Search PubMed⌕ Search

Biomedical subjects

R T Johnson

Publications and source records attributed to R T Johnson.

At least 109 records · Page 6Linked to original sources
PubMed1988

Kinetic analysis of UV-induced incision discriminates between fibroblasts from different xeroderma pigmentosum complementation groups, XPA heterozygotes and normal individuals.

The capacity of a variety of human fibroblasts to incise DNA following exposure to far ultraviolet-light is determined from the rate of single-strand DNA break accumulation in the presence of DNA synthesis inhibitors. We have quantitated incision, one of the early steps in the UV excision repair pathway, in cells form normal, xeroderma pigmentosum groups C, D, G, H and variant individuals, and in the parents of one XPA patient. On the basis of the estimated initial rates of incision the different XP cells examined in this work can be ranked as follows: XP variant much greater than XPH greater than XPH greater than XPD greater than XPC greater than XPG greater than XPA. In each cell strain breaks accumulate immediately after irradiation over a range of 0.5-20 Jm-2 with the exception of the XPC strain examined, where there is an initial delay of 15 min. The rate of incision in XPA heterozygote cells is roughly half that of normal fibroblasts. Analysis of the kinetics of break accumulation over short intervals after irradiation permits estimation of the apparent enzymatic parameters, Km and Vmax, for the incision step. The approximate values of Km and Vmax for normal and XP variant are similar while for the heterozygotes of an XPA individual Km values are normal (around 1 Jm-2), but there is only half the amount of normal enzyme activity. XPD and H cells express low levels of active enzyme, between 5 and 15% of that of the normal, but while the Km of XPH is very similar to that of normal cells, that of two XPD strains examined is between 2- and 3-fold higher.

Cells, Cultured↗
PubMed1988

Acute measles in patients with and without neurological involvement: distribution of measles virus antigen and RNA.

Using peroxidase immunohistochemistry and in situ hybridization to localize viral antigen and RNA, we studied autopsy tissues from 20 cases of acute fatal human measles (including seven patients with acute encephalomyelitis) and peripheral blood mononuclear cells from 16 patients with acute, nonfatal measles. In immunologically normal patients, virus was detected in five of nine who died five days or less after the onset of rash but in none of 11 who died later. Virus was localized to epithelial cells of lung, gut, bile duct, bladder, and skin and to lymphoid organs. Neither viral antigen nor RNA was detected in brain sections from 14 patients, including seven with acute encephalomyelitis and four with virus identified in other tissues, a finding supporting an indirect pathogenesis of post-measles encephalomyelitis. These data show that measles virus replicates in cells previously not recognized to be involved (capillary endothelium of lymph node and thymus, Hassall's corpuscles, and hepatic duct epithelium) and that invasion of the brain parenchyma during acute measles is uncommon.

Acute Disease↗
PubMed1988

The neurobiology of human immunodeficiency virus infections.

A variety of diseases of the central and peripheral nervous systems evolves during the course of human immunodeficiency virus (HIV) infections. Most are not related to documented opportunistic infections and may be the direct result of HIV infections, as large proportions of healthy and ill HIV-infected persons show evidence of nervous system infection. These diseases occur at different times during the infection and have diverse inflammatory, demyelinating, or degenerative pathological features that suggest different pathogenetic mechanisms. The route and determinants of HIV invasion of the nervous system are unknown. Within the brain, viral antigen and RNA are found predominantly in macrophages, but the reason why profound dementia and cortical atrophy result from this infection remains a mystery. By analogy to other lentivirus infections, particularly visna virus in sheep, neuropathological changes may be mediated by cytokines. Other possible pathogenetic mechanisms include toxicity of viral polypeptides, transactivation of viral or cellular genes, autoimmunity, or other opportunistic infections. Clarification of the pathogenesis of HIV-related diseases is critical to the design of rational therapies.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Immunologic studies of patients with chronic encephalitis induced by post-exposure Semple rabies vaccine.

Neurologic complications of brain tissue-derived rabies vaccine may be chronic or progressive. Lymphocytes and serum from three patients with this form of encephalitis were studied. Two patients had positive lymphoproliferation to purified myelin, two had antibody to white matter, and one had antibody to myelin basic protein. No patient had antibody to proteolipid protein, myelin-associated glycoprotein, or cerebroside.

Antibodies↗
PubMed1988

Immunologic studies of rabies vaccination-induced Guillain-Barré syndrome.

Patients with Guillain-Barré syndrome (GBS) induced by rabies vaccines prepared from either suckling mouse brain (SMB) or mature sheep brain (Semple vaccine) and patients with sporadic, idiopathic GBS were studied for antibody to myelin basic protein (MBP), P2 protein, and Schwann cells. Sera from all four Semple vaccine- and one of five SMB vaccine-induced GBS patients, but none of the sporadic GBS patients, had antibody to MBP. Sera from Semple vaccinees also had antibody to fixed, transformed Schwann cells, but similar amounts of antibody were found in sera from Semple vaccinees with CNS complications and with minor non-neurologic complications, suggesting that this antibody was not specifically linked to the development of polyneuritis. None of the sera had detectable antibody to P2 protein. We conclude that patients with GBS constitute a heterogeneous population and that different target antigens may serve as a focus for this presumed autoimmune disease.

Animals↗
PubMed1988

Caffeine induces uncoordinated expression of cell cycle functions after ultraviolet irradiation. Accelerated cycle transit, sister chromatid exchanges and premature chromosome condensation in a transformed Indian muntjac cell line.

Caffeine enhances the lethal effect of DNA-damaging agents. It also affects the timing of events in the cell cycle; the enhanced cytotoxicity may be partly due to caffeine's ability to overcome the protective damage-induced delay in S or G2 phase. When the effects of caffeine are compared in a normal Indian muntjac cell line and a simian virus 40 (SV40)-transformed, ultraviolet light (u.v.)-sensitive line in which u.v. induces many sister chromatid exchanges, different cell cycle sensitivities are seen. In the SV40-transformed line, caffeine over-rides the delay in DNA synthesis imposed by DNA damage; it initiates late cycle events after u.v. irradiation, and in some cases it induces S-phase premature chromosome condensation, apparently by inducing mitotic factors in cells where the chromatin is still replicating. Caffeine has been reported to induce similar premature chromosome condensation in cells arrested with DNA polymerase inhibitors; this is the first recognition that such events occur in response to caffeine treatment after DNA damage. Some apparent paradoxes of caffeine's action on irradiated cells can be thus explained. In the normal line, caffeine neither affects progression through the cycle nor induces premature chromosome condensation after irradiation. In both lines, caffeine increases killing and sister chromatid exchanges after u.v. irradiation; but these effects are more pronounced when exerted through the cell cycle-related mechanism.

Animals↗
PubMed1987

Slow DNA rejoining in ultraviolet-irradiated human diploid fibroblasts treated with the mitogens trypsin and insulin.

Normally in mammalian cells the postincision steps of UV-induced excision repair are much more rapid than the recognition of damage and incision. This means that at any one time the level of repair-generated single-stranded DNA breaks is very low. Here we report that detectable levels of DNA breaks accumulate in quiescent human fibroblasts which are UV irradiated a few hours after replating in conditions that stimulate progress through the cell cycle. Most DNA breaks accumulate in cultures trypsinized and seeded in medium supplemented with insulin, and irradiated in early G1. Because trypsin and insulin have no effect on UV-induced incision rates, as measured by DNA break accumulation in the presence of DNA synthesis inhibitors, we argue that our ability to detect incomplete repair-sites is due to a significant reduction in the rate of gap sealing indicative of a shift in the steady state of excision repair. Provision of DNA precursors prevents the enhancing effect of trypsin and insulin on the accumulation of DNA breaks, implying that these agents affect DNA precursor metabolism. Perturbation of the repair process, which leads to the accumulation of 1500-2000 DNA breaks/genome, is also associated with other effects including increased lethality, the appearance of double-strand breaks and the loss of NAD, the last effect presumably arising as a consequence of break-stimulated poly(ADPR) transferase activity. Addition of 3-amino-benzamide, an inhibitor of poly(ADPR) synthesis, completely blocks the decline in NAD levels, but does not change the rate of sealing of the accumulated DNA breaks. These results strongly suggest that ligation is largely, if not entirely, independent of ADP ribosylation in this system.

Adenosine Diphosphate Ribose↗
PubMed1987

Myelin basic protein as an encephalitogen in encephalomyelitis and polyneuritis following rabies vaccination.

Encephalitis and polyneuritis occurring after rabies vaccination are believed to be immunologically mediated. We studied antibody responses to neural antigens in 36 patients with major neurologic complications, 25 with minor complications, and 39 with no complications after immunization with a brain-derived, Semple rabies vaccine. Patients with major complications had significantly elevated levels of antibody to brain white matter as compared with the other groups (P less than 0.001). Assays for antibody to selected central nervous system antigens showed that high levels of serum and cerebrospinal fluid antibody to myelin basic protein correlated with the presence of major neurologic complications (both central and peripheral nervous systems). The level of antibody to cerebroside correlated best with the number of injections of vaccine, but like antibody to myelin basic protein, the antibody to cerebroside was present in the cerebrospinal fluid of patients with major complications. Some patients with major complications also had antibodies directed to the gangliosides GD1b and GT1b. No antibodies to myelin-associated glycoprotein were detected in any of the samples. These data implicate myelin basic protein as an encephalitogen in these autoimmune diseases of the human nervous system, but suggest that immune responses to cerebroside and certain gangliosides may have an augmentative role in severe disease.

Autoantibodies↗
PubMed1987

Restoration of u.v.-induced excision repair in Xeroderma D cells transfected with the denV gene of bacteriophage T4.

The heritable DNA repair defect in human Xeroderma D cells, which results in failure to incise at u.v. light-induced pyrimidine dimers, has been partially but stably corrected by transfection of immortalised cells with the denV pyrimidine dimer glycosylase gene of bacteriophage T4. Transfectants selected either for a dominant marker on the mammalian vector carrying the prokaryotic gene or for the dominant marker plus resistance to killing by u.v. light, have been shown to express the denV gene to varying degrees. denV expression results in significant phenotypic change in the initially repair-deficient, u.v.-hypersensitive cells. Increased resistance to u.v. light and more rapid recovery of replicative DNA synthesis following u.v. irradiation have been correlated both with improved repair DNA synthesis and with a novel dimer incision capability present in denV transfected Xeroderma cells but not as evident in transfected normal cells. Most of the transfectants contain a single integrated copy of the denV gene; increase in denV copy number does not result in either increased gene expression or enhanced survival to u.v. light. These results show that expression of a heterologous prokaryotic repair gene can partially compensate for the genetic defect in a human Xeroderma D cell.

Cell Line↗
PubMed1987

Scanning electron microscope analysis of structural changes and aberrations in human chromosomes associated with the inhibition and reversal of inhibition of ultraviolet light induced DNA repair.

Metaphase chromosomes appear decondensed in preparations from mitotic cells that have been irradiated with ultraviolet light (UV) and incubated with inhibitors of DNA synthesis; under these conditions DNA repair is inhibited and both single and double strand DNA breaks accumulate. After reversal of the inhibition chromosomes are condensed, but are often damaged. In this paper we show by scanning electron microscopy (SEM) that decondensed HeLa chromosomes are composed of fibre clusters similar to those previously described for the large chromosomes of the Indian muntjac. This suggests that the clusters may be a universal higher order packing unit in mammalian metaphase chromosomes. We also examine by SEM the nature of the aberrations that appear after the reversal of periods of inhibited repair; these include gaps, breaks, deletions and telomeric packing abnormalities. SEM analysis allows an extension and reconsideration of conclusions about chromatid continuity based on the study of conventional light microscope (LM) preparations.

Chromosome Aberrations↗
PubMed1987

The pathogenesis of Japanese encephalitis virus in Culex tritaeniorhynchus mosquitoes.

Culex tritaeniorhynchus were inoculated intrathoracically with mosquito and human strains of Japanese encephalitis virus and maintained at 26 degrees C or 32 degrees C. Virus titration and localization of viral antigen by avidin-biotin immunoperoxidase staining were done at intervals up to 21 days. Marked differences were noted in the tempo of organ involvement at the 2 temperatures; at both there was initial infection of fat body cells followed by selective infection of the central nervous system (CNS), with consistent infection of cells of the compound eye, patchy involvement of cephalic, thoracic and abdominal ganglia and no infection of Johnston's organ. CNS infection was always present 4 days after infection, when salivary gland involvement was first seen at 32 degrees C; at 26 degrees C CNS infection preceded salivary gland infection by 2 weeks. Late involvement of gut cells, pericardial cells and oviducts was also found, with no involvement of muscle.

Animals↗