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Biomedical subjects

C John

Publications and source records attributed to C John.

At least 19 recordsLinked to original sources
PubMed1994

Antibacterial activity of human mononuclear leukocytes against Staphylococcus aureus.

Human mononuclear leukocytes kill Staphylococcus aureus cells in vitro. The killing of the bacteria takes place even in the absence of antibodies. The presence of antibodies (in an autologous inactivated serum) usually enhances the antibacterial activity of mononuclear leukocytes. In some cases, however, this activity is markedly decreased by the serum, probably depending of the spectrum of antibodies contained in the serum. The antibacterial activity of mononuclear leukocytes is mostly due to monocytes because their depletion causes substantial drop or the activity disappearance. We failed to demonstrate in the case of S. aureus the antibacterial cytotoxicity of T lymphocytes described by some authors dealing with Gram-negative bacteria. Large differences in the structure of the bacterial cell wall underlie apparently the different sensitivity of G+ and G- bacteria to some protective mechanisms of the host. In the antibacterial assay against S. aureus, electron microscopy revealed a maximal activation of monocytes which phagocytized the bacteria although extracellular killing is not excluded. Electronoptical findings point also to a possible participation of NK cells in the antibacterial cytotoxicity against S. aureus.

Adult↗
PubMed1994

[Characterization of the dentin by a 2-dimensional ultrasonic velocity profile].

The velocity of sound is material-specific and therefore offers the opportunity for indirect physical characterization of materials. Preliminary ultrasound velocity profiles gained from ground tooth sections suggested that in the dentin core of the tooth areas of different sound velocity and thus different physical properties can be differentiated. As a base for this type of non-destructive characterization of materials an optimized and automated measurement system is presented, and its possibilities are critically discussed with regard to hardness tests. Normally, the LSV in the dentin core was found to be decreasing from the coronal to the apical regions, as well as from the outer to the inner parts near the pulp.

Biophysical Phenomena↗
PubMed1994

[The resolution of a 2-dimensional ultrasonic velocity profile of human tooth sections].

In a previous study (Löst et al. 1992, Löst et al. 1994) two-dimensional ultrasound velocity profiles of human dentin were introduced, and their possible significance and the underlying measuring system were discussed. Profiles of ultrasound velocity enable us to differentiate the structure and the elasticity of dental hard tissues. The quality of these color-coded profiles enhances with improved lateral resolution of the used ultrasound measuring system. Establishing an optimal window for displaying longitudinal sound velocities increases topological statements. Under given conditions of the measuring system an optimal lateral distance between points of measurement could be found. The differentiation of values within the profiles of ultrasound velocity is most meaningful applying a standardized window within the range of ultrasound velocity. For the used 20 MHz-ultrasound transducer a 0.2 mm lateral distance of measuring points was found to be optimal and a chosen window of ultrasound velocity in dentin from at least 2800 to 4300 m/s, respectively.

Color↗
PubMed1993

Evaluation of the impact on growth of a controlled 6-month feeding trial on children (6-24 months) fed a complementary feed of a high energy-low bulk gruel versus a high energy-high bulk gruel in addition to their habitual home diet.

Twenty-one pairs of slum children (6-24 months) were pair-matched for age and weight. The experimental group consumed a complementary feed of a high energy (1.63 Kcal/ml), but low bulk wheat gruel providing a mean 199 Kcal/child/day v. the control group which consumed an identical (1.63 Kcal/ml), but high bulk gruel providing a mean 50 Kcal/child/day for a period of 180 days. The home diet (breastmilk+family diet) provided about 470 Kcal/child/day in both groups. A comparative evaluation of growth at commencement and end of study demonstrated that: 1. weight, height, and velocity of growth in weight were significantly better in the experimental group; 2. a comparison by nutritional classifications (Indian Academy of Pediatrics and Waterlow) showed a greater benefit to the experimental group; 3. the energy intake per kg body weight was 73 and 62 Kcal, respectively, in the experimental and control groups at end of study. It is concluded that the much higher intake of the amylase-rich food (ARF) treated gruel in the experimental group was responsible for the substantially better growth.

Case-Control Studies↗
PubMed1993

Neuromodulation mediated by neurokinin-1 subtype receptors in adult rabbit airways.

The neuromodulatory actions of Septide, a selective neurokinin-1 (NK-1) agonist, and substance P (SP) were investigated in isolated rabbit tracheal smooth muscle (TSM) segments. The tissues were placed in organ baths containing modified Krebs-Ringer solution and contracted with either the agonists or electrical field stimulation (ES) with frequencies ranging from 1 to 50 Hz. The neutral endopeptidase (NEP) inhibitor, phosphoramidon (10(-6) M), had no significant effect on Septide-mediated contractions. Septide-mediated contractions were augmented in the presence of neostigmine, eliminated in the presence of atropine, and diminished in the presence of tetrodotoxin. Both SP and Septide increased ES-induced contractions in a dose-dependent manner. On the other hand, the presence of both Septide and SP did not further augment this neuromodulatory action. After NK-1 desensitization, Septide-mediated contractions were also virtually eliminated; however, the peptide's neuromodulatory action was unaffected. In contrast, the presence of GR-82334, a selective NK-1 antagonist, eliminated Septide's neuromodulatory activity. These findings provide evidence that 1) NK-1 receptors facilitate both the direct release of ACh as well as augment the release of ACh by ES and 2) the cholinergic pathways involved with these two processes may represent different mechanisms.

Acetylcholine↗
PubMed1993

Tetralogy of Fallot: intracardiac repair in 840 subjects.

Since 1967, when the first intracardiac repair was performed in this centre, until 1991, 840 symptomatic subjects with tetralogy of Fallot have undergone corrective surgery. Cardiac catheterization and angiocardiography were carried out in all patients. Cardinal findings on the clinical status of these subjects are outlined. A substantial number of patients (244; 29.0%) were > 15 years of age. Historically, a transannular pericardial gusset has been utilized in 578 (68.8%), and in 423 (93.0%) during the past decade. The incidence of residual interventricular septal defects has been 0.68% and occurrence of complete heart block after surgery 0.4%. Death occurred in 86 patients (10.2%) within 30 days of operation and later in 40 subjects (4.8%). Long-term results have been excellent with good haemodynamic status in > 90% of subjects in the follow-up period. Associated features including absent pulmonary valve, absent left pulmonary artery, and previous palliative shunts did not alter the outcome; however, a raised haematocrit (> 0.65) was associated with an increased mortality rate.

Adolescent↗
PubMed1992

Cleavage of human immunoglobulins by serine proteinase from Staphylococcus aureus.

The serine proteinase (SP) released into the environment by most strains of S. aureus cleaves human IgG, IgM and IgA of both subclasses--IgA 1 and IgA 2. SP cleaves H chains of all immunoglobulin classes and the SC of S-IgA, the L chains are degraded partially. The SP-induced cleavage results in a large spectrum of fragments under reducing conditions within a broad range of Mr (approx. 41,000 to less than 12,400). This indicates that the enzyme does not affect the Ig molecule in the hinge region only. The degree of cleavage depends on the enzyme:substrate ratio and on the duration of incubation. The generation of small fragments is associated with the loss of antigenic determinants that results from the decreased binding of the cleaved material in the ELISA method. Partial cleavage of L chains suggests that the enzyme alters part of the molecule that is involved in antigen binding. Even if the ability of antigen binding remains preserved after cleaving Ig with SP, the antibody function is disturbed by splitting off the Fc region or by its degradation into small fragments. SP has to be considered as one of the virulence factors of S. aureus that may protect bacteria against the defence mechanisms of the host.

Electrophoresis, Polyacrylamide Gel↗
PubMed1992

Evaluation of a controlled 6 months feeding trial on intake by infants and toddlers fed a high energy-low bulk gruel versus a high energy-high bulk gruel in addition to their habitual home diet.

The aim of this study was to determine the intake of 68 slum children (6-24 months old) pair matched for age and nutritional status who were fed an experimental energy dense (1.63 Kcal/ml) wheat flour gruel rendered low-viscosity with catalytic amounts of germinated wheat flour (Amylase-Rich Food, ARF) v. an identical high viscosity control gruel without ARF for a once-a-day ad lib feed in addition to the habitual home diet for a period of 180 days. The mean intake in the experimental group was 124 ml and 199 Kcal v. 31 ml and 50 Kcal in the control gruel group per child/day. The gruel feeds were well accepted and were complementary to the home diet (breastmilk plus some family diet which provided only 420-461 Kcal/day). The experimental and control gruels provided about 20 and 5 per cent of the food energy RDA, respectively. The protein RDA was nearly met by the home diet in both groups. The study demonstrated a simple means to greatly increase the food energy intake in this age group by offering high energy yet low bulk gruels with the help of the ARF technology.

Age Factors↗
PubMed1992

Two-dimensional distribution of sound velocity in ground sections of dentin.

The longitudinal velocity of sound in a specific material depends, amongst others, on the material's density and elasticity (Young's Modulus). Ultrasound therefore may be used for indirect characterization of materials. In this paper a method is described which allows high resolution measurements on coplanar ground sections of human teeth. The results are presented in two-dimensional velocity profiles. There is evidence from the first images, that longitudinal sound velocity (LSV) in dentin varies depending on the location. The use of LSV may be another way to characterize hard dental tissues physically, and to monitor induced changes.

Dentin↗
PubMed1992

In vitro stimulation of human lymphocytes by alpha, beta and delta toxins and toxoids of Staphylococcus aureus.

Alpha, beta and delta toxins of Staphylococcus aureus stimulate human peripheral blood lymphocytes to blastic transformation and formation of IgM, IgG and IgA. The toxins are efficient at concentrations that are not toxic for the cells in culture. A dose of a toxin suitable for stimulation is 100 ng/ml but a stimulation can be observed also at 10 ng/ml, in the case of Ig formation even at a concentration of 1 ng/ml. Toxoids are approximately as effective to elicit blastic transformation as the toxins themselves, their efficiency to stimulate Ig formation being somewhat lower but significant. Alpha and delta toxins and toxoids at the appropriate concentration appear to act as medium-strength polyclonal activators of lymphocytes. Beta toxin and its toxoid are weak polyclonal activators.

Bacterial Toxins↗
PubMed1991

Class IgG, IgM and IgA antibodies against Staphylococcus aureus antigens in human serum and saliva.

Using the ELISA method antibodies against the sonicate, teichoic acid (TA) and exoproducts of Staphylococcus aureus were determined in sera and saliva of healthy individuals. Main serum antibodies against all the antigens used were shown to be class IgG antibodies. However, antigens of the sonicate stimulated significantly even the systemic IgA response. In the saliva class IgA antibodies predominated, but IgG antibody levels against TA and exoproducts approached the level of IgA antibodies. Levels of IgM antibodies against all antigens tested were low in both the serum and saliva which corresponds with the anamnestic type of response. On the basis of these results one may assume that not only IgG, but also IgA antibodies are important in the systemic immunity against staphylococcal infection and in the immunity of mucous membranes; besides IgA, even class IgG antibodies play an important role.

Adolescent↗