The present invention discloses the use of bacterial IgA1 proteases to treat IgA1 deposition in tissue and organs. Bacterial IgA1 proteases specifically cleave IgA1 molecules and thus provide a means to specifically cleave and remove IgA1 depositions. Accordingly, therapeutic agents for the treatment of diseases characterized by IgA deposition are provided. In particular, therapeutic agents to treat IgA nephropathy, Dermatitis herpetiformis (DH), and Henoch-Schoenlein purpura (HS) are disclosed.