The present invention provides peptide compounds that regulate the complement system and methods of using these compounds. The invention is an isolated, purified peptide of 30 amino acids derived from human astrovirus protein, called CP1. The invention is directed to peptide compounds that are peptide mimetics, peptide analogs and/or synthetic derivatives of CP1 having, for example, internal peptide deletions and substitutions, deletions and substitutions at the N-terminus and C-terminus, and that are able to regulate complement activation. The invention further provides pharmaceutical compositions of therapeutically effective amounts of the peptide compounds and a pharmaceutically acceptable carrier, diluent, or excipient for treating a disease or condition associated with complement-mediated tissue damage.
