The effect of homologous and heterologous carriers on the immunogenicity of the galactocerebroside hapten.

Glycolipid haptens are capable of eliciting an immune response when complexed with a protein carrier. These experiments demonstrate that an immunogenic (foreign) carrier is required. Antibody to galactocerebroside can be produced in rats by injecting the hapten associated with heterologous (bovine serum albumin) but not homologous (rat serum albumin) protein. It appears after primary immunization in animals given pertussis vaccine or after repeated injections of the antigen emulsified in Freund's incomplete adjuvant. However, if Mycobacterium tuberculosis is added to the emulsion a protein carrier is unnecessary. In this case the bacilli may serve a carrier function in addition to their usual adjuvant action. Galactocerebroside, therefore, behaves in much the same way as conventional, covalently bound, non-lipid haptens. Antibody is only produced when the hapten is bound to an immunogenic carrier or in the presence of an adjuvant, capable of providing a stimulus to replace the carrier specific `helper' function of the T cell. Since galactocerebroside is a normal body constituent, the findings also define some of the conditions for the failure of tolerance to endogenous glycolipids in the central nervous system.