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Biomedical subjects

K Kristensson

Publications and source records attributed to K Kristensson.

At least 55 records · Page 3Linked to original sources
PubMed1998

Endothelial cells expressing an inflammatory phenotype are lysed by superantigen-targeted cytotoxic T cells.

The objective of this study was to investigate whether the superantigen staphylococcal enterotoxin A (SEA), which binds to HLA class II and T-cell receptor Vbeta chains, can direct cytotoxic T cells to lyse cytokine-stimulated endothelial cells (EC). In addition, we wanted to determine whether SEA-primed cytotoxic T cells could be targeted to EC surface molecules as a means of a novel cancer immunotherapy. Human umbilical vein EC (HUVEC), dermal microvascular EC (HMVEC), or the EC line EA.hy926 stimulated with gamma interferon (IFN-gamma) or tumor necrosis factor alpha (TNF-alpha) displayed upregulated HLA class II and adhesion molecule (CD54 and CD106) expression, respectively. SEA-primed T cells induced a strong cytotoxicity against IFN-gamma- and TNF-alpha-activated EA.hy926 which had been preincubated with SEA. Blocking of CD54 completely abrogated the T-cell attack. SEA-D227A, which has a mutated class II binding site, did not promote any cytotoxicity. A strong lysis was observed when a fusion protein consisting of protein A and SEA-D227A was added together with T cells to TNF-alpha-induced EA.hy926 and HUVEC precoated with monoclonal antibodies (MAb) directed against HLA class I, CD54, or CD106 molecules. Finally, an scFv antibody fragment reactive with an unknown EC antigen was fused with SEA-D227A. Both EA.hy926 and HMVEC were efficiently lysed by scFv-SEA-D227A-triggered cytotoxic T cells. Taken together, superantigen-activated T-cell-dependent EC killing was induced when EC expressed an inflammatory phenotype. Moreover, specific MAb targeting of the superantigen to surface antigens induced EC lysis. Our data suggest that directed T-cell-mediated lysis of unwanted proliferating EC, such as those in the tumor microvasculature, can be clinically useful.

Animals↗
PubMed1998

Specific interactions between retrovirus Env and Gag proteins in rat neurons.

In this work we have studied the intracellular localization properties of the Gag and Env proteins of Moloney murine leukemia virus (MLV) and human immunodeficiency virus (HIV) in dorsal root ganglion (DRG) neurons of rat. These neurons form thick bundles of axons, which facilitates protein localization studies by immunofluorescence analyses. When such neuron cultures were infected with recombinant Semliki Forest virus particles carrying the gag genes of either retrovirus, the expressed Gag proteins were localized to both the somatic and the axonal regions of the DRG neurons. In contrast, the Env proteins were confined only to the somatic region. When the Gag and Env proteins were coexpressed, the Gag proteins were also excluded from the axons. This effect of the Env proteins was shown to be dependent on the concentration of the Gag proteins in the neuron and also to be specific for homologous pairs of retrovirus proteins. Therefore, the results suggest that there are specific interactions between the Env and the Gag proteins of MLV and HIV in the DRG neurons.

Animals↗
PubMed1997

The gene for a T lymphocyte triggering factor from African trypanosomes.

An early and essential event in the protective immune response against most viruses and protozoa is the production of interferon-gamma (IFN-gamma). In contrast, during infection with African trypanosomes, protozoan parasites that cause human sleeping sickness, the increased levels of IFN-gamma do not correlate with a protective response. We showed previously that African trypanosomes express a protein called T lymphocyte triggering factor (TLTF), which triggers CD8(+) T lymphocytes to proliferate and to secrete IFN-gamma. Here, we isolate the gene for TLTF and demonstrate that the recombinant version of TLTF specifically induces CD8(+), but not CD4(+), T cells to secrete IFN-gamma. Studies with TLTF fused to the green fluorescent protein show that TLTF is localized to small vesicles that are found primarily at or near the flagellar pocket, the site of secretion in trypanosomes. TLTF is likely to be only the first example of a class of proteins that we designate as trypanokines, i.e., factors secreted by trypanosomes that modulate the cytokine network of the host immune system for the benefit of the parasite.

Amino Acid Sequence↗
PubMed1997

Interferon-gamma receptors in nociceptive pathways: role in neuropathic pain-related behaviour.

Interferon-gamma receptor (IFN-gamma R) immunoreactivity was observed in the superficial dorsal horn and lateral spinal nucleus in rat and mouse spinal cord. Dorsal rhizotomies did not reduce immunoreactivity in the rat. IFN-gamma R distribution overlapped with nitric oxide synthase-1 immunoreactivity. In wild-type mice, intrathecal injections of mouse IFN-gamma evoked biting behaviour, whereas mice with disruption of the functional gene for IFN-gamma R did not respond. Both types of mice had similar withdrawal thresholds to mechanical stimulation and reacted similarly to foot-pad carrageenan injections. In contrast to wild-type mice, IFN-gamma R knock-out mice did not show autotomy after sciatic nerve section. This study demonstrates a functional IFN-gamma R in spinal nociceptive pathways related to neuropathic pain.

Animals↗
PubMed1997

Spread of measles virus through axonal pathways into limbic structures in the brain of TAP1 -/- mice.

The spread of measles virus into the brain was studied exploiting the olfactory pathway, which represents an important route of neuroinvasion by viruses. The virus was injected into the main olfactory bulb of wild-type mice and mice with disrupted TAP1 gene (TAP refers to the Transporter associated with Antigen Presentation), which codes for products essential for the cell-mediated immune response. Virus invasion was monitored for 4 weeks by immunohistochemistry. The distribution of measles virus was found to be restricted to brain areas connected with the olfactory bulbs. However, in the wild-type mice there was a marked infiltration of lymphocytes in the infected brain structures, and the virus did not pass beyond the piriform cortex. In the TAP1 -/- mice the virus spread more extensively along olfactory projections into the limbic system and monoaminergic brainstem neurons. Infected mice of both types developed seizures, which may have been focally evoked from the piriform cortex. This study provides evidence that measles virus can spread through axonal pathways in the brain. The findings obtained in the gene-manipulated mice point out that a compromised immune state of the host may potentiate targeting of virus to the limbic system through olfactory projections.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Age-dependent induction of nitric oxide synthase activity in facial motoneurons after axotomy.

The facial nerve was transected in rats at different postnatal ages, from birth to early adulthood. NADPH-diaphorase histochemistry was performed to analyze the induction of nitric oxide synthase, the synthetic enzyme of the free radical nitric oxide, in injured facial motoneurons. In addition, in situ nick-end labeling of DNA fragmentation (TUNEL technique) was performed after axotomy at birth, to verify the occurrence of apoptosis in the damaged facial motoneurons. A striking age-dependency was found in the induction of nitric oxide synthase activity in axotomized facial motoneurons. NADPH-diaphorase positivity was not detectable in these neurons 1 and 2 days after axotomy at birth, when apoptotic changes were evident and marked. In addition, NADPH-diaphorase staining was hardly detectable in the facial nucleus 4 days after axotomies at birth, when extensive motoneuron loss was evident. NADPH-diaphorase positivity was instead induced in the facial motoneurons axotomized from the end of the first postnatal week to adulthood, when the nerve cell loss was less severe than in newborns. However, the time course of the enzyme activity induction varied considerably in relation to the animals' age. These findings are discussed in relation to the role of nitric oxide in motoneuron death or protective response to injury and of oxidative stress in neurodegeneration.

Age Factors↗
PubMed1997

Interferon-gamma alters nerve-induced redistribution of acetylcholine receptors in cultured rat skeletal muscle cells.

The influence of recombinant interferon-gamma (rIFN-gamma) on the development of acetylcholine receptor (AChR) aggregates in cocultures of rat embryonic muscle cells and spinal cord neurons was studied by counting the number of AChR aggregates in relation to cholinergic nerve fibers coming to the muscle fibers. rIFN-gamma caused no decrease in the number of cholinergic nerve fibers, but inhibited the increase in the number of AChR aggregates that occurs early during cocultivation and is an early sign in the development of neuromuscular junctions. rIFN-gamma stimulated release of nitric oxide, but no effects on aggregation of AChRs occurred after exposure to a nitric oxide synthase inhibitor, L-NG-monomethylarginine, or by the addition of nitroprusside, a generator of nitric oxide. No effect was seen on the number of AChR aggregates when the cultures were exposed to rIFN-gamma at later time points of cocultivation, when the increase in number of AChRs had already occurred. These studies indicate that the key immunoregulatory cytokine IFN-gamma can cause alterations in the early process of synapse formation and that these effects are independent of the nitric oxide release caused by the cytokine.

Animals↗
PubMed1997

Measles virus in the brain.

Measles virus can give three different forms of infections in the central nervous system. These are acute postinfectious encephalitis, acute progressive infectious encephalitis, and subacute sclerosing panencephalitis (SSPE). The postinfectious acute disease is interpreted to reflect an autoimmune reaction. The acute progressive form of brain disease, also referred to as inclusion body encephalitis, reflects a direct attack by the virus under conditions of yielding cellmediated immunity. The late progressive form of encephalitis (SSPE) has been extensively analyzed. Recent molecular genetic studies have unravelled a range of mechanisms by which a defective expression of either the matrix, the fusion, or the hemagglutinin proteins may lead to viral persistence in brain cells under conditions not allowing identification by immune surveillance mechanisms. Many aspects of virus-cell interactions have been examined by use of explant cultures of neuronal cells of human and animal origin. Some of the findings are reviewed. Experimental animals, in particular rodents, have been used to establish systems in which phenomena, pivotal to the evolution of acute as well as persistent measles virus infections in the brain, can be studied. A wide range of potentially important mechanisms has been highlighted and is discussed. More recently, mice with genetic defects in immune functions were used to evaluate consequences as to initiation and dissemination of virus infection in the brain.

Animals↗
PubMed1997

Neurobiology of cerebral malaria and African sleeping sickness.

This review is aimed at emphasizing the need for basic neuroscience research on two tropical diseases, malaria and sleeping sickness (African trypanosomiasis), that still represent major health problems and in which severe involvement of the nervous system is frequently the direct cause of death. The life cycles of the two parasites, the protozoan Plasmodium and Trypanosoma brucei, which are the causative agents of malaria and sleeping sickness, respectively, are briefly reviewed. The historical contribution to the pathogenesis and therapy of malaria by a renowned pioneer in neuroscience, Camillo Golgi, is pointed out. The different strategies for survival in the host by the intracellular Plasmodium and the extracellular African trypanosomes are summarized; such strategies include sites favorable for hiding or replication of the parasites in the host, antigenic variation, and interactions with the cytokine network of the host. In particular, tumor necrosis factor-alpha and interferon-gamma may play a role in these infections. The parasites may paradoxically interact with cytokines to their benefit. However, cytokine receptors are expressed on neuronal subsets sensitive to cytokine action, and stimulation of these subsets may cause neuronal dysfunctions during the infections. Finally, the clinical symptoms of cerebral malaria and African trypanosomiasis and research aiming at deciphering their pathogenetic mechanisms that could affect the nervous system at a molecular level are described. The need for neuroscientists in this endeavor is emphasized.

Animals↗
PubMed1997

Distinct effects of clostridial toxins on activity-dependent modulation of autaptic responses in cultured hippocampal neurons.

Clostridial neurotoxins proteolyse specific proteins implicated in synaptic vesicle exocytosis, but their actions on the release machinery in functional synapses is not well understood. Here we examine the effects of botulinum toxin A (BoNT/A) and tetanus toxin (TeTx) on autaptic transmission in cultured rat hippocampal neurons using whole-cell voltage clamp recordings. The proportion of cells responding to stimulation with an excitatory postsynaptic current (EPSC) and the magnitude of the remaining responses decreased gradually with increasing concentration of either toxin. However, the activity-dependent modulation (5 Hz repetitive stimulation) of EPSCs remaining after toxin inhibition differed markedly between the two toxins. The TeTx inhibition was associated with a persistent activity-dependent depression similar to that in control cells. In contrast, the BoNT/A inhibition was accompanied by a reversal of the modulation into facilitation, resembling that induced by lowering of the calcium concentration. These results demonstrate a difference between BoNT/A and TeTx in their mode of inhibition of synaptic vesicle exocytosis, which suggests that they exert their preferential actions at distinct steps of the release process.

Animals↗
PubMed1997

Reduction of voltage-dependent calcium currents in mumps virus-infected cultures of rat hippocampal neurons.

The effects of a mumps virus infection on functional properties of embryonic hippocampal neurons in culture were analysed with special emphasis on voltage-dependent Ca2+ channels. Cultures with higher or lower density of glial cells (not treated or treated with mitotic inhibitor, respectively) were infected with the relatively non-cytolytic RW strain of mumps virus and currents were recorded from neurons using whole cell voltage clamp. More than 65% of neurons and glial cells contained viral antigens 1-2 days post infection (p.i.). Glial cells remained infected 6-7 days p.i., while the ratio of infected versus uninfected neurons, especially in cultures with higher glial cell density, was reduced. In both infected and uninfected cultures the somal voltage-dependent Ca2+ currents were stronger in cultures with a higher glial cell density, which indicates that these currents are influenced by glial cells. Introduction of the virus into cultures caused a selective decrease in inward Ca2+ currents, which was most marked at days 6-7 p.i., and which included both infected and unifected neurons. Spontaneous synaptic currents and other ion channel conductances appeared normal in the infected cultures. Dantrolene, which inhibits release of Ca2+ from intracellular stores, decreased the neurons that died during the infection. Taken together the results show that a mumps viral infection can selectively alter the number of function of somal voltage dependent Ca2+ channels in immature hippocampal neurons and that this may reflect a disturbed glia-nerve cell interaction.

Action Potentials↗
PubMed1996

Control of parasitemia and survival during Trypanosoma brucei brucei infection is related to strain-dependent ability to produce IL-4.

We studied non-MHC gene-dependent expression of a number of cytokines in relation to host defense and survival during Trypanosoma brucei brucei (Tbb) infection in mice. In particular, the role of IL-4 was explored with use of genomically IL-4-disrupted mice and in vivo Ab blocking. Splenocytes from MHC-identical B10.Q (relatively resistant) mice showed day 5 postinfection higher numbers of IL-4 mRNA expressing cells than C3H.Q (highly susceptible). A trypanosome-derived lymphocyte triggering factor, which is released by Tbb to polyclonally activate CD8+ T cells, stimulated naive splenocytes in vitro to a higher IL-4 response in B10.Q than in C3H.Q mice. The C3H.Q mice developed an extremely high parasitemia, showed a low Ab response against the variant surface glycoprotein (VSG), and had a mean survival time of 42 days. Conversely, B10.Q mice had lower parasitemia, mounted higher anti-VSG response, and had a mean survival time of 56 days. Deletion of the IL-4 gene had no influence on the infection in C3H.Q mice, while in B10.Q mice the deletion was associated with lower anti-VSG Ab levels and higher parasitemia. Paradoxically, B10.Q mice with disrupted IL-4 gene survived longer than the wild type. Anti-IL-4 Ab-blocking experiments in vivo displayed an enhanced parasitemia and prolonged survival in infected B10.Q mice. We conclude that 1) a non-MHC gene-related and CD8+-dependent ability to produce IL-4 partly determines the susceptibility to Tbb infection; and 2) IL-4, although involved in controlling the levels of parasitemia by its effects on immunoglobulin synthesis, also can have toxic effects on the animals.

Animals↗
PubMed1996

A combinatorial library strategy for the rapid humanization of anticarcinoma BR96 Fab.

We have used a combinatorial mutagenesis strategy to humanize BR96, a monoclonal antibody that binds to the Lewis Y class of tumor antigens. This approach allows simultaneous assessment of hundreds of humanized variable regions to identify the molecules that best preserve affinity, thus overcoming the major drawback of current humanization procedures, the requirement to construct and analyze each humanized antibody separately. Murine residues of BR96 were mutated to human if they were solvent-exposed residues that did not participate in the formation of the antigen binding site and were not at the interface of the light and heavy chain. At positions that might be involved in binding to antigen, the choice between the murine and human residue was more difficult. Murine and human alternatives were incorporated into a combinatorial library at positions representing buried residues that might affect the structural integrity of the antigen binding site. By encoding this library of humanized BR96 Fabs in an M13 phage vector, we rapidly identified several candidates with nearly identical antigen binding, within 2-fold, of the chimeric Fab. Additional mutagenesis directed at sites suggested in the literature as potentially important for antigen binding in a similar anti-Lewis Y antibody yielded no further improvements.

Amino Acid Sequence↗
PubMed1996

Human and rodent interferon-gamma as a growth factor for Trypanosoma brucei.

An example for the bidirectional exchange of activating signals between a pathogen and immunocompetent cells in the host is presented. Trypanosoma brucei, which include subspecies that cause African sleeping sickness, secrete a molecule that triggers lymphocytes to produce interferon (IFN)-gamma. We now report that proliferation of T. brucei is stimulated in axenic cultures by IFN-gamma. The growth-enhancing effect on the pathogen is inhibited by anti-IFN-gamma receptor (R) antibodies and does not occur after exposure to other cytokines, i.e. IFN-alpha, IFN-beta and tumor necrosis factor (TNF)-alpha. While rodent-pathogenic T. brucei strains are stimulated by rat IFN-gamma, human pathogenic strains are more potently stimulated by human IFN-gamma. Rat and human IFN-gamma can partially block each others effects. Mice with disrupted IFN-gamma genes have reduced parasitemia and prolonged survival, while the outcome is reversed in mice that lack the IFN-gamma R gene.

Animals↗
PubMed1996

Different trypanozoan species possess CD8 dependent lymphocyte triggering factor-like activity.

Trypanosoma brucei brucei (T. b. brucei) release a molecule, trypanosome derived lymphocyte triggering factor (TLTF), which stimulates CD8+ cells to produce cytokines and to proliferate. We now report that T. evansi, T.b. gambiense and T.b. rhodesiense also contain factor(s) with similar activity. Thus, homogenates from these parasite taxa triggered mouse or rat lymphoid tissue of mononuclear cells (MNC) to produce interferon gamma (IFN-gamma) and to proliferate. These responses were dependent on CD8 since the activity was blocked by (a) anti CD8 antibodies, (b) occurred in CD8+ but not in CD8- mice and (c) was recorded in human CD8+ but not in CD4+ enriched peripheral blood mononuclear cells (PBL). The presence of TLTF or TLTF-like molecules in the trypanozoan species was also examined by T.b. brucei directed anti-TLTF Mabs using two Mabs with inhibitory activity and one with stimulatory activity. The lymphocyte triggering activity of T.b. gambiense and T.b. rhodesiense, but not T. evansi, was affected by the anti-TLTF Mabs. We conclude that T. evansi, T.b. rhodesiense and T.b. gambiense similar to T.b. brucei, all possess molecule(s) which CD8 dependently trigger lymphocytes. The latter three, related parasite taxa, share TLTF antibody binding epitopes.

Animals↗
PubMed1996

Melatonin and its new agonist S-20098 restore synchronized sleep fragmented by experimental trypanosome infection in the rat.

The experimental infection with the parasite Trypanosoma brucei in the rat provides a unique model of dysfunction of the sleep regulatory mechanisms, because the length of synchronized sleep episodes is selectively and dramatically reduced in the advanced stages of the disease. In the present study, melatonin was acutely administered (3 mg/kg SC) to trypanosome-infected rats, before the sleep onset. This treatment resulted in a significant increase of the length of synchronized sleep episodes in respect to the infected animals and to those that had received only the vehicle. Thus, melatonin restored a normal sleep pattern during the infection. Similar findings were obtained with the new melatonin agonist S-20098. The sleep parameters were not significantly modified by either melatonin or S-20098 acute administration to noninfected animals. These findings indicate that exogenous melatonin and S-20098 exert a selective regulatory action on sleep fragmentation during experimental trypanosomiasis.

Acetamides↗