In the pathogenesis of MPA and GPA, interleukin-8, C3a, and C5a are key molecules that can activate and recruit neutrophils to inflamed tissues, leading to a vicious cycle and aggravated disease course [3, 23]. These factors are also known as chemotactic factors for eosinophils [24–26].Therefore, high levels of inflammation that may enhance the production of eosinophil chemotactic factors may subsequently increase not only peripheral eosinophil count but also the likelihood of all-cause mortality. Here, C3 is linked to granulomatosis with polyangiitis.