[Study on a tumor associated antigen on a rat fibrosarcoma cell line--chemical structure of an antigen reactive to a rat natural antibody].

Conventionally bred rats possess a natural antibody (NA) in their sera, which is cytotoxic in its effect on a KMT-17 tumor cell line derived from a fibrosarcoma induced by 3-methylcholanthrene and can be absorbed by normal rat tissues. We have succeeded in isolating and purifying an antigen reactive to NA from the tumor cells as a glycosphingolipid (GSL). GSLs from the tumor cells were separated into neutral and acidic fractions. The former fraction was judged to be antigenic as detected by its capacity to absorb NA. The antigenic fraction was further separated into 7 fractions, Fr.A to Fr.G, by silicic acid chromatography. The antigenic activity was detected in only Frs.D and E, although Fr.D was a more potent antigen than Fr.E. Chemical and immunochemical analyses showed that both the fractions are lactoneotetraosylceramide (paragloboside), Gal (beta 1-4) GlcNAc (beta 1-3) Gal (beta 1-4) Glc (beta 1-1) ceramide, and that the more active GSL, Fr.D, contains larger amounts of long fatty acid chains. Inhibition studies using disaccharides and monosaccharides indicated that a N-acetyllactosamine moiety, Gal (beta 1-4) GlcNAc, is a specific site of the GSL antigen to NA. These results suggest that a sugar chain portion of this GSL is required for defining specificity and that the ceramide portion plays a role in potentiating the antigenicity of this GSL antigen.