Detection of antibodies against conformational epitopes of the myelin oligodendrocyte glycoprotein (MOG) molecule. Native MOG was induced on the surface of Flp-In T-REx 293 cells by the addition of tetracycline 48 hr before use. Sera or antibodies to be examined (serially diluted from × 4 to × 4096 for sera) followed by incubation of fluorescein isothiocyanate-labelled anti-rat immunoglobulin G antibodies. The per cent of positive cells was determined by FACScan. Normal rat serum (a) stained only 5·7% of native MOG-expressing cells, whereas anti-MOG monoclonal antibody (mAb), which recognizes the conformational epitope, stained 99% of the cells, indicating that almost of all the cells express native MOG on their surface. MOG-11 mAb did not react with native MOG (d). Anti-MOG antisera showed an intermediate value. (a) Normal rat serum × 64; (b) 8–18C5 × 10 000; (c) sera used for transfer, × 64; (d) MOG11 mAb, × 64.