PubMed Health⌕ Search

Biomedical subjects

J D Clements

Publications and source records attributed to J D Clements.

At least 91 records · Page 5Linked to original sources
PubMed1987

Presynaptic inhibition of synaptic potentials evoked in cat spinal motoneurones by impulses in single group Ia axons.

1. Single-fibre group Ia excitatory post-synaptic potentials (e.p.s.p.s) were evoked in triceps surae motoneurones. These e.p.s.p.s were reduced by conditioning stimulation of group I axons in posterior biceps-semitendinosus nerves. 2. The investigation concentrated on e.p.s.p.s of somatic origin, because the amplitude of these e.p.s.p.s is not reduced by post-synaptic conductance increases. Any reduction in these e.p.s.p.s could therefore be attributed to presynaptic inhibition. 3. The reduction in somatic e.p.s.p. amplitude was greatest when the conditioning stimulus preceded the e.p.s.p. by 30 ms, and was negligible when the conditioning interval was extended to 200-300 ms. 4. The percentage reduction of somatic e.p.s.p.s was independent of their unconditioned peak amplitude. 5. E.p.s.p.s of somatic origin were reduced by the same amount, on average, as e.p.s.p.s of dendritic origin. 6. E.p.s.p.s evoked in the same motoneurone by impulses in different Ia axons were reduced by different amounts and e.p.s.p.s evoked in different motoneurones by impulses in the same Ia axon were also reduced by different amounts. 7. Analysis of fluctuations in e.p.s.p.s before and after conditioning indicated that after conditioning, larger discrete amplitudes became less probable, while smaller discrete amplitudes became more probable. The average increment between discrete amplitudes did not alter; nor were the discrete amplitudes reduced. 8. The probabilities of transmitter release at synaptic boutons were calculated before and during presynaptic inhibition. The maximum decrease in release probability was 0.64, suggesting a reduction in calcium influx of 10-15%.

Animals↗
PubMed1986

Soiled saris: a vector of disease transmission?

We examined the relationship between uses of the sari that are potential health hazards and episodes of diarrhoea in children younger than 6 years in 247 families living in 51 slums in Dhaka, Bangladesh. These misuses appeared to be common (median of three per observation period) and were largely unrecognized by the women as possible sources of disease transmission. There appeared to be a positive correlation between the number of misuses of the sari and episodes of childhood diarrhoea.

Animals↗
PubMed1986

Effectiveness of liposomes as potential carriers of vaccines: applications to cholera toxin and human malaria sporozoite antigen.

Two antigens, cholera toxin (CT) and a synthetic albumin-conjugated 16-residue peptide derived from the circumsporozoite (CS) protein of Plasmodium falciparum sporozoites, were tested as immunogens in rabbits. The malaria peptide-albumin conjugate by itself was completely nonimmunogenic, and although cholera toxin was immunogenic it also expressed considerable native toxicity. After attachment of CT to liposomes containing ganglioside GM1, toxicity of CT was completely eliminated and antigenicity was enhanced. Therefore liposomes may be capable of reducing toxicity of certain potentially dangerous antigens such as toxins. After incorporation of the malaria peptide-albumin conjugate into liposomes a high titre of specific antibodies was induced against the malaria peptide but not against albumin. These antibodies also reacted with native CS protein. Three adjuvants, including lipid A and two types of lipophilic muramyl dipeptide, were compared and found to be effective in liposomes. Based on the conversion of synthetic P. falciparum CS peptide from a nonimmunogenic to an immunogenic form and on the 'toxoiding' effect of liposomes for CT, it is concluded that liposomes should be considered as being a useful carrier for antigens and adjuvants for vaccines for poorly antigenic or toxic substances.

Adjuvants, Immunologic↗
PubMed1986

Intracellular tetraethylammonium ions enhance group Ia excitatory post-synaptic potentials evoked in cat motoneurones.

Single fibre group Ia excitatory post-synaptic potentials (e.p.s.p.s) were recorded in cat spinal motoneurones after the neurones were injected with tetraethylammonium (TEA) ions. TEA injection increased the peak amplitude of most e.p.s.p.s. The time course of e.p.s.p.s generated at the soma was unaffected, but the time course of e.p.s.p.s generated in the dendrites was prolonged. The membrane time constant did not change after TEA injection. Somatic e.p.s.p.s were voltage clamped after TEA was injected. The reversal potential for these e.p.s.p.s was more positive than for e.p.s.p.s unaffected by TEA. Composite e.p.s.p.s added linearly, or greater than linearly, whereas in motoneurones without TEA they added linearly or less than linearly. The enhanced amplitude and prolonged time course observed in dendritic e.p.s.p.s after TEA injection was reduced by small hyperpolarizing currents. Greater than linear summation of composite e.p.s.p.s was converted to linear summation by small hyperpolarizing currents. The increase in somatic e.p.s.p.s was attributed to a more positive reversal potential for the e.p.s.p.s. We suggest that TEA decreases the relative permeability of K+ in the subsynaptic channels. We propose that in the presence of TEA, dendritic depolarization activates an inward current which amplifies and prolongs synaptic potentials spreading towards the soma.

Action Potentials↗
PubMed1986

Oral immunization of mice with attenuated Salmonella enteritidis containing a recombinant plasmid which codes for production of the B subunit of heat-labile Escherichia coli enterotoxin.

We used Salmonella enteritidis serotype dublin strain SL1438, a nonreverting, aromatic-dependent, histidine-requiring mutant, as a recipient for a recombinant plasmid coding for production of the nontoxic B subunit of the heat-labile Escherichia coli enterotoxin. The S. enteritidis derivative EL23 produced heat-labile enterotoxin subunit B that was indistinguishable from heat-labile enterotoxin subunit B produced by strains of E. coli or Salmonella typhi harboring the same plasmid. Mice immunized orally with strain EL23 developed progressively increasing mucosal and serum antibody responses to both heat-labile enterotoxin subunit B and to the lipopolysaccharide of the vaccine strain. The mucosal antibody response was shown to be immunoglobulin A specific and to be capable of neutralizing the biological activities of both E. coli heat-labile enterotoxin and cholera enterotoxin in vitro.

Administration, Oral↗
PubMed1984

Differences in cross-protection in rats immunized with the B subunits of cholera toxin and Escherichia coli heat-labile toxin.

Although cholera toxin (CT), Escherichia coli heat-labile toxin (LT), and their B subunits are known to be immunologically related, the ability of each to raise an antitoxin response that provides equally strong cross-protection against active challenge with pure heterologous toxin has not been examined previously. We immunized rats with pure preparations of the B subunits of human LT, porcine LT, and CT. Immunization with either of the LT B subunits raised greater than or equal to fourfold increases in specific mucosal immunoglobulin A antitoxin titers to homologous and heterologous LT and CT B subunits, thereby providing strong protection against active challenge in ligated ileal loops with all three respective holotoxins and with a viable LT-producing E. coli strain. In contrast, immunization with the CT B subunit raised a greater than or equal to fourfold increase in antitoxin titers only to itself and provided strong protection only against challenge with the CT holotoxin. Conjugation of the CT B subunit with the E. coli heat-stable toxin by the carbodiimide reaction yielded a cross-linked immunogen with equal antigenicity for both components; immunization with this conjugate raised greater than or equal to fourfold increases in antitoxin titers to both components, but it provided significant protection only against challenge with a viable heat-stable toxin-producing E. coli strain and not to an LT-producing E. coli strain. These observations indicate that immunization with the LT B subunits raises a heterologous antitoxin response that extends to the CT B subunit, thereby providing equally strong protection against LT and CT; however, immunization with the CT B subunit raises principally a homologous antitoxin response, so that this immunogen provides strong protection only against CT.

Animals↗
PubMed1984

Construction of a potential live oral bivalent vaccine for typhoid fever and cholera-Escherichia coli-related diarrheas.

We used the Salmonella typhi galactose epimerase (galE) mutant strain Ty21a, shown to be a safe, effective, living, attenuated oral typhoid vaccine, as a recipient for a recombinant plasmid containing the gene for production of the nontoxic B subunit of the heat-labile enterotoxin of Escherichia coli. The S. typhi derivative, strain SE12, produced heat-labile enterotoxin subunit B that was structurally and immunologically indistinguishable from heat-labile enterotoxin subunit B produced by strains of E. coli harboring the same plasmid. Tests in mice and guinea pigs showed that strain SE12 was safe when given orally and was capable of inducing a significant antitoxic antibody response when injected parenterally. Moreover, it retained the galactose sensitivity of the parent strain, preserving its utility as a typhoid vaccine. This strain may prove to be a useful live oral bivalent vaccine strain for typhoid fever and cholera-E. coli-related diarrheas.

Administration, Oral↗
PubMed1983

Vaccine for enterotoxigenic Escherichia coli based on synthetic heat-stable toxin crossed-linked to the B subunit of heat-labile toxin.

Synthetically produced Escherichia coli heat-stable toxin (ST) was conjugated to the nontoxic B subunit of the heat-labile toxin (LT) by the carbodiimide reaction. Modifying the molar ratio of toxins mixed and the ratio of carbodiimide added to the toxins permitted synthesis of conjugates with any desired degree of proportional antigenicity for each toxin component. Immunization of rats by the parenteral/peroral routes with cross-linked vaccine containing 39% ST and 61% B subunit antigenicity, with 0.06% residual ST toxicity, evoked fourfold to sevenfold increases over control values of serum IgG and mucosal secretory IgA antitoxin titers to each of the component toxins, thus providing significant (P less than 0.001) protection against challenge with either LT or ST or with viable heterologous strains which produce these toxins. These observations show that cross-linking synthetic ST to the B subunit results in a nontoxic vaccine that provides protection against all types of enterotoxigenic E. coli.

Animals↗
PubMed1983

Cloning and molecular characterization of the B subunit of Escherichia coli heat-labile enterotoxin.

We have constructed a plasmid containing the gene for production of the B subunit of the heat-labile enterotoxin (LT-B) from a human isolate of Escherichia coli, strain H10407. The 0.8-kilobase gene fragment encoding synthesis of LT-B was cloned onto plasmid pBR322 after sequential digestion of the enterotoxin plasmid of strain H10407 with restriction endonucleases PstI and HindIII. LT-B was isolated by agarose affinity chromatography from cell lysates of recombinant clones expressing the B subunit. The B subunit was isolated in its oligomeric form, was structurally identical to native B subunit when examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, dissociated to monomeric B in the presence of 5 M guanidine, was immunologically identical to native B subunit in an enzyme-linked immunosorbent assay, and contained no demonstrable A subunit in any of the assays.

Antibodies, Bacterial↗
PubMed1983

Protection against human and porcine enterotoxigenic strains of Escherichia coli in rats immunized with a cross-linked toxoid vaccine.

To compare their relative immunogenicities, we used synthetically produced Escherichia coli heat-stable toxin coupled to a protein carrier and the B subunit of porcine heat-labile toxin separately in graded dosages to immunize rats. Equivalent antigen unit dosages of each toxin raised approximately the same level of mucosal immunoglobulin A (IgA) antitoxin response and degree of protection against a challenge with respective heat-stable- or heat-labile-toxin-producing viable bacteria. Conjugation conditions were identified, therefore, which yielded a vaccine of these toxins, cross-linked by the carbodiimide reaction, that consisted of equal antigenic proportions of each toxin component as determined by enzyme-linked immunosorbent assay and expressed in antigen units. The dose-related response to immunization with this vaccine was the same as the response to its components given separately. The toxicity of the heat-stable toxin component was reduced greater than 600-fold. Immunization with optimal antigen unit dosages of the vaccine gave greater than or equal to sixfold increases in mucosal IgA antitoxin titers and provided significant (P less than 0.001) protection against challenge with heterologous serotypes of viable strains, of either human or porcine origin, that produce heat-stable or heat-labile toxin or both.

Adjuvants, Immunologic↗
PubMed1982

Development of a vaccine of cross-linked heat-stable and heat-labile enterotoxins that protects against Escherichia coli producing either enterotoxin.

A vaccine of cross-linked heat-stable (ST) and heat-labile (LT) toxins that protects against heterologous serotypes of strains of Escherichia coli which produce either the LT or ST enterotoxin was developed by conjugating ST to LT by the carbodiimide reaction. Three interrelated factors were found to affect the composition and properties of the final conjugate: (i) the amount of carbodiimide added to the toxins, (ii) the initial ratio of ST to LT, and (iii) the duration of the conjugation reaction. Optimal conjugation conditions were identified as a carbodiimide-to-toxin ratio of 10:1 by weight, an initial molar ratio of ST to LT of 100:1, and a conjugation reaction time of 96 h. This approach yielded a conjugate that contained 96% by moles and 36% by weight pure ST, determined with radioiodinated pure ST, and 34% by weight semi-pure ST, determined by the Lowry protein method. The retained antigenicities of the conjugated toxins, as determined by enzyme-linked immunosorbent assays, was greater than or equal to 82%, and their toxicities, as determined by the Y1 adrenal cell assay for LT and by the suckling mouse assay for ST, were reduced to less than or equal to 0.15%. Immunization of rats with this cross-linked ST-LT vaccine provided strong protection against challenge with either the LT or the ST toxin or with viable heterologous strains which produce these toxins, either singly or together. These observations indicate that conjugation of ST to LT results in a unique new immunogen in that ST acquires immunogenicity as a function of the reaction, LT retains most of its antigenicity, and the toxic properties of each individual toxin are greatly reduced.

Animals↗
PubMed1982

Arousal of mucosal secretory immunoglobulin A antitoxin in rats immunized with Escherichia coli heat-labile enterotoxin.

Specific serum and mucosal antitoxin levels were determined by enzyme-linked immunosorbent assays in rats immunized with Escherichia coli heat-labile enterotoxin (LT). Immunization by means of a parenteral prime followed by peroral boosts was the only approach that aroused titers of both serum immunoglobulin G (IgG) antitoxin and mucosal secretory IgA antitoxin that were increased fourfold or more over control values. Primary parenteral immunization was effective when given either intraperitoneally or subcutaneously with either Freund complete adjuvant or alum as the adjuvant. The magnitude of the nucosal secretory IgA antitoxin response and the degree of protection against challenge with either LT or viable LT-producing organisms were related to the number and dosage of peroral boosts. LT antigenicity, as determined by enzyme-linked immunosorbent assay, was progressively reduced by toxoiding it with increasing amounts of glutaraldehyde or a carbodiimide; when LT antigenicity was reduced by greater than 50%, the effectiveness of the toxoid in stimulating mucosal antitoxin and providing protection was compromised. Strong protection extended for more than 6 weeks only in rats immunized with a sufficient peroral dosage of LT to arouse mucosal secretory IgA antitoxin titers at least fourfold greater than those of controls. These observations indicate that the ability of LT to stimulate a mucosal secretory IgA antitoxin response is dependent on the antigenicity, route, and dosage of this immunogen; they suggest that the duration of protection in animals immunized by the peroral route is related to the extent of arousal of mucosal secretory IgA antitoxin.

Adjuvants, Immunologic↗
PubMed1981

Immunization of rats with heat-labile enterotoxin provides uniform protection against heterologous serotypes of enterotoxigenic Escherichia coli.

Rats immunized with Escherichia coli heat-labile (LT) enterotoxin, either in the form of the holotoxin derived from a transformed K-12 strain or the polymyxin-release form obtained from human strains which produce LT toxin alone (LT+/ST- [ST is heat-stable toxin)] or together with ST toxin (LT+/ST+), were challenged with viable organisms of 10 different serotypes, 5 LT+/ST- and 5 LT+/ST+. The serum antitoxin response was monitored by enzyme-linked immunosorbent assay, and the degree of protection was determined by challenge in ligated ileal loops. Immunization with the holotoxin provided a strong antitoxin response and protection against all 10 challenge strains. Immunization with toxin from the LT+/ST+ strain provided equally strong protection against all strains, but immunization with toxin from the LT+/ST- strain yielded only a weak antitoxin response, moderate protection against challenge with LT+/ST- strains, and no protection against LT+/ST- strains, increasing by fivefold the immunization dosage of the LT+/ST- toxin failed to enhance protection. These observations (i) establish the fact that immunization with the LT holotoxin provides uniformly strong protection against heterologous serotypes and (ii) indicate that, for reasons which remain to be determined, the immunogenicity of the polymyxin-release LT from an LT+/ST+ strain differs from that of an LT+/ST- strain.

Animals↗
PubMed1981

Subunit number and arrangement in Escherichia coli heat-labile enterotoxin.

The Escherichia coli heat-labile enterotoxin (LT) was found to have the same subunit structure as cholera toxin, namely, one A subunit and five B subunits. Reaction with a bisimidate generated all the possible cross-linked derivatives of A5B: B,2B ... 5B and A, AB ... A5B. The isolated B component, coligenoid, contained five B subunits and showed some tendency of polymerize: with a bisimidate it became covalently connected into the set B ... 5B with lesser amounts of 6B ... 10B, etc. The subunit formulas of two independently prepared samples of LT were both proved to be A5B by cross-linking, but their B pentamers migrated at different rates on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, indicating that they have different conformations. The faster (R) form could be converted to a diffuse slower (C) form by incubating it at 50 degrees C or at 37 degrees C with 0.2 M galactose, which is the terminal sugar of ganglioside GM1, the natural receptor for LT. Cholera toxin resembled the R form more than the C form of LT.

Bacterial Toxins↗
PubMed1981

Protection in rats immunized with Escherichia coli heat-stable enterotoxin.

Rats immunized with a semipurified preparation of the Escherichia coli heat-stable (ST) enterotoxin conjugated with a protein carrier were protected against challenge with semipurified or purified ST and viable organisms of multiple heterologous serotypes that produce only ST (LT-/ST+), but they were not protected against heal-labile (LT) toxin or viable strains which produce LT either alone (LT+/ST-) or together with ST (LT+/ST+).

Animals↗