Inhibition of interleukin-6 release and T-cell proliferation by synthetic mirror pseudo cord factor analogues in human peripheral blood mononuclear cells.

The effects of synthetic alkyl ((alkyl 6-deoxy-a-D-gluco-heptopyranosyluronate) 6-deoxy-a-D-gluco-heptopyranoside) uronates, a novel type of mirror pseudo cord factor, on the in vitro modulation of interleukin-6 production and T-cell proliferation in human peripheral blood mononuclear cells, were investigated. Synthetic mirror pseudo cord factors with alkyl chains ranging from C16 to C18 have very weak interleukin-6-inducing capacities and lack mitogenic activities for T-cell proliferation. However, they could inhibit IL-6 release induced by sonicated Bacillus Calmette-Guérin (S-BCG), bacterial endotoxin, and phytohaemagglutinin in a dose-dependent manner. Inhibition was observed not only with mononuclear cells but also with purified monocytes. Furthermore, these synthetic compounds could suppress T-lymphocyte proliferation stimulated by sonicated Mycobacterium tuberculosis H37Rv (S-H37Rv) antigens, S-BCG antigens, as well as by recombinant 65 kDa mycobacterial heat-shock protein. In contrast, these compounds failed to inhibit the phytohaemagglutinin-induced T-cell proliferation. We conclude that the inhibition of cytokine release and T-cell proliferation by synthetic mirror pseudo cord factors was due to direct blocking of the function and/or activity of monocytes or antigen-presenting cells.

Modulation of endotoxin-induced monokine release in human monocytes by lipid A partial structures that inhibit binding of 125I-lipopolysaccharide.

We have previously shown that the synthetic tetraacyl precursor Ia (compound 406, LA-14-PP, or lipid IVa) was not able to induce the production of tumor necrosis factor, interleukin-1, and interleukin-6 in human monocytes but strongly antagonized lipopolysaccharide (LPS)-induced formation of these monokines. This inhibition was detectable at the level of mRNA production. To achieve a better understanding of molecular basis of this inhibition, we investigated whether lipid A precursor Ia (LA-14-PP), Escherichia coli-type lipid A (LA-15-PP), Chromobacterium violaceum-type lipid A (LA-22-PP), and synthetic lipid A partial structures and analogs (LA-23-PP, LA-24-PP, and PE-4) were able to influence the binding of 125I-LPS to human monocytes and compared this inhibitory activity with the agonistic and antagonistic action in the induction of monokines in human monocytes. 125I-LPS (20 ng per well) was added to human monocytes in the presence or absence of unlabeled rough Re mutant-derived LPS (Re-LPS) or lipid A compounds, and specific LPS binding was determined after 7 h. This binding was found to be dependent on CD14 as shown by the use of an anti-CD14 monoclonal antibody. Compound LA-14-PP was found to inhibit the binding of 125I-LPS to the cells in a similar dose-response to that of unlabeled LPS. This shows that the inhibitory capacity on LPS binding does not correlate with the monokine-inducing capacity because Re-LPS is active in inducing tumor necrosis factor, interleukin-1, and interleukin-6, while LA-14-PP is not. The strong capacity of LA-14-PP to inhibit 125I-LPS binding, however, correlates with the strong inhibitory capacity of this compound on LPS-induced monokine production. Compounds LA-15-PP, LA-23-PP, and LA-24-PP were active in the inhibition of 125I-LPS binding but were 5- to 10-fold weaker than Re-LPS and LA-14-PP. Of all lipid A structures tested, compound LA-22-PP expressed the weakest inhibitory capacity on LPS binding. These compounds showed again that the activity of binding inhibition does not correlate with the monokine-inducing capacity. We assume that the inhibitory effects of lipid A partial structures on LPS-induced monokine production have their origin in a competitive inhibition between LPS and the lipid A partial structures for the same binding site on the cell membrane.

Biological activity of synthetic phosphonooxyethyl analogs of lipid A and lipid A partial structures.

We investigated the biological activity of four new synthetic analogs of lipid A, termed PE-1, PE-2, PE-3, and PE-4. All compounds contain an alpha-oxyethyl-linked (-O-CH2-CH2-) phosphoryl group in position 1 of the reducing glucosaminyl residue (GlcN I) of lipid A. PE-1 is a hexaacylated analog of Escherichia coli lipid A (compound 506). PE-2 differs from PE-1 in carrying two myristic acid residues at GlcN I. PE-3 has the same acylation pattern as PE-2, but GlcN I is present in the beta anomeric form. Finally, PE-4 represents an analog of tetraacyl precursor Ia (compound 406). Structure-activity relationships of these compounds were determined by measuring their capacity to induce tumor necrosis factor alpha, interleukin 1, and interleukin 6 release by human mononuclear cells and to cause mitogenicity of murine spleen cells. The results show that replacement of the glycosidic phosphoryl residue by a phosphonooxyethyl group had no substantial effect on the biological activity of compounds. However, the anomeric configuration of GlcN I was found to be of great biological relevance, as, in general, the alpha anomer (PE-2) expressed high activity, and the beta anomer (PE-3) expressed low mediator-inducing and mitogenic activity. The absence of the 3-hydroxyl groups within the acyl residues at GlcN I in PE-2 was found to only slightly affect the induction of monokines in human mononuclear cells compared with that of PE-1 or lipid A (506). These stable 1-phosphonooxyethyl analogs of lipid A may be candidates in the development of immunomodulators for the treatment of systemic endotoxicosis.

Inhibition of endotoxin or lipid A-induced tumor necrosis factor production by synthetic lipid A partial structures in human peripheral blood mononuclear cells.

Most of the toxic reactions during Gram-negative infections are mediated by inflammatory cytokines induced by endotoxin, also termed lipopolysaccharide (LPS). To evaluate the possibility of synthetic derivatives of LPS to antagonize endotoxin-mediated activities, we have examined the effect of synthetic lipid A partial structures, precursor Ia (compound 406 or LA-14-PP) and lipid X (compound 401) on in vitro LPS or lipid A-induced release of tumor necrosis factor (TNF) by human peripheral blood mononuclear cells. In agreement with previous reports it was shown that LPS of Salmonella abortus equi and synthetic Escherichia coli-type lipid A (compound 506 or LA-15-PP) have potent TNF-inducing capacity. The maximum release of TNF was found after stimulation with 1 to 10 ng/ml of LPS or 10 to 1000 ng/ml of lipid A. Synthetic precursor Ia and lipid X failed to induce TNF release, but could inhibit LPS or lipid A-induced TNF release in a dose-dependent manner. Inhibition was not due to a shift of the kinetic of cytokine release, and was observed in the early stage of TNF production. Moreover, we found that the synergistic effect of interferon-gamma with LPS in induction of TNF release could also be counteracted by the addition of synthetic precursor Ia. The observation that precursor Ia failed to inhibit the induction of TNF by Bacillus Calmette-Guérin, Staphylococcus aureus cowan I or lipopeptide indicated that specific mechanisms are involved in suppression by lipid A partial structures on LPS-induced cytokine production.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of lipopolysaccharide-induced production of tumor necrosis factor, interleukin 1, and interleukin 6 by synthetic precursor Ia of lipid A.

Endotoxin (lipopolysaccharide, LPS) induces the production of mediators of inflammation, which exerts pathophysiological effects such as fever or shock in mammals. In the present study we have investigated the modulation of LPS by the synthetic non-active tetraacylated precursor Ia of lipid A (compound 406) in the induction of tumor necrosis factor (TNF), interleukin 1 (IL-1) and interleukin 6 (IL-6) in human peripheral blood mononuclear cells (PBMC) and in human peripheral blood monocytes (PBMo). PBMC stimulated with LPS released TNF in a concentration dependent manner. Release of biologically active TNF, IL-1 and IL-6 was first detectable 4 h after LPS stimulation. Compound 406 alone in all concentrations tested did not induce TNF, IL-1 or IL-6 release, intracellular TNF or IL-1 beta, or mRNA for TNF or IL-1. Added to PBMC 1 h before LPS compound 406 enhanced or suppressed TNF release and suppressed IL-1 and IL-6 release depending on the ratio of concentrations between stimulator (LPS) and modulator (compound 406). In contrast to LPS stimulation alone TNF, IL-1 and IL-6 release in presence of compound 406 was delayed and first detectable after 6 to 8 h. Compound 406 was able to suppress LPS-induced intracellular TNF and IL-1 beta in PBMC. Added to PBMo 1 h before LPS it totally inhibited the production of mRNA for TNF and IL-1. When added to PBMC 1 h after LPS, TNF release was suppressed in a concentration-dependent way and release of biologically active TNF, IL-1 and IL-6 could again be detected for the first time after 4 h. Compound 406 was not able to inhibit phorbol 12-myristate 13-acetate (PMA)-induced TNF and IL-1 release in PBMo which suggests that its modulating effect is LPS-specific. This study provides evidence that the modulating effect of compound 406 on the LPS induction of TNF, IL-, 1 and IL-6 could be due to competitive binding.

Inhibition of endotoxin-induced interleukin-6 production by synthetic lipid A partial structures in human peripheral blood mononuclear cells.

The effect of two synthetic lipid A partial structures, compound 406 (or LA-14-PP, identical in structure to the lipid A precursor, known as Ia or IVa) and compound 401 (lipid X), on the in vitro modulation of endotoxin (lipopolysaccharide)-induced interleukin-6 production by human blood mononuclear cells was investigated. Lipopolysaccharide of Salmonella abortus equi and synthetic Escherichia coli-type lipid A (compound 506, or LA-15-PP) had potent interleukin-6-inducing capacities. The maximum release of interleukin-6 was found after stimulation with 1 to 10 ng of lipopolysaccharide or 10 to 100 ng of synthetic E. coli-type lipid A per ml. Both synthetic lipid A partial structures (compounds 406 and 401) failed to induce interleukin-6 release. However, they inhibited lipopolysaccharide- or lipid A-induced interleukin-6 production in a dose-dependent manner. Inhibition was found not only in mononuclear cells but also in purified monocytes and was not due to a shift in the kinetics of cytokine production. Suppression was manifested in the early stage of interleukin-6 production. Inhibition was also found in the presence of recombinant gamma interferon, indicating that compound 406 and recombinant gamma interferon act in different, independent pathways. Our data, therefore, indicate that the inhibition of interleukin-6 production by lipid A partial structures may help elucidate the mechanism of interaction of the lipid A component of lipopolysaccharide with immune cells in the inflammatory reaction during gram-negative infection.

Bacterial endotoxin: molecular relationships between structure and activity.

The significance of endotoxins in bacterial infection and their role as bacterial surface antigens (O antigens) have stimulated investigations into their chemical nature and the mechanisms of their biologic action during the last few decades. This article summarizes some of the recent results and emphasizes structure-activity relationships.

Induction and modulation of interleukin 1 production by defined partial structures of lipopolysaccharide.

Bacterial lipopolysaccharides (LPS) consist of a hydrophilic heteropolysaccharide component and a covalently linked hydrophobic lipid portion termed lipid A. Lipid A is responsible for most of the toxic and immunoregulatory effects of LPS. In studying the structure-function relationship of lipid A partial structures we now report that certain synthetic analogues, with themselves being biologically "inactive", exert immunomodulating effects on LPS-induced Interleukin 1 production in vitro.

Suppressive effect of lipid A partial structures on lipopolysaccharide or lipid A-induced release of interleukin 1 by human monocytes.

Experiments were designed to investigate the significance of lipid A partial structures, precursor Ia (compound 406), and lipid X (compound 401) to serve as antagonists of interleukin 1 (IL-1) release from human mononuclear cells and monocytes induced by lipopolysaccharide (LPS, endotoxin) of Salmonella abortus equi or synthetic Escherichia coli lipid A (compound 506). A definite inhibition mediated by lipid A partial structures on IL-1 release induced by LPS or lipid A was found in repeated experiments. The inhibitory effect was exerted not only on IL-1 release, but also on IL-1 peptide synthesis at the intracellular level. The results also show that lipid A partial structures have suppressive effects even when added 1-4 h after LPS or lipid A. We conclude from these results that lipid A partial structures (precursor Ia and lipid X) have potent immunomodulatory effects on LPS- and lipid A-induced IL-1 release and may become useful reagents to study the mechanism of interaction of LPS and lipid A with cells of the immune system.

Tumor necrosis factor alpha and lymphotoxin production in Hodgkin's disease.

It is likely that the characteristic histologic features of Hodgkin's disease reflect cytokine production by the tumor cell population. Tumor necrosis factor alpha (TNF-alpha) and lymphotoxin (tumor necrosis factor beta [TNF-beta]) are important inflammatory mediators with wide-ranging effects within the lymphoreticular system. The aim of the present study was to investigate TNF-alpha and lymphotoxin production in the Hodgkin's disease-derived cell lines L428 and L540. At the product level, both cytokines could be demonstrated by immunostaining with specific monoclonal antibodies. TNF-alpha could be demonstrated by means of an enzyme-linked immunosorbent assay in culture supernatants from both cell lines as well as in cell lysates of L428 and L540 cells. Cytotoxic activity could be achieved only in L428 supernatants. This cytotoxic activity could not be blocked by the addition of a polyclonal antibody against TNF-alpha, but was partially inhibited with the monoclonal antibody against lymphotoxin. Synthesis of TNF-alpha and lymphotoxin in both L428 and L540 was confirmed by demonstrating the intracellular-specific messenger RNA (mRNA) using specific cDNA clones in Northern blot analysis. In situ hybridization studies with the TNF-alpha cDNA probe gave positive hybridization signals in L428 and in L540. These results demonstrate the transcription, translation, and export of TNF-alpha and lymphotoxin in cultured Hodgkin's disease-derived cell lines. In addition, results of preliminary experiments are presented in which we demonstrate Reed-Sternberg cells positive for TNF-alpha protein and mRNA in different Hodgkin's disease tissue biopsies, indicating that, at least for TNF-alpha, our cell line data are relevant to the neoplastic population present in Hodgkin's disease tissue.

Induction of tumor necrosis factor-alpha release by lipopolysaccharide and defined lipopolysaccharide partial structures.

We have investigated the release of tumor necrosis factor-alpha (TNF-alpha) by human mononuclear cells (MNC) and isolated human monocytes/macrophages stimulated with S- and R-form lipopolysaccharide (LPS), natural lipid A, and natural and synthetic partial structures thereof. We found that LPS of Salmonella minnesota (S. min.) Rb2, which represents a partial structure of wildtype LPS of Salmonella abortus equi (S.a.e.) lacking the O-chain and parts of the outer core region, was the most active inducer of all substances tested, even more active than the wildtype LPS. Lipid A also induced the production of TNF-alpha by monocytes/macrophages but was less active than wildtype LPS. The natural Escherichia coli (E. coli) type hexaacyl lipid A (compound 506) was more active than the natural S. min. type heptaacyl lipid A (compound 516). The 1- and 4'-monodephospho partial structures (compounds 505 and 504) of E. coli lipid A were less active and represented the smallest structures tested that were able to induce TNF-alpha release by monocytes/macrophages. Synthetic tetraacyl lipid A precursor Ia of E. coli lipid A, lacking non-hydroxylated fatty acids (compound 406), and the monosaccharide precursor lipid X did not induce the release of TNF-alpha in MNC or isolated monocytes/macrophages. This might indicate that the ability of a lipid A structure to induce the release of TNF-alpha is closely connected with the conditions to be at least hexaacylated and/or to contain hydroxylated fatty acids. These results demonstrate a structure-dependent hierarchy of LPS and natural or synthetic partial structures in their capacity of inducing TNF-alpha release by monocytes/macrophages.

Interleukin 1 and tumor necrosis factor: studies on the induction by lipopolysaccharide partial structures.

Minimal concentration ranges of lipopolysaccharides, natural and synthetic lipid As, and partial structures were established for the induction of release of IL-1 and TNF from human MNC. LPS was more potent than lipid A. Partial structures of lipid A lacking nonhydroxylated fatty acids were inactive, but in combination with LPS or lipid A exhibited time-dependent synergistic or antagonistic effects.