SETBP1 and granulomatosis with polyangiitis: To investigate whether GPA patients in remission have an effective humoral immune response against TSST-1, we measured the IgG levels of anti-TSST-1, anti-SEA, anti-SEB and total IgG in the plasma of SA+ and SA− GPA patients in remission, as well as in age- and sex-matched HCs.