Pneumocystis carinii Cell Wall β-Glucans Initiate Macrophage Inflammatory Responses through NF-κB Activation

Abstract

␤-Glucans are major structural components of fungi. We have recently reported that the pathogenic fungus Pneumocystis carinii assembles a ␤-glucan-rich cell wall that potently activates alveolar macrophages to release pro-inflammatory cytokines and chemokines. Purified P. carinii ␤-glucans predictably induce both cytokine generation and associated neutrophilic lung inflammation. Herein, we demonstrate that P. carinii ␤-glucaninduced macrophage stimulation results from activation of NF-B. Although analogous to macrophage activation induced by bacterial lipopolysaccharide (LPS), P. carinii ␤-glucan-induced macrophage NF-B activation exhibits distinctly different kinetics, with slower induction and longer duration compared with LPS stimulation. Macrophage activation in response to P. carinii ␤-glucan was also substantially inhibited with the NF-B antagonist pyrrolidine dithiocarbamate. In addition to different kinetics of NF-B activation, P. carinii ␤-glucan and LPS also utilize different receptor systems to induce macrophage activation. Macrophages from Toll-like receptor 4-deficient and wild type mice produced equivalent amounts of tumor necrosis factor ␣ when stimulated with P. carinii ␤-glucan. However, Toll-like receptor 4-deficient macrophages were refractory to stimulation with LPS. In contrast, MyD88-deficient macrophages exhibited a significant (though partial) blunted response to P. carinii ␤-glucan. These data demonstrate that P. carinii ␤-glucan acts as potent inducer of macrophage activation through NF-B utilizing cellular receptors and signaling pathways distinct from LPS.

PneumocystisCell Wall β-Glucans Induce Dendritic Cell Costimulatory Molecule Expression and Inflammatory Activation through a Fas-Fas Ligand Mechanism

“…Our current data support earlier studies that dectin-1 serves as a major receptor for fungal ␤-glucans found on DCs and macrophages (29,33,34). Additional recent studies from our laboratory further document the ␤-glucans stimulate macrophages through MyD88-dependent mechanisms (6). Other investigations have demonstrated that dectin-1 may act synergistically with TLR2 to mediate cytokine generation by DCs and macrophages in response to zymosan, a glucan-rich cell wall fraction of yeast (35).…”

“…The final preparations were assayed for soluble endotoxin with the Limulus amebocyte lysate assay method and found to consistently contain Ͻ0.125 U of endotoxin (5). Our prior studies have further demonstrated that host cell responses to Pneumocystis ␤-glucans occur through mechanisms distinct from those induced by LPS (6). All Pneumocystis ␤-glucan preparations were analyzed for their proinflammatory signaling capacities.…”

“…Of particular interest, Pneumocystis species cause life-threatening pneumonia in susceptible hosts, with lung damage largely resulting from exaggerated lung inflammation secondary to infection, rather than from the pathogen itself (2-4). Our recent investigations have shown that the ␤-glucan cell wall components of Pneumocystis are chiefly responsible for initiation of lung inflammation during this infection (5,6).…”

The relationship between Candida species cultured from the respiratory tract and systemic inflammation in critically ill patients with ventilator-associated pneumonia

“…[26][27][28] Studies with Pneumocystis jiroveci and fungi have demonstrated that ß-glucans can stimulate the release of inflammatory markers, such as IL-1 and TNF-a, through NF-jB activation, trigger fungicidal responses, and generate reactive oxygen intermediates. [29][30][31][32] These observations provide a mechanism by which Candida may play a causal role in the increased inflammatory markers and may potentiate worse clinical outcomes. 33 In a recent study, rats instilled with live Candida albicans developed increased pulmonary TNF-a and increased rates of pseudomonal pneumonia; whereas, rats instilled with normal saline or ethanol destroyed the Candida albicans.…”

Cycloartenyl Ferulate downregulates lipopolysaccharide stimulated iNOS mRNA via NF-kB suppression in RAW 264.7 macrophages

“…Immunofluorescence was employed to detect translocation of the p65 component of NF-B to the nucleus (Lebron et al, 2003). Briefly, RAW 264.7 macrophages were seeded onto sterile 22 x 22-mm glass cover slips in 6-well tissue culture plates and pretreated with 30μM CAF overnight followed by LPS for 2 hours prior to fixation with 3.7% paraformaldehyde for 30 min at room temperature.…”