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Biomedical subjects

B Singh

Publications and source records attributed to B Singh.

At least 685 records · Page 38Linked to original sources
PubMed1988

Contribution of antigen processing to the recognition of a synthetic peptide antigen by specific T cell hybridomas.

Most antigens recognized by T cells require unfolding or partial degradation (processing) followed by association with Major Histocompatibility Complex (MHC) molecules. We examined the processing requirements for the presentation of antigen to two T cell hybridomas which recognize the alpha-helical synthetic polypeptide antigen Poly 18, Poly [EYK(EYA)5], in association with I-Ad. Hybridoma A.1.1 responds to EYK(EYA)4 as the minimum antigenic sequence while hybridoma B.1.1 recognizes (EYA)5 sequence. It was found that these hybridomas responded to Poly 18 and to minimum peptide sequences presented by glutaraldehyde and chloroquine treated antigen presenting cells (APC), suggesting that antigen processing is not a requirement for the activation of these cells. The reactivity pattern of hybridoma B.1.1 in the presence of glutaraldehyde fixed APC revealed that antigens containing lysine were presented with much less efficiency than antigens without lysine, suggesting an interaction of these residues with the antigen presenting cell surface. We discuss the possibility that alanine residues in the alpha-helical Poly 18 form a hydrophobic ridge which may be required for appropriate interaction between antigen, the T cell receptor, and MHC molecules.

Animals↗
PubMed1988

Paracetamol-associated coma, metabolic acidosis, renal and hepatic failure.

A case of metabolic acidosis, acute renal failure and hepatic failure following paracetamol ingestion is presented. The diagnostic difficulty at presentation is highlighted. Continuous arteriovenous haemofiltration proved a valuable means of maintaining fluid and electrolyte balance. The patient recovered.

Acetaminophen↗
PubMed1988

A double-blind comparison of felodipine and hydrochlorothiazide added to metoprolol to control hypertension.

Seventy-six uncomplicated hypertensive patients treated in General Practice, whose seated diastolic blood pressure (Phase V) (dBP) remained greater than or equal to 95 mmHg after a minimum of 4 weeks treatment with metoprolol 50 mg b.i.d. as antihypertensive monotherapy, were randomized to receive the selective 'calcium antagonist' felodipine 5 mg b.i.d. or hydrochlorothiazide 12.5 mg b.i.d. in addition to metoprolol 50 mg b.i.d. The trial duration was 8 weeks, the dose of the felodipine or hydrochlorothiazide being doubled after 4 weeks if 'control' of BP (dBP less than 90 mmHg) was not achieved on the initial doses. Over the trial period of 8 weeks, felodipine reduced dBP from 102 to 85 mmHg and hydrochlorothiazide from 101 to 91 mmHg; the dBP reduction in the felodipine group was greater than that in the hydrochlorothiazide group (17 vs 9 mmHg) and the attained dBP lower in the felodipine group. About half of the patients in each group required the higher dose. Both regimes were effective and well tolerated. In the dosages used, felodipine was a slightly more effective antihypertensive drug than hydrochlorothiazide when added to metoprolol. There was no apparent difference in the tolerability of the two regimes.

Adult↗
PubMed1988

Protein-binding capacity of microquantities of tannins.

The physiological effect of tannins is studied in terms of their protein-binding or precipitation capacity. A number of assays based on binding of hemoglobin or bovine serum albumin (BSA) and subsequent determination of unbound protein in supernatant or tannin in a protein-tannin complex are available but with various limitations. These methods are unable to estimate protein-binding capacity, if the quantity of tannin available is low. In the method reported here, tannins or other phenolics were applied on chromatography paper and reacted with BSA and unbound BSA was washed off. The protein in the tannin-protein complex was measured spectrophotometrically after staining with Ponceau S. It required microquantities of sample. Using this method the protein-binding capacity of total leaf extract and hydrolyzable and condensed tannins of Quercus incana, Q. semecarpofolia, and Q. dilatata was determined. The protein binding capacities of ellagic acid and quercetin (microgram BSA/mg) were 297.3 and 78.0, respectively.

Hydrolysis↗
PubMed1988

Interrelationship of thermal and sleep-wakefulness changes elicited from the medial preoptic area in rats.

The study investigated the possible interrelationship between changes in sleep-wakefulness and body temperature, primarily induced by manipulation of the noradrenergic system in the medial preoptic area. Saline, norepinephrine, and its alpha- and beta-blockers were injected in the medial preoptic area and in some control areas of rats, during their sleeping and active periods. 5-Hydroxytryptamine was injected in the medial preoptic area in another group of animals. Simultaneous changes in sleep-wakefulness and the body temperature were continuously recorded. Norepinephrine produced hypothermia and arousal, whereas alpha-adrenergic blockers induced hyperthermia and sleep. These changes in body temperature and in sleep-wakefulness did not follow an identical time course. 5-Hydroxytryptamine induced hyperthermia without affecting sleep-wakefulness. It is suggested that there are different neuronal mechanisms in the medial preoptic area that bring about the drug-induced changes in temperature and sleep-wakefulness.

Animals↗
PubMed1988

The histidine-221 to tyrosine substitution in v-mos abolishes its biological function and its protein kinase activity.

The viral mos gene encodes a cytoplasmic transforming protein termed p37mos. Evidence gathered from a number of experimental approaches is consistent with p37mos having a serine/threonine protein kinase activity. To gain further understanding of the p37mos-associated biochemical activity, we constructed a mutation in the v-mos gene by oligonucleotide-directed mutagenesis yielding a histidine to tyrosine substitution at residue 221 in p37mos. Based upon nucleotide sequences, the histidine residue at the corresponding position is conserved in all the serine/threonine protein kinases from yeast to man, and is absent in protein-tyrosine kinases. The mutant p37mos (Tyr-221) was expressed in yeast and assayed for kinase activity. The mutant protein was inactive as judged by a loss of autophosphorylation activity in vitro, thus providing further support for the conclusion that p37mos is a protein kinase. When the mutant v-mos gene was introduced into a retroviral vector, pDD102, and assayed for focus-forming ability on NIH/3T3 cells, it was found to be inactive at both 37 and 30 degrees. In contrast, the wild-type v-mos had transforming activity at both temperatures. These results extend our earlier findings on the correlation between transforming ability and protein kinase activity. A histidine to tyrosine substitution at the corresponding position of the v-mos protein and the yeast CDC28 gene product causes a similar effect on the kinase activity. Therefore, this residue and/or the sequence near the N-terminal side of the conserved predicted phosphate transfer domain, near the middle of the complete catalytic domain, might be specifically involved in the catalytic activity of serine/threonine protein kinases in general.

Amino Acid Sequence↗
PubMed1988

Serum immunoglobulin E levels in patients with head and neck cancer.

Serum immunoglobulin E levels were estimated in 50 patients with head and neck cancer and in 25 controls. Mean serum IgE value was significantly higher in patients with various sites of cancer in the head and neck region other than carcinoma of the tonsil. The levels increased with advancement in the stage of cancer. There was, however, no difference in mean serum IgE value with respect to the character of the lesion, to the histopathological type of growth or to radiotherapy. In patients with carcinoma of the tonsil, the mean serum IgE concentration was significantly lowered.

Adult↗
PubMed1988

Effect of tannin-rich leaves of oak (Quercus incana) on various microbial enzyme activities of the bovine rumen.

1. The objective of the present experiment was to study the effects of oak (Quercus incana) leaves rich in tannins on various enzyme activities of the bovine rumen. 2. The procedure employed was incubation of tannin-rich, very-low-tannin or virtually tannin-free leaves in nylon-gauze bags in the rumen, and determination of enzyme activities in microbes tightly bound to the solid matrix and in microbes loosely plus tightly attached to the solid matrix. 3. The activities of urease (EC 3.5.1.5), carboxymethylcellulose, glutamate dehydrogenase (EC 1.4.1.2) and alanine aminotransferase (glutamic-pyruvic transaminase) (EC 2.6.1.2) were significantly lower in the tannin-rich group, whereas the activities of glutamate ammonia ligase (glutamine synthetase) (EC 6.3.1.2; both gamma-glutamyltransferase (EC 2.3.2.2) and the forward reaction) were higher in the tannin-rich group. These changes were more marked in micro-organisms tightly bound to the solid matrix than in the more complex microbial compartment. 4. The protein, DNA and RNA contents, and protein: RNA ratio, were significantly lower in the tannin-rich group, whereas no difference was observed for protein: DNA between the groups. 5. Effects of tannin-containing extracts of oak leaves on various rumen enzymes in vitro showed a trend similar to that observed in nylon-gauze bags, suggesting that the changes observed in various compartments were due to the tannins of oak leaves.

Alanine Transaminase↗
PubMed1988

Mapping of the T-cell recognition sites of Pseudomonas aeruginosa PAK polar pili.

The polar pili of Pseudomonas aeruginosa consist of a subunit protein, pilin, which is a 144-residue polypeptide that contains a hydrophobic N-terminal region and eight hydrophilic regions distributed throughout the remainder of the molecule. T cells from mice immunized with pili or whole bacteria gave good pilus-specific T-cell proliferation responses. To delineate the T-cell antigenic regions of the pilin, T-cell blasts were generated from lymph nodes of pilus-primed BALB/c mice. These blasts were tested in vitro in T-cell proliferation assays for reactivity against the fragments of the pilin subunit prepared by enzymatic digestion. Citraconylation followed by trypsin digestion (cT) of the pilin subunit cleaved the protein into four fragments, cTI (residues 1 to 30), cTII (residues 31 to 53), cTIII (residues 54 to 120), and cTIV (residues 121 to 144). The ability to stimulate the T cells was found to reside in the cTI and cTIII regions, but not in the cTII or cTIV regions. A subfragment of cTIII, containing residues 82 to 104, was identified as the major T-cell recognition site within the cTIII region of the pilin molecule. A cross-reactivity was observed between pili from two strains of P. aeruginosa, namely, PAK and PAO, at the T-cell level. This cross-reactivity probably resulted from the sequence homology in the hydrophobic N-terminal region of these two molecules.

Animals↗
PubMed1988

Lectin mediated agglutination of Candida kefyr cells and their spheroplasts grown in sterol enriched growth medium and its correlation with lipid composition.

Supplementation of the growth medium with erosterol, cholesterol and lanosterol enriched the Candida kefyr cells, presumably cell membranes with sterols. Sterol enriched C. kefyr cells showed a decrease in percentage of PHA and Con-A mediated agglutination. Sterol supplementation also increased the sterol: phospholipid ratio and in such cells unsaturated fatty acids predominated over saturated ones. The overall effect of these changes resulted in rigidifying the cell membranes as indicated by shift of break in Arrhenius plots of Mg2+ ATPase. This showed that lectin mediated agglutination of yeast cells may be affected by its membrane fluidity.

Agglutination↗
PubMed1988

Identification of the protein product of the c-mos proto-oncogene in mouse testes.

The mouse c-mos proto-oncogene RNA is expressed primarily in mouse gonadal tissues and embryos. Until now, the c-mos protein has not been identified. Utilizing two different site-directed affinity purified anti-peptide antibodies, we have identified a 43 kDa c-mos protein in mouse testes and in germ cell preparations derived from testes. This 43 kDa testicular protein was found to be structurally related to a bacterially expressed c-mos protein by peptide mapping. Immunoblots of whole mouse sections were employed to establish that the c-mos protein is expressed primarily in the testes.

Animals↗
PubMed1988

Clinical response to feeding a high polyunsaturated fat diet in normal and diabetic rats.

Dietary fat composition can influence membrane composition in a variety of cell types. Changes in dietary fat can alter the structure and function of lymphocyte membranes, liver plasma membranes, brain synaptosomes and cardiac mitochondria. In diabetics, uptake of glucose is enhanced due to a greater passive permeability of the intestine to glucose. This enhanced absorption from the intestine can be partially corrected by insulin administration and islet cell transplantation. In clinical practice, however, a more commonly used therapeutic modality for diabetics is diet modification. In this study, when diabetic rats were fed a high fat diet, high or low saturated to polyunsaturated fatty acid, there was an improvement in the plasma and urine glucose. This improved clinical response was also observed in the glycosylated hemoglobin response in the animals fed the high polyunsaturated to saturated fatty acid diet. The clinical improvement observed after feeding with these diets, however, was not seen during the oral and intravenous glucose tolerance tests. This study shows that dietary alteration can improve the clinical response in diabetic animals.

Animals↗
PubMed1988

Effect of high/low dietary linoleic acid levels on the function and fatty acid composition of T-lymphocytes of normal and diabetic rats.

T-lymphocytes play a central role in the initiation, regulation and effector functions of immune responses. Changes in membrane composition can alter the membrane fluidity, receptor distribution and consequently function of these cells. Altered immune response in the diabetic state may be attributed partly to diabetes induced alterations in the metabolism of essential fatty acids. We have investigated the effect of dietary linoleic acid on T cell membrane composition and T cell mediated immune responses in normal and diabetic rats. Streptozotocin induced diabetes was found to produce lower T cell proliferative responses in mixed lymphocyte reactions and upon mitogen stimulation. Feeding of a diet rich in linoleic acid did not improve these responses. Feeding a diet low in linoleic acid further lowered the T cell dependent immune responses. We also found lower levels of 18:2 omega 6 fatty acids in the membrane phospholipids of these T cells. Levels of 20:4 omega 6 fatty acids were altered as a result of diabetes and diet composition. These fatty acids are the precursors of prostaglandins which are known to influence immune responses. It is concluded that diabetes results in significant alterations in T cell membrane composition and function in a manner that can be manipulated by modifications of the fatty acid composition of the diet. The present study suggests that diet fat modification may be important in regulating T cell-mediated immunity in insulin dependent diabetes mellitus.

Animals↗
PubMed1988

Plasmodium falciparum: inhibition/reversal of cytoadherence of Thai isolates to melanoma cells by local immune sera.

The effect of sera on the cytoadherence in vitro of Plasmodium falciparum-infected erythrocytes to melanoma cells was examined. Sera from 19 healthy individuals living in endemic malarious areas in Thailand and 24 patients with P. falciparum malaria were tested against four local P. falciparum isolates. Out of 57 sera examined, 12 (21%) showed significant inhibition (greater than 50%) of cytoadherence for at least one isolate. Anti-malarial IgG antibody titres were determined for all 57 sera and although 11 of the 12 inhibitory sera had relatively high titres, 36 out of 47 sera with similarly high titres showed no significant inhibitory activity. Convalescent sera were no more effective than corresponding acute sera in inhibiting the cytoadherence of erythrocytes infected with any of the four heterologous isolates examined. Sera which significantly inhibited cytoadherence were also capable of reversing cytoadherence, and pooled plasma, from healthy individuals living in malarious areas, was effective in significantly reversing the in vitro cytoadherence of all the five parasite isolates examined. The results confirm the antibody mediated strain-specific nature of the inhibition of cytoadherence and stress the difficulty in selecting immune sera potentially useful for the immunotherapy of cerebral malaria patients in Thailand.

Animals↗
PubMed1987

Processing and presentation of insulin. I. Analysis of immunogenic peptides and processing requirements for insulin A loop-specific T cells.

The processing and presentation of insulin by B hybridoma cells to insulin A loop-specific T cell hybridomas was investigated. We found that the activation of these T cells requires insulin to be processed in a manner that permits unfolding of the molecule and prevents extensive proteolysis. An analysis of insulin peptides formed by either enzymatic digestion in vitro or solid phase synthesis revealed that a conformational determinant comprised of residues A1-A14 disulfide-linked to B7-B15 is most immunogenic to these T cells. Reduction and/or proteolysis of this peptide markedly decreases its immunogenicity. The pork insulin A1-A14/B7-B15 peptide differs only at residue A4 from its mouse insulin homolog. Thus, Glu A4 forms part of the antigenic site recognized by a pork insulin/I-Ad-specific mouse T cell. This insulin peptide can be induced to assume an alpha-helical configuration in a hydrophobic environment. In addition, virtually all of the residues of this peptide are identical with those predicted to be situated in amphipathic regions of the native insulin molecule. N-Ethylmaleimide and bacitracin, which inhibit the activity of two cytosolic enzymes that cleave insulin, enhance the antigen presentation of insulin. This suggests that these enzymes may participate in the nonlysosomal antigen processing of insulin by a B lymphocyte. A comparison of the relative avidity of several T cell hybridomas, which have the same apparent specificity for this insulin peptide, showed that an increase in their avidity was associated with a degeneracy in their fine specificity. Our data demonstrate that the efficiency of processing and presentation of a given antigenic determinant is related to the conformation of the determinant and the specificity and avidity of the T cell.

Animals↗
PubMed1987

Glycosylation of bacterial cellulases prevents proteolytic cleavage between functional domains.

Glycosylated cellulases from Cellulomonas fimi were compared with their non-glycosylated counterparts synthesized in Escherichia coli from recombinant DNA. Glycosylation of the enzymes does not significantly affect their kinetic properties, or their stabilities towards heat and pH. However, the glycosylated enzymes are protected from attack by a C. fimi protease when bound to cellulose, while the non-glycosylated enzymes yield active, truncated products with greatly reduced affinity for cellulose.

Actinomycetales↗