An immune complex selective affinity matrix utilizing a synthetic peptide.

A synthetic peptide possessing an amino acid sequence patterned on the globular head region of human complement component 1 subcomponent q (C1q) was tested for immunoglobulin binding. The peptide designated complementary binding peptide 2 (CBP2) was able to inhibit Staphylococcus aureus Protein A and human C1q from binding rabbit immunoglobulin at peptide concentrations for 50% inhibition of 1 and 10 microM, respectively. When attached to a solid-phase matrix in a column, CBP2 was able to bind immune complexes consisting of horseradish peroxidase plus rabbit antiperoxidase antibody or alkali-aggregated human immunoglobulins. A 1:4 mixture of immune complex to free immunoglobulin when passed over the CBP2 column demonstrated selective immune complex binding. Further controls established that CBP2 was in fact binding the immunoglobulin component of the immune complexes in a reversible fashion. The immune complex specificity of the column suggested a functional affinity was forming when CBP2 interacted with immune complexes. The possibility that the sequence of CBP2 is part of the immunoglobulin binding site of human C1q is discussed.