This is a Phase 2, multicenter study of OMS721 in subjects with the following diseases: IgA Nephropathy (IgAN), Lupus Nephritis, Membranous Nephropathy (MN), or C3 Glomerulopathy, including Dense Deposit Disease. Two cohorts will be enrolled. Cohort 1 will be subjects with corticosteroid dependent IgAN, LN, MN, or C3 Glomerulopathy. Cohort 1 subjects will all receive OMS721 in an uncontrolled, open-label design. Cohort 2 will be subjects with IgA nephropathy who are not receiving corticosteroids. This cohort will be randomized to receive either OMS721 treatment or D5W vehicle in a randomized double-blind design. Approximately 26 subjects will be enrolled (16 in Cohort 1 and 10 in Cohort 2).