptors, such as Toll-like receptors (TLRs), these responses are only useful when a cell comes into direct contact with a microbe and must not be spuriously activated by soluble stimuli. In this study we show that, despite its ability to bind both soluble and particulate ß-glucan polymers, Dectin-1 signalling is only activated by particulate ß-glucans, which cluster the receptor in synapse-like structures from which regulatory tyrosine phosphatases CD45 and CD148 (also known as PTPRC and PTPRJ, respectively) are excluded (Supplementary Fig. 1). The 'phagocytic synapse' now provides a model mechanism by which innate immune receptors can distinguish direct microbial contact from detection of microbes at a distance, thereby initiating direct cellular antimicrobial responses only when they are required.

Staphylococcus aureus evades lysozyme-based peptidoglycan digestion that links phagocytosis, inflammasome activation, and IL-1beta secretion.

IL-1beta produced by phagocytes is important for protection against the mucosal pathogen Staphylococcus aureus. Processing and maturation of this cytokine requires activation of the multiprotein inflammasome complex. We observed that the bacterial cell wall component peptidoglycan (PGN) must be particulate and internalized via phagocytosis to activate NLRP3 inflammasomes and IL-1beta secretion. In the context of S. aureus infection of macrophages, we find that phagocytosis and lysozyme-based bacterial cell wall degradation are necessary to induce IL-1beta secretion. Further, an S. aureus enzyme, PGN O-acetyltransferase A, previously demonstrated to make cell wall PGN resistant to lysozyme, strongly suppresses inflammasome activation and inflammation in vitro and in vivo. These observations demonstrate that phagocytosis and lysozyme-based cell wall degradation of S. aureus are functionally coupled to inflammasome activation and IL-1beta secretion and illustrate a case whereby a bacterium specifically subverts IL-1beta secretion through chemical modification of its cell wall PGN.

Differential use of CARD9 by dectin-1 in macrophages and dendritic cells.

The pattern recognition receptors TLR2 and Dectin-1 play key roles in coordinating the responses of macrophages and dendritic cells (DC) to fungi. Induction of proinflammatory cytokines is instructed by signals from both TLR2 and Dectin-1. A recent report identified a role for CARD9 in innate anti-fungal responses, demonstrating CARD9-Bcl10-mediated activation of NF-kappaB and proinflammatory cytokine induction in murine bone marrow-derived DC stimulated via Dectin-1. We now report that Dectin-1-CARD9 signals fail to activate NF-kappaB and drive TNF-alpha induction in murine bone marrow-derived macrophages. However, priming of bone marrow-derived macrophages with GM-CSF or IFN-gamma permits Dectin-1-CARD9-mediated TNF-alpha induction. Analysis of other macrophage/DC populations revealed further variation in the ability of Dectin-1-CARD9 signaling to drive TNF-alpha production. Resident peritoneal cells and alveolar macrophages produce TNF-alpha upon Dectin-1 ligation, while thioglycollate-elicited peritoneal macrophages and Flt3L-derived DC do not. We present data demonstrating that CARD9 is recruited to phagosomes via its CARD domain where it enhances TLR-induced cytokine production even in cells in which Dectin-1 is insufficient to drive cytokine production. In such cells, Dectin-1, CARD9, and Bcl10 levels are not limiting, and data indicate that these cells express additional factors that restrict Dectin-1-CARD9 signaling for TNF-alpha induction.