Marked enhancement of macrophage activation induced by synthetic muramyl dipeptide (MDP) conjugate using monoclonal anti-MDP antibodies

Enhancement of the immune response to hepatitis B virus vaccine by antigen specific IgM

In the present study, modulation of antibody response induced by Hepatitis B virus vaccine-IgM complex was investigated. Purified IgM-type anti HBv monoclonal antibody (1B11) was complexed to commercially available HBv vaccine (GenHevac B Pasteur, France) at varying concentrations of HBsAg (0.5, 1, 1.5 microg of HBsAg) and used to immunize BALB/c mice. An enhanced humoral immune response was obtained with the HBv vaccine-IgM complex at all the doses compared with those immunized by vaccine alone and increased antibody levels were observed with increased concentrations of HBsAg in vaccine formulation. Immunization with HBv vaccine-IgM complex mostly generated IgG-type antibodies in the sera of mice, and also gave rise to the development of hybrid cells which predominantly produced IgG-type monoclonal antibodies. Hence, results from this study indicate that 1B11 can be effectively used to obtain a better immune response to HBv vaccine.

Synthesis and immunological evaluation of the conjugates composed from a muramyl peptide GMDP and tuftsin

The conjugates of a muramyl dipeptide analog GMDP (N-acetylglucosaminyl beta 1-->4 N-acetylmuramyl-L-alanyl-D-isoglutamine) and tuftsin (Thr-Lys-Pro-Arg) were synthesized from unprotected GMDP by mixed anhydride procedure. The identity of the conjugates was confirmed by high resolution NMR and their immunomodulating properties were determined in various tests. It was found that the conjugate in which the GMDP carboxyl group forms an amide bond with the epsilon-amino group of tuftsin lysyl residue exceeds GMDP in all the activities determined. Synergism of GMDP and tuftsin was found in phagocytosis stimulation assay.

Endogenous synthesis of peptidoglycan in eukaryotic cells; a novel concept involving its essential role in cell division, tumor formation and the biological clock

Degradation products of peptidoglycan, the universal bacterial cell wall constituent, were previously found in animal tissues and urine. Reassessment and quantitative analysis of available data lead to an original concept, i.e. that eukaryotic cells synthesize peptidoglycan. We present a model in which this endogenously synthesized peptidoglycan is essential for the processes of eukaryotic cell division and sleep induction in animals. Genes for peptidoglycan metabolism, like those for lysine biosynthesis in plants, are probably inherited from endosymbiotic bacteria, the ancestors of mitochondria and chloroplasts. Corollaries of this concept, i.e. roles for peptidoglycan metabolism in tumor formation and in the biological clock, are supported by abundant evidence. We propose that many interactions between bacteria and eukaryotes are conditioned by their common genetic heritage.

Muramyl peptide-binding sites are located inside target cells

Using flow cytometry and fluorescence polarization analysis, specific muramyl peptide-binding sites were shown to be located inside T-lymphocytes, macrophages and neuroblastoma cells, but not inside B-cells. No binding sites were found on the cell surface. The number of binding sites for each cell type was determined. Two types of binding sites were observed for myelomonocytic WEHI-3 cells with Kd values of 21 and 540 nM. Inhibition analysis demonstrated that for effective binding, an intact glycopeptide molecule and D-configuration of isoglutamine residue are important.

Uptake of muramyl dipeptide fluorescent congeners by normal rabbit bronchoalveolar lavage cells: a study using flow cytometry

Muramyl dipeptide (MDP) is the minimal adjuvant-active structure of mycobacterial cell walls and is known to activate monocytes/macrophages, but mechanisms involved with uptake and activation of these cells have not been completely defined. Earlier studies addressing uptake of MDP and the question of receptors have utilized radioligands and murine peritoneal macrophages. We used fluorescent congeners of MDP and flow cytometry to explore kinetics and specificity of uptake by bronchoalveolar cells of normal rabbits. Both washed cells and cell suspensions from which the fluorescent congeners were not washed were used, and incubation was carried out primarily at 4 degrees C. Fluorescence microscopy consistently revealed intracellular but no visible membrane fluorescence of alveolar macrophages. Uptake was dose dependent but was not saturable up to concentration limits of fluoresceinated muramyl tripeptide (MTP-FITC) imposed by the system, and was partially inhibited by excess unlabeled MDP, consistent with specific inhibition. Alveolar macrophages, but not lymphocytes, demonstrated specific uptake at 4 degrees C, with rapid on- and off-times. Uptake was enhanced 7-fold at 37 degrees C. Uptake was greater by larger, more granular macrophages than by smaller, less granular macrophages, but no difference in uptake was found when cells of similar size but different densities were compared. The exact mechanism of the rapid uptake at 4 degrees C is uncertain but appears to be competed for by unlabeled MDP.

Antibody-mediated enhancement of hormone activity

The enhancement of hormone activity by antibodies has been known for many years; however, investigation into the molecular basis of the phenomenon has only recently begun. A number of mechanisms for this enhancement, including "buffering" or slow release, bivalency and Fc region, and conformational and receptor "restriction" effects, have been documented or proposed. The availability of panels of monoclonal antibodies of distinct combining site specificity have aided in these studies and contributed substantially to our understanding of hormone-receptor interactions.

In vitro regulation by muramyl dipeptide of interferon production from peripheral blood mononuclear cells of healthy volunteers

We investigated the effect of N-acetyl-muramyl-L-alanyl-D-isoglutamine (MDP) on interferon (IFN)-alpha and -gamma production by peripheral blood mononuclear cells from healthy subjects. MDP, on its own, was found to lack the ability to induce IFN production. However, this synthetic adjuvant was able to modulate IFN production induced by other stimuli. In cultures from a considerable number of tested donors, MDP enhanced IFN-gamma levels induced by phytohaemagglutinin. This effect was further potentiated after depleting the PBMNC cultures of their adherent cells. In contrast, MDP significantly suppressed the Sendai virus-induced IFN-alpha and this effect was reversed following adherent cell depletion. Identical regulatory effects on IFN production were exerted by the adjuvant active analogue of MDP, namely murabutide. The adjuvant inactive stereoisomer, MDP (DD) exhibited a similar enhancing effect on IFN-gamma but had a significantly lower inhibitory activity on IFN-alpha production. The potential value of this generation of immunomodulators in the treatment of viral infections and in models for studying the regulation of IFN at the molecular level is discussed.

Marked enhancement in vivo of adjuvant activity of muramyl dipeptide to protein antigens and to synthetic weak immunogens with monoclonal anti-muramyl dipeptide antibodies

Priming of mice with complexes of antigen coupled to muramyl dipeptide and monoclonal anti-muramyl dipeptide antibodies enhanced the adjuvant activity of muramyl dipeptide on the humoral response to the antigen. The enhancement did not occur with free (uncoupled) muramyl dipeptide and required the presence of an adjuvant-active hapten within the complex as well as the Fc fragment of the monoclonal antibody. This system proved highly effective in eliciting antibodies to synthetic weak immunogens whereas muramyl dipeptide, on its own, exerts very little or no adjuvant activity. The effect was not due to a general polyclonal activation and was restricted to the antigen coupled to the synthetic adjuvant. Possible pathways involved in this phenomenon are discussed.