Stachybotrys chartarum-induced hypersensitivity pneumonitis is TLR9 dependent

Area of Science:

• Immunology
• Pulmonology
• Microbiology

Background:

• Hypersensitivity pneumonitis (HP) is an inflammatory lung disease caused by repeated exposure to inhaled antigens.
• T helper type 1 (Th1) immune responses, involving IL-12 and IFN-γ, are implicated in HP pathogenesis.
• Stachybotrys chartarum (SC), a fungus, is associated with respiratory illnesses including HP.

Purpose of the Study:

• To develop and characterize a murine model of SC-induced HP.
• To investigate the role of toll-like receptor 9 (TLR9) in SC-induced granulomatous lung inflammation.

Main Methods:

• A murine model was established by sensitizing and challenging mice with SC spores.
• Analysis included histological examination for granulomatous inflammation and immune cell infiltration (neutrophils, CD4+, CD8+ T cells).
• Pulmonary cytokine and chemokine expression (TNF-α, IL-12, IFN-γ) was measured.
• Experiments utilized wild-type and TLR9-deficient (TLR9-/-) mice to assess TLR9 dependency.

Main Results:

• SC exposure induced granulomatous inflammation with multinucleated giant cells, mimicking human HP.
• SC challenge led to increased pulmonary expression of TNF-α, IL-12, and IFN-γ.
• TLR9-/- mice showed significantly reduced peribronchial inflammation, immune cell accumulation/activation, and type 1 cytokine/chemokine levels.
• SC-induced granulomatous inflammation was dependent on IFN-γ, and T-cell IFN-γ production was IL-12 dependent.

Conclusions:

• TLR9 is critical for the development of type 1 granulomatous lung inflammation in response to inhaled SC.
• Dendritic cell responses mediated by TLR9 are essential for initiating this inflammatory process.
• The findings highlight TLR9 as a key factor in the immune response to fungal antigens causing HP.