IL21 and tuberculosis: SMAD4 is a downstream signaling molecule of TGFβ. Increased expression of TGFβ (and IL‐10) in the bronchoalveolar lavage cells of TB patients (compared to other lung diseases) may suppress effective anti‐TB immunity (Bonecini‐Almeida et al., 2004; David & Massagué, 2018). SMAD4 is crucial for differentiation of TH17 cells through IL‐21 (56).