Allergic Bronchopulmonary Aspergillosis (ABPA) is a hypersensitivity reaction to the colonization of airways by Aspergillus species, most commonly Aspergillus fumigatus. It primarily affects patients with asthma or cystic fibrosis (CF). 🦠 Pathophysiology & Key Features Hypersensitivity Reaction: ABPA is driven by an exaggerated T-helper 2 (Th2) immune response to Aspergillus antigens. Airway Colonization: The fungus colonizes the airways and mucus without actual tissue invasion. Inflammation: The allergic reaction causes chronic airway inflammation, obstruction, and, if untreated, leads to bronchiectasis (permanent airway widening) and pulmonary fibrosis. Symptoms: Worsening asthma symptoms (wheezing, shortness of breath), cough productive of thick, often brownish/greenish mucus plugs, and occasionally fever or malaise.