A genetic system to elicit and monitor antipeptide antibodies without peptide synthesis.

We present a simple and flexible procedure to elicit and assay anti-peptide antibodies without peptide synthesis. It consists of expressing the peptide of interest in the form of a genetic insert within two different "recipient" bacterial proteins. One hybrid protein is used as immunogen for the induction of antibodies against the inserted peptide and the other as antigen for monitoring the anti-peptide antibodies raised. The two "recipient" proteins used are the MalE and the LamB proteins from E. coli. The MalE hybrid proteins can be affinity purified on an amylose column using mild nondenaturing conditions and can be crystalized for structural studies; LamB hybrid proteins express the inserted peptide on the cell surface so that intact bacteria can be used as a reagent. We chose, as a model peptide, a B-cell epitope from the pre-S(2) region of Hepatitis B virus. With both MalE and LamB hybrid proteins, high titres of anti-preS antibodies, able to react with native HBsAg particles, were induced in mice. The anti-peptide antibody titres recorded by ELISA were comparable to those obtained when either a synthetic peptide, or the hybrid proteins, were used as immobilized antigen.