Delayed hypersensitivy and experimental interstitial pneumonitis

Area of Science:

• Immunology
• Pathology
• Pulmonary Medicine

Background:

• Prior sensitization with Mycobacterium tuberculosis components can modulate host responses to subsequent challenges.
• Complete Freund's adjuvant (CFA) induces significant inflammatory and granulomatous reactions in the lungs.

Purpose of the Study:

• To investigate the impact of prior sensitization with killed H37Ra tubercle bacilli on pulmonary reactions to intravenous (IV) challenge with CFA.
• To compare these reactions with those in nonsensitized controls.

Main Methods:

• Rabbits were sensitized with killed H37Ra tubercle bacilli or left unsensitized.
• Both groups received an intravenous (IV) challenge with complete Freund's adjuvant (CFA).
• Pulmonary reactions, including cellularity, infiltrate volume, arteritis, and lesion progression, were assessed at 24 hours, 2 weeks, and 8 weeks post-challenge.

Main Results:

• Rabbits dying within 24 hours showed acute arteritis before granuloma formation.
• Sensitized rabbits exhibited increased exudative cells and parenchymal infiltrate at 2 and 8 weeks compared to controls.
• Obliterative, granulomatous arteritis was present in both groups and unaffected by sensitization.
• Pulmonary lesions and infiltrate diminished by 8 weeks in both sensitized and nonsensitized rabbits.

Conclusions:

• Prior sensitization with killed tubercle bacilli enhances early pulmonary inflammation following CFA challenge but does not alter the development of arteritis or lesion regression.
• The study highlights the complex interplay between prior sensitization and acute inflammatory responses in the lung.