Comparative study of the effects of peptidoglycan monomer and structurallyrelated adamantyltripeptides on humoral immune response to ovalbumin in the mouse

Peptidoglycan monomer, GlcNAc-MurNAc-L-Ala-D-isoGln-mesoDAP(omega NH2)-D-Al a-D-Ala (PGM) originating from Brevibacterium divaricatum and synthetic ada mantyltripeptides, diastereoisomers of D,L-(adamant-2-yl)Gly-L-Ala-D-isoGln (AdTP1 and AdTP2) exhibit immunomodulating activity. An experimental model in the mouse has been established with suboptimal amounts of ovalbumin (OV A) as the immunogen, and parallel testing of adjuvant activity of these thr ee immunomodulators was carried out in Balb/c, C57B16 or CBA mice. Tested c ompounds (100 or 700 mu g/mouse) mixed with OVA in saline (50 mu g/mouse) w ere administered s.c. Anti-OVA was assayed by ELISA in the sera of mice tak en 7 days after the boosters (given on days 14 and 28). The treatment with PCM and one of the diastereoisomers, AdTP2, resulted in significantly highe r increase in anti-OVA IgG levels (stimulation index up to 46) with respect to controls and groups treated with AdTP1. The effect of AdTP2 treatment w as comparable to that of PCM in most experiments after the first booster, b ut after the second booster PGM exhibited markedly better effect. PGM and A dTP2 also induced markedly higher levels of IgG1 and IgG2 anti-OVA subclass es than detected in controls and AdTP1 treated mice, indicating that these two immunomodulators might upregulate both Th1-like and Th2-like immune res ponses. (C) 2000 Elsevier Science Ltd. All rights reserved.