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Biomedical subjects

D Chowdhury

Publications and source records attributed to D Chowdhury.

At least 19 recordsLinked to original sources
PubMed2001

Stepwise activation of the immunoglobulin mu heavy chain gene locus.

The immunoglobulin heavy chain (IgH) gene locus spans several megabases. We show that IgH activation during B-cell differentiation, as measured by histone acetylation, occurs in discrete, independently regulated domains. Initially, a 120 kb domain of germline DNA is hyperacetylated, that extends from D(FL16.1), the 5'-most D(H) gene segment, to the intergenic region between Cmu and Cdelta. Germline V(H) genes were not hyperacetylated at this stage, which accounts for D(H) to J(H) recombination occurring first during B-cell development. Subsequent activation of the V(H) locus happens in at least three differentially regulated domains: an interleukin-7-regulated domain consisting of the 5' J558 family, an intermediate domain and the 3' V(H) genes, which are hyperacetylated in response to DJ(H) recombination. These observations lead to mechanisms for two well-documented phenomena in B-cell ontogeny: the sequential rearrangement of D(H) followed by V(H) gene segments, and the preferential recombination of D(H)-proximal V(H) genes in pro-B cells. We suggest that stepwise activation may be a general mechanism by which large segments of the genome are prepared for expression.

Acetylation↗
PubMed2001

Axonal Guillain-Barré syndrome: a critical review.

Axonal Guillain-Barré Syndrome (GBS) was first described by Feasby et al. in 1986, challenging the existent notion of GBS being a primarily demyelinating disease. The severe course and slow recovery commonly seen in these patients was ascribed to axonal degeneration. Other authors challenged this claim on several grounds. Amidst these controversies, epidemics of a similar illness were reported from China, which were given the acronym AMAN, having exclusive motor involvement in contrast to the cases already described in which both motor and sensory involvement were present (AMSAN). Pathologically, Wallerian degeneration, minimal lymphocytic response, absent demyelination or inflammation and periaxonal macrophages are prominent features. Ultrastructural studies have revealed node of Ranvier to be the prime target of immune attack. A frequent occurrence of antecedent Campylobacter jejuni infection and a strong association between elevated titres of IgG GM1 and axonal GBS on a background of preceding C. jejunii infection has been observed and molecular mimicry between lipopolysaccharides of C. jejuni and neural epitopes has been proposed as a mechanism of injury. Clinically axonal variant is similar to AIDP, but a more severe course, with frequent respiratory involvement, ventilator dependence and significant residue may be seen. Diagnosis is essentially electrophysiological. Treatment is similar to AIDP, preferential benefit of either IVIG or plasmapheresis needs to be further evaluated. A critical review of existing literature in axonal GBS is presented.

Axons↗
PubMed2001

Estimation of mortality and morbidity due to strokes in India.

In order to control the stroke problem, its magnitude should be assessed. India is ranked among the countries where the information on stroke is minimal. We decided to review the information available in order to estimate the mortality and morbidity due to stroke in India. Information was collected through electronic search, hand search and contact with experts. Each article was reviewed for relevance and epidemiological rigor. The demographic data were as derived from published government figures. The prevalence from individual studies was pooled and weighted based on sample size. Analysis was done separately for males and females at 10-year intervals (20 years onwards). A total of 7 studies was located, but 2 were discarded. All were done in rural areas except 2 which also included urban areas. The prevalence was estimated as 203 per 100,000 population above 20 years amounting to a total of about 1 million cases. The male to female ratio was 1.7. Around 12% of all strokes occurred in population below 40 years. The estimation of stroke mortality was seriously limited by the method of classification of cause of death in the country. The best estimate derived was 102,000 deaths; which represented 1.2% of total deaths in the country. There is need to initiate steps to collect data on morbidity and mortality due to stroke in the country as a first step towards control measures.

Adolescent↗
PubMed2001

Reversible posterior leukoencephalopathy syndrome: a report of 2 cases.

Reversible posterior leukoencephalopathy syndrome (RPLE) is an increasingly recognised disorder, most commonly associated with malignant hypertension, toxaemia of pregnancy or the use of immunosuppressive agents. Two cases of RPLE syndrome occurring in the setting of accelerated hypertension and eclampsia are described. Both patients had seizures, altered sensorium and typical findings on neuroimaging. They had complete clinical and radiological recovery. The clinical course, pathophysiology and neuroimaging features of RPLE syndrome are discussed.

Adolescent↗
PubMed2000

Congenital myasthenic syndrome: report of four cases and brief review of literature.

The term 'congenital myasthenic syndrome' (CMS) encompasses a number of heterogeneous disorders characterised by myasthenic symptoms since birth, usually with positive family history and absence of acetyl choline receptor antibodies. Recent advances in electrophysiology and ultrastructural analysis of neuromuscular junction have made it possible to identify the various defects underlying these disorders. We report four cases of CMS, with a review of literature.

Adult↗
PubMed1999

Usefulness of triiodothyronine (T3) treatment after surgery for complex congenital heart disease in infants and children.

This is a study of the use of T3 infusion in the postoperative period in 6 pediatric patients who underwent complex cardiac surgical procedures under cardiopulmonary bypass. Normalization of serum T3 levels was reflected in a marked decrease in requirement of inotropic support, conversion to normal sinus rhythm, and progressively improving clinical course.

Child, Preschool↗
PubMed1999

Distinct functions of eukaryotic translation initiation factors eIF1A and eIF3 in the formation of the 40 S ribosomal preinitiation complex.

We have used an in vitro translation initiation assay to investigate the requirements for the efficient transfer of Met-tRNAf (as Met-tRNAf.eIF2.GTP ternary complex) to 40 S ribosomal subunits in the absence of mRNA (or an AUG codon) to form the 40 S preinitiation complex. We observed that the 17-kDa initiation factor eIF1A is necessary and sufficient to mediate nearly quantitative transfer of Met-tRNAf to isolated 40 S ribosomal subunits. However, the addition of 60 S ribosomal subunits to the 40 S preinitiation complex formed under these conditions disrupted the 40 S complex resulting in dissociation of Met-tRNAf from the 40 S subunit. When the eIF1A-dependent preinitiation reaction was carried out with 40 S ribosomal subunits that had been preincubated with eIF3, the 40 S preinitiation complex formed included bound eIF3 (40 S.eIF3. Met-tRNAf.eIF2.GTP). In contrast to the complex lacking eIF3, this complex was not disrupted by the addition of 60 S ribosomal subunits. These results suggest that in vivo, both eIF1A and eIF3 are required to form a stable 40 S preinitiation complex, eIF1A catalyzing the transfer of Met-tRNAf.eIF2.GTP to 40 S subunits, and eIF3 stabilizing the resulting complex and preventing its disruption by 60 S ribosomal subunits.

Animals↗
PubMed1995

Synaptotagmin I and 1B4 are identical: implications for synaptotagmin distribution in the primate brain.

We have determined that the human cDNA sequence of the previously described primate brain mRNA species 1B4 is nearly identical (99.95% similarity) to that of human Synaptotagmin I. The apparent identity of Synaptotagmin I with 1B4, whose distribution in the brain of the monkey Cynomolgous was determined previously by Northern blot and in situ hybridization (ISH) analyses, reveals the Synaptotagmin I is differentially expressed in the primate brain. Primate Synaptotagmin I mRNA is enriched in hindbrain structures relative to forebrain structures by Northern blot analysis. By ISH analysis, primate Synaptotagmin I mRNA is highly expressed in occipital cortex and lateral geniculate (visual system components) and differentially expressed across topographic cortical boundaries between inferior and superior temporal gyrus (a polymodal zone with visual, auditory and somatosensory inputs) and between areas 17 and 18 of the visual cortex (primary and secondary visual areas). Cortical expression is also enriched in layers V and VI, which contain large pyramidal projection neurons. Synaptotagmin I's greater association with large projection neurons and with some components of visual sensory transduction could reflect a requirement of these neural components for greater synaptic activity. Synaptotagmin I expression in the primate brain is also dissimilar to Synaptotagmin I expression in rodents. Thus, variation of Synaptotagmin I expression has occurred during mammalian evolution, perhaps as a consequence of the larger size and neurotransmitter requirements of primate neurons.

Base Sequence↗
PubMed1995

The role of bronchodilators in the management of bronchiolitis: a clinical trial.

A randomized clinical trial was conducted on young children with bronchiolitis admitted to hospital with moderate illness to determine the efficacy of the bronchodilators Salbutamol and ipratropium bromide, either as a single drug or in combination, given as a nebulized solution, compared with a normal saline placebo. Eighty-nine patients, aged from 23 days to 11 months, were randomized into four groups, depending on administered drug or placebo, as follows: group 1--Salbutamol (n = 20); group 2--ipratropium bromide (n = 23); group 3--combined Salbutamol and Ipratropium bromide (n = 24); group 4--normal saline (n = 22). The groups were identical with respect to age, sex, family history of atopy, respiratory syncytial virus (RSV) positivity and enrollment score. They were scored using the clinical parameters of wheezing, retractions and respiratory rate at enrollment, at 30 and 60 minutes after the first nebulization, and after 60 minutes following completion of subsequent nebulization at 6, 12, 24 and 36 hours. We did not find any significant difference in the rate of improvement and the final score (p = 0.49) in the four groups. The same finding was also noted in children aged more than 3 months (p = 0.35) and in those positive for RSV infection (p = 0.18). The lengths of hospitalization in the four groups were also similar (p = 0.79). It is concluded that there is no role for the nebulized bronchodilators Salbutamol and Ipratropium bromide, either as a single agent or in combination, compared with normal saline placebo in treating young children in hospital with bronchiolitis.

Administration, Inhalation↗
PubMed1993

A unified model of immune response. II: Continuum approach.

In an earlier paper in this journal (1990, J. theor. Biol. 145, 207-215) we developed a unified model for normal immune response, autoimmune response and AIDS, where the concentration of each type of cell involved in the immune response is represented by a discrete automaton and the population dynamics of the relevant cells are formulated in terms of dynamical maps in discrete time. In this paper we study the continuum version of this unified model where the cell concentrations are represented by real variables whose evolution with continuous time is described by differential equations. We discuss possible ways to extend this model incorporating new experimental results and to generalize it along the new emerging trends in network theories of immune response. Our work also illustrates some of the relative advantages and disadvantages of the discrete and continuum formulations of the models of immune response.

Autoimmunity↗
PubMed1991

A discrete model for immune surveillance, tumor immunity and cancer.

In this paper we propose a model of tumor immunity in terms of discrete automata where each automation describes the concentration of one particular type of cell involved in immune response. In contrast to the earlier models of normal immune response, there is more than one type of cell surface antigen in this model. As a consequence, the tumor can evade destruction through humoral response by changing its identity. However, the tumor can be killed by the killer cells through cell-mediated response unless protected by a high concentration of the suppressor T cells.

Computer Simulation↗