Schwann Cell Marker Defined by a Monoclonal Antibody (224–58) with Species Cross‐Reactivity. II. Molecular Characterization of the Epitope

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Abstract
A monoclonal antibody (mAb) designated 224–58 (IgM‐K) has been raised by fusion of Sp2/0‐Ag14 mouse hybridoma cell line with spleen cells of a mouse immunized with human brain myelin. This mAb binds specifically to mouse, rat, and human Schwann cells membrane. Serological tests showed that mAb 224–58 reacted with total lipid extract, but not with total protein extract of human myelin. Combination of ELISA, complement fixation, and immunoautoradiographic detection on silica gel TLC allowed us to determine that mAb 224–58 reacted with sulfomonogalactolipids, namely 3′‐sulfogalac‐tosylceramide (SGC) and 3′‐sulfogalactosyl 1‐O‐alkylether 2–O‐acylglycerol (seminolipid). The fine molecular structure of the epitope recognized by mAb 224–58 was established by studying the cross‐reactivity of this mAb toward closely related sulfolipids and by comparing its reactivity after submitting either purified sulfolipids or total lipid extracts to various chemical and enzymatic treatments. The lipidic hapten‐binding site to mAb 224–58 is dependent on (1) the sulfoester on carbon 3 of the galactose molecule, (2) the osidic bond, and (3) the carbonyl group of the fatty acid. Interestingly enough, neither the amide bond and the long‐chain base nor the OH group of the fatty acid belongs to the antigenic determinant recognized by mAb 224–58.