Table 1.

Predisposing host factors and immunopathogenesis of invasive, saprophytic, and allergic bronchopulmonary aspergillosis

Patient populations	Predisposing host factors	Clinical and histological features
Acute leukemia, myelodysplastic syndrome, aplastic anemia, other causes of marrow failure	Neutropenia	Hyphal angioinvasion with vascular thrombosis and tissue infarction; scant inflammatory response; may evolve to cavitation
Allogeneic HSCT after neutrophil recovery	Immunosuppression for GVHD (e.g., corticosteroids, T-cell-depletion; tumor necrosis factor-□ inhibition)	Inflammatory fungal pneumonia; angioinvasion with coagulative necrosis resembling aspergillosis classically associated with neutropenia may occur [20–22]
Solid organ transplantation	Immunosuppression to prevent allograft rejection	May range from an acute inflammatory pneumonia to a chronic necrotizing aspergillosis; in lung transplant recipients, Aspergillus tracheobronchitis may affect the anastomotic site and cause dehiscence
Advanced AIDS	CD4+ T-cell count generally < 100/ul; immunocompromising conditions (e.g., neutropenia) and other opportunistic infections often co-exist	Acute to slowly progressive necrotizing pneumonia; variable histological findings: neutrophilic infiltrates, vascular invasion, walled-off abscesses and cavitation occur; extrapulmonary dissemination observed [23]
Chronic granulomatous disease	Defective NADPH oxidase	Varies from acute pneumonia to slowly progressive disease; pyogranulomatous inflammation without hyphal vascular invasion or coagulative necrosis; “mulch pneumonitis” is an acute hypersensitivity response to a large aerosolized exposure [24]
Pre-existing structural lung disease (e.g., emphysema, prior cavitary tuberculosis)	Comorbid conditions, including diabetes, malnutrition, inhaled and low-dose systemic corticosteroids	Chronic necrotizing pulmonary aspergillosis: slowly progressive invasive fungal pneumonia with inflammatory necrosis [25]
Aspergilloma	Pre-existing structural lung diseases, e.g. bronchiectasis or prior cavitary tuberculosis	“Fungal ball” composed of hyphal elements in pre-existing cavity; erosion into adjacent vessels can cause life-threatening hemoptysis; surgical resection is the definitive treatment for hemoptysis from aspergilloma
Allergic bronchopulmonary aspergillosis (ABPA)	Allergic disease; can be an important complication of cystic fibrosis [26]	Airway plugging with hyphae, mucous, and inflammatory cells; hyphae do not invade lung parenchyma; airway and lung hypereosinophilic inflammation; goblet cell hyperplasia; central bronchiecatasis in advanced disease

Table is adapted from [4].