Induction of antibodies against a peptide hapten does not require covalent linkage between the hapten and a class II presentable T helper peptide.

Following immunization with a complex antigen, a B cell internalizes this antigen through an interaction between its surface immunoglobulins and an epitope of the antigen. Enzymatic processing of the antigen frees one or more short peptide determinants (TD) which bind to class II molecules of the B cell. If the complex TD-MHC II is recognized by the receptor of a T helper cell, T cell help is provided leading to the expansion of an antibody-producing B cell clone specific for the epitope. We present experimental evidence proving that the induction of anti-peptide hapten antibodies does not require covalent linkage between the peptide hapten and the peptide behaving as TD. Indeed, high anti-peptide hapten antibody titers are induced if an emulsion of TD and hapten are injected in the same immunization site. This result suggests a way to manipulate antibody production with useful applications to research and therapy.