For example, IL-33-stimulated M2 macrophages play a critical role in the recruitment of leukocytes by producing chemokines (Kurowska-Stolarska et al., 2009), whereas IL-33-polarized M2 macrophages significantly decreased keratitis caused by Pseudomonas aeruginosa (Hazlett et al., 2010). Here, IL33 is linked to keratitis.