Isolation of a novel lipid hapten, cytolipin S, from rat spleen

Antisera against rat erythrocytes contain agglutinins directed against unknown lipid determinants. Complement-fixation shows more reactivity with lipid extracts of rat spleen than of other rat tissues. The isolation of the reactive lipid from rat spleen, cytolipin S, is described. Cytolipin S is a glycosphingolipid containing glucose, galactose, and galactosamine with molar ratios of 1:2:1. It migrates on TLC like asialo GM1 (more slowly than cytolipin R, a ceramide tetrasaccharide, or cytolipin F, a ceramide pentasaccharide). Asialo GM1 and cytolipin S, when properly combined with auxiliary lipids, react very similarly with anti-rat erythrocyte sera by complement-fixation. However, cytolipin S is much more effective than asialo GM1 in inhibiting the hemagglutination reactions. It is concluded that cytolipin S and asialo GM1 are ceramide tetrasaccharides having different chemical structures and that the structural differences probably will be found in the carbohydrate linkages other than that between the terminal and penultimate residues.