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M Volkert

Publications and source records attributed to M Volkert.

At least 19 recordsLinked to original sources
PubMed1999

2-Mercaptoacetate, an inhibitor of fatty acid oxidation, decreases the membrane potential in rat liver in vivo.

In former work, intraperitoneal injection of 2-mercaptoacetate (MA), an inhibitor of fatty acid oxidation, increased food intake in rats, which was attenuated by hepatic branch vagotomy, and intraportal injection of MA increased the discharge rate in hepatic vagal afferents. In the present study, we investigated, whether intraperitoneal injection or intraportal infusion of MA affects the hepatic membrane potential in rats in vivo. The liver cell membrane potential was measured in anesthetized Sprague-Dawley rats with the microelectrode technique. Intraperitoneal injection of MA at a dose of 800 micromol/kg body wt significantly decreased the hepatocyte membrane potential by 3.8 mV, whereas at a dose of 400 micromol/kg, the depolarization (1.5 mV) of the membrane was not significant. In another strain of Sprague-Dawley rats, however, MA (400 micromol/kg) produced a significant depolarization of the hepatocyte membrane 50 min (2.6 mV) and 2 h (2.9 mV) after intraperitoneal injection. Intraportal infusion of MA (400 micromol/kg) significantly depolarized the membrane 20 and 50 min after infusion by 3.3 and 4.1 mV, respectively. MA at a dose of 800 micromol/kg also depolarized the membrane (4.8 mV after 50 min). These findings in principle are consistent with the "potentiostatic" hypothesis, postulating a link between the hepatic membrane potential, afferent vagal activity, and the control of food intake.

Animals↗
PubMed1998

Hyperpolarization of the cell membrane of mouse hepatocytes by lactate, pyruvate, and fructose is due to Ca2+-dependent activation of K+ channels and of the Na+/K+-ATPase.

Using superfused mouse liver slices combined with a conventional microelectrode technique, we investigated: (1) the ionic mechanisms involved in the hyperpolarization of the hepatocyte membrane induced by lactate and other gluconeogenic substrates; (2) whether these mechanisms are similar to those underlying the hyperpolarization induced by cell swelling in hypo-osmotic medium; and (3) whether the hyperpolarizing effect of lactate on the hepatocyte membrane is related to gluconeogenesis. Lactate (5 mmol/l) hyperpolarized the hepatocyte membrane after an exposure of 10-20 min, and the hyperpolarization was still present after 70 min. The hyperpolarization induced by lactate, pyruvate (5 mmol/l) and fructose (10 mmol/l), and by exposure to hypo-osmotic medium (250 mosmol/l) was antagonized by ouabain, tetraethylammonium (TEA), and cetiedil (lactate; hypo-osmotic medium). Hyperpolarization induced by lactate was eliminated or attenuated by agents impairing activation of Ca2+-dependent K+ channels, by amiloride, and by a blockade of non-selective cation channels with flufenamic acid and gadolinium. Thapsigargin, increasing cytosolic Ca2+, mimicked lactate's hyperpolarizing effect. Lactate's effect was dependent on extracellular Ca2+. Finally, lactate's hyperpolarizing effect was reduced by inhibiting gluconeogenesis. These findings suggest that metabolism of lactate hyperpolarizes hepatocytes by mechanisms analogous to those underlying the hyperpolarization induced by cell swelling in hypo-osmotic medium. Gluconeogenesis from lactate may cause cell swelling, subsequent activation of Ca2+-dependent K+ channels and of the Na+/K+-ATPase, and thus hyperpolarize the hepatocyte membrane.

Amiloride↗
PubMed1985

High-dose survival in the lymphocytic choriomeningitis virus infection is accompanied by suppressed DTH but unaffected T-cell cytotoxicity.

Provided that intracerebral inoculation is applied, an increase in the virus dose from 10(2) to 10(4) LD50 of lymphocytic choriomeningitis virus (LCMV) leads to strikingly reduced mortality. To analyse the background for this autointerference, we measured several virologic and immunologic variables in mice infected with these doses of virus. In the high-dose mice we found generally higher organ virus titres and serum interferon titres than in the low-dose mice. Since we could demonstrate that virus-specific T-cell cytotoxicity in spleen, peripheral blood, and meningeal exudate was similar after intracerebral infection with large and small virus doses, and since the LCMV infection in the brain qualitatively and quantitatively was independent of the size of virus inoculum, the explanation for the survival of the high-dose animals is obviously not lack of possibilities for interaction between cytotoxic T cells and infected sensitive targets in the central nervous system. On the other hand, high doses of virus caused a clear suppression of the LCMV-specific delayed-type hypersensitivity (DTH). In addition, when splenocytes from high-dose animals were transferred either intravenously or locally into the footpad of newly virus-challenged mice, DTH was markedly suppressed as compared with the response after transfer of spleen cells from low-dose mice. We therefore conclude that autointerference in the LCMV infection is due to a selective suppression of Td function. Large amounts of persistent virus late after infection with high doses of virus suggest a central role for Td function also in virus clearance. Finally, our results indicate the existence of two subsets of K,D region-restricted T cells, one mediating cytotoxicity and the other mediating DTH. This possibility is discussed.

Animals↗
PubMed1985

Different isotype profiles of virus-specific antibodies in acute and persistent lymphocytic choriomeningitis virus infection in mice.

The humoral immune response to lymphocytic choriomeningitis virus (LCMV) was analysed by the use of a sensitive ELISA. Our results show that LCMV carriers of the C3H strain, previously believed to be completely tolerant to the virus, do in fact produce LCMV-specific antibodies and, moreover, that a significant proportion of these antibodies belong to IgG subclasses which are considered T-cell dependent. This finding, together with the fact that T-cell deficient mice made little or no LCMV-specific antibodies, makes it reasonable to infer that C3H carriers have not only virus-primed B cells, but also virus-primed T-helper cells. However, the isotype profiles of the virus-specific antibodies detected were markedly different in carriers and in immune mice. Firstly, much greater inter-individual variation was observed in the carrier population than in the immune mice. Secondly, in immune mice IgG2a antibodies dominated the humoral response, whereas in carriers the virus-specific activity in this subclass was very low. In contrast, LCMV-specific antibodies of the IgG1 subclass were present in similar titres in immune mice and in the majority of the carriers. Evaluation of the IgG2b response revealed that most carriers had little or no LCMV-specific activity in this subclass, although a few had antibody levels comparable to those in immune mice. These findings are discussed in relation to the question of the state of immunity in LCMV carriers and its consequence for immune-complex disease.

Acute Disease↗
PubMed1983

Fatal meningitis following lymphocytic choriomeningitis virus infection reflects delayed-type hypersensitivity rather than cytotoxicity.

Fatal meningitis following intracerebral inoculation of lymphocytic choriomeningitis virus (LCMV) reflects an immunopathological lesion believed to be mediated by cytotoxic T cells. The results presented here demonstrate that pretreatment with cyclophosphamide (Cy; 150 mg/kg body weight) 2 days before intracerebral infection significantly reduced the lethality of the infection. However, this treatment did not impair the antiviral cytotoxic response as measured in the spleen. On the other hand, virus-specific delayed-type hypersensitivity (DTH) was significantly reduced. This reduction seems to be the result of a Cy-induced lack of non-committed ancillary cells since: (1) virus-primed spleen cells from Cy-pretreated donors conferred normal LCMV-specific DTH to naive recipients; (2) transfer of virus-primed spleen cells from untreated donors did not increase the suppressed DTH response of the Cy-pretreated mice; and (3) inoculation of irrelevant antigen and antigen-primed spleen cells into the footpads of Cy-pretreated, infected mice resulted in a significantly reduced footpad swelling as compared with untreated, infected controls. Taken together, these results indicate that LCMV-induced meningitis does not solely represent T-cell-mediated cytotoxicity in vivo but that a fatal outcome of the infection critically involves not only effector T cells but also ancillary cells.

Animals↗
PubMed1983

Virus elimination in acute lymphocytic choriomeningitis virus infection. Correlation with virus-specific delayed-type hypersensitivity rather than cytotoxicity.

The immunological effector mechanism responsible for the elimination of virus in murine acute non-fatal extracranial lymphocytic choriomeningitis virus infection was studied. In this infection virus clearance is generally regarded as the result of a direct action of virus-specific cytotoxic T cells (Tc cells) on virus-producing target cells in the infected mouse. However, by manipulating the antiviral immune response by pretreatment with various doses of cyclophosphamide, we found lack of correlation between Tc-cell activity and the clearance of virus. In contrast, we observed a conspicuous correlation between the host's ability to mount a virus-specific delayed-type hypersensitivity (DTH) response and its capacity to combat virus. Moreover, pretreatment with silica and carrageenan prolonged viraemia without impairment of the peak Tc-cell response. These findings indicate that Tc cells have little or no capacity to eliminate virus, at least in the absence of an inflammatory response, and our findings suggest that virus clearance reflects a DTH-like process.

Animals↗
PubMed1983

Studies on the role of mononuclear phagocytes in resistance to acute lymphocytic choriomeningitis virus infection.

The role of mononuclear phagocytes in various phases of the acute lymphocytic choriomeningitis virus (LCMV) infection was studied. The anti-macrophage agent carrageenan delayed virus clearance. Carrageenan was most effective when given before virus inoculation, suggesting that it interfered with early events in the host response to the virus. Correspondingly, carrageenan enhanced early virus multiplication. Pretreatment with carrageenan apparently did not inhibit induction of the T-cell response and had little or no direct effect on T-cell-dependent anti-viral activity. The LCMV-induced natural killer response was also unimpaired by this treatment. Taken together, these findings suggest that resident macrophages constitute a barrier to the initial multiplication of LCMV. A breakdown of this macrophage barrier results in a more disseminated infection, which the specific immune response has difficulty in eliminating. Adoptive transfer experiments with pre-irradiated recipients showed that T-cell-dependent virus clearance required interaction between donor-derived primary immune spleen cells and radiosensitive host cells. T cells did not seem to constitute the radiosensitive host component, since athymic (nude) mice functioned well as recipients. Together with previously published data, this finding strongly suggests that T-cell-dependent virus clearance involves cooperation between T cells and non-committed cells, probably monocytes.

Animals↗
PubMed1979

The timing of the immune response in relation to virus growth determines the outcome of the LCM infection.

In the present study earlier observations of a dual role of the immune response against lymphocytic choriomeningitis (LCM) virus were confirmed and extended. At different times after intracerebral (i.c.) inoculation of the virus, groups of immunosuppressed recipients were transplanted with primary effector cells or memory cells, and the mortality was recorded. The brains and blood of untransplanted immunosuppressed recipients were titrated at intervals after the i.c. challenge, and so were the brains of mice receiving peak primary effector cells at various times relative to the i.c. challenge. The results showed a definite correlation between the brain virus titre at the time of the immune attack and the clinical outcome of the LCM infection. Furthermore, the results indicated that the extent of the extraneural infection is not unimportant but may affect the outcome of the infection through competition for the effector cells. The possible implications of these findings are discussed.

Animals↗
PubMed1976

Immunological unresponsiveness of nude mice to LCM virus infection.

The acute LCM infection in nude mice runs a course which is clinically inapparent, and neither a humoral nor a cell-mediated immune response could be detected. Furthermore, during this infection the blood virus titers reached extremely high values. These observations are contrary to what is seen when ordinary normal mice are infected with the LCM virus but identical with the events following infection of ordinary but immune-deficient mice. Despite the absence of immune responses to the virus in the nude mice the very high virus titers obtained within the first few days of the infection declined somewhat during the following weeks. This and the other observations made are discussed briefly in the light of the current hypothesis concerning the immune status of the nude mice and the pathogenesis of the LCM virus infection in mice.

Animals↗
PubMed1976

The interplay between target organ concentrations of lymphocytic choriomeningitis virus and cell mediated immunity in baby mice.

Circumstantial evidence has been presented which supports the view that the fatal LCM virus infection is due to an immunological conflict in the host animal. Hitherto, this outcome of the infection has only been observed in intracerebrally infected mice. In the present study, the intraperitoneal infection in young mice was investigated and the results revealed a new example of this immunological conflict. In mice infected a few days after birth, concentrations of the virus in the brain are high, while the CMI response is non-measurable. If the infection is induced when the mice are 28 days old or more, there is little virus in the CNS, but a strong CMI response can be demonstrated. All the mice in these two age groups survive. If mice are infected when they are 17-19 days old, however, they raise a moderate CMI response nine days after infection and, at the same time, their brains contain virus in high titres. The mortality among mice infected at this age is 100%, indicating that this combination is fatal. The lives of these animals can be saved by anti theta serum or if they are transplanted with syngeneic lymphoid cells sensitized to LCM virus. Our results strongly suggest an interplay between, on the one hand, the spread and the magnitude of the virus infection in the brain and, on the other, the cell mediated immune response. This interplay seems to be decisive for the clinical outcome of the LCM infection in mice.

Age Factors↗
PubMed1975

T lymphocyte function as the principal target of lymphocytic choriomeningitis virus-induced immunosuppression.

Plaque-forming cell responses against sheep erythrocytes, Escherichia coli lipopolysaccharide, pneumococcal polysaccharide, and polyvinylpyrrolidone were examined in mice infected with lymphocytic choriomeningitis virus. A 92 to 96 percent reduction of the thymus-dependent anti-sheep erythrocyte responses was observed 2 to 4 weeks after infection. However, the thymus-independent responses against the three other antigens were close to normal at all stages of the infetion. Studies on allograft immunity of infected C3H mice against DBA/2 mastocytoma cells revealed a severe suppression of the T cell-mediated cytotoxic response which was temporally related to the impaired humoral responsiveness against sheep erythrocytes. The capacity of spleen cells from infected mice to restore immune responsiveness of lethally irradiated recipients against sheep erythrocytes was significantly reduced. The adoptive responses, however, were clearly improved when normal thymus cells were added to the inferior spleen cells. Moreover, it appeared that the spleen cells from immunosuppressed donor mice could not confer suppression to normal lymphoid cells. The presented findings are consistent with the assumption that a numeric deficiency of T cells, or cells belonging to some T cell subpopulation, is the primary cause of lymphocytic choriomeningitis virus-induced immunosuppression.

Animals↗
PubMed1975

The activity of T and B lymphocytes in immunity and tolerance to the lymphocytic choriomeningitis virus in mice.

Treatment with anti-theta serum and the Wigzell column technique for cell separation was employed to study the separate functions of the B and T lymphocytes in the late states of immunity to the LCM virus in mice. The cell preparations examined were mixtures of spleen and lymph node cells from immune mice. The results revealed that the anti-viral effect of such cells after transfer to virus carriers was unimpaired in T cell-enriched and B cell-deprived cell preparations. The anti-viral effect was also retained in cell preparations deprived so much of B cells that no antibody was produced in the virus carrier mice receiving transplants of these cells. The results strongly indicate that the anti-viral effect of late immune cells is not only T cell-dependent but that it is also mediated solely by T cells and, moreover, that antibodies have no or very little influence on the virus elimination. The observation that antibody production could be caused neither by column-passed cells nor by anti-theta serum-treated cells, but was obtained by mixtures of these cells, demonstrates that co-operation between T and B cells is crucial for the LCM antibody response. Accordingly, the convincing demonstration of the absence in the persistent virus carriers of cells which, in respect of antibody production, are able to co-operate either with column-passed or with anti-theta serum-treated immune cells, implies that such animals are extremely deficient as regards immune function of both B and T LCM-primed lymphocytes.

Animals↗
PubMed1975

Persistent LCM virus infection in the mouse. Immunity and tolerance.

The initiation of persistent infections with the Traub strain of the LCM virus is dependent not only on the number of immunocompetent cells present in the infected animals but probably also on the fact that the virus depresses the development of the bone marrow cells and causes a pronounced immunosuppression at the T cell level. By analysing the events leading to the termination of the virus carrier state by adoptive immunization, it was clearly demonstrated that the cellular immunity provoked was solely responsible for the virus elimination. Furthermore, helper T cells were shown to be necessary for the production of antibodies, which also occurs in adoptively immunized mice. In view of this finding, further experiments were performed, which strongly indicated that neither LCM-primed B cells nor LCM-primed helper T cells are present in mice that are persistent virus carriers. Similarly, neither cellular immunity to the LCM virus nor the presence of enhancing factors or suppressor cells could be detected. It is concluded that C(3)H mice that are persistent virus carriers have developed a humoral as well as a cellular immunological tolerance to the LCM virus.

Animals↗
PubMed1974

Twp populations of T lymphocytes immune to the lymphocytic choriomeningitis virus.

In this report seven different parameters were employed to investigate the spleen and lymph node cells from mice at the early and the late state of immunity to the lymphocytic choriomeningitis (LCM) virus. Distinct differences were observed. Morphological studies revealed a different size distribution of the cells in the preparations from the early and the late state of immunity. The cell mixtures of early immune cells contained many more large and blast-like lymphoid cells than the other. Where the cell function was concerned, the cytotoxic activity against LCM virus-infected target cells was almost entirely a function of the early immune cells, and our data strongly indicate that enhancement does not play any role for the disappearance by time of this cell activity. The antiviral effect after transfer to acutely infected animals was also predominantly a function of the early immune cells and the same was the case concerning the ability to protect against a lethal acute infection. However, the early immune cells were almost inactive after transfer to chronically infected virus carriers, whereas transplants of late immune cells to such mice had a very strong antiviral effect. The resistance to X irradiation also varied. Even high X-ray doses could not destroy the function of early immune cells, whereas the function of the late immune cells was readily impaired by X-ray treatment. The early and the late immune cells have one thing in common-both are susceptible to treatment with anti-theta serum. Because of the differences observed between the early and the late immune cells, it is concluded that they belong to different cell populations. However, because of the common susceptibility to anti-theta serum, probably both populations are T-cell lymphocytes. The implications of the results and the role of the different cells in the combat of the viral infection are discussed.

Animals↗
PubMed1974

Defects in the immune system of mice infected with lymphocytic choriomeningitis virus.

Acute lymphocytic choriomeningitis virus infection of adult mice is associated with general immunosuppression, which develops during the 2nd week of the infection and persists for a period of 2 to 3 months. Studies of some cellular events in the immune system of infected mice brought to light a number of findings which seemed relevant to this immunosuppressive effect. Colony-forming stem cells, which may act as the precursors of the lymphoid cells, were temporarily inhibited during the first period of the infection. Presumably this inhibition also affected the thymus cells, which decreased dramatically at the same time. At a later stage of infection, defects developed within the population of immunocompetent cells, and this was most probably a consequence of the preceding suppression of the precursor cells. The defects in the immunocompetent cells were temporally related to the immunosuppression and seemed to be the ultimate cause of this phenomenon. At all events, antibody-forming cells were not damaged by the virus. In studies of neonatally infected baby mice, it was found that the development of immunological responsiveness was completely abolished for the first 2 weeks of life. It is therefore probable that the generation of immunocompetent cells was also affected in the babies. Evidence was obtained supporting the hypothesis that this effect played an important role for the induction of tolerance to the virus in the neonatally infected mice.

Animals↗
PubMed1973

Studies on cell-mediated immunity to lymphocytic choriomeningitis virus in mice.

A large amount of experimental evidence has already been presented indicating the great importance of the cell-mediated immunity in the pathogenesis of the LCM virus infection in mice. In this laboratory a method which makes it possible to measure this cellular immunity quantitatively in vitro has been developed. The method is based on the determination of the radioisotope released after the interaction between specifically sensitized lymphocytes and syngeneic (1)Cr-labeled LCM virus-infected target cells. By using this technique the time-course of the cell-mediated immunity has been established in acutely infected mice and in virus carriers adoptively immunized with syngeneic sensitized lymphocytes. Lymphocytes from acutely infected mice showed a strong lysing effect on the target cells, with a sharp maximum at about the 9th day after infection. The cell-mediated immunity in adoptively immunized virus carrier mice showed the same time-course, but in these animals the lytic effect of the lymphoid cells was considerably less pronounced. Lymphocytes from untreated virus carriers did not, however, have any effect on the target cells, and in these animals it was not possible to demonstrate any evidence of enhancing antibodies, In experiments employing serial dilutions of sensitized lymphocytes in normal cells a direct linear relationship between the number of sensitized lymphocytes and target cell destruction was found. These experiments seem to indicate that the underlying mechanism in the cytotoxic reaction is a direct cell-to-cell interaction.

Animals↗