Identification of a neodeterminant in complexes of human brain Thy-1

Human Thy-1 glycoprotein was purified from brain cortex membranes. Antibodies were produced in rabbits by immunization with purified Thy-1 and with brain homogenate. Both preparations of antibodies reacted with monomers of 125I-labeled Thy-1. In addition, the antibodies against the purified antigen also recognized a determinant which was absent, or present in very low amounts, in homogenates of human brain. Analysis by gel filtration in Nonidet-P40 or deoxycholate revealed the presence of complexes of purified Thy-1 that were specifically precipitated by antibodies against this determinant. It was also shown that anti-monomer antibodies were unable to react with the complex form of Thy-1. These complexes seemed to be composed of a varying number of Thy-1 molecules. By treatment with sodium dodecyl sulfate, the multimers were completely dissociated into monomers. The tendency to complex formation seems to be unique for human Thy-1, since Thy-1 analogues of other species do not show this property when isolated.