| Primary graft dysfunction (PGD) |
| Acute cellular rejection |
| Lymphocytic bronchiolitis |
| Humoral rejection (e.g. de novo anti-human leukocyte antigen antibodies) |
| Gastro-oesophageal reflux and microaspiration |
| Infection |
| Viral |
| Bacterial |
| Fungal |
| Persistent neutrophil influx and sequestration (bronchoalveolar lavage neutrophilia) |
| Autoimmunity (collagen V sensitisation) |