The binding of the synthetic immunoadjuvant N-acetyl-muramyl-l-alanyl-d-isoglutamine (MDP, for muramyl dipeptide) to human and rabbit sera containing peptidoglycan (PG) antibodies was investigated. Studies were performed by employing the corresponding 14C or 125I-labeled compounds in Farr-type binding and inhibition assays. Whereas MDP did not react with naturally occurring or experimentally induced PG-antibodies, the analog of MDP MDP-l-Lys-d-Ala did bind to hyperimmune rabbit anti-PG sera, but not to the human sera tested. These studies indicate that the radioimmunoassays employed basically are applicable for the selection of nonimmunogenic MDP analogs possessing immunoadjuvant activity.
The work at Pasteur Institute was supported by INSERM Grant C.R.L. No. 77-4060.1.