Biomedical subjects
Publications and source records attributed to V Kumar.
Immuno-compromised patients are susceptible to a variety of opportunistic infections. Systemic aspergillosis is one such common infection in neutropenic subjects. A case of primary cutaneous aspergillosis with fungimia in a diabetic is reported.
The bactericidal activity (BA) of cefadroxil, a semisynthetic cephalosporin antibiotic, against M. tuberculosis H37Rv was studied in Middlebrook 7H9 medium. Cefadroxil showed good BA (average fall of viable counts = log10 0.32 colony forming units/ml/day) against the log phase culture of M. tuberculosis H37Rv. Its minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were found to be 15 micrograms/ml or less. The MIC of cefadroxil for 29 clinical isolates of M. tuberculosis and a laboratory strain, M. tuberculosis H37Rv was also determined by agar dilution method using Middlebrook 7H11 agar as a screening procedure. The MIC of cefadroxil was found to be 10 micrograms/ml or less for M. tuberculosis H37Rv and 16 (55.1%) of 29 clinical isolates tested. The MIC for 3 of 10 drug sensitive and 9 of 19 drug resistant isolates was 40 or more, a concentration much higher than the peak plasma concentration (28 micrograms/ml) attained in human beings. The higher MIC observed in 12 of 29 clinical isolates irrespective of their susceptibility pattern requires further studies to assess the usefulness of cefadroxil in the treatment of tuberculosis.
We report a 76-year-old man who presented with hepatitis. IgM antibodies to herpes simplex virus were positive and scraping from skin lesions showed presence of herpetic inclusion bodies. The patient died 4 days after the onset of illness.
To assess central nervous system (CNS) involvement with normal CNS examination, multimodality evoked potentials were obtained in 25 patients with confirmed multisystem sarcoidosis. Twelve patients had abnormal evoked potentials: brainstem auditory evoked potentials (BAEP) were abnormal in 5, median nerve somatosensory evoked potentials (SEP) were abnormal in 4, and visual evoked potentials (VEP) were abnormal in 6 patients. Contrast-enhanced magnetic resonance imaging (MRI) of the brain in two patients with abnormal evoked potentials revealed no supportive structural lesions. Multimodality evoked potentials can detect subclinical neurosarcoidosis and are an important adjunct to neuroradiology in the diagnosis of neurosarcoidosis.
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The frequency of intestinal parasitic infections was studied retrospectively in 1,029 cancer patients presenting with symptoms of diarrhoea. Intestinal parasites were diagnosed by stool examination, using both the direct and concentration techniques and also the modified acid fast stain. Parasitic infection was found in 16.5% of the cases. The majority of the patients with intestinal parasitosis had cancer of the haemopoietic system and were on anticancer chemotherapy. The most prevalent parasites were Entamoeba histolytica/Entamoeba dispar (8.5%) and Giardia lamblia (3.1%). Much more rare were Strongyloides stercoralis (0.6%), Cryptosporidium parvum (0.3%) and Isospora belli (0.1%). All the patients with intestinal parasites were negative for HIV antibodies.
Accelerated population ageing experienced in the last few decades is an unprecedented phenomenon. Currently, this is more in the developing countries. Soon three-fourths of the elderly will be in the developing world. From 1990 to 2025, the elderly population in Asia will rise from 50 per cent of the world's elderly to 58 per cent, in Africa and Latin America from 5 to 7 per cent, but in Europe the figure will drop from 19 to 12 per cent of the world's elderly. The life span has increased in India from 32 yr in 1947 to more than 62 yr now. From the morbidity point of view, almost 50 per cent of the Indian elderly have chronic diseases and 5 per cent suffer from immobility. There are several vulnerable groups and a big disadvantaged lot are elderly females who are one of the fastest growing segments, which will increase to become 4 times the current figure, by 2025. In spite of professional disinterest in the speciality, recent trends indicate the beginning of sensitization of medical teachers, advancing speciality of psychosocial gerontology and availability of some research funds. Importance of training of health professionals and priorities in gerontological research are also under consideration. Infections still take a heavy toll of our elderly population apart from well known degenerative disorders. Limitations of a developing country further influence the morbidity pattern in various ways. Nutritional deficiencies are common and often subclinical thus escaping the desired interventions. Coronary heart disease, hypertension, mental and many other disorders in the elderly have been reported as isolated observations highlighting differences from those made in the Western countries. Socio-economically, the traditional support of extended families is rapidly undergoing erosion making the elderly further vulnerable. This causes more emotional and psychological problems while the State finds itself helpless in providing a comprehensive care to its large chunk of elderly population. It will be important to surmise and predetermine the future factors that are going to modify the diverse patterns of morbidity, disability and mortality in regional context.
Life on earth is subjected to strict regimen of cyclical changes. Of all geophysical changes, the most prominent are the daily changes between day and night and the regular succession of annual seasons. Synchronization to environmental day-night and seasonal cycles is key to survival. Night-time and day-time environments differ in illumination, temperature, food supplies and predators. Organisms have, therefore, developed highly specialized temporal programmes to get better adapted to activity either during night or during the day. Many species use annual cycle of changes in daylength as "calendar" to synchronize and/or to time their daily and seasonal physiological and behavioral functions. This is described as photoperiodism. The minimum daylength (photoperiod) that will induce a physiological response is the "critical daylength" (CD). CD requirement is quite stringent. CD is species-specific; CD may be response-specific as well. Switching 'on' and 'off' the seasonal responses in many species is regulated by the development of photorefractoriness-a phenomenon when organism remains no longer capable to continue its stimulatory response to a photoperiod. Photorefractoriness may be qualitatively different between species. Broadly, two categories of photorefractoriness are described: absolute refractoriness and relative refractoriness. What causes photorefractoriness and at what level in the brain photorefractoriness occurs are unknown. A photoperiodic response system has three principal components: a photoreceptor that interprets photic input, a clock that measures photic signal, and a neurosecretory system that translates photic signal into endocrine secretions. Both retinal and extra-retinal structures are involved in the photoperiodic photoreception. In insects, mollusks, crustaceans, fishes, amphibians, reptiles and birds, the photoreception occurs largely through extra-retinal photoreceptors (ERRs) localized in the hypothalamus. In adult mammals, brain photoreceptors are apparently absent and light input is only through eyes. Endogenous circa-rhythms believed to be involved in photoperiodism are synchronized to changes in illumination of the environment with either the time of day (circadian rhythm) or the season of the year (circannual rhythm). The Suprachiasmatic nuclei (SCN) of the hypothalamus in mammals function as the clock. The SCN monitors the photoperiodic message and decodes it by dictating the changes in rhythm in melatonin secretion in the pineal gland. The hypothalamic paraventricular nuclei (PVN) are also an integral component of the neural network mediating photoperiodism in mammals. The location of SCN homologue and the role of PVN in mediating photoperiodism in non-mammalian vertebrates is still unclear. Furthermore, how various components of photo-neuroendocrine circuitry are functionally linked together is unknown.
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Adaptation in the temporal environment is key to survival. This is achieved by the manifestation of periodicity in occurrence of vital behavioural and physiological processes at regular intervals--the biological rhythms. Biological rhythms (= biological clocks) are ubiquitous, can be demonstrated persisting at any level of organization in the living world, and are generated and controlled by some central pacemaker(s), mostly located in the brain. In mammals, the suprachiasmatic nucleus (SCN) of the anterior hypothalamus is the principal site of the endogenous circadian pacemaker, regulating many daily physiological and behavioural functions, although other neural structures could also be contributing to the circadian timekeeping system. In other vertebrates, the neural site(s) of the circadian pacemaker is(are) still unclear. An organism without brain can have the biological clock, as well, for fully functional 24-hour temporal organization has been identified in several invertebrates, including unicellular Paramecium and Gonyaulax as well as filamentous fungus, Neurospora. This article attempts to provide an update of the informations which have accumulated over the past decade about understanding of the neurophysiological and molecular bases of circadian rhythms in animals.
T cells present in bone marrow cell (BMC) grafts promote engraftment in histoincompatible hosts, but they or other T cells may also initiate lethal graft-vs.-host disease (GVHD). The purpose of this study was to determine whether T cells from donors tolerant of host alloantigens were able to prevent natural killer (NK) cell-mediated rejection of BMC grafts without causing GVHD. Previous studies have shown that H2d C.B-17 SCID BMC grafts were rejected by (BALB/c x B6)F1 (CB6F1,H2d/b) host NK cells, and that this rejection was reversed by adding H2d T cells to the donor inoculum. T cells tolerant of H2d/b alloantigens were produced by irradiating (3 Gy) BALB/c newborn mice, and infusing CB6F1 BMCs. Tolerance was assessed by donor (H2b+) cell chimerism, acceptance of CB6F1 skin grafts, the inability of adoptively transferred lymphocytes to initiate GVHD in irradiated CB6F1 mice, and the inability of spleen or thymus cells to generate cytolytic T lymphocytes against H2b target cells in vitro. Whole or H2-Kb-depleted BMCs isolated from tolerant donors were able to proliferate in both BALB/c and H2b/d (C57BL/6 x DBA/2)F1 hosts as determined by incorporation of a radiolabelled DNA precursor in the spleen. Furthermore, thymocytes from tolerant donors were able to prevent rejection of H2d SCID BMCs. Because the percentage of donor F1 cells was so high in these chimeras, we generated BALB/c to CB6F1 SCID BMC chimeras; the percentage of BALB/c cells was approximately 100%, the BMCs grew well in irradiated CB6F1 hosts, and their lymph node cells failed to cause a graft-vs.-host (GVH) reaction in CB6F1 hosts. Thus, GVHD may be prevented without inhibiting the ability of donor T cells to promote engraftment. Perhaps separate T cells, or separate functions of a common T cell subset, induce GVHD and enhance engraftment of stem cells.
NK cells require an intact bone marrow microenvironment to acquire lytic function. In mice rendered osteopetrotic by 17beta-estradiol treatment, NK1.1 positive cells are arrested in a nonlytic state. Culture with as little as 2 ng/ml of murine IL-15 (mIL-15), a cytokine produced by macrophages and stromal cells, causes these immature NK1.1+ cells to acquire lytic activity. By contrast, approximately 10- to 50-fold greater amount of mIL-2 was required to induce similar level of cytotoxicity. After culture with mIL-15, the relatively low expression of B220, CD11b, and Ly-49 molecules on immature NK1.1+ cells was increased to levels comparable to those of mature splenic NK1.1+ cells. mIL-15 also caused a greater expansion of NK1.1+CD3- cells as compared with NK1.1+CD3+ cells. We conclude that IL-15 is a specific maturation factor for NK cells and that it can mimic the marrow microenvironment in vitro.
T cell receptor (TCR)-recognizing regulatory cells, induced after vaccination with self-reactive T cells or TCR peptides, have been shown to prevent autoimmunity. We have asked whether this regulation is involved in the maintenance of peripheral tolerance to myelin basic protein (MBP) in an autoimmune disease model, experimental autoimmune encephalomyelitis (EAE). Antigen-induced EAE in (SJL x B10.PL)F1 mice is transient in that most animals recover permanently from the disease. Most of the initial encephalitogenic T cells recognize MBP Ac1-9 and predominantly use the TCR V beta 8.2 gene segment. In mice recovering from MBP-induced EAE, regulatory CD4+ T cells (Treg) specific for a single immunodominant TCR peptide B5 (76-101) from framework region 3 of the V beta 8.2 chain, become primed. We have earlier shown that cloned B5-reactive Treg can specifically downregulate responses to Ac1-9 and also protect mice from EAE. These CD4 Treg clones predominantly use the TCR V beta 14 or V beta 3 gene segments. Here we have directly tested whether deletion/blocking of the Treg from the peripheral repertoire affects the spontaneous recovery from EAE. Treatment of F1 mice with appropriate V beta-specific monoclonal antibodies resulted in an increase in the severity and duration of the disease; even relapses were seen in one-third to one-half of the Treg-deleted mice. Interestingly, chronic disease in treated mice appears to be due to the presence of Ac1-9-specific T cells. Thus, once self-tolerance to MBP is broken by immunization with the antigen in strong adjuvant, TCR peptide-specific CD4 Treg cells participate in reestablishing peripheral tolerance. Thus, a failure to generate Treg may be implicated in chronic autoimmune conditions.
We have previously shown that three distinct DNA-binding activities, in crude form, are necessary for the ATP-dependent assembly of a specific and stable multiprotein complex at a yeast origin of replication. Here we show the purification of one of these DNA binding activities, referred to as origin binding factor 2 (OBF2). The purified protein is a heterodimer composed of two polypeptides with molecular mass values of 65 and 80 kDa as determined by SDS/PAGE. Purified OBF2 not only binds DNA but also supports the formation of a protein complex at essential sequences within the ARS121 origin of replication. Interestingly, OBF2 binds tightly and nonspecifically to both duplex DNA and single-stranded DNA. The interaction with duplex DNA occurs at the termini. N-terminal sequencing of the 65-kDa subunit has revealed that this polypeptide is identical to the previously identified HDF1 peptide, a yeast homolog of the small subunit of the mammalian Ku autoantigen. Although the potential involvement of Ku in DNA metabolic events has been proposed, this is the first requirement for a Ku-like protein in the assembly of a protein complex at essential sequences within a eukaryotic origin of replication.
Extravesicular and intravesicular zinc bindings were evaluated in brush border membrane vesicles isolated from rat kidney cortex. The process was found to be time-, temperature- and substrate concentration-dependent and displayed saturability. Zn2+ influx measurements revealed a progressive uptake and massive accumulation at equilibrium which was 50 times higher than the amount that could have been accommodated by the intravesicular space calculated from the equilibrium uptake of D-glucose. Initial (5 s) and equilibrium uptakes (2 h) were found not to be osmotically sensitive as modified by adding mannitol to the medium. It was concluded from these results that the uptake involved massive binding of the Zn2+ to the brush border membranes components. The ionophore A23187 enhanced the rates of uptake and efflux of Zn2+ without affecting equilibrium values, suggesting binding of Zn2+ to interior sites of the membranes. Zn2+ flux measurements led to the conclusion that two vesicular pools of Zn2+ bindings existed: a small external pool, accessible to cation chelator (EGTA) or competitive cation cadmium and large intravesicular pool. Accumulated 65Zn was quickly removed from its internal sites only after the membrane had been permeabilized by the cation ionophore A23187 in association with exchangeable ions like zinc and cadmium. Scatchard plot analysis revealed two distinct types of extravesicular binding sites. High affinity extravesicular zinc binding sites reached saturation at 1.6 mM zinc, had a Kd of 137 microM and the number of binding sites were 12 nmol/mg protein. Low affinity extravesicular zinc binding sites could not be saturated under experimental conditions up to 3.2 mM zinc. It had a Kd of 526 microM and the number of binding sites 28 nmol/mg protein. Interestingly intravesicular binding of zinc revealed only one type of high affinity binding sites (Kd of 104 microM and number of maximal binding sites 400 nmol/mg protein). Furthermore, kinetic analysis of inhibitory effect of Cd2+ on extravesicular zinc bindings showed an increase in Kd of both types of binding sites but there was no significant change in number of maximal binding sites. Extravesicular zinc binding was temperature-sensitive. Arrhenius plot showed the break point at 30 degrees C. The apparent energies of activation were 13.36 Kcal/mol and 3.1 Kcal/mol below and above the break points respectively. The inhibitory effect of sulfhydryl blocking agents on extravesicular zinc binding suggest the involvement of -SH groups in zinc translocation. An increase in initial zinc uptake was observed in the presence of outwardly directed proton gradient. Intravesicular pool of 65Zn was displaced by unlabelled 2 mM Zn2+ or 2 mM Cd2+ but not by calcium present in the bathing medium. It is inferred that intravesicular binding sites have a high affinity and are specific for zinc. It is concluded from the present study that in the first instance the binding of zinc to the exofacial zinc binding component and concomitantly its translocation across the membrane, and subsequently massive binding of zinc to interior sites of brush border membranes occurs.
During the evolution of the autoimmune response to myelin basic protein (MBP), at least two distinct lymphocyte populations arise, one that is specific for determinants within the protein antigen and another that is specific for the receptors displayed by the antigen-specific lymphocytes themselves. The T-cell receptor (TCR)-specific lymphocytes appear to oppose the action of the pathogenic effector cells, which predominantly utilize the TCR V beta 8.2 gene segment. We will discuss our work suggesting that both CD4 and CD8 cells specific for different TCR determinants on the V beta 8.2 chain are involved in the regulation of MBP-specific CD4 T cells mediating experimental autoimmune encephalomyelitis. We suggest that a crucial balance between the effectors and regulators is decisive for the clinical manifestation of autoimmunity.
BACKGROUND: Copper-containing amine oxidases catalyze the oxidative deamination of primary amines to aldehydes, in a reaction that requires free radicals. These enzymes are important in many biological processes, including cell differentiation and growth, would healing, detoxification and signalling. The catalytic reaction requires a redox cofactor, topa quinone (TPQ), which is derived by post-translational modification of an invariant tyrosine residue. Both the biogenesis of the TPQ cofactor and the reaction catalyzed by the enzyme require the presence of a copper atom at the active site. The crystal structure of a prokaryotic copper amine oxidase from E. coli (ECAO) has recently been reported. RESULTS: The first structure of a eukaryotic (pea seedling) amine oxidase (PSAO) has been solved and refined at 2.2 A resolution. The crystallographic phases were derived from a single phosphotungstic acid derivative. The positions of the tungsten atoms in the W12 clusters were obtained by molecular replacement using E. coli amine oxidase as a search model. The methodology avoided bias from the search model, and provides an essentially independent view of a eukaryotic amine oxidase. The PSAO molecule is a homodimer; each subunit has three domains. The active site of each subunit lies near an edge of the beta-sandwich of the largest domain, but is not accessible from the solvent. The essential active-site copper atom is coordinated by three histidine side chains and two water molecules in an approximately square-pyramidal arrangement. All the atoms of the TPQ cofactor are unambiguously defined, the shortest distance to the copper atom being approximately 6 A. CONCLUSIONS: There is considerable structural homology between PSAO and ECAO. A combination of evidence from both structures indicates that the TPQ side chain is sufficiently flexible to permit the aromatic grouf to rotate about the Cbeta-Cgamma bond, and to move between bonding and non-bonding positions with respect to the Cu atom. Conformational flexibility is also required at the surface of the molecule to allow the substrates access to the active site, which is inaccessible to solvent, as expected for an enzyme that uses radical chemistry.