Thy-1 antigens have been isolated from C57BL/10 mouse brain. Thy-1 antigenic activity was followed during purification by measuring the rat-mouse cross-reacting determinants of the Thy-1 molecule that were recognized by a rabbit antiserum prepared against Thy-1 glycoprotein isolated from rat brain. After solubilization with deoxycholate, mouse brain Thy-1 antigens were purified by affinity chromatography to Lens culinaris lectin and by gel filtration. A 923-fold enrichment in Thy-1 activity and a 26% yield were obtained; the antigenic activity was associated with a glycoprotein of m.w. 25,000 estimated by SDS gel electrophoresis on 10% acrylamide gels.

The serologic and biochemical properties of Thy-1 molecules purified from mouse (Thy-1.2) brain were very similar to those of Thy-1 molecules purified from rat (Thy-1.1) brain and thymus. Heteroantisera produced against mouse brain Thy-1 glycoprotein detected mouse-specific as well as rat-mouse cross-reacting determinants of the Thy-1 molecule but did not discriminate between Thy-1.1 or Thy-1.2 alloantigens.

The presence of Thy-1.2 determinants on purified Thy-1 glycoprotein could be demonstrated only in the absence of detergent. In deoxycholate, monomeric Thy-1 molecules were unable to block either binding or cytoxic activity of anti-Thy-1.2 sera; after removal of deoxycholate, aggregated Thy-1 molecules could partially block the binding or the cytotoxic activity of anti-Thy-1.2 sera. Other antigenic determinants of the molecule were not affected by detergent.

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This work was supported by the National Cancer Institute of Canada.

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