Multiple antigen peptide. A novel approach to increase detection sensitivity of synthetic peptides in solid-phase immunoassays.

We describe a novel approach to detect antibodies to synthetic peptide antigens in solid-phase radioimmunoassays, using a multiple antigen peptide (MAP) system. The MAPs consist of multiple copies of peptides that are synthesized as single units on a branching lysyl matrix using a solid-phase peptide synthesis method. The efficacy of the MAP approach in solid-phase immunoassays was compared with the conventional approach using a monomeric peptide of the immunodominant epitope of the circumsporozoite proteins of two species of malaria. Two monomeric peptides with 12 and 17 residues were found to bind poorly to plastic surfaces at a concentration up to 30 micrograms/ml, and showed no immunoreactivity to specific polyclonal or monoclonal antibodies, while the corresponding MAP-containing peptides showed excellent binding capacity and immunoreactivity at a concentration of 0.11 microgram/ml. The immunoreactivity of MAP-containing peptides was also superior to that of monomeric peptides conjugated to a protein carrier. The effects of various arrangements of lysyl branching of MAP on antigenicity were also studied, and the optimal number for lysyl branching of MAP was found to be octameric. Thus, the MAP, by enhancing the coating capacity and the avidity of synthetic peptides, provides increased sensitivity and reliability for the use of synthetic peptide to study antigen-antibody interactions on solid surfaces.