[Granulomatous diseases and pathogenic microorganism]

Area of Science:

• Pulmonology
• Immunology
• Microbiology
• Radiology
• Pathology

Background:

• Granuloma formation is a chronic inflammatory response involving macrophages and T cells, typically considered a defense mechanism against persistent antigens.
• Traditional classification divides granulomas into infectious and non-infectious types, but recent evidence suggests microorganisms may play a role in non-infectious diseases.
• Distinguishing between infectious and non-infectious granulomatous lung diseases can be challenging due to morphological similarities and difficulties in identifying causative agents.

Purpose of the Study:

• To clarify the mechanisms of non-infectious granulomatous lung diseases and the role of pathogenic microorganisms.
• To discuss the potential microbial etiology of conditions like sarcoidosis and hypersensitivity pneumonitis.
• To explore advancements in imaging and histopathology for diagnosing granulomatous lung diseases.

Main Methods:

• Review of high-resolution computed tomography (HRCT) findings characteristic of various granulomatous lung diseases.
• Discussion of histopathological features and differential diagnosis considerations, emphasizing the challenge of identifying causative agents.
• Presentation of specific cases linking microorganisms (Propionibacterium acnes, thermophilic actinomycetes, Mycobacterium avium complex) to granulomatous lung conditions.

Main Results:

• HRCT provides characteristic but often non-specific imaging patterns for granulomatous lung diseases.
• Propionibacterium acnes is implicated as a potential cause of latent infection in sarcoidosis.
• Farmer's lung is linked to thermophilic actinomycetes, and Hot Tub Lung to Mycobacterium avium complex, suggesting hypersensitivity reactions.
• The distinction between infectious and non-infectious granulomas is blurred, with potential for microbial involvement in seemingly non-infectious diseases.

Conclusions:

• Pathogenic microorganisms may contribute to granuloma formation in diseases previously considered non-infectious.
• A balanced host-defense mechanism against microorganisms is crucial in these immunologic reactions.
• Further research is needed to elucidate the precise role of microbes and refine diagnostic and therapeutic approaches for granulomatous lung diseases.