A synthetic adjuvant,
N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP), failed to produce
polyarthritis with a wide dose range in a water-in-oil
emulsion of
mineral oil such as
liquid paraffin,
Drakeol, or heavy
mineral oil. MDP, however, produced moderate to severe
arthritis with almost 100% incidence in a water-in-oil
emulsion made up of Difco incomplete adjuvant, which consists of Bavol F as an oil vehicle and
Arlacel A as an emulsifier. N-acetylmuramyl-L-alanyl-L-
isoglutamine did not produce
arthritis, whereas 4,6-diacetyl-MDP produced the disease. Bacterial peptidoglycans, such as
disaccharide peptides which were N-acetylglucosaminyl-N-acetylmuramyl-L-alanyl-D-isoglutaminyl-meso-diaminopimelyl-D-
alanine and N-acetylglucosaminyl-6,o-acetyl-N-acetylmuramyl-L-alanyl-D-isoglutaminyl-meso-diaminopimelyl-D-alanine, also produced
polyarthritis with low incidence in Difco oil but not in the other
mineral oils described above. MDP and bacterial
disaccharide peptides were able to produce the disease even in the latter
mineral oil only when the concentration of
Arlacel A was increased from 15% to 20 to 30% in the oil. We concluded that one of the minimal essential structures responsible for development of this disease is MDP, although the role of the oil vehicle remained uncertain, and there is no direct correlation between granulona formation and arthritogenicity of MDP.