A synthetic complement C1q-like peptide selectively interacts with immune complexes

A water-soluble peptide possessing an immune complex selective affinity was synthesized and its primary structure established as: Leu-Glu-Gln-Gly-Glu- Asn-Val-Phe-Leu-Gln-Ala-Thr-Ser-Asp-Asp-Cys. This peptide, designated as C1 q-like peptide (CLP), represents a possible immune complex binding epitope of complement C1q. CLP has a hydrophilicity value of 0.21. At 0.5 mu M, it inhibited by 50% natural human C1q from binding to horseradish peroxidase-r abbit anti-peroxidase immune complex. CLP failed to inhibit Staphylococcus aureus protein A from binding monomeric IgG. When coated to a microplate, C LP showed selective binding to the immune complex, and could be used for ap plication in immunochemical detection of immune complex.