The invention relates to C2a inhibitors, which bind to C2a and block the functional activity of C2a in complement activation. The inhibitors include antibody molecules, as well as homologues, analogues and modified or derived forms thereof, including immunoglobulin fragments like Fab, F(ab′)2 and Fv,b small molecules, including peptides, oligonucleotides, peptidomimetics and organic compounds. A monoclonal antibody, which bound to C2a and blocked its ability to activate complement was generated and designated 175-62. The hybridoma producing this antibody was deposited at the American Type Culture Collection, 10801 University Blvd., Manassas, Va. 20110-2209, under Accession Number PTA-1553.