CD8A and hypersensitivity pneumonitis: In the lungs of affected individuals, a T helper 1 (TH1) alveolitis is seen with an accumulation of CD4+ T cells, elevated CD4/CD8 ratio, and release of proinflammatory cytokines, for example, tumour necrosis factor α (TNF-α) and interferon γ (IFN-γ).1 Eventually, non-necrotising granulomas are formed, which can lead to organ function impairment and sometimes failure.1