Human antiidiotypic antibody against opiate receptors

Sera containing antibodies to β-endorphin from 2 patients with major depressive disorder were shown to have antiidiotypic antibodies that specifically inhibited reactivity between anti-β-endorphin IgG and β-endorphin. Autologous and homologous antiidiotypic anti-anti-β-endorphin IgG antibodies were isolated by affinity chromatography. The purified antiidiotypic did not bind β-endorphin but competed with [¹²⁵I]β-endorphin for rat brain opiate receptors. Normal IgG that was similarly treated had negligible competitive effects. The antibody bound to the membrane preparation; such binding was inhibited by opiate receptor ligands. Binding of the antiidiotype to a 60,000- dalton protein from rat brain was detected by Western immunoblot analysis. This protein corresponds in molecular weight to proteins proposed to be components of opiate receptors. These findings imply that immune reactivity to neuropeptides could contribute to psychiatric impairment.