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Peptidoglycan monomer, GlcNAc-MurNAc-L-Ala-D-isoGln-mesoDAP(wNH2)-D-Ala-D-Ala (PGM, PLIVA, Croatia) is a non-toxic, apyrogenic and water-soluble natural compound of bacterial origin. The detailed study and characterization of its adjuvant properties has recently been systematically performed in mice model1-3. The studies revealed that PGM, when given to mice together with the antigen, enhances the level of specific IgGs in the sera and not affects either total or specific IgEs. Subclass analysis of specific IgGs revealed that PGM stimulated both IgG1 as well as IgG2a and IgG2b classes of antibodies. Analysis of IFN-g and IL-4 production from OVA specific cells isolated from draining lymph nodes of immunised mice, revealed stimulative action of PGM on production of both cytokines, indicating that PGM is stimulator of both Th1 and Th2 types of immune response. Its action is very fast and short upon parenteral administration, because of its fast degradation by the amidase present in mammalian blood. Its metabolites, the pentapeptide (PP) and the disaccharide (DS), are not adjuvant active compounds. In view of those findings we hypothesized that PGM-s adjuvant action might be improved in appropriate formulations where PGM's availability would be prolonged.The goal of this study was to test whether oil based and liposome based adjuvant formulations containing PGM would improve its adjuvant efficacy. In experimental model in mice, using OVA as an antigen, PGM in Incomplete Freund's adjuvant (IFA) induced significantly higher levels of OVA-specific antibodies (measured by ELISA) in comparison to both PGM and IFA alone. Quantification of OVA-specific IgG1 and IgG2a (by ELISA) revealed that Th1/Th2 balance was directed towards Th1 direction with this formulation, similar to the one obtained using Complete Freund's adjuvant (CFA). Liposome based formulations were prepared by encapsulating PGM into large multilamellar negatively charged vesicles using synthetic dipalmitoyl phosphatidylcholine. Such preparation raised higher OVA-specific IgG levels in immunised mice sera in comparison to both, PGM in saline, and to empty liposomes. Th1/Th2 balance (measured by ratio of specific IgG1/IgG2a) was not significantly changed with this formulation in comparison to the Th1/Th2 balance obtained in mice immunised with the OVA alone in saline.In conclusion, both approaches - liposome based and oil based - improved adjuvant efficacy of PGM.1Tomašić J et al. Comparative study of the effects of peptidoglycan monomer and structurally related adamantyltripeptides on humoral immune response to ovalbumin in the mouse. Vaccine 2000 ; 18:1236-43.2Halassy Špoljar B et al. Influence of adjuvant-active peptidoglycan monomer on specific T cell responses in mice. Vaccine 2002 ; 20: 3543-35503Halassy B et al. Adjuvant activity of peptidoglycan monomer and its metabolic products. Vaccine 2002 ; in press |
