The occurrence of anti-3-fucosyllactosamine antibodies and their cross-reactive idiotopes in preimmune and immune mouse sera.

The carbohydrate determinant 3-fucosyllactosamine (3-FL), Gal(beta 1-4)[Fuc alpha 1-3]GlcNAc-R, which is also known as SSEA-1 or as the X determinant, is very immunogenic in BALB/c mice. Many monoclonal antibodies directed against this structure have been obtained by immunization of mice with murine teratocarcinomas and human carcinomas and myeloid cells. We have undertaken an analysis of the regulation of these antibodies and of their idiotypic, structural, and genetic diversity. We have described previously the preparation of syngeneic monoclonal anti-idiotypic antibodies (6C4 and 6B1) that reacted with 50% of a panel of monoclonal anti-3-FL antibodies. In this study, we have examined the occurrence of anti-3-FL antibodies and their cross-reactive idiotopes in the sera of unimmunized and immunized mice. All BALB/c sera examined had more naturally occurring antibodies against 3-FL than against four other glycolipid antigens, and the 6C4 and 6B1 idiotopes were also detected in these sera. Approximately 25% of the anti-3-FL antibodies could be removed from a pool of BALB/c sera by a 6C4 affinity column, and the eluate from this column exhibited strong binding to 3-FL antigens. After a single i.v. injection of a 3-FL-positive glycolipid coated on Salmonella minnesota, anti-3-FL titers rose in BALB/c mice. The level of 6B1 idiotope rose in most mice, but the idiotope level showed no correlation with anti-3-FL titers. Naturally occurring antibodies against 3-FL were also noted in the sera of AKR, C3H/He, DBA/2, BALB/c-nu/nu, and CBA/CaHN mice but not in C57BL/6, SM, or CBA/N mice. A single i.v. injection of antigen elicited an antibody response in C3H/He mice but not in C57BL/6, SM, or DBA/2 mice. These data indicate that several strains of mice have more naturally occurring IgM antibodies against the 3-FL structure than against other glycolipids, and that this response may be genetically regulated. The 6C4 and 6B1 cross-reactive idiotopes that we have identified previously on monoclonal antibodies are also present in preimmune and immune sera. The existence of a population of B lymphocytes that are primed against the 3-FL determinant accounts in part for the immunogenicity of this structure.