The specificity of murine polyclonal and monoclonal antibodies to the haptenic drug chlorhexidine induced by chlorine-generated chlorhexidine-protein conjugates.

Polyclonal and monoclonal antibodies to the antibacterial agent chlorhexidine (1,1'-hexamethylene bis [5-(p-chlorophenyl)]biguanide, mol. wt = 505) were raised using a chlorine-generated N-chloro chlorhexidine-keyhole limpet haemocyanin (NCC-KLH) conjugate as the immunogen. Antibodies were detected by ELISA, using a semi-chlorhexidine derivative conjugated to human serum albumin (SC-HSA) as the antigen. Free chlorhexidine could completely inhibit both polyclonal and monoclonal antibody binding to SC-HSA. Direct binding and inhibition ELISA studies revealed that the N-chlorination of chlorhexidine does not significantly alter its specificity as an immunogen or antigen and that chlorhexidine has two identical epitopes. Each epitope consists of the p-chlorophenyl biguanide structure of which the terminal p-chlorophenyl group appears to be immunodominant. Chlorhexidine is, therefore, a symmetrical divalent hapten and this implies that it may be capable of eliciting immediate hypersensitivity reactions by divalent interaction with antibodies induced by chlorine-generated N-chloro-chlorhexidine-protein immunogens. The clinical significance of these findings is discussed.