Immunological reactions with lysolecithin-solubilized myelin.

Rat brain myelin purified by ultracentrifugation in a sucrose gradient was solubilized with lysolecithin. The water soluble protein—lipid complexes obtained were antigenic and encephalitogenic and in a complement fixation system reacted more efficiently with anti-myelin sera than intact myelin itself. Increasing the lysolecithin/myelin ratio above the minimum required to render myelin completely soluble reduced the amount of complement fixed. This suggests that solubilization increases the number of accessible antigenic sites, while further addition of lysolecithin to the molecular surface interferes with its antibody combining capacity. Following isopycnic centrifugation the maximum complement-fixing activity was present in a fraction having a density of 1.04 at 10°, corresponding to one of three peaks of galactocerebroside concentration. Antibody to lysolecithinized myelin reacts with the myelin moiety of the complex and not with lysolecithin, since it can be removed by absorption with particulate myelin and it will not react with lysolecithinized red cell ghosts. Anti-rat myelin antiserum cross-reacts with lysolecithinized myelin from other mammalian species; to a lesser degree with frog, and only minimally with dogfish myelin. It is suggested that solubilization by lysolecithin may prove a convenient starting point for immunochemical studies on myelin by providing lipid—protein complexes which reflect the structure of the native material.