| Summary: | Patients with granulomatosis with polyangiitis (GPA) are prone to disease relapse. Currently, no good biomarkers are available to predict relapses in individual patients. This study aimed to determine whether patients at risk for relapse can be distinguished based on increased in vitro autoantibody production.Eighty-four proteinase 3 (PR3) anti-neutrophil cytoplasmic antibody (ANCA) positive GPA outpatients were prospectively monitored for up to two years and 32 healthy controls were included. At periodic intervals peripheral blood mononuclear cells were isolated, cultured and in vitro production of total and PR3-ANCA-specific IgG was determined. Moreover, serum ANCA titers were measured by indirect immunofluorescence.Sixteen patients (21%) relapsed during the follow-up period. At time of inclusion no significant differences were present for ANCA production between relapsing and non-relapsing patients. Samples before relapse exhibited increased serum ANCA titers and in vitro PR3-ANCA IgG levels compared with inclusion samples from non-relapsing patients. When evaluating changes over time, increasing serum ANCA titers were observed prior to relapse compared to a 1-year follow-up from non-relapsing patients. No significant change in in vitro PR3-ANCA levels occurred prior to relapse, compared to non-relapse patients.While differences were observed for the serum ANCA titer in relapsing and non-relapsing patients, monitoring in vitro PR3-ANCA IgG production does not improve relapse prediction in GPA patients.
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