C3 and Henoch-Schoenlein purpura: For example, IgA nephropathy is caused by IgA deposition in the kidneys; immunoglobulin A vasculitis (IgAV) is a systemic disease caused by IgA and complement component 3 (C3) deposition in small blood vessels; and there are related studies suggesting that Kawasaki disease may be a type of IgA vasculitis (Noval Rivas et al., 2019).