Recognition of angiotensin II: Antibodies at different levels of an idiotypic network are superimposable

Genetic and sequence information are reported for an angiotensin II-reactive antibody (Ab1, MAb 110) and an anti-anti-idiotypic antibody (Ab3, MAb 131) that have identical antigen binding properties and that are related by an anti-idiotypic antibody (Ab2-β) that satisfies accepted biochemical criteria for an internal image-bearing antibody. The sequences of the variable regions of the Ab3 and of the Ab1 are nearly identical, even though the Ab1 is an antibody to a peptide and the Ab3 is an antibody to a globular protein. Significantly, amino acid residues that make critical contacts with antigen in the crystal structure of the Ab3-antigen complex are highly conserved in Ab1, suggesting that the epitopes of the Ab2-β recognized by the Ab3 do indeed resemble the bound structure of the antigen.