M1 macrophages can secrete proinflammatory mediators such as tumor necrosis factor (TNF)-α and IL-6 to aggravate lung injury (Kim et al., 2007), while M2 macrophages are beneficial for lung tissue repair and homeostasis in asthma (Moreira et al., 2010). In severe asthma, especially in the steroid-resistant manifestation, M1 macrophages play a leading role in the pathogenesis  (Liu et al., 2014). Here, TNF is linked to asthma.