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Biomedical subjects

S K Kundu

Publications and source records attributed to S K Kundu.

At least 19 recordsLinked to original sources
PubMed2003

Dielectric relaxation behavior of a liquid crystal showing an unusual type of antiferroelectric-ferroelectric-antiferroelectric phase sequence.

The temperature and frequency dependent dielectric relaxation behavior of a liquid crystalline (S)-(+)-1-methylheptyl 4-[2-(4-alkoxyphenyl) thiophene-5-carbonylthiooxy] benzoate system is reported. Interesting successive antiferroelectric-ferroelectric-antiferroelectric (AF-FE-AF) phase transitions are observed in this system resembling the successive phase transitions observed in crystalline Rochelle salt. The smectic-C* (SmC*) to AF1 phase transition (around 103.0 degrees C) is first order in nature, predicted from the use of Orihara and Ishibashi theory. It is also found that a contribution of the ferroelectric SmC* phase ordering penetrates even in the antiferroelectric AF1 (SmC(*)(A)) and AF2 (SmC(*)(A)) phases very close to the SmC*-AF1 and SmC*-AF2 phase boundaries (critical regions). It is suggested that this type of mixing of AF and FE phases might cause surface induced ferroelectric- or ferroelectric-type ordering near the AF-FE phase transitions. A soft mode with Debye-type dispersion was observed in the SmA phase. The thermal behaviors of dielectric dispersion, absorption, and dielectric strength in different phases are also reported and discussed.

Journal Article↗
PubMed2001

Dielectric investigation of electrically oriented ferroelectric smectic mixture CS-1013.

From dielectric spectroscopic study, a first-order ferroelectric phase transition has been observed in ferroelectric smectic mixture CS-1013 having the phase sequence Cr-SmC*-SmA-N*-Iso. Frequency (100 Hz-10 MHz) and temperature-dependent dielectric measurements have been performed on an electrically aligned sample (thickness 15+/-1 microm) gold coated on glass plates. In the unidirectionally aligned sample, two dielectric relaxation modes (Goldstone mode and soft mode) have been clearly observed in the ferroelectric SmC* phase while only one relaxation mode (soft mode) is visualized in the paraelectric SmA phase. Low-frequency molecular relaxation was also observed in the smectic phases. The experimental results have also been analyzed at different temperatures and biasing voltages for an understanding of the dynamics of dielectric processes in the ferroelectric phase. Finally, we proposed the "pseudospin" model for understanding the ferroelectric-antiferroelectric transition in liquid crystals. We associate the tilt angle straight theta and the pitch of the helix, respectively, with biaxial (b) and uniaxial (u) anisotropy parameters as fluctuating parameters around their stability limit (corresponding to the crystalline values). Here, the director acts as the pseudospin variable. This gives rise to a transverse Ising type (or anisotropic Heisenberg model under the mean-field approximation). It is then shown that such a model with fluctuations of (b) and (u) would explain the ferroelectric and antiferroelectric phase transitions in such liquid crystals. Using Landau theory and the stability conditions, we have also shown, in brief, the feasibility of different types of phase transitions in the ferroelectric liquid crystal system.

Journal Article↗
PubMed1999

Frequency of class I HLA-restricted anti-HIV CD8+ T cells in individuals receiving highly active antiretroviral therapy (HAART).

Peptide/MHC tetrameric complexes were used to enumerate the frequency of HLA class I-restricted epitope-specific CD8+ T cells in 18 HLA-A*0201 HIV type 1-infected asymptomatic patients. HLA-A*0201 molecules were complexed to HIV Gag p17 (amino acids 77-85) and reverse transcriptase (amino acids 464-472) peptides, biotinylated, and bound to streptavidin-phycoerythrin to form tetramers. We show in this study that 17 of 18 HIV-1-infected asymptomatic patients have circulating frequencies of 1/50-1/1000 CD8+ T cells that recognize both Gag and Pol CTL epitopes or either epitope alone. The functional nature of these cells is open to interpretation, as we show that despite relatively high frequencies of fresh epitope-specific CD8+ T cells, variant epitope sequences in viral plasma progeny were rare. In addition, the majority of tetramer-positive cells did not display discernible fresh CTL activity; only after restimulation with specific peptide in culture was there an expansion of epitope-specific CD8+ cells, correlating with high CTL activity. These data suggest that fresh tetramer-stained cells probably represent memory precursors; we demonstrate, with the application of highly active antiretroviral therapy, that the interruption of chronic antigenic stimulation causes significant reductions in the frequency of these cells in five of six patients. In conclusion, this study provides evidence that persistently replicating viral populations are probably required to maintain high frequencies of HIV-1 epitope-specific CD8+ T cells in asymptomatic chronically infected individuals

Amino Acid Sequence↗
PubMed1998

Role of preimmunization virus sequences in cellular immunity in HIV-infected patients during HIV type 1 MN recombinant gp160 immunization.

The effect of patient preimmunization virus sequences on CTL responses during gp160 immunization were studied. Ten HLA-A2+, HIV+ asymptomatic patients with CD4+ T cells >500/mm3 were given two courses of HIV-1 MN rgp160 vaccine over a 2-year period. Envelope epitope-specific CTL responses, using PBMCs, were measured against peptide-coated autologous B lymphoblastoid cell lines. Optimum CTL epitopes were determined by HLA-A2-binding affinity of 9- to 10-mer peptides containing the HLA-A2.1-binding motif. Ten of the high- or intermediate-binding peptides were conserved among >50% of reported clade B HIV strains. These peptide-specific CTL activities and the patient virus sequences in peptide-coding regions were monitored. Six patients showed envelope peptide-specific CTL responses, which correlated with the presence of whole envelope antigen-specific CTL responses. Five of these patients, who showed responses to epitopes in the gp41 region (aa 814-824), had preimmunization virus similar to the vaccine sequence in this region. Three patients who did not show these epitope-specific responses had initially different sequences in the HIV gene encoding that region. The epitope-specific CTL responses appear to reflect recall responses, as only patients infected with virus containing the vaccine sequence developed them and they could be recalled with a second set of vaccine injections. This appears to be reminiscent of the concept of T cell "original antigenic sin." This vaccine was also immunogenic as measured by gp160-specific lymphocyte-proliferative responses. However, increased immune responses did not impact the HIV load or CTL epitope sequences during therapy.

AIDS Vaccines↗
PubMed1998

A pilot clinical trial of HIV antigen-pulsed allogeneic and autologous dendritic cell therapy in HIV-infected patients.

A pilot study was carried out to assess the safety and antigen-presenting properties of allogeneic or autologous dendritic cells (DCs) in six HLA-A2+, HIV-infected patients. Allogeneic DCs obtained from the peripheral blood of HLA-identical, HIV-seronegative siblings were pulsed with recombinant HIV-1 MN gp160 or synthetic peptides corresponding to HLA-A2-restricted cytotoxic epitopes of envelope, Gag, and Pol proteins. The antigen-pulsed cells were infused intravenously six to nine times at monthly intervals and HIV-specific immune responses were monitored. One allogeneic DC recipient with a CD4+ T cell count of 460/mm3 showed increases in envelope-specific CTL- and lymphocyte-proliferative responses, as well as in IFN-gamma and IL-2 production. Another allogeneic DC recipient with a CD4+ T cell count of 434/mm3 also showed an increase in HIV envelope-specific lymphocyte-proliferative responses. A recipient of autologous DCs with a CD4+ T cell count of 730/mm3 showed an increase in peptide-specific lymphocyte-proliferative responses after three infusions. Three other allogeneic DC recipients with CD4+ T cell counts <410/mm3 did not show increases in their HIV-specific immune responses. No clinically significant adverse effects were noted in this study and CD4+ T cell numbers and plasma HIV-1 RNA detected by RT-PCR of all six patients were stable during the study period. Thus, both allogeneic and autologous DC infusions were well tolerated and in patients with normal or near normal CD4+ T cell counts administration of these antigen-pulsed cells enhanced the immune response to HIV. However, since no effect on viral load was observed there was no evidence that this approach provided clinical benefit.

Cell Division↗
PubMed1997

Effect of therapeutic immunization with recombinant gp160 HIV-1 vaccine on HIV-1 proviral DNA and plasma RNA: relationship to cellular immune responses.

Therapeutic vaccination has been proposed as a strategy to augment immune mechanisms to control viral replication and slow clinical progression of HIV infection to disease. Following recombinant gp160 (r-gp160) immunization in three clinical trials, plasma HIV-1 RNA and cellular proviral DNA were assessed by quantitative polymerase chain reaction (PCR) in 76 HIV-seropositive subjects with CD4+ T cell counts > or = 300/mm3. Immunization increased HIV-specific cellular immune responses (e.g., cytotoxic T lymphocyte [CTL] activities, lymphocyte proliferative responses); however, there were no significant effects of immunization or cellular immune responses on measures of plasma RNA or cellular DNA viral load.

AIDS Vaccines↗
PubMed1997

Allogeneic dendritic cell induction of HIV-specific cytotoxic T lymphocyte responses from T cells of HIV type 1-infected and uninfected individuals.

The potential benefit of T cell-based vaccination for HIV-1 infection remains to be determined. Cytotoxic T lymphocytes (CTLs) appear to clear substantial populations of HIV-1 virus in vivo, although CTL activity may contribute to the decline in CD4+ T cell count observed in the course of the disease. To investigate further the role of specific CTL responses in the control of HIV-1 replication, we raised primary CTL lines against a panel of conserved HIV-1 epitopes using blood-derived dendritic cells as antigen-presenting cells (APCs). Specific primary human CTL responses were induced against HLA-A*0201-restricted peptides with dendritic cells from HIV-1-seronegative donors. This method of immunization elicited cytotoxic activities capable of recognizing endogenously processed antigen. The CTL induction protocol was extended in order to explore the capacity of HLA-matched allogeneic dendritic cells to evoke novel CTL responses in T cells from an HIV-seropositive asymptomatic individual. Allogeneic peptide-pulsed dendritic cells from a healthy sibling were capable of eliciting a CTL response directed against an HIV epitope (env814: SLLNATDIAV) that was initially not detected in the CTL effector population of the HIV-1-infected patient. The possibility of manipulating CTL specificity directed against multiple conserved HIV-1 epitopes represents a significant step in the evaluation of T cell-based vaccination for treatment of disease.

Antigens, Viral↗
PubMed1997

Heterogeneity of cytokine functions in HIV infection.

Immunological responses, especially cytokines, play important roles in determining the persistence of infectious agents in chronic diseases. Th1 responses enhance cellular immunity to control infection whereas Th2 immune responses down-regulate these effector immune responses. It has been suggested that the Th1 to Th2 switch is involved in human immunodeficiency virus (HIV) disease progression. We studied the regulatory role of interleukin-4 (IL-4; Th2 response) on interferon-gamma (IFN-gamma; Th1 response) in HIV infection and its role in the generation of HIV-specific cytotoxic T lymphocytes (CTL) in an in vitro system. Forty HIV-infected, asymptomatic individuals and 20 HIV-seronegative individuals were included in this study. Peripheral blood mononuclear cells were stimulated with phytohaemagglutinin and tetanus toxoid in the presence or absence of IL-4 to determine the effect of IL-4 on IFN-gamma production and HIV-Env-specific CTL activity. IL-4 showed a dual effect on IFN-gamma production in HIV patients. IL-4 down-regulated IFN-gamma production in HIV-seronegative individuals and in 55% of HIV patients whereas it stimulated IFN-gamma production in 45% of HIV patients. IL-4 increased HIV-Env-specific CTL activity in five of seven patients of the latter group. IL-4 has multiple biological activities, e.g. IL-4 inhibits IFN-gamma production as well as stimulates CTL generation which in turn produces IFN-gamma. Understanding the biological significance of these interactions is of importance for immunotherapeutic approaches against HIV infection.

Cell Culture Techniques↗
PubMed1996

Purification of commercial coomassie brilliant blue R-250 and characterization of the chromogenic fractions.

Coomassie brilliant blue R-250 (CBB) is a popular and widely used dye for detection of proteins by gel electrophoresis. However, commercially available CBBs are complex mixtures of numerous chromogenic compounds that vary from lot to lot, thereby giving an undesirable level of variation in reproducibility, precision, and specificity in staining gels. We have developed a silica gel column chromatographic method for purification of commercial CBBs in high yield and have standardized each lot to perform equivalently in staining proteins as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and quantitative scanning densitometry. This is a major improvement in protein purity determinations by quantitative scanning densitometry. A thinlayer chromatographic method for quality control testing of the purified CBB lots was also developed. Plasma desorption mass spectrometry was used to identify components of silica gel column fractions. Scanning densitometry was the technology used to establish performance equivalency between different CBB preparations. The less polar chromogenic compounds are nonblue and/or fluorescent in color, contain mono- or unsulfonated structures, and lack significant protein binding capacity. The more polar chromogenic compounds are green and blue-green in color, contain tri- and tetrasulfonated moieties, compared to the disulfonated structure of CBB, and bind to protein at least 40 times more effectively than pure CBB. The concentrations of these highly polar chromogens differ from lot to lot and act as "inhibitors" in protein staining, thereby causing variability in protein staining.

Chromatography, Thin Layer↗
PubMed1996

Polyethylene glycol-modified interleukin-2 and thymosin alpha 1 in human immunodeficiency virus type 1 infection.

The safety and antiviral effects of polyethylene glycolated interleukin-2 (PEG-IL-2) and thymosin alpha 1 in addition to zidovudine were studied in 12 human immunodeficiency virus (HIV)-infected subjects with 50-250 CD4 T cells/mm3. PEG-IL-2 was administered by intravenous infusions every 2 weeks at 10(6) IU/m2 for 20 weeks. Thymosin alpha 1 was administered subcutaneously at 400 microgram/m2 after four doses of PEG-IL-2, escalating to 1600 microgram/m2 weekly for an additional 2 months. Significant elevations of CD4 T cell numbers of 30%-40% were seen after PEG-IL-2 infusions, but no additional increase in CD4 cell count was observed with thymosin alpha 1. Virologic monitoring by polymerase chain reaction quantitation of proviral DNA and plasma RNA and p24 antigen assays showed no evidence of increased HIV activation during PEG-IL-2 or thymosin alpha 1 therapy. Patients tolerated both PEG-IL-2 and thymosin alpha 1 without significant toxicities.

Antiviral Agents↗
PubMed1995

Characterization of HLA-A 0201-restricted cytotoxic T cell epitopes in conserved regions of the HIV type 1 gp160 protein.

CTL activity is a major component of the host immune response associated with control of HIV replication in the course of infection. Emerging populations of HIV overcome the protective effector mechanisms with variant sequences unrecognized by CTL. Therefore, a critical element for containment of virus spread might be the establishment of an immune response against highly conserved epitopes. In this study, we selected a panel of nonamer or decamer peptides, with demonstrated binding affinity for HLA-A 0201, to define novel highly conserved envelope-derived epitopes of HIV-1. CTL activities were characterized from PBMC of five HLA-A2+, HIV-1-infected individuals given recombinant gp160. CTL activity derived from patient PBMC stimulated in vitro with peptide was demonstrated against at least two novel minimal env-encoded conserved epitopes. One epitope, KLTPLCVTL (aa 120-128), is highly conserved among HIV-1 strains of the B subtype. Analysis of a CTL clone reactivity to a distinct epitope (aa 814-823) demonstrated fluctuations in the recognition of peptides corresponding to natural virus variants found in vivo.

Amino Acid Sequence↗
PubMed1995

Description of an in vitro platelet function analyzer--PFA-100.

A new in vitro system for the detection of platelet dysfunction, PFA-100, has been developed. It provides a quantitative measure of platelet function in anticoagulated whole blood. The system comprises a microprocessor-controlled instrument and a disposable test cartridge containing a biologically active membrane. The instrument aspirates a blood sample under constant vacuum from the sample reservoir through a capillary and a microscopic aperture cut into the membrane. The membrane is coated with collagen and epinephrine or adenosine 5'-diphosphate. The presence of these biochemical stimuli, and the high shear rates generated under the standardized flow conditions, result in platelet attachment, activation, and aggregation, slowly building a stable platelet plug at the aperture. The time required to obtain full occlusion of the aperture is reported as the "closure time." We have found that impairment of von Willebrand factor, or inhibition of platelet receptors glycoprotein Ib or IIb/IIIa with monoclonal antibodies or peptides, resulted in abnormal closure times. An antifibrinogen antibody, in contrast, failed to show any effect. The test appears to be sensitive to platelet adherence and aggregation abnormalities. The PFA-100 system has potential applications in routine evaluation of platelet function in the clinical setting because of its accuracy, ease of operation, and rapid turnaround of results.

Bleeding Time↗
PubMed1994

Effects of thermal exposure on binding of heparin in vitro to the arterial wall and to clot and on the chronic angiographic luminal response to local application of a heparin film during angioplasty in an in vivo rabbit model.

Experimentally, heparin inhibits mechanisms that promote fibrosis, neointimal cellular proliferation, and thrombin bound to fibrin at the surface of intraluminal thrombus, but only in relatively high concentrations. A preliminary hypothesis was tested and confirmed in vitro that initial binding of 3H-heparin to mechanically injured porcine aorta is concentration-dependent over a 1,000-50,000 units/ml range (r = 0.9). The hypothesis was then tested in vitro that thermal exposure during contact of heparin to arterial tissue and to clot would enhance binding of the drug. 3H-heparin binding to clot, whole blood particulates, and washed erythrocytes was markedly enhanced by exposure to temperatures > 70 degrees C. Thermal exposure (80 degrees C x 40 s) also enhanced tissue persistence of the drug within porcine aorta subjected to a shear rate of 1,100(-1) in an annular Baumgartner chamber perfused with normal saline at 37 degrees C for 48 h. Heparin in vitro anticoagulant activity persisted after thermal exposure and binding to tissues. A new method was developed for local application of a heparin film that provides a maximum concentration with a tolerable systemic dose during an angioplasty procedure. In an in vivo rabbit model of mural fibrosis after iliac artery angioplasty, the 1-month mean angiographic luminal diameter loss (23% compared to the acute postangioplasty result by computer image analysis) in response to conventional balloon angioplasty (BA) and laser balloon angioplasty (LBA) was the same (P > 0.05). Local application of a heparin film (3,000 units at a concentration > 100,000 units/g), however, reduced the mean % loss in diameter 1 month after LBA (12%), but not after BA (29%), compared to arteries subjected to angioplasty without local heparin (P < .05). The results are consistent with the hypothesis that thermal energy enhances heparin binding to tissues and that local application of a heparin film favorably modulates arterial luminal responses to LBA, but not to BA, in this animal model.

Angioplasty, Balloon↗
PubMed1994

Relationship of HIV-1 provirus load, CD8+ CD11+ T cells and HIV-1 envelope-specific cytotoxic T lymphocytes in HIV-infected asymptomatic offients.

The course of human immunodeficiency virus (HIV) infection progresses from an acute infection, through a prolonged asymptomatic phase, to an immunocompromised state. Some of the possible mechanisms underlying immune dysfunction include decreased HIV-specific cytotoxic T lymphocyte (CTL) activity, increased suppressor T cells, and/or increased HIV load. However, no study has been carried out to correlate all these factors. In this study, 26 patients showed > 3 log DNA copy number/10(6) CD4+ T cells, and seven patients had < 3 log DNA copy/10(6) CD4+ T cells. Patients with higher virus load had greater than 15% (19-45%) CD8+ CD11+ T cells. HIV-1 envelope-specific, HLA-restricted CTL activity (> 10%) was observed in 11 of 25 asymptomatic patients, and the remaining 14 patients lacked CTL activity (< 10%) in bulk assay. Although CTL activity was undetectable in these individuals, there was no significant difference in the frequency of activated CTL and their precursors in limiting dilution analysis. The patients with undetectable CTL activity had a higher percentage of CD8+ CD11+ T cells and a higher HIV-1 DNA copy number/million CD4+ T cells. Each of these parameters were significantly correlated with CD4+ T-cell numbers. The inverse relationship of CD8+ CD11+ T cells and virus load with HIV-specific CTL activity observed in this study may be one of the underlying factors which determines the course of HIV infection.

CD11 Antigens↗
PubMed1994

Human immunodeficiency virus envelope glycoproteins.

Given the long-term clinical latency and high level of replication of human immunodeficiency virus (HIV), it is not surprising that HIV has developed a method of persistence involving production of novel variants in its proteins. Therapeutic vaccines attempt to harness enhanced immune mechanisms to control viral replication, and thus prevent disease progression. A major problem in the development of a vaccine is the great variety of viral quasispecies in HIV infection worldwide and within the lifetime of a given individual. Furthermore, the protective immune parameters that correlate with the ability to control disease progression remain undefined. Manufacturers have followed a number of paths to select an immunogen. At present, investigators are monitoring different immune and viral parameters to measure the effects of therapeutic vaccination. This monitoring ranges from HIV-specific cellular and humoral immunity to viral load markers and skin tests to recall antigens. Two possible major limitations to this treatment approach are the declining potency of the immune response and the ability of the virus to produce escape mutants, particularly during disease progression as viral replication increases. The latter escape mechanism could be similar to the specific pol mutations that enable the virus to escape the impact of drug therapy. Although apparent safety has been observed in phase II/III studies using several HIV envelope-based therapeutic vaccines, investigators have documented reproducible immunogenicity only in HIV-seropositive individuals with CD4+ T cells > 400/mm3. A convincing impact of vaccine therapy on viral load or the course of HIV disease has not been demonstrated.

AIDS Vaccines↗
PubMed1993

Safety and efficacy of polyethylene glycol-modified interleukin-2 and zidovudine in human immunodeficiency virus type 1 infection: a phase I/II study.

The safety and efficacy of combined therapy with polyethylene glycolated (PEG) interleukin (IL)-2 and zidovudine was assessed in 19 human immunodeficiency virus type 1 (HIV-1)-seropositive subjects in a phase I/II open-label dose-ranging study. During courses of three weekly infusions of PEG IL-2, dose-limiting side effects were seen at 5 x 10(6) IU/m2 and reversible encephalopathy in 1 subject at 3 x 10(6) IU/m2. Significant increases were seen in CD4 cell counts (P < .01), NK cell activity (P < .05), and HIV-specific cytotoxicity (P < .01). Virologic monitoring (quantitative DNA polymerase chain reaction and p24 antigen assay) showed no evidence of increased HIV activation. Patients with CD4 cells < 200/mm3 were entered into a chronic dosing phase. PEG IL-2 was given at 14-day intervals at doses of 10(6) IU/m2 for 8 weeks and 3 x 10(6) IU/m2 for up to 16 weeks, resulting in mean CD4 cell count elevations of 16% and 33%, respectively. PEG IL-2 appears to warrant further investigation, especially in subjects with CD4 cell counts < 200/mm3, to determine whether increased lymphocyte numbers will translate into improved clinical outcome.

Adult↗
PubMed1993

Breath acetone analyzer: diagnostic tool to monitor dietary fat loss.

Acetone, a metabolite of fat catabolism, is produced in excessive amounts in subjects on restricted-calorie weight-loss programs. Breath acetone measurements are useful as a motivational tool during dieting and for monitoring the effectiveness of weight-loss programs. We have developed a simple, easy-to-read method that quantifies the amount of acetone in a defined volume of exhaled breath after trapping the sample in a gas-analyzer column. The concentration of acetone, as measured by the length of a blue color zone in the analyzer column, correlates with results obtained by gas chromatography. Using the breath acetone analyzer to quantify breath acetone concentrations of dieting subjects, we established a correlation between breath acetone concentration and rate of fat loss (slope 52.2 nmol/L per gram per day, intercept 15.3 nmol/L, n = 78, r = 0.81). We also discussed the possibility of using breath acetone in diabetes management.

Acetone↗