Glucuronoxylomannan (AAPS) from the edible wood ear mushroom Auricularia auricula-judae has been demonstrated to exhibit immunostimulatory properties through its binding to TLR4. However, the mechanisms of immune modulation by AAPS in mammalian cells remains unclear. In the present study, we demonstrated that AAPS induced immunostimulatory effects were regulated by reactive oxygen species, mitogen-activated protein kinases, protein kinase C-α and NF-κB. AAPS remarkably increased the phagocytosis and bactericidal activity of macrophages. In lipopolysaccharide-activated macrophages, AAPS induced endotoxin tolerance like effect characterized by the downregulation of nitric oxide, interleukin-6 and TNF-α via the downregulation of NF-κB activation. Our findings provide firm scientific evidences for the immunoenhancing properties of wood ear mushroom, and the potential of AAPS to be strong candidates for the development of new carbohydrate-based nutraceutical supplements in the management of immunity related disorders in the future.

Based on its potential bioactivities and sustainable source, polysaccharide (glucuronoxylomannan) from fruit bodies of Tremella fuciformis (TFP) aroused attention in food, pharmaceutical and cosmetic industry. The present study aimed at revealing its chain conformational and physicochemical properties. By using HPSEC-MALLS-Visc-RI measurement, worm-like cylinder model calculation and AFM observation, we manifested that TFP existed as flexible chains in 0.15 M NaCl (pH 7.4) solution, with the persistence length of 9.20 nm and chain diameter of 0.97 nm. Meanwhile, TFP solution exhibited shear-thinning behavior with C* at 5.3 mg mL-1, owning the feature of entangled polysaccharide. TFP solution changed from liquid-like to solid-like behavior as frequency increases, and the crossover points shifted to lower frequencies with concentration increasing. Besides, the strong moisture retention ability of TFP was evaluated. These characteristics indicated that TFP could be utilized to design microstructure system and applied as stabilizer or moisture holding ingredient in food, pharmaceutical and cosmetic system.

The development of novel antifungal agents with high efficacy, low drug tolerance and few side effects is urgent. MSI-1 (GIWKFLKKAKKFWK-NH2), a cationic antimicrobial peptide, may be an attractive antifungal agent because of its structural characteristics, perfect stability against pH and high-temperature/salt, low toxicity towards mammalian cells and low potential for emergence of drug tolerance. In this study, the antifungal activity of MSI-1 in vitro and in a murine model of cryptococcal meningoencephalitis was evaluated. Zeta potential assay, flow cytometry, fluorescence microscope, transmission electron microscopy and microscale thermophoresis were performed to clarify the mechanisms underlying MSI-1 against C. neoformans. The results showed that MSI-1 exerted effective anti-cryptococcal activity in vitro, with MICs of 8-16 μg/mL and MFCs of 8-32 μg/mL, and in a C neoformans-infected mouse model, with significantly improved animal survival, decreased production of pro-inflammatory cytokines and alleviated lung injury, because the potent and rapid fungicidal activity of MSI-1 could effectively eliminate fungal counts in mouse organs. We confirmed that the positively charged peptide bound to C. neoformans by electrostatic attraction after interacting with glucuronoxylomannan (the primary component of C. neoformans capsule). Subsequently, MSI-1 increased the membrane fluidity of fungal cells and the cell membrane permeability, causing destabilized membrane integrity and leading to the final death of fungi. Collectively, MSI-1 possessed potent anti-cryptococcal activity via its notable membrane disruption effect and may be a potential candidate for use in antifungal infection induced by C. neoformans, especially azole-resistant cryptococcus.

In this study, a glucuronoxylomannan named TAP-3 was obtained from high-value Tremella aurantialba Bandoni et Zang. Physicochemical analysis revealed that TAP-3, which had a molecular weight of ∼624 kDa, mainly consisted of d-mannose (Man), d-xylose (Xyl), and d-glucuronic acid (GlcA) in a molar ratio of 3.0:1.0: 1.0. Structural analyses of its depolymerized fragments clarified that TAP-3 contained a (1 → 3) and (1 → 2)-linked α-Manp backbone, side chains formed by β-Xylp and β-GlcpA linked to the C-2 position of α-Manp, and acetyl groups connected to the sixth hydroxyl positions of Manp. TAP-3 showed marked immune enhancement activity, promoting NO, IL-1β and TNF-α secretion from macrophages. The critical membrane receptor of TAP-3 was identified to be TLR4, and the chain length was essential for its immunoregulatory activity. These findings expand knowledge of the structural types of glucuronoxylomannan and illustrate its biological activity as an immunopotentiator.

Cryptococcus neoformans and Cryptococcus gattii cause life-threatening meningoencephalitis or lung diseases in immunocompetent individuals or immunocompromised ones. C. neoformans and C. gattii are subdivided into five serotypes based on their capsular glucuronoxylomannan (GXM). C. neoformans consists of serotypes A, D, and AD hybrid, and C. gattii consists of serotypes B and C. Given structural differences of GXM between C. neoformans and C. gattii, it remains unclear that how innate immune system recognizes GXM. Here, we report that C-type lectin receptor Dectin-3 (MCL encoded by Clec4d) is a direct receptor for GXMs from C. neoformans serotype AD (C.n-AD) and C. gattii serotype B (C.g-B). GXMs from C.n-AD and C.g-B activated NF-κB and ERK pathways to induce pro-inflammatory cytokine production, whereas it was completely abolished due to deficiency of Dectin-3 or caspase recruitment domain family member 9 (CARD9). Upon pulmonary C.n-AD and C.g-B infection, Dectin-3- and CARD9-deficient mice were highly susceptible and showed augmented lung injury due to impairment of alveolar macrophage accumulation and killing activities. Our study provides the first biological and genetic evidence demonstrating that Dectin-3 recognizes GXM of C.n-AD and C.g-B to initiate host defense against cryptococcosis.

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.