TLR9-Dependent IL-23/IL-17 Is Required for the Generation of Stachybotrys chartarum–Induced Hypersensitivity Pneumonitis

Abstract

Hypersensitivity pneumonitis (HP) is an inflammatory lung disease that develops following repeated exposure to inhaled particulate antigen. Stachybotrys chartarum (SC) is a dimorphic fungus that has been implicated in a number of respiratory illnesses, including HP (1). In this study we have developed a murine model of SC- induced HP that reproduces pathology observed in human HP and hypothesized that TLR9–mediated IL-23/IL-17 responses are required for the generation of granulomatous inflammation induced by inhaled SC. Mice that undergo i.p. sensitization and i.t. challenge with 106 SC spores developed granulomatous inflammation with multinucleate giant cells, accompanied by increased accumulation of T cells. SC sensitization and challenge resulted in robust pulmonary expression of IL-17 and IL-23. SC-mediated granulomatous inflammation required intact IL-23/IL-17 responses and required TLR9, as TLR9−/− mice displayed reduced IL-17 and IL-23 expression in whole lung associated with decreased accumulation of IL-17 expressing CD4+ and γδ T cells. As compared to SC-sensitized dendritic cells (DC) isolated from WT mice, DC isolated from TLR9−/− mice had a reduced ability to produce IL-23 in responses to SC. Moreover, shRNA knockdown of IL-23 in DC abolished IL-17 production from splenocytes in response to antigen challenge. Finally, the i.t. reconstitution of IL-23 in TLR9−/− mice recapitulated the immunopathology observed in WT mice. In conclusion, our studies suggest that TLR9 is critical for development of Th17-mediated granulomatous inflammation in the lung in response to SC.

Toll-Like Receptor 9-Mediated Inflammation Triggers Alveolar Bone Loss in Experimental Murine Periodontitis

“…TLR9 has also been reported to be critical for the development of Th17-mediated granulomatous inflammation in the lung in response to Stachybotrys chartarum sensitization (50). The study demonstrated decreased expression of several proinflammatory cytokines, as well as IL-17 and IL-23, in TLR9 KO cells (50). Another in vivo investigation reported significant synergy between TLR2 and TLR9 for induction of the MyD88-dependent splenic cytokine and chemokine response to Streptococcus pneumoniae (46).…”

“…For example, a study using an in vivo model of hypersensitivity pneumonitis revealed that TLR2 and TLR9 cooperated in neutrophil recruitment and IL-17-associated cytokine production such that both neutrophil recruitment and cytokine production were significantly decreased in double-KO mice (TLR2/9 Ϫ/Ϫ ) compared to their levels in TLR2 Ϫ/Ϫ mice (49). TLR9 has also been reported to be critical for the development of Th17-mediated granulomatous inflammation in the lung in response to Stachybotrys chartarum sensitization (50). The study demonstrated decreased expression of several proinflammatory cytokines, as well as IL-17 and IL-23, in TLR9 KO cells (50).…”

Repeated Mouse Lung Exposures toStachybotrys chartarumShift Immune Response from Type 1 to Type 2

“…The type 2 and type 17 pathways have been shown to be important in the development of hypersensitivity pneumonitis from S. chartarum (41). The multiple-dosed group had increases in the numbers of CD45…”

The Putative Role of Viruses, Bacteria, and Chronic Fungal Biotoxin Exposure in the Genesis of Intractable Fatigue Accompanied by Cognitive and Physical Disability

“…Immune activation following mold exposure can also be mediated by TLR9 [264]. Engagement of these receptors on dendritic cells following aerial exposure to SC can lead to increased IFN (production by activated Th1 cells [265]). However, in other tissues, activation of these receptors by SC leads to the production of IL-23 and IL-17 and the development of pathogenic Th17 cells [265].…”

“…Engagement of these receptors on dendritic cells following aerial exposure to SC can lead to increased IFN (production by activated Th1 cells [265]). However, in other tissues, activation of these receptors by SC leads to the production of IL-23 and IL-17 and the development of pathogenic Th17 cells [265]. Other mycotoxins such as aflatoxin increase the production of forkhead box P3 (FoxP3) and regulatory T cells and promote a T helper 2 (Th2)-biased immune system [266].…”