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J D Clements

Publications and source records attributed to J D Clements.

99 records · Page 6Linked to original sources
PubMed1980

Properties of homogeneous heat-labile enterotoxin from Escherichia coli.

Recently, the heat-labile enterotoxin (LT) of Escherichia coli has been purified to homogeneity and partially characterized (Clements and Finkelstein, Infect. Immun. 24:760-769, 1979). This study extends our observations on the physicochemical properties of LT. The toxin has an isoelectric point of pH 8.0, as compared with choleragen and choleragenoid, which have isoelectric points of pH 6.75 and 7.75, respectively. Sedimentation equilibrium measurements established an approximate molecular weight for LT of 91,440. LT had an even more marked affinity than choleragen for agarose-containing matrixes in gel filtration. Of several mono- and disaccharides tested, only galactose and lactose were highly efficient in removing 125I-labeled LT from agarose-containing columns. LT dissociated into subunits (designated A and B) during gel filtration in the presence of 5 M guanidine. These subunits were immunologically distinct and possessed unique and shared antigenic determinants to the corresponding A and B subunits of choleragen. During gel filtration of LT at pH 6.5 and room temperature, a spontaneously occurring toxoid of LT, analogous to choleragenoid, was discovered and designated "coligenoid." This product contains only the B subunits of the toxin. A partial amino acid sequence of the B subunit of LT revealed a remarkable homology to the primary structure of cholera toxin B. Within the first 20 amino acids of the two chains, only 5 differ, and these differences may be attributable to single base substitutions.

Amino Acids↗
PubMed1980

Liposomes as vehicles for vaccines.

Lipid A from Shigella flexneri LPS, or acylated derivatives of muramyl dipeptide (MDP), were incorporated into the lipid bilayer of liposomes to enhance the adjuvanticity of the liposomes in rabbits. Liposomes containing lipid A induced antibodies against lipid A, phosphocholine, phosphatidylcholine, and sphingomyelin. Lipid A was resolved into eight fractions, some of which did, and others of which did not, induce antibodies against liposomes. Anti-liposome antibodies also were induced (in the absence of liposomes) by complete Freund's adjuvant, and by acid treated bacterial cells coated with lipid A, but were not induced either by lipid A or liposomes alone, or by liposomes containing acylated MDP. We tested the liposomes for the ability to enhance the immunogenicity of a protein antigen. The antigen consisted of liposomes having acylated MDP and ganglioside GM1 (the receptor for cholera toxin, or CT) in the lipid membrane, and CT bound to the outer surface of the liposomes. The liposomal antigen (having surface-bound CT) produced a much greater anti-CT titer than that obtained by injection of CT alone. We conclude that liposomes containing only phosphatidylcholine, cholesterol, and dicetyl phosphate are poorly immunogenic, but that antibodies against them can be induced by inclusion of lipid A. Liposomes that are appropriately formulated can strongly enhance the immunogenicity of a liposome-bound protein antigen.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1979

Isolation and characterization of homogeneous heat-labile enterotoxins with high specific activity from Escherichia coli cultures.

The heat-labile enterotoxin (LT) has been isolated in homogeneous form with high specific activity from three sources: cell-free supernatant, NaCl extract, and whole-cell lysates of an enterotoxigenic Escherichia coli strain. In vitro immunological assays were used in lieu of tedious and highly variable bioassays to recognize fractions with activity. This revealed that the major portion of the LT remained adherent to columns containing agarose, from which it could be eluted quantitatively in practically homogeneous form by galactose. Isolated LT has remarkable similarities to the cholera enterotoxin (choleragen) in both subunit structure and amino acid composition, although there are also notable differences in these two enterotoxins, which are related immunologically and by mode of action. Unlike choleragen, in which the A region is totally nicked, E. coli LT, depending on its source, is activated by proteolytic processing. The activity of LT is equivalent to that of choleragen in bioassays on adrenal cells, in rabbit skin, and in rabbit ileal loops, especially when, depending on the source of material, the LT has been activated by treatment with trypsin. The whole-cell lysate is the richest source of LT.

Amino Acids↗
PubMed1978

Demonstration of shared and unique immunological determinants in enterotoxins from Vibrio cholerae and Escherichia coli.

Immunodiffusion and biological neutralization studies demonstrated that the heat-labile enterotoxin (LT) from Escherichia coli has antigenic determinants in common with each of the isolated subunits (A and B) of the enterotoxin (choleragen) from Vibrio cholerae. Each of the enterotoxins also possesses unique antigenic specificities. Monospecific antiserum to LT was prepared by immunization with antigens derived by immune precipitation of E. coli cell-free supernatant with isolated specific anticholeragenoid antibodies. This antiserum neutralized the biological acitivity of both LT and cholera enterotoxin and recognized antigens of both in immunodiffusion. This antiserum was adsorbed with choleragenoid to remove antibodies directed against the shared "B" immunological determinants. The neutralizing effect of the antiserum on cholera toxin was completely removed, but the neutralizing activity against the E. coli preparations was retained, although somewhat reduced. Antisera to the isolated subunits (A and B) of cholera enterotoxin neutralized the biological activity of cholera enterotoxin and LT. These antisera also recognized the homologous and heterologous antigens in immunodiffusion. Multiple forms or conformations of LT and its components may explain the diversity of the properties which have been reported for it.

Antigens, Bacterial↗
PubMed1976

Vibrio cholerae adherence and colonization in experimental cholera: electron microscopic studies.

Colonization of the intestinal epithelium by Vibrio cholerae was examined in two model systems, in ligated ileal loops of adult rabbits and in the patent gut of infant rabbits, using both scanning and transmission electron microscopy. Time studies in the adult model showed a lag period of up to 1 h before the attachment of significant numbers of the vibrios. The bacteria appeared initially in small patches on the sides of the villi, predominantly along the transverse furrows. The number of adherent bacteria steadily increased, reaching a maximum between 4 and 7 h, when a dense mat of bacteria several layers thick covered much of the villi. After this time there was a rapid decline in the number of V. cholerae bound. By 12 to 16 h only a few bacteria could be seen on the surface of the villi, which had a rough, patchy appearance at these later times. Globular protrusions, with vibrios attached, may play a role in the clearance of bacteria. Colonization and clearance in the patent intestine of the infant rabbit occurred much as in the adult model. However, the bacteria adhered more uniformly and there was no lag in attachment. In both models the majority of bacteria were aligned horizontally with the epithelial surface, but some were attached in an end-on manner, with their flagella extending into the lumen. The bacteria adhered via their surface coats directly to the tips of the microvilli, except for a few vibrios that were partly embedded into the brush border. Some changes in the microvilli occurred as a consequence of the bacterial attachment.

Animals↗
PubMedDate not supplied

Vaccines against enterotoxigenic bacterial pathogens based on hybrid Salmonella that express heterologous antigens.

In this report, we examine two aspects in the development of a vaccine against enterotoxigenic bacterial pathogens based on hybrid Salmonella that express heterologous antigens. First, we describe the construction of a non-toxic fusion peptide for immunization against Escherichia coli that produce heat-labile (LT) and heat-stable (ST) enterotoxins. For that construction, the 5' terminus of the gene coding for ST was fused to the 3' terminus of the gene coding for the binding subunit of LT(LT-B). The ST gene was constructed synthetically with appropriate restriction sites to permit in-frame, downstream insertion. Maximum expression of ST antigenicity was obtained when a seven-amino-acid proline-containing linker was included between the LT-B and ST moieties. The purified LT-B/ST fusion peptide consisted of a single polypeptide chain with an apparent molecular weight of 18,000. The LT-B/ST fusion peptide was non-toxic and immunologic determinants of both LT and ST were recognized by antibodies directed against the native toxins. Animals immunized with either crude or purified preparations containing the hybrid molecule produced antibodies that were able to recognize native toxin in vitro. Significantly, these antibodies were able to neutralize the biological activity of native ST. The second aspect reported here examines a mechanism for stabilizing expression of heterologous antigens in attenuated Salmonella mutants by integration of the heterologous gene (LT-B) into the chromosome of the carrier. A comparative in vitro study of the levels of expression of LT-B between the cointegrate strain and an isogenic strain carrying the LT-B gene on a multicopy plasmid demonstrated that the initial levels of expression of both strains is similar, that the plasmid-carrying strain loses the ability to express the heterologous antigen very quickly and that the cointegrate continues to maintain and express the antigen without the requirement for a stabilizing antibiotic.

Animals↗