Immunochemistry of a synthetic peptidoglycan-precursor pentapeptide

Production and Characterization of Monoclonal Antibodies against the Vasoconstrictive Peptide Human Urotensin-II

We report the production and characterization of four monoclonal antibodies (MAbs) against human urotensin-II (hU-II). The antibodies were raised against human hU-II, which contains the C-terminus cyclic ring (CFWKYC) that is conserved across species. Multiple selection assays were applied to ensure antibody potency and reactivity against the ring structure. The MAbs reacted via ELISA with hU-II bound to plastic, immunoprecipitated [(125)I-Y(9)] hU-II, bound to biotinylated hU-II in BIAcore analysis and, by Western analysis, recognized the full-length human preprourotensin-II expressed in transfected HEK293 cells. All four MAbs cross-reacted with porcine A, porcine B, rat, mouse, and goby U-II in ELISA. By competitive RIA, hU-II(5-11) (identical to the C-terminus of goby U-II) reacted equivalently to hU-II and goby U-II. The IC(50)s were 0.8 nM for one MAb and 1.6 nM for the others. All four MAbs reacted 15-fold less potently with hU-II(5-10) and 50-fold less potently with hU-II(5-10) amide. Thus, the ring structure and terminal Val/Ile comprise the binding site for this group of MAbs. This panel of antibodies could be useful tools to help delineate the biology and pharmacology of U-II. They may also be of diagnostic value in monitoring hU-II in body fluids.

Changes in mu opioid receptors and rheological properties of erythrocytes among opioid abusers

Opioids, reported originally to bind to specific receptors in the brain, now also appear to bind to receptors on blood cells. The high prevalence of anemia among chronic opioid users leads us to propose that chronic opiate use results in elevated mu opioid receptor levels on human erythrocytes and that these receptor changes may affect erythrocyte membrane properties. Blood samples from 17 opioid-dependent subjects (based on the Diagnostic and Statistical Manual of Mental Disorders, 4th edition or DSM-IV) and 15 drug-free controls were assayed for mu opioid receptors on erythrocytes using a flow cytometry immunoassay. Deformability and the hydration status of erythrocytes were studied by ektacytometry. Data were analyzed by independent t-tests, tests of correlation, chi square and cluster analyses. As expected, the percentage of erythrocytes from opioid-dependent subjects with opioid receptors (opioid receptor levels) was significantly higher (47.4 +/- 38.3%) than controls (22.8 +/- 30.1%) (t = 2.01, df = 30, p < 0.05). Also, the opioid-dependent patients showed a wide variation in the percentage of erythrocytes bearing opioid receptors and data analyses of these patients showed two strongly defined clusters. One subgroup consisted of nine individuals with very high receptor levels (mean = 81.5%) while the other had eight patients with low receptor levels (mean = 9.1%) that were not significantly different than the receptor levels of controls. Ektacytometry of opioid dependent patients with high opioid receptor levels showed changes in rheological parameters of erythrocytes, such as deformability index and cellular hydration. For example, a positive correlation was observed between opioid receptor levels and deformability indices among opioid-dependent patients (r = 0.74, p < 0.005). Our findings indicate that the mu opioid receptor is present on human erythrocytes, although with considerable variation in receptor levels, and that the levels of this receptor are significantly elevated with chronic opioid exposure. Moreover, erythrocytes with high opioid receptor levels from chronic opiate users seem to have high deformability. This study may offer clues to the biological properties of peripheral blood cells that may be mediated by mu opioid receptors and lead to a better understanding of some of the clinical effects of opioid use.

A competitive radioimmunoassay for peptidoglycan monomer

The preparation and characterization of the essential components to be used in the radioimmunoassay of peptidoglycan monomer (PGM) is described. In order to raise the anti-peptidoglycan monomer antibodies 14C-labelled peptidoglycan monomer-bovine serum albumin conjugate was prepared by the coupling of 14C-peptidoglycan monomer to bovine serum albumin in the presence of glutaraldehyde in 0.1 M NaHCO3 at pH 8.3. The prepared conjugate elicited anti-PGM response in rabbits. A synthetic analog of peptidoglycan monomer, Boc-L-tyrosyl-peptidoglycan monomer was prepared by condensation of unprotected peptidoglycan monomer and N-hydroxysuccinimidester of Boc-L-tyrosine in the presence of triethylamine and the obtained disaccharide-hexapeptide was labelled with Na125I. This compound exhibited the ability of binding to anti-peptidoglycan monomer antibodies. The prepared compounds, namely anti-PGM antibodies and 125I-labelled Boc-L-tyrosyl-peptidoglycan monomer, were used as essential components in competitive radioimmunoassay for peptidoglycan monomer determination in mammalian and human sera and plasma, respectively.

Immunoelectron microscopic studies on the localization of peptidoglycan peptide subunit pentapeptides in bacterial cell walls

The peptide subunit pentapeptide H-L-Ala-D-Glu(L-Lys-D-Ala-D-Ala-OH)-NH2 of peptidoglycan was localized in the cell walls of several Gram-positive bacteria employing the indirect immunoferritin technique. Specific antibodies to the D-alanyl-D-alanine moiety of non-crosslinked peptide subunit pentapeptide were raised in rabbits by immunization with synthetic immunogen albumin-(CH2CO-Gly-L-Ala-L-Ala-D-Ala-D-Ala-OH)39. Specificity of these antibodies for the peptide subunit pentapeptide and not for the peptide subunit tetrapeptide was corroborated in a Farr-type radio-active hapten binding assay. Specificity of labelling with ferritin was established by immunoelectron microscopic controls, and by the excellent correlation between specific labelling of cells with ferritin and the particular peptidoglycan primary structure of bacterial strains investigated. Cells of Lactobacillus gasseri, Streptococcus pyogenes and Staphylococcus aureus revealing non-crosslinked peptide subunit pentapeptides in their peptidoglycans could specifically be labelled. Lactobacillus acidophilus and Bacillus subtilis, on the contrary, missing such pentapeptides, failed in labelling. The implication of this method to possibly localize the points of attack of penicillin or cycloserine is discussed.

Antibodies to peptidoglycan in patients with spondylarthritis: a clue to disease aetiology?

Although the aetiology of the spondylarthritic diseases, ankylosing spondylitis and Reiter's syndrome, is obscure, a clue to the pathogenesis might be an animal model, adjuvant arthritis. Rats with this disease develop a spectrum of pathology with marked similarity to the spondylarthritides. Since peptidoglycan, a major cell wall component of most bacteria is causally implicated in adjuvant arthritis, we sought evidence that peptidoglycan exposure accompanies both Reiter's syndrome and ankylosing spondylitis. Antibodies to the D-Ala-D-Ala moiety of peptidoglycan were measured by a sensitive and specific ELISA. Antibodies were elevated significantly in patients with ankylosing spondylitis or Reiter's syndrome, but not in patients with rheumatoid arthritis or degenerative joint disease in comparison with normal controls. The findings should be considered preliminary, since only a minority of patients had increased antibody titres. However, the findings are compatible with the hypothesis that peptidoglycan is causally related to spondylarthritis. Antibodies to other moieties in the peptidoglycan molecule might be a more sensitive test for significant exposure.

Detection of soluble peptidoglycan in urine after penicillin administration

A unique enzyme-linked immunosorbent assay was developed to detect soluble peptidoglycans in biological fluids. It makes use of the similar affinities of vancomycin and purified rabbit antibodies to peptidoglycan precursor sequences found in soluble peptidoglycans. This assay has been used to detect as little as 500 pg of soluble peptidoglycan per ml of serum and 5 pg/ml of urine. Studies of normal individuals and Staphylococcus aureus-infected patients revealed only a few sera with detectable levels of soluble peptidoglycans. Studies of normal volunteers who were given a single oral dose of 250 mg of penicillin VK showed that about half had detectable levels of soluble peptidoglycans in their urine up to 6 h after ingestion. This suggests that soluble peptidoglycans can be released by indigenous bacteria in detectable amounts. In one volunteer, a detectable level of soluble peptidoglycan in the urine at 6 h decreased to an undetectable level at 12 h. Such an ephemeral appearance of soluble peptidoglycan in the urine could account for the small number of human sera that had detectable levels of soluble peptidoglycan.

Evidence for the secretion of soluble peptidoglycans by clinical isolates of Staphylococcus aureus

Four isolates of Staphylococcus aureus from patients with endocarditis and bacteremia were capable of secreting high-molecular-weight soluble peptidoglycans when grown in a minimal cell wall medium containing penicillin G. Vancomycin was not able to substitute for penicillin G in triggering this secretion. Secretion reflected de novo synthesis of soluble peptidoglycan and was strongly dependent on time of incubation (30 to 60 min), and number of bacteria (2 X 10(8) to 5 X 10(8) colony-forming units per ml), but not on penicillin G concentration (10 to 250 micrograms/ml). The incorporation of alanine into the peptidoglycans secreted in vitro by these isolates incubated in the presence of penicillin G under optimal conditions was variable. The least incorporation of alanine into peptidoglycan occurred with an isolate from a patient treated with nafcillin who had no detectable antipeptidoglycan titer.

Antibody levels to bacterial peptidoglycan in human sera during the time course of endocarditis and bacteremic infections caused by Staphylococcus aureus

Sera from patients with endocarditis and bacteremia due to Staphylococcus aureus were compared for peptidoglycan-binding capacity with those from normal blood donors. Those patients treated with beta-lactam antibiotics had higher antigen-binding levels than normal donors and patients treated exclusively with vancomycin (P less than 0.01). The factor responsible for this activity was purified by affinity chromatography from a normal donor and shown to be an immunoglobulin. Specificity studies indicated that the immunodominant determinant was a peptide sequence found in peptidoglycan precursors. Since soluble peptidoglycan molecules having the precursor peptide sequence are known to be secreted by some gram-positive bacteria like Micrococcus luteus when grown in the presence of beta-lactam antibiotics, these soluble molecules may constitute the "natural" immunogen. Such a hypothesis is consistent with the study of the peptidoglycan-binding capacities in the sera of these patients during the course of treatment. For most of the responding patients studied (four of four with bacteremia and seven of nine with endocarditis), a significant increase in peptidoglycan-binding capacity was observed in sera taken 1 to 5 weeks after the initiation of beta-lactam antibiotic therapy (compared with the initial serum studied). No such increase in the peptidoglycan-binding capacity over a similar time span was noted in the sera of people not receiving beta-lactam antibiotics (none of seven).

Specific antibodies to the N-termini of the interpeptide bridges of peptidoglycan

The synthetic peptides Gly5-epsilon-Ahx and L-Ala3-epsilon-Ahx, with structural similarity to the interpeptide bridge peptides of staphylococci or micrococci, respectively, were convalently linked to human serum albumin via their carboxylgroups. Antisera to these synthetic peptidyl-protein antigens contained fairly high amounts of antibodies with specificity to the N-terminal parts of the peptide chains attached to the carrier proteins. Antisera to (Gly5-epsilon-Ahx)20-albumin gave, without exception, strong precipitin reactions in latex-agglutination with staphylococcal peptido-glycans. The antisera completely failed, however, in any reaction with peptidoglycans of micrococci or other bacteria which did not have these oligo-glycine peptides typical for staphylococci. On the contrary, antisera to (l-Ala3-epsilon-Ahx)22-albumin strongly precipitated micrococcalpeptidoglycans with oligo-L-alanine interpeptide bridges (e.g. Micrococcus varians. Micrococcus roseus), but showed no significant reaction with peptidoglycans of staphylococci or other bacteria lacking oligo-L-alanine interpeptide bridges.

The infectious etiology of rheumatoid arthritis. New considerations

Several possible mechanisms of chronic inflammatory arthritis that might be initiated by infectious agents are discussed. Some recent information on mycoplasma infections, long-term virus infections, and shed bacterial components provides the bases for new experimental approaches. Currently, evidence of involvement of mycoplasma or viral agents in rheumatoid arthritis is tenuous. Chronic peptidoglycan-immune-complex formation is a consideration that has been discussed, but only recently pursued in depth. It may well be that experimental studies on the infectious etiology of rheumatoid arthritis will be revitalized through an appreciation of the bacterial antigen load in the gastrointestinal tract. The perimental vehicles for testing this possibility are available and should be directly applicable at the clinical level.

The immunochemistry of peptidoglycan. Antibodies against a synthetic immunogen cross-reacting with an interpeptide bridge of peptidoglycan

An albumin-peptide conjugate was synthesized, which carries pentaglycine peptides with C-terminal glycine residues as found in the interpeptide bridges of the peptidoglycan of many staphylococci. Immunization of rabbits with this synthetic immunogen yielded antisera containing predominantly antibodies against the peptide moiety of the conjugate. The quantitative precipitin and the Ouchterlony agar gel reaction with several synthetic protein-peptide-conjugates, immunoaffinity chromatography of the antisera on Sepharose-(Gly-Gly-Gly-Gly-Gly)n and hapten inhibition studies with several synthetic peptides and peptide derivatives demonstrated that the antibodies were highly specific for oligoglycine peptides with C-terminal glycine. These antibodies also reacted strongly with staphylococcal peptidoglycans with an interpeptide bridge composed of pentaglycine peptides or of pentaglycine peptides in which part of the glycine residues were replaced by L-serine. In contrast, all the peptidoglycans lacking interpeptide bridges composed of glycine residues gave no precipitin reaction at all. The final proof for identical determinant groups of albumin-(CH2CO-Gly-Gly-Gly-Gly-Gly)31 and the staphylococcal peptidoglycans applied in the precipitin reaction was furnished by double gel diffusion studies and by hapten inhibition of the precipitin reaction between antisera to albumin-(CH2CO-Gly-Gly-Gly-Gly-Gly)31 and the corresponding peptidoglycans. For rapid screening of the different peptidoglycans, a latex agglutination test was elaborated. Purified antibodies were adsorbed to latex particles, and the titers with the particular peptidoglycans were then determined. The test was highly sensitive, in that 10 nanograms of peptidoglycan could still be detected.

[Biological activity of bacterial peptidoglycan (mucopeptide) (author's transl)]

A brief survey on the ultrastructure, the chemical composition and the immunological properties of bacterial cell wall peptidoglycan (mucopeptide) is presented. This paper deals with the various recently discovered biological activities of peptidoglycan. These could be divided into three different groups, namely: 1. Endotoxin-like properties: pyrogenicity, induction of the local Shwartzman reaction, increase in non-specific resistance to bacterial infection, release of 5-hydroxytryptamine from rabbit platelets, complement activation,gelation of amebocyte lysate. 2. Inflammatory reactions of skin and internal organs, aggressin activity (virulence factor), inhibition of phagocytosis of bacteria by granulocytes and macrophages, inhibition of growth of cell cultures, cytotoxity to granulocytes and macrophages. 3. Potentiation of humoral and cellular immune responses (adjuvant), enhancement of tumor defense in experimental animals. The potential mechanisms of action of peptidoglycan are discussed and attention is focused on the implications of the various peptidoglycan activities for medicine.