Aim: Characterize the role of humoral immune response in mechanisms of action of muramyl dipeptide immune stimulators.
Materials and methods: Mice were immunized by a complex of muramyl peptides (CMP) obtained from Salmonella typhi peptidoglycan and consisting of 3 components: 1) N-acetyl-D-glucoasminyl-(beta1- > 4)-N-acetyl-D-muramoyl-L-alanyl-D-isoglutaminyl-meso-diaminopimelic acid (GMtri); 2) N-acetyl-D-glucosaminyl-(beta1- > 4)-N-acetyl-D-muramoyl-L-alanyl-D-isoglutaminyl-meso-diaminopimeloyl-D-alanine (GMtetra) and 3) GMtetra dimer (diGMtetra), in which monomeric residues of GMtetra are linked by an amid bond between carboxyl group of terminal D-alanine of one of GMtetra residues and omega-amino group of meso-diaminopimelic acid of the other GMtetra residue.
Results: Immunization resulted in a multifold increase of IgM, IgG1 and IgG2a titers against CMP. Antibodies were directed against the whole molecule of diGMtetra and did not recognize its fragments. Sera of mice immunized with CMP protected the mice from lethal infection with Gram-negative (S. typhimurium) but not Gram-positive (Staphylococcus aureus) microorganisms.
Conclusion: Induction of protective antibodies may present a novel mechanism of action of muramyl dipeptide immune stimulators.