Relation of structure to function in bacterial O-antigens. IV. Fractionation of the components

Purification and characterization of lipopolysaccharides

Lipopolysaccharides are the major components on the surface of most Gram-negative bacteria, and recognized by immune cells as a pathogen-associated molecule. They can cause severe diseases like sepsis and therefore known as endotoxins. Lipopolysaccharide consists of lipid A, core oligosaccharide and O-antigen repeats. Lipid A is responsible for the major bioactivity of endotoxin. Because of their specific structure and amphipathic property, purification and analysis of lipopolysaccharides are difficult. In this chapter, we summarize the available approaches for extraction, purification and analysis of lipopolysaccharides.

Column liquid chromatography of endotoxins

A new, fast and highly reproducible column liquid chromatographic method was elaborated for the analysis and small-scale preparative isolation of endotoxin from Serratia marcescens Bizio (ATCC No. 264). This procedure detects contaminants of such preparations with high sensitivity and it is capable of separating them from endotoxic components. Extensive heterogeneity of both 5% trichloroacetic acid and phenol-water-extracted endotoxin preparations was recorded. Heterogeneity among the endotoxic components of purified preparations could also be detected by this method. Measurements of biological activities, such as Limulus amoebocyte lysate activation, lymphoblastogenesis (mitogenicity) and tumor necrosis factor (TNF) liberation were carried out on the chromatographically separated fractions. During these studies, non-toxic but in vitro TNF-generating components of crude endotoxin extracts were also detected.

Thin-layer chromatography of endotoxins, their derivatives and contaminants

Thin-layer chromatographic (TLC) separation techniques were used to analyze the heterogeneity of various preparations which included smooth and rough endotoxins (ET), Lipid A precipitates and synthetic Lipid A samples and a novel cytotoxic bacterial lipid. Furthermore, carbohydrate-rich split products (PS) of ET were also separated on commercial silica-coated plates. Satisfactory results were obtained by two-dimensional TLC or by the combination of chromatography followed by high-voltage electrophoresis in the separation of PS of ET cleaved by mild acetic hydrolysis. Several spray reagents were found which were eminently suitable to detect carbohydrate containing compounds. Less specific but generally useful spray reagents were also developed which gave strong color reactions with lipids, proteinaceous and carbohydrate containing split products of the ET preparations. Improved chromatographic resolution has also revealed substantial heterogeneity in both rough and smooth ET samples. Three biological activities of the separated components could be determined. These were antigenicity detected by reactivity with monoclonal antibodies on the TLC plates, endotoxicity, determined by the Limulus amoebocyte lysate (LAL) test and direct cytotoxicity of P815 cells in vitro. Considerable amounts of non-endotoxic and non-antigenic contaminants could be detected in all preparations tested. Significant amounts of free Lipid A were also found in smooth ETs. Thus a new level of complexity is recognized by TLC within these preparations.

Role of antibody response helper factors in immunosuppressive effects of friend leukemia virus

The primary antibody response of BALB/c splenocytes to sheep erythrocytes in vitro was suppressed by infection with Friend leukemia virus (FLV), with the response capacity decreasing with increasing duration of infection. The acquisition of normal antibody responses was amplified by macrophage-produced antibody response helper factor(s). FLV-infected mice were treated with bacterial lipopolysaccharide to induce the release of these helper factors into the serum. Similar to the loss of antibody response capacity by their splenocytes, the FLV-infected mice progressively lost the ability to produce helper factors in response to lipopolysaccharide. In vitro cultures of FLV-infected cells also showed a depressed ability to produce helper factor activity both spontaneously and in response to lipopolysaccharide stimulation. The reconstitution of normal levels of exogenous helper factors to FLV-infected splenocytes restored the antibody response to normal or even elevated levels. These studies indicate that the mechanism for suppression of antibody responses by FLV involves the depression of antibody response helper factor production.

Studies on the optimal conditions of CSF generation by endotoxic LPS and its PS derivative in mice

Not only the endotoxic LPS preparations, but a non-toxic, lipid-free, non-mitogenic hydrolytic breakdown product of it (called PS) is also capable of inducing colony stimulating factor (CSF) release (1). Due to difficulties to reproduce above findings it became necessary to study the optimal conditions to obtain CSF active PS preparations. It was found that the CSF generating component of the highly heterogeneous PS mixture is sensitive to acidic hydrolyses, but it is less sensitive than the toxic site in the lipid moiety of the LPS. Carefully controlled optimal hydrolytic conditions give PS preparations which have less than one percent residual endotoxicity but maintained 40 to 80% of the original CSF generating capacity. Prolonged hydrolysis will destroy this activity too. Optimal dose of LPS and PS for CSF induction in mice differed widely. For LPS the optimal dose is 25 micrograms, injecting more gave a much reduced or non-detectable CSF level. Optimal dose for PS was 160 micrograms, and this generated a significantly higher CSF level than 25 micrograms LPS. At concentrations below 25 micrograms, LPS was clearly more active than PS. The CSF level reached its peak at 3-4 hours after other LPS or PS injection. Intravenous route was sometimes but not always more effective than intraperitoneal.

Serum levels of glycosyltransferases and related glycoproteins as indicators of cancer: biological and clinical implications

Many studies have suggested that malignant transformation is associated with fundamental changes in the cell surface; similar changes have been described for normal stem cells and cells of embryonic or fetal origin. There is now evidence that the tumor cell secretes or sheds glycoproteins and glycosyltransferases into the surrounding medium and into serum. There are claims that some of these serum glycoproteins and glycosyltransferases are associated with, or specifically related to, the extent of tumor growth and may serve as a cancer marker. A cancer-associated galactosyltransferase isoenzyme (GT-II) has been described and purified. Different isoelectric forms of fucosyltransferase have also been described as indicative of malignancy. The articles to be published in CRC Critical Reviews in Clinical Laboratory Sciences will analyze the evidence for the association of these membrane factors with tumor growth. In order to better understand the possible significance of altered glycoproteins and of increased or different forms of glycosyltransferases during tumor growth, recent data on glycoprotein synthesis will be discussed including the new concepts on the control of glycoprotein synthesis through lipid intermediates. The possible mechanisms whereby malignant transformation could alter glycoprotein synthesis will be discussed with particular emphasis on the significance of these alterations to the biology of the malignant cell. Changes in surface membrane glycoproteins have long been implicated in the ability of a cell to metastasize. Secretion and/or shedding of the cell surface may also be important in the process of metastasis and in altering the host immune response. Detection and the study of these "shed" materials in patients appear to be indicating a new approach to cancer biology detection and therapy.

Mitogen-induced amplification of blastogenesis in lipopolysaccharide-precultured lymphocytes

Human peripheral blood lymphocytes were cultured in vitro with lipopolysaccharide (LPS) for 48 h. After washing, stimulation with a concanavalin A (ConA) or pokeweed mitogen (PWM) resulted in a synergistic blastogenic response that was greater than the sum of the independently stimulated control cultures. Addition of fresh autologous lymphocytes after LPS preculture produced an additional increment of synergy. The nature of the responding and helping effects was determined by coculturing irradiated or nonirradiated lymphocyte suspensions that had been precultured with either LPS or ConA/PWM. Such studies indicated that amplification was the result of a mitogen-activated helper activity, which facilitated the blastogenic response to LPS. Experiments with lymphocytes resolved into T- and B-cell-enriched fractions indicated that the LPS-responsive cells were of the B type and that the help was provided by a mitogen-activated T-cell population. These studies indicated that LPS can induce human B-cell blastogenesis; however, a helper function must be provided by a T-cell subpopulation. This helper activity is inducible by pretreatment of the T cells with plant lectins.

Isolation of two protein-free and chemically different lipopolysaccharides from Bordetella pertussis phenol-extracted endotoxin

Endotoxin prepared from several Bordetella pertussis strains in both immunological phases I and IV gave two lipopolysaccharide peaks (LPS-I and LPS-II) when analyzed on hydroxylapatite columns in a phosphate buffer containing 0.1% sodium dodecyl sulfate; these lipopolysaccharides, present in the ratio of 2:3, are true endotoxins by both chemical and biological criteria. Endotoxins isolated from Escherichia coli, Salmonella typhimurium, and Shigella flexneri gave single lipopolysaccharide peaks when analyzed by the same procedure. Upon hydrolysis with acetic acid (pH 3.4) at 100 degrees C for 1 h, LPS-I released a polysaccharide (PS-I); the linkage broken was that of the glycosidic bond of a non-phosphorylated 3-deoxy-oct-2-ulosonic acid. Treatment with 0.25 M mineral acid at 100 degrees C for 30 min was required to free the polysaccharide moiety (PS-II) of LPS-II, the linkage broken being the glycosidic bond of a phosphorylated 3-deoxy-oct-2-ulosonic acid. Chemical and physical differences of the polysaccharide moieties PS-I and PS-II present in LPS-I and LPS-II have been described previously (25). By using the technique of 125I labeling, it was shown that the totality of labeled proteins present in the endotoxin extracted from Bordetella pertussis by the phenol-water procedure could be separated from the lipopolysaccharide by column chromatography on hydroxylapatite; it follows that these proteins are not linked by covalent bonds to the lipopolysaccharide.

Restoration of depressed antibody responses of leukemic splenocytes treated with LPS-induced factors

Lipopolysaccharide and a nontoxic derivative, PS, from Serratia marcescens were studied in terms of their effects on normal and Friend leukemia virus depressed splenocytes. These materials caused a marked increase in the number of antibody producing cells by both groups of splenocytes. MDP, a synthetic analogue of myobacterial cell walls, produced a similar adjuvant response by normal and leukemic splenocytes. Combinations of PS or LPS and BCG or MDP resulted in synergistic immunostimulatory responses. A soluble factor associated with these materials appeared to mediate the response, since cell-free supernatants from LPS stimulated splenocytes or serum from LPS treated mice resulted in similar immunostimulation.

Effect of immune sera upon enhanced in vitro antibody responses

Immunization of rabbits with S marcescens bacteria in Freund's incomplete adjuvant resulted in development of anti-Serratia sera with bacterial agglutinating properties as well as LPS modulating properties. The antisera reacted with the LPS in counterimmunoelectrophoretic assays. Such antisera also stimulated the LPS induced enhancement of specific anti-SRBC responses from normal spleen cell cultures but did not further enhance the stimulated responses of similar cultures incubated with the smaller molecular weight PS-rich derivative. The antisera had no effect on LPS or PS enhanced nonspecific background anti-SRBC response as compared to normal rabbit serum-treated controls. These results point to a possible role for immune complexes as an enhancer of the immunostimulating activities of LPS antibody-treated cultures and also indicate a difference between LPS and PS as immunomodulators.

Biological and physicochemical properties of the lipopolysaccharide of Chromatium vinosum

The lipopolysaccharide (LPS) of Chromatium vinosum has anticomplementary activity. This anticomplementary activity is destroyed by alkaline digestion of the LPS and is suppressed by both Mg2+ and Ca2+ ions. Treatment of the LPS with ethylenediaminetetraacetic acid, sodium deoxycholate, or dimethyl sulfoxide did not affect its toxicity toward mice; however, alkaline-treated LPS was not toxic. Treatment of the LPS with sodium deoxycholate, dimethyl sulfoxide, or sodium dodecyl sulfate resulted in reversible dissociation into subunits. Aggregation of the subunits into the original form was achieved by removing the dispersing agent by dialysis against distilled water followed by freezing and thawing. Electron micrographs of phenol-extracted LPS showed long filaments. Electron micrographs of sodium deoxycholate- and sodium dodecyl sulfate-treated and dialyzed LPS showed a mixture of small subunits and short filaments, whereas dimethyl sulfoxide-treated and dialyzed LPS contained only small ovoid spheres. The LPS produced an ordered series of multiple bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A similar banding pattern was observed for Salmonella abortus-equi and Proteus mirabilis LPS. The C. vinosum LPS appears to be mitogenic for mouse spleen cells.

Immunogenic and toxic properties of a purified lipopolysaccharide-protein complex from Pasteurella multocida

An immunogenic fraction from Pasteurella multocida was found to consist chiefly of a high-molecular-weight protein-polysaccharide complex containing 25 to 27% protein and 10.7% carbohydrate. The starting material was obtained by differential centrifugation at 105,000 X g of saline extract of P. multocida cells and further purified by gel filtration on Sepharose 2B. Three peaks were usually obtained after gel filtraion.pharose 2B. Three peaks were usually obtained after gel filtration. The component in the first peak amounted to about 10% of the starting material and eluted in the void volume. It was predominately carbohydrate, although some protein was present. Two inoculations of 10 to 20 mug of the first component induced up to 80% protection in mice against a challenge inoculation with P. multocida that killed 100% of the controls. The second, or major, component amounted to about 75 to 95% of the starting material. This fraction contained 25 to 27% protein and 10.7% carbohydrate. Small amounts, 10 to 20 mug, induced active immunity in mice and turkeys, but large amounts could be lethal; the mean lethal dose was 195 mug for mice and 5.7 mug for 10-day-old chicken embryos. The components in the third peak were primarily proteins that gave reactions of nonidentity with the antigens of peak II in gel diffusion. The components present in the third fraction were definitely less effective in the induction of protective immunity than those present in the first or second. Analyses of the protective antigen(s) by the isoelectric focusing procedure in a pH 3 to 10 gradient showed that all of the precipitinogenic activity was found in the range of pH 3 to 4, with a peak at pH 3.7.

Immunologic properties of bacterial lipopolysaccharide (LPS). II. The unresponsiveness of C3H/HeJ Mouse spleen cells to LPS-induced mitogenesis is dependent on the method used to extract LPS

The C3H/HeJ mouse strain, previously shown to be a nonresponder to bacterial lipopolysaccharide (LPS)-induced mitogenesis in vitro, was demonstrated by the present studies to be competent to respond mitogenically to LPS, but only to LPS preparations obtained by selected extraction methods. These preparations appear to be confined to LPS isolated by mild extraction techniques, such as TCA or butanol. In contrast, those obtained by techniques utilizing phenol were only weakly stimulatory or completely nonstimulatory for spleen cells from the C3H/HeJ. All LPS preparations tested, on the other hand, were highly stimulatory for cells from another mouse strain, namely the C3H/St. The critical importance of the method of extraction of LPS on its mitogenic activity for C3H/HeJ cells was stressed by experiments in which LPS was prepared from Escherichia coli K235 using either of two procedures. In these experiments, phenol-extracted LPS, although mitogenic in the C3H/St, was completely nonstimulatory in the C3H/HeJ; whereas, butanol-extracted LPS was highly stimulatory in both strains of mice. This striking difference was attributed to a destructive effect of phenol on LPS, as demonstrated by the fact that treatment of butanol LPS with phenol resulted in a total loss of its mitogenic activity in the C3H/HeJ, but in only a partial loss in the C3H/St. In general, the mitogenic response observed with selected LPS preparations in the C3H/HeJ was quantitatively lower and more transient than that seen with the C3H/St, although qualitatively these responses appeared to be similar. This was evidenced by the observation that in both mouse strains LPS was a specific mitogen for B cells, a property which was also attributed in both strains to the same distinct structural region of the LPS molecule, that is lipid A. A preparation of LPS that failed to stimulate B cells from the C3H/HeJ nonetheless had the capacity to block activation of these B cells by a stimulatory preparation of LPS. These results strongly suggest that mitogenic stimulation of B cells by LPS is a function of the structural integrity of both the LPS molecule and putative B-cell receptors for LPS.

Biological activities of endotoxins detoxified by alkylation

It has been previously observed that lipopolysaccharides can be detoxified by alkylation and yet retain their adjuvant activity. Our present findings confirm these results and show, moreover, that these derivatives did not lose their capacity to protect mice against lethal irradiation and lost only partially their ability to interrupt pregnancy or to induce blast transformation of murine B-lymphocytes. However, in contrast with lipopolysaccharides, these alkylated preparations did not enhance the nonspecific resistance of mice to a bacterial infection. The various bilogical functions of endotoxins can therefore be separated and are not uniformly related to their toxicity.

Degradative effect of phenol on endotoxin and lipopolysaccharide preparations from Serratia marcescens

It has been established that the well-known deproteinizing action of hot 45% aqueous phenol on whole cells or isolated and purified endotoxin of Serratia marcescens 08 is caused by the cleavage of a phenol-sensitive linkage within the lipid moiety. As a result of this degradation, both the lipopolysaccharide and simple protein fragments retained a part of the lipid moiety. Although not proceeding at the same fast rate as the cleavage of the lipid moiety, such phenol treatment also caused a partial hydrolysis of the O-specific side chain and ester-bound fatty acids. Hydrolysis of the O-specific side chain accounted for 5% of the lipopolysaccharide and that of ester-bound fatty acids accounted for 11% of the total fatty acid content after 60 min of treatment. It is suggested that the presence of these degradation products is one of the main causes of the heterogeneity of endotoxin and lipopolysaccharide preparations.

In vitro transformation of mouse bone-marrow-derived (B) lymphocytes induced by the lipid component of endotoxin

An analysis of which component of lipopolysaccharide, the lipid or the polysaccharide, is mitogenic for mouse B-lymphocytes has been performed. A purified glycolipid derived from a rough mutant of Salmonella minnesota (R595) that does not contain any o-polysaccharide at all is more mitogenic than an intact lipopolysaccharide derived from a smooth strain of S. minnesota. Results using fractions produced by several different chemical modifications of whole lipopolysaccharide confirm this result. Acid hydrolysis separates lipopolysaccharide into two components. The lipid fraction is mitogenic, whereas the polysaccharide fraction is not. Those procedures which degrade or modify only the lipid moiety while preserving the antigenic integrity of the polysaccharide also destroy mitogenicity. These include alkaline hydrolysis and deacylation by a more specific treatment with potassium methylate. The lipid preparations are fully active on highly purified B-lymphocyte populations (prepared by anti-theta antiserum and complement), whereas they have no effect on highly purified T-lymphocyte populations (prepared by anti-immunoglobulin and complement). These data demonstrate that the lipid moiety of endotoxin is the B-lymphocyte mitogen, whereas the polysaccharide has no demonstrable mitogenic activity.

Isolation and purification of endotoxin by hydrolytic enzymes

Various commercial hydrolases were used in an attempt to degrade the endotoxic lipopolysaccharide macromolecule. Some inert components, such as peptides and nucleic acids, could be removed from endotoxin preparations. As a result, endotoxic activity, measured by pyrogenicity, Shwartzman reaction, and mouse lethality, was increased. The remarkable resistance of endotoxin to hydrolases led to the use of such enzymes for the liberation and purification of endotoxin from whole bacterial cells.

Further studies of the chemical composition of the lipopolysaccharide of Pseudomonas aeruginosa

1. Qualitative and quantitative analytical results for the lipopolysaccharide from acetone-dried cells of Pseudomonas aeruginosa (N.C.T.C. 1999) are presented and possible contamination of the material with nucleic acid was further examined. 2. Additional sugars detected (only in large-scale hydrolysates) were mannose and arabinose; traces of spermidine and putrescine were also found. 3. The heptose component is l-glycero-d-mannoheptose. 4. The thiobarbituric acid-positive component is a 3-deoxy-2-octulonic acid, of which only 35-40% links lipid A to the polysaccharide. This linkage is not broken by hydrolysis with acetic acid up to 0.08m. 5. Liberation of lipid A required hydrolysis with 0.1m-hydrochloric acid, which substantially degraded the polysaccharide moiety. 6. Fractions obtained from the degraded polysaccharide by high-voltage electrophoresis were examined; in these, the alanine/galactosamine molar ratio is approx. 1. 7. Hydrazinolysis of whole lipopolysaccharide showed that at least 40% of the alanine is in amide linkage, possibly with galactosamine. 8. Lipid A, solubilized by alkaline methanolysis was fractionated; most of the phosphorus of the higher-molecular-weight fractions was released as P(i) by a phosphomonoesterase. 9. Hydrazinolysis of lipid A destroyed approx. 80% of the glucosamine, and glycosidically linked glucosamine oligosaccharides could not be isolated.

Alteration of physical, chemical, and biological properties of endotoxin by treatment with mild alkali

Treatment with alkali is one of several methods for removing fatty acids from bacterial endotoxins and, in the process, detoxifying the material. Saponification of fatty acid esters is the major detectable chemical change produced by alkali; however, kinetic studies of mild alkaline hydrolysis of endotoxin failed to correlate rates of detoxification with rates of loss of ketodeoxyoctonates, heptose, O-acetyl groups, or fatty acid esters. The alterations occurring during the critical stages of hydrolysis apparently changed the essential chemical conformation of endotoxic particles before cleavage of a significant amount of material took place. The rates of both saponification and detoxification were markedly increased by carrying out the reaction in media of ethyl alcohol or dimethylsulfoxide instead of water.

An extracellular lipopolysaccharide-phospholipid-protein complex produced by Escherichia coli grown under lysine-limiting conditions

Lysine limitation during growth of the lysine-requiring mutant of Escherichia coli 12408 resulted in the excretion of a complex containing 60% of lipopolysaccharide, 26% of extractable phospholipid and 11% of protein. The complex was obtained from the culture filtrate in yields of about 0.5g./l. by precipitation with chloroform or gel filtration; some purification steps are described. The greater part of the phospholipid consisted of phosphatidylethanolamine, which contained four main fatty acids; two monoenoic acids and a cyclopropane acid were esterified mainly in the beta-position, and a saturated acid was located mainly in the gamma-position. The protein component was relatively insoluble and contained an excess of acidic over basic amino acids and little cystine. The lipopolysaccharide resembled in composition the intracellular lipopolysaccharides from rough strains of E. coli. Both protein and lipopolysaccharide constituents of the complex were serologically active; the complex was less toxic than the purified lipopolysaccharide. In the electron microscope the complex showed a mixture of particles of various sizes and shapes. Rods and hollow spheroids (diameter 12-200mmu) were most common and resembled the particles previously found surrounding cells actively excreting the complex. The chloroform-precipitated material showed a tubular lamellar structure. Soluble lipopolysaccharide prepared from the complex also consisted of hollow spheres and rods.