Influence of a synthetic adjuvant (MDP) on qualitative and quantitative changes of serum globulins.

Administered to guinea-pig, a synthetic compound, N-acetyl-muramyl-L-alanyl-D-isoglutamine (MDP), has been previously shown to substitute for Mycobacteria in Freund's complete adjuvant. Moreover, MDP increases the humoral immune response even when administered in an aqueous solution to mice. In the present report, it was demonstrated that administered to guinea-pig in a water-in-oil emulsion, MDP or active analogues favoured the production of IgG2 antibodies against ovalbumin. In contrast, derivatives of MDP which had no adjuvant activity failed to induce this particular class of immunoglobulins. MDP without antigen, in contrast with LPS or FCA, did not induce changes in immunoglobulin levels in mice. Administered in mice with an antigen, MDP induces an increase of IgG1 although the immunoglobulin levels are lower than those observed after immunization with adjuvants injected in a water-in-oil emulsion.