The disclosure provides peptide compounds that regulate the complement system and methods of using these compounds. Specifically the disclosure provides an isolated, purified peptide of 30 amino acids derived from human astrovirus protein, called CP1. The peptide compounds disclosed include peptide mimetics, peptide analogs and/or synthetic derivatives of CP1 having, for example, internal peptide deletions and/or substitutions, deletions and/or substitutions at the N-terminus and C-terminus, and that are able to regulate complement activation. The disclosure further provides pharmaceutical compositions comprising 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.
