IL5 and asthma: Furthermore, Th2 cells can secrete specific cytokines, such as IL-13, IL-5, and IL-4, to cause asthma and immune abnormalities [29], and the presence of asthma can increase the number of circulating Th2 memory cells, which increases atopy and enhances Th2 responses, such as increasing serum IgE and eosinophil levels, in IgG4-RD [28, 30]; this phenomenon explains why the relapse rate of patients with a history of asthma is increased.