Restoration and stimulation of the in vitro immune response of B cells to sheep erythrocytes by interleukins and muramyl dipeptide (MDP)

The in vitro effect of new muramyl peptide derivatives on cytotoxic activity of NK (natural killer) cells from hamsters bearing Ab Bomirski melanoma

The modulation of NK activity by muramyl dipeptides derivatives against Ab (amelanotic) Bomirski melanoma and human erythroleukemia K562 cells was studied in vitro. The stimulatory effect was observed for 3 of 7 muramyl dipeptides: MDP(L-Ala)C921, MDPC857 and L18-MDP(Ala) in relation to cytotoxic activity of NK cells obtained from peripheral blood and spleen of healthy and Ab Bomirski melanoma bearing hamsters. An increased of cytotoxic activity NK cells isolated from animals before and during the transplantable phase of the tumor against K562 was found. A similar stimulation was received for NK cells obtained from animals against their own melanoma cells. The most significant influence of examined MDP derivatives on the cytotoxic activity of NK cells were obtained from animals between 10 to 12 days of tumor growth. The extent of the modulation of cytotoxic activity of NK cells was dependent on its initial value both in healthy control and Ab Bomirski melanoma bearing hamsters. If natural cytotoxic activity was high the stimulatory effect of the examined MDP derivatives was only slightly expressed.

Potential adjuvants for synthetic vaccines. I. Modulators of macrophage activation

The synthesis and biological activities of several glycopeptidolipids derived from muramyl dipeptide (MDP) are described. In combination with gamma interferon (INF-gamma) MDP derivatives 3c and 3d carrying glycyrrhetinic acid as rigid beta-aglycone synergise the action of the lymphokine in the release of H2O2 by activated human macrophages, while MDP derivatives 3a and 6a carrying the more flexible diphytanyl glycerol beta-aglycone inhibit it.

Comparative study of immunomodulatory properties of muramyl peptides on immune system cells of young and old mice

The immunomodulatory effects of two synthetic muramyl peptides (MP): muramyl dipeptide and glucosaminyl- muramyl dipeptide have been compared. It was shown, that MP effects on immune response are a consequence of the alteration in T lymphocyte regulators balance. MP action on old mice immune response and lymphocyte function was stimulating only: increasing of T helper precursors frequency and IL-1 production by macrophages. In the latter both MPs acted as correctors, recovering the decreased IL-1 production by old mice macrophages to young control level.

Flow cytometric analysis of opposite effects of a monokine on proliferation and differentiation of murine B lymphocytes

A 35,000 mw factor able to replace macrophages (FRM) in the induction of the in vitro antibody response to sheep erythrocytes has been isolated from the supernatant of murine resident peritoneal macrophage cultures. Purified FRM, when added at the outset of cultures, induced B cells to generate an antigen-specific antibody response. The signals provided by FRM in the process of B cell activation were analyzed using a polyclonal model. Cell cycle analysis by multiparameter flow cytometry after acridine orange staining showed that FRM, on its own, did not trigger the transition of B cells from the G0 to the G1 stage of the cell cycle. In addition, FRM affected neither the basal intracellular free calcium level ([Ca2+]i) nor the rapid increase in [Ca2+]i induced by crosslinking of membrane immunoglobulin (mIgM) with anti-mu antibodies. In parallel with its positive effect on B cell differentiation, FRM markedly reduced both proliferation and cell cycle progression of B cells stimulated with anti-mu plus interleukin 4 (IL-4). Indeed, the addition of FRM to such cultures led to a preferential accumulation of cells in the early G1 compartment of the cell cycle and to a decreased frequency of cells in all other phases including G1B, S and G2/M.

Increased expression of alkaline phosphatase activity in stimulated B lymphocytes by muramyl dipeptide

We have recently shown that the synthetic immunomodulator muramyl dipeptide (MDP) acts on murine B lymphocytes. It synergizes with interleukin 2 and interleukin 4 to stimulate, respectively, the differentiation and the proliferation of B cells. In the present study, MDP was shown to increase the proliferation of B cells stimulated by lipopolysaccharide (LPS). Moreover, the expression of alkaline phosphatase activity induced by LPS was markedly enhanced by MDP. These effects were time- and dose-dependent. The present report suggests that the biochemical mechanism by which MDP exerts its effects may involve protein phosphorylation-dephosphorylation pathways.

Muramyl dipeptide (MDP) synergizes with interleukin 2 and interleukin 4 to stimulate, respectively, the differentiation and proliferation of B cells

The synthetic immunomodulator muramyldipeptide (MDP) can stimulate B cells. MDP, when used alone, was apparently unable to induce the differentiation or proliferation of resting B cells. In contrast, MDP appeared to synergize with a single recombinant interleukin (IL) to stimulate either their differentiation or proliferation. We used single interleukins to avoid synergistic and antagonistic effects inherent in the use of several factors. IL-2 was found to be sufficient to restore the specific immune response of resting B cells to sheep erythrocytes; MDP greatly increased the number of plaque-forming cells of such IL-2-stimulated B cells. In contrast, IL-4 and interferon-gamma (IFN-gamma), either alone or in the presence of MDP, had no effect in this differentiation assay. MDP was also able to stimulate polyclonally activated B cells. IL-4 increased the proliferation of anti-IgM-stimulated B cells, leading to enlargement and driving more cells into the cell cycle; these effects were further enhanced by MDP, more cells being induced to proliferate, to enlarge, and to progress into the cycle with a higher frequency of cells in the G1B, S, and G2/M compartments. Intracellular free calcium levels were not increased by IL-4 and/or MDP, and the two compounds did not modify the anti-IgM-induced calcium mobilization. Therefore, MDP appears to amplify cytokine effects in B cell activation, by a mechanism which does not appear to involve free calcium mobilization.

Photoaffinity labelling of macrophages and B-lymphocytes using 125I-labelled aryl-azide derivatives of muramyldipeptide

Two 125I-labelled aryl-azide derivatives of MDP have been synthesized. Photoaffinity labelling experiments demonstrated cell surface binding sites for muramylpeptides on activated B-lymphocytes and intracellular muramylpeptides binding protein(s) of 40-45 kD in rat alveolar macrophages.

N-acetylmuramyl-L-alanyl-D-isoglutamine stimulates the immune response of B cells. Use of fast protein liquid chromatography to purify a novel monokine involved in this effect

The immune response of murine B cells, which requires the presence of various cytokines, was stimulated by N-acetylmuramyl-L-alanyl-D-isoglutamine. A novel monokine involved in this effect has been partially purified from the conditioned medium of peritoneal macrophages by using affinity chromatography on Blue-Sepharose and high-performance liquid chromatography. Hydrophobic interaction chromatography was highly efficient in removing almost all protein contaminants. The resulting biologically active material exhibited heterogeneity in ion-exchange chromatography, and apparent isoelectric points between 5.2 and 5.5 on chromatofocusing. Its apparent molecular weight, as determined by size-exclusion filtration, was about 35,000. Preliminary results on the kinetics of appearance of intracellular biological activity suggested that the monokine could also be obtained from cytoplasmic extracts.

The synthetic immunomodulator muramyl dipeptide (MDP) can stimulate activated B cells

The synthetic immunomodulator muramyl dipeptide (MDP) has previously been shown to be able to synergize with lymphokines in enhancing the specific immune response of purified splenic B cells. Here, we have examined the effect of MDP in the process of B cell activation. We found that MDP alone was ineffective on the proliferation of either murine resting or in vivo activated B cells, whereas it enhanced the DNA synthesis of B cells once stimulated with anti-IgM antibodies. In agreement with these findings, cell cycle analysis by flow cytometry after acridine orange staining indicated that MDP by itself could not trigger the entry into the G1 phase of the cell cycle of nonactivated B lymphocytes. In contrast, in the presence of anti-IgM antibodies plus BSF-1, MDP promoted further cell cycle progression preferentially into the G1B compartment and also through the G2/M phase. A kinetic study showed that MDP was the most effective when added after the activation of B cells by anti-IgM antibodies plus BSF-1. Our present results suggest that functional receptors for MDP may be expressed on already cycling B cells.

Enhancement of B-cell stimulation by muramyl dipeptide through a mechanism not involving interleukin 1 or increased Ca2+ mobilization or protein kinase C activation

Muramyl dipeptide (MDP) enhanced mitogenic stimulation of mouse lymphocytes by polyclonal B cell activators (peptidoglycan, lipopolysaccharide, Staphylococcus aureus Cowan I cells, and pokeweed mitogen), but not by T-cell mitogens (phytohemagglutinin and concanavalin A). Only adjuvant-active MDP analogs were effective, whereas adjuvant-inactive MDP analogs, muramic acid, peptidoglycan pentapeptide, and low Mr digests of peptidoglycan were not. The half-maximal enhancement was seen at 5-10 microM MDP and occurred at both optimal and suboptimal concentrations of B cell mitogens. The enhancing effect of MDP was exerted on the B cells, since it was T cell- and macrophage-independent and was not mediated by IL-1. MDP was effective during the first 12 hrs of culture, and most strongly enhanced the mitogen-induced DNA synthesis, although significant enhancement of RNA synthesis and B cell differentiation into antibody-secreting cells was also observed. The enhancement of mitogenic response was not due to changed requirements for extracellular or intracellular Ca2+ or to increased activation of protein kinase C. These results demonstrate a novel immunoenhancing effect of MDP that should be useful in the studies on the mechanism of B cell activation.

A novel muramyl peptide derivative stimulates tumoricidal activity of macrophages and antibody production by B cells

A novel analog of MDP, the 3'-iodo-4'-azido-L-phenylalanine methyl ester derivative of N-acetyl-L-alanyl-D-isoglutamine, has been prepared. This compound is capable of activating macrophages to the tumoricidal state and increasing the specific immune response of B cells. It thus appears to exhibit similar biological activities to MDP. Moreover, this compound is of potential interest for receptor photolabelling studies.

Muramyl dipeptide induced augmentation of the proliferative response of thymocytes to phytohemagglutinin

N-Acetylmuramyl-L-alanyl-D-isoglutamine (MDP) augmented the proliferative response of thymocytes to phytohemagglutinin (PHA). The augmenting effect of MDP disappeared by passage of glass-nonadherent thymocytes through Sephadex G-10 (G-10) column or by removal of low density cells by the Ficoll-Conray gradient centrifugation. The diminished augmenting effects of MDP on the proliferative response of glass-nonadherent-G-10 nonadherent thymocytes was restored by the addition of the G-10 adherent cells. When G-10 adherent cell fraction was extensively depleted of macrophages by glass adherence and EA-rosetting, it was found that neither the macrophage-depleted G-10 adherent cell fraction nor the macrophage fraction supported by itself the proliferative response of G-10 nonadherent thymocytes. However, addition of macrophage fraction together with the macrophage-depleted G-10 adherent cells did support the proliferation of G-10 nonadherent thymocytes. It was further shown that peritoneal exudate macrophages could be substituted for thymic macrophage fraction. These results suggested that both the G-10 adherent-glass nonadherent cells and macrophages were essential for the MDP-induced augmentation of the proliferative response of thymocytes to PHA and these cells exerted different accessory roles in this response.