Tfh1 cells were also increased and positively correlated with IgG4-RD activity, independent of IgG4 levels (144).In MPA/GPA, Tfh2 cells increased significantly, promoting B cell proliferation, differentiation, and germinal center formation by secreting IL-4 and IL-21 (78, 79). The gene discussed is IL21; the disease is microscopic polyangiitis.