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S Samanta

Publications and source records attributed to S Samanta.

At least 37 records · Page 2Linked to original sources
PubMed1998

Borrelia burgdorferi-infected, interleukin-6-deficient mice have decreased Th2 responses and increased lyme arthritis.

Recently, interleukin (IL)-6 was shown to be one of the earliest factors that trigger the differentiation of naive T cells into effector Th2 cells in vitro. Lyme arthritis was studied in IL-6-deficient mice, since joint inflammation is influenced by the T helper cell response against Borrelia burgdorferi. Arthritis incidence increased in B. burgdorferi-infected IL-6-deficient mice compared with that in controls. Furthermore, splenocytes of B. burgdorferi-infected IL-6-deficient mice produced significantly less IL-4 in response to Borrelia antigens than did C57BL/6 (B6) mice, and B. burgdorferi-specific IgG2b levels were significantly reduced in IL-6-deficient mice at 60 days of infection. These results extend previous in vitro observations by demonstrating an in vivo role for IL-6 in the differentiation of CD4 T cells toward a Th2 phenotype and further show that CD4 T cell responses influence murine Lyme arthritis.

Animals↗
PubMed1997

Hamycin inhibits IL-8-induced biologic response by modulating its receptor in human polymorphonuclear neutrophils.

IL-8, a neutrophil chemotactic agent, is involved in a large number of neutrophil-driven acute and chronic inflammatory diseases. We have found that hamycin, an antifungal agent, reduces IL-8-induced migration and binding of 125I-labeled IL-8 to neutrophils by 66 and 75%, respectively. Other IL-8-induced biologic functions, such as superoxide generation, intracellular Ca2+ mobilization, and enzyme release were also reduced in hamycin-treated cells by 50 to 75%. Anti-IL-8R Ab (C-X-CR1) and IL-8 itself failed to protect the cells from the effect of hamycin. Scatchard analysis of IL-8 binding data demonstrated that while the normal cells expressed 23,000 +/- 1,704 receptors/cell (Kd = 3.5 nM), the number was reduced to 8,000 +/- 592 receptors/cell (Kd = 3.43 nM) in hamycin-treated cells. Chemical cross-linking of 125I-labeled IL-8 to its receptor followed by 10% SDS-PAGE analysis and autoradiography showed that the signals in hamycin-treated cells were considerably reduced compared with those in controls. In the immunoblot, however, the signals in control and hamycin-treated cells were almost identical. The intensity of the fluorescence emission of diphenyl hexatriene at 430 nm and membrane microviscosity measured by diphenyl hexatriene were considerably reduced in hamycin-treated cells, resulting in a reduced number of functional IL-8R, presumably by conformational change in the receptor. The study suggests that hamycin may be a potent immunomodulator of the IL-8R for alleviation of inflammatory distress.

Adjuvants, Immunologic↗
PubMed1997

A Ca2+-dependent autoregulation of lipopolysaccharide-induced IL-8 receptor expression in human polymorphonuclear neutrophils.

IL-8, a potent neutrophil chemotactic agent, is known to be a key mediator in several inflammatory diseases. We found that 10 ng/ml of serum-activated LPS (Escherichia coli) efficiently up-regulated IL-8R on the surface of neutrophils within 30 min of LPS stimulation by 115 to 120% through de novo protein synthesis. After 30 min of LPS stimulation, reduction of IL-8R level was initiated and the normal level was restored within 2 h of LPS interaction. EDTA or EGTA and bestatin separately inhibited the receptor down-regulation by 98%, indicating the involvement of metalloprotease(s), more specifically an aminopeptidase in the process. Induction and subsequent reduction of IL-8 binding in serum-activated LPS-stimulated cells have been demonstrated in autoradiography. Intracellular Ca2+ level in these stimulated neutrophils was increased and decreased with alteration of IL-8R level. Although IL-8 binding was drastically reduced, the total IL-8R level, as detected by anti-IL-8R Ab measured by 125I-labeled anti-rabbit IgG, remained almost unaltered, indicating that minimal proteolysis occurred in IL-8R. Anti-IL-8R Ab and IL-8 itself could prevent this down-regulation significantly, suggesting that the susceptible epitope(s) might be in the IL-8 binding domain of the receptor. Under Ca2+-depleted conditions, the proteolysis was inhibited, which was accelerated upon addition of 1 mM of CaCl2. The study demonstrates that LPS-induced up-regulation of IL-8R leads to amplified IL-8-mediated biologic responses of neutrophils that are restored to normal level by activation of a Ca2+-dependent aminopeptidase. This may be useful for understanding the regulation of LPS-mediated inflammatory responses of neutrophils during bacterial infection.

Aminopeptidases↗
PubMed1997

Ablation of interleukin-12 exacerbates Lyme arthritis in SCID mice.

The administration of interleukin-12 (IL-12) antibodies to Borrelia burgdorferi-infected C3H/HeN-scid mice increased the severity of acute Lyme arthritis. These results contrasted with the reduction of Lyme arthritis by IL-12 antibodies in immunocompetent animals. These data suggest that downregulation of innate immunity in SCID mice in the absence of B- and T-cell responses leads to an exacerbation of joint inflammation.

Animals↗
PubMed1997

B7-1 and B7-2 monoclonal antibodies modulate the severity of murine Lyme arthritis.

We assessed the role of B7-1 and B7-2 costimulatory molecules on the course of murine Lyme borreliosis because experimental Lyme arthritis is dependent, at least partially, upon the development of the host immune response and these costimulatory molecules have been implicated in CD4+ T-cell differentiation. We demonstrated that Borrelia burgdorferi infection upregulated the surface expression of B7-1 and B7-2 in macrophages and B7-2 expression in B cells. Anti-B7-2 monoclonal antibody (MAb) or both anti-B7-2 and anti-B7-1 MAbs produced a dose-dependent increase in the severity of Lyme arthritis in C3H/HeN mice. In contrast, the administration of an anti-B7-1 MAb reduced the degree of arthritis. These effects occurred independently of significant alteration in B. burgdorferi-specific immune responses, including splenocyte proliferative responses to B. burgdorferi, B. burgdorferi antibody levels and specificity, and mRNA levels of gamma interferon, interleukin-4 (IL-4), IL-10, and IL-12 in the spleen. These results demonstrate that signaling delivered by B7-1 and B7-2 plays a role in determining the severity of acute murine Lyme arthritis.

Animals↗
PubMed1995

Trypsin digestion of the inositol trisphosphate receptor: implications for the conformation and domain organization of the protein.

Limited digestion of rat cerebellum microsomal vesicles with trypsin resulted in the proteolysis of the 240 kDa inositol 1,4,5-trisphosphate receptor (IP3R) and the formation of a 94 kDa species that remained membrane-bound and retained immunoreactivity to an antibody raised against the C-terminal sequence of this protein. The appearance of the 94 kDa species was associated with a loss of [3H]IP3 binding sites in the membrane and the appearance of [3H]IP3 binding sites in the soluble fraction. The 94 kDa fragment retained reactivity to biotinylated concanavalin A. In vitro phosphorylation of the IP3R in membranes with cyclic AMP-dependent protein kinase and [gamma-32P]ATP produced an unlabelled 94 kDa fragment after tryptic digestion. According to current models of the cerebellar IP3R this would place the proteolytic site between the phosphorylation site at serine-1755 and the first transmembrane segment of the IP3R. A second antibody raised to amino acids 401-414 in the N-terminal region of the receptor recognizes a 68 kDa fragment released into the soluble fraction after trypsin treatment. The time course of release of the 68 kDa fragment was correlated with the appearance of soluble binding sites, and the fragment was bound by IP3-Affigel resin. A large proportion of the 68 kDa fragment remained associated with the membrane fraction and could be specifically immunoprecipitated from detergent extracts of digested membranes by anti-C-terminus antibody. Our results provide experimental evidence to further localize the ligand binding domain and suggest that regions of the N-terminus and C-terminus may be non-covalently associated.

Animals↗
PubMed1993

Detergent solubility of the inositol trisphosphate receptor in rat brain membranes. Evidence for association of the receptor with ankyrin.

Rat cerebellar membranes sedimenting at 10,000 x g contain significantly greater amounts of [3H]D-myo inositol 1,4,5-trisphosphate- (IP3) binding sites that are resistant to extraction by Triton X-100 than membranes sedimenting at 100,000 x g. Scatchard analysis of the Triton X-100-resistant binding site revealed the presence of a single binding site with an 8-fold higher affinity for IP3 than present in 10,000 x g membranes. The Triton X-100-resistant binding site displayed high specificity for Ins(1,4,5)P3 and was sensitive to inhibition by both heparin and calcium. A polyclonal antibody to the C terminus of the IP3 receptor (IP3R) and biotinylated concanavalin A recognized the same 235 kDa band in Western blots of membrane and Triton X-100-insoluble fractions. The ligand binding activity of the IP3R could be measured in immunoprecipitates obtained from detergent-soluble extracts treated with IP3R antibody. An antibody to chick erythrocyte ankyrin also immunoprecipitated [3H]IP3-binding sites and immunoreactive IP3R protein. These effects of ankyrin antibody were prevented by preadsorption to erythrocyte ghosts and were not reproduced by spectrin antibodies. Cross-reactivity of the ankyrin antibody with the IP3R was excluded by the demonstration of selective loss of immunoreactive ankyrin protein when IP3R antibody immunoprecipitates were boiled in SDS buffers or when membranes were alkali-treated. These results suggest that a population of IP3R in brain may be attached to an isoform of ankyrin. This may mediate interactions of the IP3R with the cytoskeleton and account for observations regarding the detergent insolubility of the protein.

Animals↗
PubMed1993

Myoinositol tris-phosphate-phytase complex as an elicitor in calcium mobilization in plants.

Mobilization of Ca2+ from microsomal/vacuolar fractions was detected when InsP6-phytase was added after a definite time of hydrolysis which coincides with the time (20-30 min) of optimal production of Ins(2,4,5)P3 bound to phytase. The in vitro constituted Ins(1,4,5)P3 or Ins(2,4,5)P3-phytase complex is also effective in releasing Ca2+. InsP3-phytase complex releases 45% more microsomal Ca2+ than that released by free InsP3 under identical conditions. Other inositol-phytase complexes are ineffective. Furthermore InsP3-phytase complex is recognised by putative receptor associated with microsomal fraction suggesting that the myoinositol tris-phosphate-phytase complex can act as an elicitor in Ca2+ mobilization in plant systems where phytate and phytase occur.

6-Phytase↗
PubMed1993

Stability and long-term durability of Raman spectroscopy.

OBJECTIVE: The purpose of this study was to assess in the clinical setting the reliability and long-term stability of Raman spectroscopy as implemented in the RASCAL multiple gas analyzer, and to describe/analyze failure modes that manifest in regular use. METHODS: Twenty-one RASCAL analyzers were tested for accuracy and precision. Without any prior external calibration or alignment, all gas analyzers were systematically tested over a consecutive 36-hour period with standard gas mixtures. Data were analyzed by evaluating the difference between the predicted value and observed value (bias residual) as reported by each RASCAL: All service data (29 months) also were analyzed for information on durability and failure modes. RESULTS: The RASCAL exhibited a significant tendency to overread high concentrations of agent (isoflurane/enflurane); 4 of 16 instruments misread an agent by more than +/- 0.30%. Four of 16 instruments could not properly identify volatile agents in low concentrations (0.31 vol%). Inventory records show that water contamination led to the replacement of gas sample sets an average of 1.5 +/- 1.2 times per case over the 29-month period. Although many instruments had not been externally calibrated for over 63 days, linearity proved acceptable for CO2, O2, N2O, and N2. A rationale for instrument behavior and major failure modes, based on the instrument design, was developed. CONCLUSIONS: The manufacturer's suggested calibration intervals (30 days) were found to be more than adequate for reliable gas analysis using Raman spectroscopy. Without the benefit of frequent calibrations and as time passes, volatile agent quantification can be expected to drift significantly upward.

Anesthesiology↗
PubMed1991

Optimization of a trileaflet valve design.

This study investigates the fundamental principles that should govern the basic design of an optimal trileaflet valve. The geometry of the leaflets is described in terms of radius of the base (Rb), radius of the commissures (Rc), height of the valve (H), height of the commissures (Hs), and angle of the open leaflet to vertical (beta). Using computer-aided design software and these design parameters, a computer model of the valve was constructed. Choosing the parameters empirically did not produce an optimal valve. The four criteria for optimal performance were defined as: (1) a certain minimum coaptation height, (2) no folds in the leaflet, (3) minimum valve height, and (4) minimum leaflet flexion. Mathematical relationships were established between the design parameters and the performance parameters. These relationships indicated that the parameters Rc, Hs, and beta could be used to minimize valve height; however, a reduction in valve height must be balanced against the accompanying increase in leaflet flexion. For an optimal valve, the design parameters were Rb = 10 mm, then Rc = 8 to 10 mm, H = 11.5 mm, Hs = 2.4 to 2.6 mm, and beta = 4 degrees to 11 degrees . The optimal valve of any radius can be designed by scaling Rc, H, and Hs with respect to Rb. These design parameters were similar to those of the natural aortic valve. Trileaflet bioprosthetic valves designed on these principles are expected to have enhanced efficiency and longevity.

Bioprosthesis↗
PubMed1988

Induced electric and magnetic fields due to wave propagation in a tubular bone.

Electric and magnetic fields in tubular bones induced due to the propagation of travelling axisymmetric torsional waves, are determined in the paper by accounting for the piezoelectricity, inhomogeneity and anisotropy of osseous tissues. Using the derived expressions and experimentally determined values of the involved physical constants, numerical values of the displacement and stress fields, and also the induced fields are computed for points at different locations of the bone specimen.

Animals↗
PubMed1987

Effect of material damping on bone remodelling.

This paper considers the effect of internal material damping on the stresses, strains, and surface and internal remodelling behaviour in a section of axisymmetrical bone with a force-fitted axially oriented medullary pin. The bone response to several loading situations is modelled using visco-elastic equations. An approximate method is developed to analyse the proposed mathematical model. By considering a numerical example, the effect of material damping on the remodelling stresses is quantified.

Adaptation, Physiological↗
PubMed1982

Effects of exogenous 1,3-diaminopropane and spermidine on senescence of oat leaves : I. Inhibition of protease activity, ethylene production, and chlorophyll loss as related to polyamine content.

Excision and dark incubation of oat (Avena sativa L., var. Victory) leaves cause a sharp increase in protease activity, which precedes Chl loss. Both these senescence processes are inhibited by exogenously applied 1,3-diaminopropane (Dap), which occurs naturally in leaf segments. The inhibition of protease activity is much greater in vivo than in vitro, suggesting inhibition of protease synthesis as well as protease action by Dap. Chl breakdown in leaves of radish and broccoli, which also senesce rapidly in the dark, is only slightly inhibited by DaP. These differences between cereal and dicotyledonous plants are correlated with the natural occurrence of Dap in cereals. In the light, Dap promotes, rather than retards, the loss of Chl in oat leaves. This resembles previously described effects of other polyamines. Addition of Mg(2+) to the medium does not antagonize this effect. In the dark, the accumulated Dap also inhibits ethylene production and decreases titer of other polyamines. Addition of Ca(2+) to the incubation medium containing Dap competitively reduces the effects of Dap. Thus, Dap, like other polyamines, seems to require an initial attachment to a membrane site shared with Ca(2+) before exerting its antisenescence action.

Journal Article↗