However, a previous in vitro study suggested that titanium activates macrophages, which promote the secretion of chemokine (C–C motif) ligands 17 and 22 (CCL17 and CCL22), inducing Th2 differentiation.[16] In serum cytokines measured by cytokine multiplex array, the patient’s serum CCL22 level at the development of EGPA increased compared to that at the development of MPA. This evidence concerns the gene CCL17 and microscopic polyangiitis.