Biomedical subjects

K Kristensson

Publications and source records attributed to K Kristensson.

At least 91 records · Page 5Linked to original sources

PubMed1994

Trypanosoma brucei and the nervous system.

African sleeping sickness, characterized by a peculiar pain syndrome and prominent neuropsychiatric symptoms, is caused by the parasite Trypanosoma brucei (T.b.). In experimental T.b. infections, a molecule released from the trypanosomes has been isolated that binds to the CD8 molecule of T cells, whereby T cells are activated to secrete interferon gamma. This cytokine binds to the parasites and triggers them to proliferate, establishing a peculiar bidirectional activating signal system. The hypothesis is presented that the molecules involved in these bidirectional signals might also interact with neurons, thus causing brain dysfunctions. Studies on the molecular interactions between parasites and the nervous system in sleeping sickness might reveal basic mechanisms underlying other neuropsychiatric diseases.

Animals↗

PubMed1994

Isoprenoids in aging and neurodegeneration.

During aging the human brain shows a progressive increase in levels of dolichol, a reduction in levels of ubiquinone, but relatively unchanged concentrations of cholesterol and dolichyl phosphate. In a neurodegenerative disease, Alzheimer's disease, the situation is reversed with decreased levels of dolichol and increased levels of ubiquinone. The concentrations of dolichyl phosphate are also increased, while cholesterol remains unchanged. This study shows that the isoprenoid changes in Alzheimer's disease differ from those occurring during normal aging and that this disease cannot, therefore, be regarded as a result of premature aging. The increase in the sugar carrier dolichyl phosphate may reflect an increased rate of glycosylation in the diseased brain and the increase in the endogenous anti-oxidant ubiquinone an attempt to protect the brain from oxidative stress, for instance induced by lipid peroxidation.

Adult↗

PubMed1994

Ubiquinone-10 protects neurons from virus-induced degeneration.

Cultured neurons from rat dorsal root ganglia and cerebral cortex were infected with Sendai virus, which gives a productive replication with lysis of most neurons, and with the RW strain of mumps virus, which undergoes defective replication causing degeneration of only 30-40% of the neurons within 5 days after initial infection. In Sendai virus-infected cells the amount of polyisoprenoid lipids was enhanced. In mumps virus-infected cultures there were transient reductions in the contents of cholesterol, dolichol, and ubiquinone-9 in the cultures, whereas the reduction in the ubiquinone-10 level was progressive, reaching 20% of its original value 21 days after infection. Treatment of mumps virus-infected cultures with ubiquinone-10 protected the neurons from degeneration, whereas no effects were observed on exposure to ubiquinone-9. Linolenic acid (18:3) and arachidonic acid (20:4), but not myristic acid (14:0) and palmitic acid (16:0), also had significant neuroprotective effects.

Animals↗

PubMed1994

Rotavirus causes selective vimentin reorganization in monkey kidney CV-1 cells.

The effect of rotavirus infection on cytoskeletal organization was examined in cultured African green monkey kidney (CV-1) cells. Rhesus rotavirus caused significant and selective changes in the organization of the vimentin filament network without having any effect on microtubules or actin. Double-immunofluorescence studies showed that at 6 h post-infection, and in the absence of cytopathic effect, the normal arrays of vimentin fibres radiating from multiple sites around the nucleus were lost. Vimentin fibres became irregularly distributed in the cytoplasm and were totally disrupted in the later stages of infection. Vimentin reorganization occurred independent of extracellular Ca2+ levels.

Actin Cytoskeleton↗

PubMed1994

Human Th0-type T helper-cell clone supports antigen-specific immunoglobulin production in scid/beige-hu mice.

Tetanus toxoid-specific T cells have been generated from human splenic lymphocytes by an initial 6-day stimulation period with antigen, followed by a proliferation period with recombinant IL-2 and human feeder cells. Proliferating T cells were subsequently cloned by limiting dilution. A human T-cell clone that was functionally characterized showed: (i) a specific proliferative response to tetanus toxoid in the presence of autologous Epstein-Barr virus (EBV)-transformed lymphoblastoid cells; (ii) a phenotype characteristic for the helper/inducer CD4+/CD8-/CD450R0+ T cells, and (iii) a lymphokine profile, as determined by mRNA analysis, representative of Th0-like human CD4+ T helper cells. This tetanus toxoid-specific T-cell clone which showed antigen-dependent helper activity for antibody production by autologous B cells in vitro could also provide T-cell help to antigen-specific human B cells transplanted into severe combined immunodeficiency (scid/beige) mice.

Aged↗

PubMed1994

A new approach for the pathogenesis of human African trypanosomiasis.

From Trypanosoma brucei brucei, a molecule has been isolated which triggers the production of IFN-gamma by CD8+ T-cells. IFN-gamma modulates events in the hosts immune- and nervous system and provides a growth stimulus for the parasites. Furthermore, a molecule with IFN-gamma-like immunoreactivity has been detected in rat dorsal root ganglion cells and certain neurons in the brain. This neuron-derived IFN-gamma-like molecule differs in molecular weight from lymphocyte-derived IFN-gamma but shares important biological activities with the latter, which includes a growth stimulus for trypanosomes. Trypanosomes localized to sensory ganglia and infected rats develop a severe thermal hyperalgesia. Intrathecal injection of IFN-gamma causes in rats a sustained phase of nociceptive flexor reflex facilitation, which can be partially blocked by nitro-L-arginin-ester, an inhibitor of nitric oxide synthase, indicating that nociceptive effects of the IFN-gamma is mediated by activation of the L-arginin-nitric oxide pathway.

Animals↗

PubMed1994

Sleep and timekeeping changes, and dysregulation of the biological clock in experimental trypanosomiasis.

The rest-activity and body temperature 24 hours cycles, as well as the pattern of spontaneous sleep, were investigated in rats after infection with Trypanosoma brucei brucei. In the infected rats, which were entrained to a 12 hours/12 hours photoperiod, a considerable hypokinesia was detected during the hours of darkness. In most of the infected animals, the body temperature cycle displayed a lower amplitude and an advance of about 3 hours in respect to control rats; in addition, the body temperature rhythm was not significant in some infected rats. The relative proportion of slow wave synchronized sleep, as well as the rapid-eye movement (REM) latency, were significantly reduced in the infected animals, in which sleep was considerably fragmented. The induction of Fos (the protein encoded by the immediate early gene c-fos), in response to light stimulation during the early subjective night, was severely impaired in the hypothalamic suprachiasmatic nuclei in trypanosome-infected rats. Altogether these data point out a disruption of locomotor activity and body temperature 24 hours cycle and a major disorganization of sleep during experimental trypanosomiasis. In addition, our findings indicate that the molecular and functional correlates of the synchronizing action of the suprachiasmatic nuclei, which play a major role of biological clock of endogenous biological rhythms, could be altered during trypanosome infection.

Animals↗

PubMed1994

Antigen-specific human immunoglobulin production in SCID mice transplanted with human peripheral lymphocytes is dependent on CD4+ CD45RO+ T cells.

Severe combined immunodeficient (SCID) mice, lacking mature T and B cells and virtually devoid of endogenous serum immunoglobulins, spontaneously produce large amounts of human immunoglobulin after transplantation with human peripheral blood lymphocytes (PBL). Moreover, after immunization with antigen an active immune response resulting in a production of specific antibodies can be induced. Here we report that human T cells must be co-transplanted with B cells into the SCID mice for immunoglobulin production to occur. Resting human B cells could be activated to immunoglobulin production in the absence of human monocytes and a specific antibody response to tetanus toxoid (TT) could be induced, suggesting that the human B cells could present antigen to T cells in the SCID environment. Production of human immunoglobulins, as well as specific antibodies, was obtained only if CD4+ T cells of the memory phenotype, i.e. expressing CD45RO, were present. No human immunoglobulin, either of IgM or of IgG isotype, was found in SCID sera if mice were co-transplanted with human B cells and CD45RA expressing CD4+ T cells. However, FACS analysis revealed that the transplanted CD45RA+ cells became activated and differentiated towards CD45RO+ cells within 1-2 weeks. These cells also gained the lymphokine gene expression pattern associated with CD45RO+ cells, as demonstrated by polymerase chain reaction (PCR) analysis, and could support immunoglobulin production in SCID mice transplanted with fresh B cells. In fact, after differentiation of CD4+ CD45RA+ T cells towards expression of CD45RO, either in vivo in the SCID mouse or in vitro, these cells could interact with and activate human B cells to immunoglobulin production. Furthermore, in vitro activated and differentiated CD4+ CD45RA+ T cells from vaccinated donors were also able to support production of TT-specific antibodies provided the antigen was administered.

Animals↗

PubMed1993

Microtubule-associated protein 2 appears in axons of cultured dorsal root ganglia and spinal cord neurons after rotavirus infection.

The immunohistochemical distribution of microtubule-associated protein 2 (MAP2), being normally restricted to nerve cell bodies and dendrites, became altered in rat dorsal root ganglia and spinal cord neurons in cultures infected with rhesus rotavirus. MAP2 appeared in axons of both sources of neurons as displayed with monoclonal antibodies to MAP2a + b and MAP2a + b + c at 48 hr post-infection (p.i.). Other cytoskeletal elements, i.e., tau, MAP1, MAP5, neurofilament, actin, and tubulin, did not reveal any alterations in the rotavirus-infected neurons. One of the rotavirus cytosolic proteins, the inner capsid protein vp6, was expressed in axons at 48 hr p.i. simultaneously with the appearance of MAP2, while two other viral proteins, vp4 and NS28, remained in the nerve cell bodies. By quantitative enzyme-linked immunosorbent assay (ELISA) a binding of single-shelled rotaviruses, which express vp6 on their surfaces, to purified MAP2 was found. There was no binding of these viral particles to tau or tubulin proteins. This study indicates that a selective interaction between certain viral and neuronal cytoskeletal proteins can occur and that a non-cytolytic viral infection can cause alterations in the polarized sorting of neuronal proteins.

Animals↗

PubMed1993

Measles virus-induced hippocampal neurodegeneration in the mouse: a novel, subacute model for testing neuroprotective agents.

The hamster neurotropic (HNT) strain of measles virus causes non-inflammatory encephalopathy in Balb/c mice, associated with neurodegeneration in hippocampal CA1 and CA3 regions. This loss of pyramidal cells can be prevented by twice daily systemic treatment with 1 mg/kg dizocilpine (5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclo-hepten-5,10-imine maleate; MK-801) for 7 days. By varying the MK-801 treatment protocol, we now found that drug administration during the last 4 days prior to sacrifice (i.e. days 4-7 post inoculation, p.i.) is essential for neuroprotection. In contrast, MK-801 treatment during the first days (days 0-4 p.i.) did not prevent the neuronal necrosis. These data suggest that the concentration of an excitotoxic factor in the mouse brain increases after virus inoculation, reaching toxic levels by days 4-5 p.i. This novel 'subacute' mouse model of neurodegeneration therefore constitutes an attractive tool for mechanistic and interventional studies in excitotoxicity research.

Animals↗

PubMed1993

CD8 is critically involved in lymphocyte activation by a T. brucei brucei-released molecule.

T. brucei brucei released a lymphocyte triggering factor (TLTF), which triggered purified CD8+, but not CD4+, T cells to interferon gamma (IFN-gamma) mRNA expression and secretion and to [3H]thymidine incorporation. TLTF also induced mRNA for transforming growth factor beta, but not for interleukin-4. The action of this TLTF on mononuclear cell (MNC) cultures was blocked by anti-CD8 antibodies and by soluble CD8. MNCs from a mutant mouse strain lacking CD8 expression were not triggered by TLTF. IFN-gamma provides a growth stimulus for T. brucei brucei, and infected CD8- mice had much lower parasitemia and survived longer than CD8+ mice. The host-parasite interaction in experimental African trypanosomiasis thus involves parasite release of TLTF, which by binding to CD8 triggers CD8+ cells to produce the parasite growth-promoting cytokine IFN-gamma.

Animals↗

PubMed1993

T cell activation by a Trypanosoma brucei brucei-derived lymphocyte triggering factor is dependent on tyrosine protein kinases but not on protein kinase C and A.

Trypanosoma brucei brucei releases a lymphocyte-triggering factor (TLTF) that activates CD8+ T cells. We here study second messenger mechanisms in this activation, i.e. the effects of protein kinase C (PKC), protein kinase A (PKA) and tyrosine kinases (TPK) inhibitors on TLTF-induced interferon-gamma (IFN-gamma) secretion and proliferation in lymphoid cell cultures. The effects were compared to those obtained by phytohemagglutinin (PHA) stimulation. Rat spleen mononuclear cells (MNC) and spleen MNC from a mutant mouse strain possessing CD8+ T cells but lacking CD4+ T cells were used as responder cells. Although both the PKC and the PKA inhibitors suppressed PHA-induced IFN-gamma secretion and proliferation of rat MNC and mouse CD8+ CD4- MNC, they had no effect on the same TLTF-induced responses. The TPK inhibitor genistein, however, strongly suppressed TLTF-induced activation of both types of responder cells to IFN-gamma secretion and the TLTF-induced proliferation of mouse CD8+ CD4- MNC. The suppressive effects of the drugs could be overcome by ionomycin and tetradecanoylphorbol acetate, which show that the effects were not due to drug nonspecific cellular toxicity of the drugs. We conclude that TLTF activates CD8+ T cells through pathways other than the PKC- or PKA-dependent signal transduction, and that TPK may be involved in the triggering.

Animals↗

PubMed1993

The endoplasmic reticulum-associated VP7 of rotavirus is targeted to axons and dendrites in polarized neurons.

Rotavirus, which matures and is retained in the endoplasmic reticulum, was used to examine how polarized dorsal root ganglion and spinal cord neurons distributed cytoplasmic and endoplasmic reticulum-associated proteins. A remarkable observation was that NS28, a trans-endoplasmic reticulum-membrane protein which functions as a receptor for budding particles, remained in the cell body during the whole course of infection (48 h) while the VP7 glycoprotein, which is endoplasmic reticulum associated and usually retained in the endoplasmic reticulum, was targeted to axons already 4 h post infection. VP7 was furthermore transported in an endo-beta-N-acetylglucosaminidase H sensitive form through the secretory pathway. The segregated appearances of NS28 and the endo-beta-N-acetylglucosaminidase H sensitive VP7 indicate that VP7 enters a transport compartment separate from NS28. Brefeldin A treatment rapidly disintegrated the Golgi apparatus of the neurons and rapidly blocked axonal transport of Sendai virus glycoproteins, while axonal transport of rotavirus VP7 was not blocked, suggesting that VP7 uses an intracellular pathway in neurons which does not involve the Golgi apparatus.

Animals↗

PubMed1993

Interferon-gamma promotes proliferation of rat skeletal muscle cells in vitro and alters their AChR distribution.

Recombinant interferon-gamma (IFN-gamma) caused a dose-dependent increase in the proliferation of myoblasts in cultures of rat skeletal muscles as determined by bromodeoxyuridine incorporation. As a result of this proliferation the number of myotubes increased in the cultures, while the fusion index was unchanged. In myotubes exposed to IFN-gamma there was a change in the distribution of nicotinic acetylcholine receptors (nAChR) as detected by binding of FITC-conjugated alpha-bungarotoxin with a significant decrease in the number of linear aggregates and an increase in diffusely distributed receptors.

Acetylcholinesterase↗

PubMed1993

Mumps virus alters aggregation of acetylcholine receptors in cultured rat skeletal muscle cells.

Cultured myoblasts, but not myotubes, from rat skeletal muscles were infected with the RW strain of mumps virus. Such myoblasts then fused to form myotubes containing viral antigen. The infected myotubes showed a significant decrease in the number of dorsal, linear acetylcholine receptor (AChR) aggregates as determined by FITC-conjugated alfa-bungarotoxin. Infected myotubes co-cultivated with spinal cord cells showed no increase in the number of dorsal, linear AChR aggregates, compared to normal, uninfected myotubes. In addition, an increased proliferation of the myoblasts, which remained uninfected in the infected cultures, was noted. This may indicate a release of a growth stimulating factor from the virus containing cells. This study shows that mumps virus infection can lead to an altered receptor organization in a morphologically preserved cell.

Animals↗

PubMed1993

A Trypanosoma brucei brucei-derived factor that triggers CD8+ lymphocytes to interferon-gamma secretion: purification, characterization and protective effects in vivo by treatment with a monoclonal antibody against the factor.

A protein factor that stimulates CD8+ lymphocytes to produce and secrete IFN-gamma has been purified from Trypanosoma brucei brucei (T.b. brucei). This was accomplished by raising monoclonal antibodies (MoAbs) against a fraction of T.b. brucei obtained by gel filtration, which contained high levels of material inducing rat mononuclear cells (MNC) to IFN-gamma production. MoAbs from four hybridomas strongly inhibited trypanosome-induced IFN-gamma production. One of them (MO1) was used for purification of the trypanosome-derived lymphocyte triggering factor (TLTF) by affinity chromatography. SDS electrophoresis of the purified TLTF displayed a band of 42-45 kDa MW. Gel filtration of homogenates of whole parasites yielded several peaks of IFN-gamma-inducing activity with a lowest MW of 41-46 kDa. Bioactivity of all peaks was blocked by MO1, suggesting that a single molecule, or a single epitope of additional molecules, is responsible for the different peaks with IFN-gamma-inducing activity. IFN-gamma released from MNC stimulates T.b. brucei growth. Blocking of TLTF in vitro with MO1 inhibited MNC-supported growth of the parasites. To study the in vivo relevance of TLTF in the course of experimental African trypanosomiasis, MO1 was used to treat rats and mice at different times after infection. Treatments instituted at different time-points after infection suppressed parasite growth, abrogated the IFN-gamma production by splenocytes induced by the infection and prolonged survival of the animals. The data support the hypothesis that TLTF and IFN-gamma have a crucial regulatory function in the parasite-host interactions and that these molecules influence the disease course during experimental African trypanosomiasis.

Animals↗

PubMed1993

Differential susceptibilities of mice genomically deleted of CD4 and CD8 to infections with Trypanosoma cruzi or Trypanosoma brucei.

The role of CD4+ and CD8+ T cells in the surveillance of Trypanosoma cruzi or Trypanosoma brucei brucei was studied in mice which lacked CD4 or CD8 molecules and which were generated by embryonic stem cell technology. Whereas wild-type mice infected with T. cruzi (Tulahuén strain) displayed low levels of parasitemia and no mortality, striking increases in parasite growth and mortality occurred in both CD8- and CD4- mice. On the contrary, CD8- and, to a lesser degree, CD4- mice showed enhanced resistance to T. b. brucei. T-cell-dependent immunoglobulin G-specific responses were produced in CD8- but not CD4- mice. Normal T-cell proliferative responses were measured in both CD4- and CD8- mice. Interleukin-4 production after concanavalin A or anti-CD3 monoclonal antibody stimulation was strikingly enhanced in CD8- but not CD4- spleen cells, whereas gamma interferon production was normal in both CD4- and CD8- spleen cells. Spleen and lymph node cells from CD8- (but not CD4-) mice at 20 days postinfection with T. cruzi had higher levels of interleukin-4 mRNA than the wild-type controls, as shown in a competitive polymerase chain reaction assay. On the other hand, CD4- (but not CD8-) mice at 20 days postinfection with T. cruzi had lower levels of gamma interferon mRNA than the wild-type mice.

Actins↗

PubMed1993

Scrapie prions alter receptor-mediated calcium responses in cultured cells.

The molecular basis of neurologic dysfunction in prion diseases is unknown. Spongiform degeneration of neurons is the most characteristic neuropathologic change which raises the possibility of abnormal ion channel function. Here we examined the regulation of Ca2+ fluxes in two cell lines chronically infected with scrapie prions, designated ScN2a (scrapie-infected mouse neuroblatoma) and ScHaB (scrapie-infected hamster brain) cells. In uninfected HaB cells, bradykinin caused increases in intracellular Ca2+ concentration ([Ca2+]i) by release of Ca2+ from internal stores and influx of extracellular Ca2+ whereas, in N2a cells, bradykinin increased [Ca2+]i exclusively from internal stores. Prion infection of both cell lines markedly reduced or eliminated bradykinin-activated increases in [Ca2+]i, whether driven by internal or extracellular sources. Stressing the cells with high extracellular [Ca2+], 8 to 20 mM, led to cytopathologic changes in ScHaB but not in ScN2a cells. Cytopathology was not preceded by an increase in [Ca2+]i. These findings indicate that scrapie infection induces abnormalities in receptor-mediated Ca2+ responses and raise the possibility that nerve cell dysfunction and degeneration in prion diseases is related to ion channel aberrations.

Animals↗