The immune response to mycobacterial infections in CF is multifaceted, comprising mucociliary clearance (impaired in CF (Elborn, 2016)) and a major role of CD4 T cells that produce the macrophage-activating cytokine interferon-gamma (IFN-γ), and tumour necrosis factor alpha (TNF-α) – involved in granuloma formation (Richards and Olivier, 2019; Pereira et al., 2020). The gene discussed is CD4; the disease is cystic fibrosis.