Search PubMed⌕ Search

Biomedical subjects

C John

Publications and source records attributed to C John.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1991

Effect of metalloproteinase from Staphylococcus aureus on in vitro stimulation of human lymphocytes.

Metalloproteinase (MP) produced by the majority of Staphylococcus aureus strains exerts, in a wide concentration range (0.1-100 micrograms/ml), no cytotoxic action on mononuclear leukocytes of human peripheral blood. The enzyme itself does not appreciably stimulate proliferation and differentiation of lymphocytes in culture, but affects the stimulation of both T and B lymphocytes by polyclonal activators. The action is dose-dependent. High doses of MP (100 micrograms/ml) lower the blastic transformation after stimulation with Con A, SpA, NDCM, S. aureus strain Wood 46 and with suboptimal doses of PWM. Optimal concentrations of the enzyme potentiate the stimulation of lymphocytes by PWM, PHA, S. aureus strains Cowan 1 and Wood 46, and by NDCM. The same potentiation effect was achieved whether the enzyme was added concurrently with the mitogen or 18 h later. This implies that the beginning of cell activation is not affected. A high MP concentration decreases the production of Ig in culture after stimulation with PWM whereas lower concentrations of MP enhance this production. Production of Ig after stimulation with NDCM and Wood 46 is decreased by MP. The possible action of exoproteinase from S. Aureus on the immune response during infection is discussed.

Cells, Cultured↗
PubMed1990

Specific in vivo binding of [125I]-iodomelatonin to melatonin receptors in rat brain.

The in vivo distribution of [125I]-2-iodomelatonin in rat brain was determined at different time intervals after intraarterial injection. After one hour, radioactivity in brain areas devoid of melatonin receptors had washed out to very low concentrations, but significant retention occurred in the medial basal hypothalamus (mbh) which contained the median eminence and in the anterior pituitary gland (ap), areas known to contain high concentrations of melatonin receptors. Coinjection of unlabelled melatonin reduced radioactivity concentrations in the ap and mbh by 44% and 75% respectively at one hour, whereas radiotracer concentrations in other regions remained unchanged. These results indicate the potential for the in vivo study of melatonin receptor concentration changes in human brain in disease states by means of single photon emission computed tomography.

Animals↗
PubMed1990

[Phagocyte function deficiency determined by methods using chemotaxis and chemiluminescence].

The chemotactically oriented and not oriented migration of polymorphonuclear leucocytes was examined in 21 patients with acute ulcerative gingivitis, using the method of assessment of chemotaxis under an agarose layer. In the same group of patients also the chemiluminescence of leucocytes was assessed. In 16 patients the chemotactically oriented and non-oriented cell migration was reduced. In four patients both types of activity were enhanced. The chemiluminescent leucocyte activity was reduced in all patients of this group.

Chemotaxis, Leukocyte↗
PubMed1989

The immunological properties of listerial complex Ei.

Factor Ei, besides exerting toxic reactions, is amphipathic, antigenic, chemotaxinogenic, causes blastic transformation, adjuvant effect, hypersensitivity (MIF, skin test), activates the RES (splenomegaly), increases the macrophage production, prevents listerial infection in mice, mycobacterial infection in guinea pigs and enhances the effect of BCG experimental tuberculosis and neoplasia in mice (Sa 180).

Animals↗
PubMed1988

Effect of serine proteinase from Staphylococcus aureus on in vitro stimulation of human lymphocytes.

In a broad concentration range (0.1-100 micrograms/ml) the serine proteinase (SP) from Staphylococcus aureus has no cytotoxic effect on human peripheral blood lymphocytes and does not stimulate them in culture. However, it affects the action of a number of polyclonal activators. In a concentration of 100 micrograms/ml SP completely eliminates blastic transformation after stimulation with B cell mitogens (NDCM, S. aureus and Escherichia coli), lowers the blastic transformation after stimulation with PWM and SPA, and does not affect the blastic transformation after stimulation with PHA. SP (100 micrograms/ml) reduces the concentration of Ig in stimulated cultures (stimulation with PWM, NDCM, S. aureus and E. coli) far below the Ig level of unstimulated controls. This effect can be ascribed to an influence on cell stimulation, not to the proteolytic cleavage of secreted Ig, although SP can partially digest Ig. The effect on lymphocyte stimulation takes place when the SP is added to the culture together with the mitogen, or 18 h after the mitogen. This implies that SP does not affect the first stage of stimulation.

Adult↗
PubMed1987

Medical care and demographic characteristics of 'difficult' patients.

This pilot study describes the medical care and demographic characteristics of "difficult" patients as compared with randomly selected patients of a community-based family practice center. Ninety-two difficult patients were identified by asking physicians to indicate those patients whose care they considered difficult. Charts of 166 randomly selected patients were then compared with those of the difficult patients. The difficult patient group was older, more often divorced or widowed, and had a higher percentage of women than the random patient group. The difficult patient group also had more acute problems, chronic problems, medications, x-ray examinations, blood tests, physician referrals, and visits to the family practice center. After covariance analysis adjusting for age and sex, significant differences remained between the two groups for chronic problems, blood tests, medications, and visits to the family practice center. The two patient groups did not differ significantly in household composition, payment status, or provider continuity. The data suggest that, although there are different types of difficult patients, there may be certain medical and demographic features that are common to many of them. Many physicians suspect that difficult patients suffer from a "thick-chart syndrome," a syndrome confirmed to exist by this study.

Adult↗
PubMed1986

Synthesis of 2,6-anhydro-S-[ethylmercury(II)]-1-thio-D-glycero-L-manno-heptitol+ ++ and bis(2,6-anhydro-1-thio-D-glycero-L-manno-heptitol)mercury(II), and the study of their interaction with beta-D-galactosidase from E. coli.

Two competitive inhibitors of beta-D-galactosidase activity, namely, 2,6-anhydro-S-[ethylmercury(II)]-1-thio-D-glycero-L-manno-heptitol (4) and bis(2,6-anhydro-1-thio-D-glycero-L-manno-heptitol)mercury(II) (6), with inhibition constants of 8.0 X 10(-4) M and 1.9 X 10(-4) M, were synthesized. Compound 6 was incorporated into the crystalline enzyme by cocrystallization. The stoichiometry of the enzyme-inhibitor complex was 1:4, corresponding to one molecule of inhibitor per active site of the enzyme. Compound 4 was found to be unstable against X-ray irradiation, whereas compound 6 was submitted to X-rays for several days without any radiation damage.

Alkylmercury Compounds↗