Absence of Binding of MDP, a Synthetic Immunoadjuvant, to Anti-Peptidoglycan Antibodies¹

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.