Peptide-induced memory (IgG) response, cross-reactive with native proteins, requires covalent linkage of a specific B cell epitope with a T cell epitope.

In order to raise antibodies synthetic peptides are often coupled to a carrier protein to provide the necessary T cell determinants. Alternatively, a short synthetic determinant with a distinct sequence motif which can be presented by major histocompatibility complex (MHC) class II to T cells, can be linked directly to a B cell epitope. Recently, it has been suggested that covalent linkage between a class II-presentable T helper peptide and a B cell epitope is not required to induce antibodies against a B cell determinant (Sarobe et al., Eur. J. Immunol. 1991. 21: 1555). Therefore, we investigated the ability of an H-2d-restricted T cell determinant (AA 111-120 FERFEIFPKEK) from the influenza virus hemagglutinin, to support B cell responses to different proven B cell determinant peptides, derived from human alpha 1-antitrypsin. Antibodies against B cell epitopes crossreactive with native alpha 1-antitrypsin could be raised only when these B epitope peptides were covalently coupled to the T cell determinant through a peptide bond. No antibodies were raised against the B cell epitope when the free peptides (T and B cell epitopes) were just mixed or when the T cell epitope was conjugated via m-maleimidobenzoyl succinimide ester or bis-maleimidohexane to the B cell determinant. Antibodies against the T cell determinant were raised in all cases, regardless of the mode of presentation: just mixed with or covalently coupled to the B cell determinant. The results indicate that a covalent bond between T cell and B cell determinants in general is needed to induce anti B cell determinant antibodies cross-reactive with the native protein.