TLRs Govern Neutrophil Activity in Aspergillosis

Abstract

Polymorphonuclear neutrophils (PMNs) are essential in initiation and execution of the acute inflammatory response and subsequent resolution of fungal infection. PMNs, however, may act as double-edged swords, as the excessive release of oxidants and proteases may be responsible for injury to organs and fungal sepsis. To identify regulatory mechanisms that may balance PMN-dependent protection and immunopathology in fungal infections, the involvement of different TLR-activation pathways was evaluated on human PMNs exposed to the fungus Aspergillus fumigatus. Recognition of Aspergillus and activation of PMNs occurred through the involvement of distinct members of the TLR family, each likely activating specialized antifungal effector functions. By affecting the balance between fungicidal oxidative and nonoxidative mechanisms, pro- and anti-inflammatory cytokine production, and apoptosis vs necrosis, the different TLRs ultimately impacted on the quality of microbicidal activity and inflammatory pathology. Signaling through TLR2 promoted the fungicidal activity of PMNs through oxidative pathways involving extracellular release of gelatinases and proinflammatory cytokines while TLR4 favored the oxidative pathways through the participation of azurophil, myeloperoxidase-positive, granules and IL-10. This translated in vivo in the occurrence of different patterns of fungal clearance and inflammatory pathology. Both pathways were variably affected by signaling through TLR3, TLR5, TLR6, TLR7, TLR8, and TLR9. The ability of selected individual TLRs to restore antifungal functions in defective PMNs suggests that the coordinated outputs of activation of multiple TLRs may contribute to PMN function in aspergillosis.

Translocation of proteins homologous to human neutrophil p47phox and p67phox to the cell membrane in activated hemocytes of Galleria mellonella

“…For this purpose we employed continuous and discontinuous sucrose gradient systems to obtain subcellular fractions after cellular disruption and the location of neutrophil phox and homologous hemocyte proteins established by Western blot analysis. For identification of hemocyte plasma membranes, antisera raised against membrane bound TLR1 [48] was employed. Studies clearly show that both p47 phox and the 47 kDa homologous protein in insect phagocytes, are cytosolic in resting cells and become associated with the plasma membrane after stimulation with PMA (Figs.…”

“…12-15) consisting of 34% (wt/wt) sucrose, characteristic of the neutrophil membrane fraction. Antibodies to insect TLR1 (plasma membrane marker, Toll-like receptor 1 [48]) were employed to locate hemocyte membranes within the continuous sucrose gradient. TLR1 reactivity occurred at approximately 34% (wt/wt) sucrose (Fig.…”

IL‐23 and the Th17 pathway promote inflammation and impair antifungal immune resistance

“…PMN are essential in the initiation and execution of the acute inflammatory response to fungi [22]. The finding that PMN were abundantly recruited to sites of infections in the face of a relevant fungal growth in condition of Th17 cell activation led us to hypothesize that the IL-23/IL-17-dependent pathway could adversely affect the antifungal effector functions of PMN.…”

Mannan and peptidoglycan induce COX‐2 protein in human PMN via the mammalian target of rapamycin

“…The study of the response of PMN to PAMP has focused on the induction of cytokines, the activation of oxidant production, the release of granular components, and the modulation of apoptosis [9][10][11]. However, few data are available regarding the activation of the arachidonic acid (AA) cascade, yet this seems of interest in view of the important role of eicosanoids in connecting innate and adaptive immunity [12][13][14][15] and the attention paid to the pharmacological modulation of both the eicosanoid receptors and the enzymes involved in their biosynthesis in many clinical settings [16,17].…”

“…This group of stimuli is of chief importance, since early protection against pathogens relies on the recognition by phagocytes of unique pattern molecules, termed pathogen-associated molecular patterns (PAMP), which are recognized through pattern-recognition receptors (PRR) by the host innate immune system. The TLR family (for review see [1, 2]), the nucleotide-binding oligomerization domain (NOD) family proteins (for review see [3][4][5]), the lectin C-type receptors such as the b-glucan receptor dectin-1 [6], and the mannose receptor (MR) family (for review see [7, 8]) include a wide array of PRR able to interact with many structural signatures expressed in microorganisms.The study of the response of PMN to PAMP has focused on the induction of cytokines, the activation of oxidant production, the release of granular components, and the modulation of apoptosis [9][10][11]. However, few data are available regarding the activation of the arachidonic acid (AA) cascade, yet this seems of interest in view of the important role of eicosanoids in connecting innate and adaptive immunity [12][13][14][15] and the attention paid to the pharmacological modulation of both the eicosanoid receptors and the enzymes involved in their biosynthesis in many clinical settings [16,17].…”