SPI1 and respiratory system disorder: For example, a conditional PU.1‐deficient mouse line displayed attenuated allergic airway inflammation and reduced gene expression of the M2 macrophage markers Ym‐1 and Retnla in lung tissues following exposure to allergens (Qian et al., 2015); this suggested that Spi1 expression plays a significant role in alternative activation of macrophages to an M2 phenotype in that respiratory disease.