The interaction of mannose binding lectin (MBL) with mannose containing glycopeptides and the resultant potential impact on invasive fungal infection

Endogenous Antimicrobial-Immunomodulatory Molecules: Networking Biomolecules of Innate Immunity

Endogenous antimicrobial-immunomodulatory molecules (EAIMs) are essential to immune-mediated human health and evolution. Conventionally, antimicrobial peptides (AMPs) have been regarded as the dominant endogenous antimicrobial molecule; however, AMPs are not sufficient to account for the full spectrum of antimicrobial-immunomodulatory duality occurring within the human body. The threat posed by pathogenic microbes is pervasive with the capacity for widespread impact across many organ systems and multiple biochemical pathways; accordingly, the host needs the capacity to react with an equally diverse response. This can be attained by having EAIMs that traverse the full range of molecular size (small to large molecules) and structural diversity (including molecules other than peptides). This review identifies multiple molecules (peptide/protein, lipid, carbohydrate, nucleic acid, small organic molecule, and metallic cation) as EAIMs and discusses the possibility of cooperative, additive effects amongst the various EAIM classes during the host response to a microbial assault. This comprehensive consideration of the full molecular diversity of EAIMs enables the conclusion that EAIMs constitute a previously uncatalogued structurally diverse and collectively underappreciated immuno-active group of integrated molecular responders within the innate immune system's first line of defence.

Current State of Carbohydrate Recognition and C-Type Lectin Receptors in Pneumocystis Innate Immunity

Pneumocystis jirovecii is one of the most common fungal pathogens in immunocompromised individuals. Pneumocystis jirovecii pneumonia (PJP) causes a significant host immune response that is driven greatly by the organism’s cell wall components including β-glucans and major surface glycoprotein (Msg). These ligands interact with a number of C-type lectin receptors (CLRs) leading to downstream activation of proinflammatory signaling pathways. This minireview provides a brief overview summarizing known CLR/Pneumocystis interactions.

Mannose-binding lectin and associate serine protease complex modulates neutrophil respiratory burst and gene expression in Capra hircus

Neutrophils are an essential cellular component of the innate immune system, responsible for multiple effector mechanisms and aspects of inflammation. Neutrophil priming results in a rapid elevation in antimicrobial activities and can be measured by reactive oxygen species production, bacterial endocytosis, and de-novo synthesis of components such as interleukins. Mannose binding lectin (MBL), a C-type lectin pathogen recognition receptor is associated with immune functions including complement activation, opsonization and modulating immune responses. Whether MBL opsonization of pathogen can induce neutrophil priming has not been studied so far. Hence, studies were performed using MBL and neutrophils of Capra hircus (domestic goat) to evaluate the effects of MBL + MASPs interactions on neutrophil functions. It was found that MBL + MASPs opsonization of zymosan stimulates neutrophil functions including increased oxidative burst, enhanced endocytosis and modulates the expression level of NCF4, XBP1, CCL2, and CR1 genes. The results suggest that MBL-MASP complex can regulate neutrophil functioning.

Leukotriene B4-Mediated Neutrophil Recruitment Causes Pulmonary Capillaritis during Lethal Fungal Sepsis

Candida albicans bloodstream infection causes fungal septicaemia and death in over half of afflicted patients. Polymorphonuclear leukocytes (PMN) mediate defense against invasive candidiasis, but their role in protection versus tissue injury and sepsis is unclear. We observe PMN intravascular swarming and subsequent clustering in response to C. albicans yeast in a lethal septic mouse and human pulmonary circulation model. Live C. albicans sequester to the endothelium and are immediately captured by complement-dependent PMN chemotaxis, which is required for host survival. However, complement activation also leads to Leukotriene B4 (LTB4)-mediated intravascular PMN clustering and occlusion, resulting in capillaritis with pulmonary hemorrhage and hypoxemia. This clustering is unique to fungi and triggered by fungal cell wall components. PMN clustering is absent in mice lacking LTB4-receptor, and capillaritis is attenuated upon pharmacological LTB4 blockade without affecting phagocytosis. Therefore, therapeutically disrupting infection-induced capillaritis may limit organ injury without impairing host defense during fungal sepsis.

Candida albicans infection and intestinal immunity

Fungal infections cause high rates of morbidity and mortality in intensive care and immunocompromised patients, and can represent a life-threatening disease. As a microorganism commonly found in the intestine, Candida albicans (C. albicans) can invade the gut epithelium barrier via microfold cells and enter the bloodstream. The defensive potential of the intestinal barrier against invasive C. albicans is dependent on innate and adaptive immune responses which enable the host to eliminate pathogenic fungi. The lamina propria layer of the intestine contains numerous immune cells capable of inducing an innate cellular immune response against invasive fungi. This review focuses on the immune response triggered by a C. albicans infection in the intestine.

Clinical features and risk factors for blood stream infections of Candida in neonates

Candida species are the leading cause of invasive fungal infections in children admitted to hospital. However, few data exist with regard to the clinical features, risk factors and prognosis for candidemia in neonates. The present retrospective study included 40 neonates from the Affiliated Children's Hospital of the Capital Institute of Pediatrics (Beijing, China) in the time period between January 1, 2006 and December 31, 2010 (candidemia group, n=19; non-candidemia group, n=21). The clinical characteristics, prognosis and previously identified risk factors for the two groups were recorded. According to the forward stepwise multivariate logistic regression analysis, administration of antibiotics >2 weeks prior, the use of glycopeptide antibiotics, maternal candidal vaginitis and secondary gastrointestinal surgery were identified as predictors of candidiasis. When compared with the non-gastrointestinal dysfunction group, the proportion of neonates that had been subjected to parenteral nutrition, central venous catheters, gastrointestinal surgery, secondary gastrointestinal surgery, repeated tracheal intubation and glycopeptide antibiotic administration was significantly higher in the gastrointestinal dysfunction group (P<0.05). Long-term application of antibiotics, use of glycopeptide antibiotics, maternal candidal vaginitis and secondary gastrointestinal surgery appeared to be the risk factors of candidemia in neonates. The neonates co-existed with gastrointestinal dysfunction suffering from candidemia were likely to experience growth retardation at 6 months after hospital discharge. Candidemia is potentially life-threatening situation for neonates, and if patients do not succumb it may affect their early development.

MBL-mediated opsonophagocytosis of Candida albicans by human neutrophils is coupled with intracellular Dectin-1-triggered ROS production

Mannan-binding lectin (MBL), a lectin homologous to C1q, greatly facilitates C3/C4-mediated opsonophagocytosis of Candida albicans (C. albicans) by human neutrophils, and has the capacity to bind to CR1 (CD35) expressed on circulating neutrophils. The intracellular pool of neutrophil Dectin-1 plays a critical role in stimulating the reactive oxygen species (ROS) generation through recognition of β-1,3-glucan component of phagocytized zymosan or yeasts. However, little is known about whether MBL can mediate the opsonophagocytosis of Candida albicans by neutrophils independent of complement activation, and whether MBL-mediated opsonophagocytosis influence the intracellular expression of Dectin-1 and ROS production. Here we showed that the inhibited phagocytic efficiency of neutrophils as a result of blockage of Dectin-1 was compensated by exogenous MBL alone in a dose-dependent manner. Furthermore, the expressions of Dectin-1 at mRNA and intracellular protein levels were significantly up-regulated in neutrophils stimulated by MBL-pre-incubated C. albicans, while the expression of surface Dectin-1 remained almost unchanged. Nevertheless, the stimulated ROS production in neutrophils was partly and irreversibly inhibited by blockage of Dectin-1 in the presence of exogenous MBL. Confocal microscopy examination showed that intracellular Dectin-1 was recruited and co-distributed with ROS on the surface of some phagocytized yeasts. The β-1,3-glucanase digestion test further suggested that the specific recognition and binding site of human Dectin-1 is just the β-1,3-glucan moiety on the cell wall of C. albicans. These data demonstrate that MBL has an ability to mediate the opsonophagocytosis of Candida albicans by human neutrophils independent of complement activation, which is coupled with intracellular Dectin-1-triggered ROS production.

Interplay between Candida albicans and the mammalian innate host defense

Candida albicans is both the most common fungal commensal microorganism in healthy individuals and the major fungal pathogen causing high mortality in at-risk populations, especially immunocompromised patients. In this review, we summarize the interplay between the host innate system and C. albicans, ranging from how the host recognizes, responds, and clears C. albicans infection to how C. albicans evades, dampens, and escapes from host innate immunity.

Adjunctive immunotherapy with recombinant cytokines for the treatment of disseminated candidiasis

Despite the discovery in the last decade of azoles and echinocandins as novel and potent antimycotic drugs, systemic Candida infections are still accompanied by an unacceptably high burden of morbidity and mortality. A rational novel therapeutic approach would be the use of adjuvant immunotherapy, with the aim of improving host defence against Candida. Increases in our understanding of the mechanisms that underlie the pathogenesis of Candida infections, such as the role played by pattern recognition receptors and the induction of proinflammatory cytokines during the early phases of infection, have led to the hypothesis of a potential therapeutic role of recombinant cytokines in systemic candidiasis. In the present review, we give an update of both experimental data and proof-of-principle studies in humans that argue for the use of adjunctive immunotherapy with recombinant cytokines in invasive Candida infections. Sufficiently powered studies on the role of cytokine-based treatment regimens for invasive candidiasis are needed to fully demonstrate the feasibility of this immunotherapeutic approach to improve the prognosis of severe invasive Candida infections.

Cell wall glycoproteins participate in the adhesion of Sporothrix schenckii to epithelial cells

Sporothrix schenckii is the etiologic agent of sporotrichosis. This fungal infection is an emerging disease potentially fatal in immunocompromised patients. The adhesion to host cells is a crucial early event related with the dissemination of pathogens. In order to clarify the mechanisms of adhesion of S. schenckii yeast cell to epithelial cells, we studied the biochemical basis of this process. The electrophoretic analysis of cell wall protein from S. schenckii coupled at ConA and stained with HRP, revealed nine different proteins with MW ≥ 180, 115, 90, 80, 58, 40, 36, 22 and 18 kDa. Using ligand-like assay with biotinylated S. schenckii surface proteins, five proteins with MW ≥ 190, 180, 115, 90 and 80 kDa which have affinity to epithelial cells were identified. The adhesion of yeast to epithelial monolayer was significantly inhibited when S. schenckii was pretreated with concanavalinA (ConA) and wheat germ agglutinin (WGA) lectins, alkali, periodate, trypsin, endoglycosidase H (EndoH), salt solutions and detergents. The ability of adhesion of S. schenckii yeast was recovered by blocking the lectin with sugar complementary. These data suggest that surface glycoprotein with mannose and glucose residue could be participate in the process of fungal adhesion to epithelial cells.