Monoclonal antibodies to immunodeterminants of lipoteichoic acids

A continuum of anionic charge: structures and functions of D-alanyl-teichoic acids in gram-positive bacteria

Teichoic acids (TAs) are major wall and membrane components of most gram-positive bacteria. With few exceptions, they are polymers of glycerol-phosphate or ribitol-phosphate to which are attached glycosyl and D-alanyl ester residues. Wall TA is attached to peptidoglycan via a linkage unit, whereas lipoteichoic acid is attached to glycolipid intercalated in the membrane. Together with peptidoglycan, these polymers make up a polyanionic matrix that functions in (i) cation homeostasis; (ii) trafficking of ions, nutrients, proteins, and antibiotics; (iii) regulation of autolysins; and (iv) presentation of envelope proteins. The esterification of TAs with D-alanyl esters provides a means of modulating the net anionic charge, determining the cationic binding capacity, and displaying cations in the wall. This review addresses the structures and functions of D-alanyl-TAs, the D-alanylation system encoded by the dlt operon, and the roles of TAs in cell growth. The importance of dlt in the physiology of many organisms is illustrated by the variety of mutant phenotypes. In addition, advances in our understanding of D-alanyl ester function in virulence and host-mediated responses have been made possible through targeted mutagenesis of dlt. Studies of the mechanism of D-alanylation have identified two potential targets of antibacterial action and provided possible screening reactions for designing novel agents targeted to D-alanyl-TA synthesis.

Scavenger cells with gram-positive bacterial lipoteichoic acid infiltrate around the damaged interlobular bile ducts of primary biliary cirrhosis

BACKGROUND/AIMS

Gram-positive bacterial DNA is frequently detectable in gallbladder bile of primary biliary cirrhosis (PBC) patients. To advance these findings, lipoteichoic acid (LTA) of gram-positive bacteria with high antigenicity was examined in liver specimens and bile from PBC patients and controls.

METHODS

LTA was examined by Western blotting in the gallbladder bile from 15 PBC, 11 cholecystolithiasis and six normal subjects, and by immunohistochemistry in liver specimens from 16 PBC, six primary sclerosing cholangitis (PSC), eight chronic viral hepatitis C (CVH-C) and five normal subjects.

RESULTS

In the gallbladder bile, there was no significant difference in the positive rate of LTA between PBC and controls. LTA-containing mononuclear cells were frequently detected in the portal tracts, particularly around the bile ducts and in hepatic sinusoids in PBC, while they were infrequent or occasional in control livers. These LTA-containing cells were sinusoidal endothelial cells and Kupffer cells, and portal monocytes, which frequently expressed scavenger receptor class B type 1.

CONCLUSIONS

LTA derived from bacterial fragments may reach the bile, not only in the diseased state but also under normal conditions. Such LTA may be involved in the development and progression of portal tract lesions, particularly bile duct lesions, in PBC.

Extracellular and cellular distribution of muramidase-2 and muramidase-1 of Enterococcus hirae ATCC 9790

A substantial portion of the second peptidoglycan hydrolase (muramidase-2) activity of Enterococcus hirae ATCC 9790 (formerly Streptococcus faecium) is present in the supernatant culture medium. In contrast, nearly all muramidase-1 activity is associated with cells in the latent, proteinase-activatable form. Muramidase-2 activity is produced and secreted throughout growth, with maximal levels attained at or near the end of exponential growth in a rich organic medium. Muramidase-2 activity in the culture medium remained high even during overnight incubations in the absence of proteinase inhibitors. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of supernatant culture medium concentrated by 60% saturated ammonium sulfate precipitation showed the presence of several Coomassie blue-staining bands. One intensely staining protein band, at about 71 kDa, selectively adsorbed to the insoluble peptidoglycan fraction of cell walls of E. hirae, retained muramidase-2 activity, and reacted in Western immunoblots with monoclonal antibodies to muramidase-2. The mobility of extracellular muramidase-2 in sodium dodecyl sulfate-polyacrylamide gel electrophoresis was indistinguishable from that of muramidase-2 extracted with 6 M guanidine hydrochloride from intact bacteria. Muramidase-2 appears to have only a limited number of binding sites on the peptidoglycan of E. hirae cell walls but binds with high affinity. Although high levels of muramidase-2 activity were present in supernatants of stationary-phase cultures, the bacteria were resistant to autolysis. Thus it appears that the peptidoglycan in walls of intact cells of E. hirae is somehow protected from the hydrolytic action of extracellular muramidase-2.

Sandwich immunoassay for the detection of lipoteichoic acid

A sandwich immunoassay has been developed for the detection of lipoteichoic acid (LTA), a major cell wall constituent of gram-positive bacteria, from whole blood and ISOLATOR supernate. Monoclonal antibodies were produced to purified LTA from Streptococcus mutans, BHT and were further characterized for crossreactivity with gram-positive and negative bacteria and for reactivity to substituted and unsubstituted LTA. Eight monoclonal antibodies were identified that reacted exclusively with gram-positive bacteria. Those antibodies able to capture 3H-LTA were chosen to develop a sandwich immunoassay. The assay has a sensitivity of 0.2 ng LTA/mL in PBS, 0.5 ng/mL in whole blood and 2.0 ng/mL in whole blood that has been processed through the ISOLATOR. Further development of this assay may lead to the rapid detection of LTA from body fluids.

Adherence of group B streptococci to adult and neonatal epithelial cells mediated by lipoteichoic acid

We have investigated the role of lipoteichoic acid in mediating the adherence of different serotypes of group B streptococci to human adult and neonatal epithelial cells. Pretreatment of neonatal buccal and vaginal epithelial cells with lipoteichoic acid, but not with deacylated lipoteichoic acid, induced a marked inhibition in the adherence of all strains tested. Pretreatment of bacteria with substances known to bind lipoteichoic acid, such as monoclonal and polyclonal antipolyglycerophosphate antibodies and albumin, also resulted in adherence inhibition. Group B streptococci adhered in 6- to 10-fold-higher numbers to buccal epithelial cells from neonates older than 3 days than to those from neonates less than 1 day old. This increase in receptiveness for group B streptococci was paralleled by an increased ability of epithelial cells from older neonates to bind group B streptococcal lipoteichoic acid. These data suggest a role for the lipid portion of lipoteichoic acid in the adherence of different serotypes of group B streptococci to vaginal and neonatal epithelial cells.

Mediation of Staphylococcus saprophyticus adherence to uroepithelial cells by lipoteichoic acid

Treatment of uroepithelial cells with lipoteichoic acid from Staphylococcus saprophyticus resulted in a decrease in the adherence of this organism. Similar effects were observed when bacteria were pretreated with the lipoteichoic acid ligands albumin and anti-polyglycerophosphate monoclonal antibodies. Lipoteichoic acid might behave as an adhesin of S. saprophyticus.

The ability to sensitize host cells for destruction by autologous complement is a general property of lipoteichoic acid

Previous studies have demonstrated that lipoteichoic acid (LTA) from Streptococcus pneumoniae binds to erythrocytes and renders them susceptible to lysis by autologous complement. The present study was performed to determine whether LTA from two other gram-positive bacterial species had the ability to render mammalian cells susceptible to lysis by autologous complement. Human erythrocytes were sensitized with LTA from S. pneumoniae, Streptococcus pyogenes, or Lactobacillus fermentum. Under incubation in normal autologous serum, lysis was observed with each of the LTA-sensitized erythrocyte preparations. When erythrocytes from a C2-deficient patient were sensitized with the LTA preparations and then incubated in autologous, C2-deficient serum, the erythrocytes sensitized with S. pyogenes or L. fermentum LTA demonstrated relatively little lysis, whereas the erythrocytes sensitized with S. pneumoniae LTA yielded near-total lysis. After reconstitution of the C2-deficient serum with purified human C2, lysis was observed with all three LTA preparations. When erythrocytes from an agammaglobulinemic patient were sensitized with either the S. pyogenes or the L. fermentum LTA, they were not lysed in the presence of autologous agammaglobulinemic serum, whereas the erythrocytes sensitized with S. pneumoniae LTA were completely lysed. Serum obtained from the agammaglobulinemic patient after reconstitution with intravenous pooled gamma globulin was able to lyse autologous erythrocytes sensitized with each of the three LTA preparations. These results demonstrate that the ability to render host cells susceptible to lysis by autologous complement is a general property of LTA. Whether activation of the autologous complement occurs by the classical or alternative pathways and whether it is antibody dependent depends on the nature of the bacterial LTA.

Antibodies to liposomes, phospholipids and phosphate esters

Polyclonal and monoclonal antibodies to liposomes having various phospholipid compositions have been produced. Binding of the anti-lipid bilayer antibodies is influenced both by the chemical composition and the physical state of the liposomal lipids. The antibodies to liposomes have a 'subsite' in the binding site that recognizes small soluble phosphorylated haptens such as nucleotides (e.g., ATP). The capacity of anti-liposome antibodies to bind to phosphate is also shared by antibodies to numerous other substances, including lipid A from Gram-negative bacterial lipopolysaccharide, cardiolipin, DNA, polynucleotides, and lipoteichoic acids from Gram-positive bacteria. Because of similarities of chemical structures between all of these molecules widespread immunological cross-reactivities are observed.

Antibodies to lipoteichoic acid from Staphylococcus aureus. Specificity of murine monoclonal and human antibodies

Two monoclonal antibodies against staphylococcal lipoteichoic acid (LTA) were made by fusing P3X63Ag8 myeloma cells and splenocytes from mice immunized with purified LTA. Both were isotyped as being IgM kappa. Their specificities were determined by enzyme-linked immunosorbent assays indicating that both antibodies reacted with the glycerol-phosphate backbone, while one of them also had some affinity for the alanyl substituent. Antibodies in serum from 7 multiple sclerosis (MS) patients and serum and cerebrospinal fluid (CSF) from 7 non-MS patients apparently reacted with the sugar moiety of LTA. In contrast, CSF antibodies from 6 of the 7 MS patients and 1 of the 7 non-MS patients had affinity for the alanine residue. This non-MS patient also had serum antibodies against the alanine residue. None of the other sera tested appeared to contain such antibodies.

Interaction of anti-kojibiose antibody with the lipoteichoic acids from Streptococcus faecalis and Streptococcus faecium

Antisera prepared in rabbits by immunization with p-aminophenyl beta-kojibioside conjugated to bovine serum albumin (antikojibiose sera), readily agglutinated whole cells of Streptococcus faecalis or Streptococcus faecium, and showed specific reactions with the lipoteichoic acids (LTAs) of these streptococci by passive hemagglutination, microscale enzyme-linked immunosorbent assay, and crossed immunoelectrophoresis. The interaction of the antikojibiose sera with the LTAs was inhibited best by kojibiose [alpha-D-glucopyranosyl-(1----2)-D-glucose], somewhat less by the dextran from which the kojibiose was prepared, and not measurably by maltose [alpha-D-glucopyranosyl-(1----4)-D-glucose]. The sera reacted only minimally in only the most sensitive assay (microscale enzyme-linked immunosorbent assay) with LTA from group A streptococci (this LTA contains a single kojibiosyl residue as part of the glycolipid moiety of the molecule and failed to react with the Lactobacillus fermentum LTA which is substituted with alpha-D-galactopyranosyl-(1----2)-D -glucosyl units.