Abstract
A radioimmunoassay for Nα-(N-acetylmuramyl-alanyl-D-isoglutaminyl)-Nε-stearyl-lysine (MDP-Lys-L18) was established. Antibody to MDP-Lys-L18 was obtained from rabbits by immunization with MDP-Lys-L18 conjugated with bovine serum albumin (BSA). 3H-MDP-Lys-L18 labelled at C9 and C10 of the stearyl residue was used. The ammonium sulfate method was adopted for the separation of bound and free fractions. Though the protein binding of MDP-Lys-L18, which was due to the stearyl residue in the molecule, influenced the sensitivity of the radioimmunoassay, the lower limit for the quantitative determination of MDP-Lys-L18 in serum was estimated to be 500pg/ml and the coefficient of variation of this assay was between 3 and 5%.