Action of Riley's plasma enzyme-elevating virus in mice

Infection of mice with lactate dehydrogenase-elevating virus destroys the subpopulation of Kupffer cells involved in receptor-mediated endocytosis of lactate dehydrogenase and other enzymes

In previous experiments in rats, we have shown that the rapid plasma clearance of a number of clinically important enzymes is due to receptor-mediated endocytosis by Kupffer cells and other resident macrophages. Others have shown that infection of mice with lactate dehydrogenase-elevating virus, a virus that proliferates in macrophages, leads to reduced plasma elimination of these enzymes. This paper integrates these two sets of experiments. Plasma elimination of intravenously injected, radioactively labeled lactate dehydrogenase M4 and mitochondrial malate dehydrogenase in mice was shown to be caused in part by uptake in liver, spleen and bone. Uptake of lactate dehydrogenase M4 by these tissues was, to a large extent, saturable and the two dehydrogenases competitively inhibited each other's clearance. These results suggest that, also in mice, these enzymes are partly cleared from plasma by endocytosis by way of a common receptor on cells (probably macrophages) from liver, spleen and bone marrow. Morphometrical data showed that normal mouse liver contains 23 x 10(6) Kupffer cells/cm3. This number was reduced to about 30% of that of controls 24 hr after infection of mice with lactate dehydrogenase-elevating virus but returned to normal within the next 9 days. The saturable component of uptake of lactate dehydrogenase M4 by liver, spleen and bone had disappeared 24 hr after infection with the virus, and did not return after the Kupffer cell population had recovered. Our findings suggest that lactate dehydrogenase M4 is, to a large extent, removed from the circulation by way of a receptor on a subpopulation of macrophages that is permissive for replication of lactate dehydrogenase-elevating virus.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological relationships among stress, viruses, and cancer in experimental animals

Anxiety-induced psychoneural stimulation, via the hypothalamic-pituitary axis, activates the adrenal cortex to release corticosteroids, which elicit various alterations of corticoid-sensitive cell-mediated immunologic processes. Stress sensitive murine tumor-host experimental models have been utilized to demonstrate various effects of stress upon aspects of tumor development. Although many of the observed anxiety-induced alterations of tumor-related parameters can be interpreted in terms of corticoid-induced modifications of immune functions, other observations are more difficult to interpret, and may be caused in part by corticosteroid-independent modulation of lymphocyte functions. In the case of tumors induced by oncogenic viruses, anxiety-induced plasma corticoid elevations may also act independently of the immune system to stimulate tumor development via hormone binding sites on proviral DNA. Rigorously controlled environmental and experimental conditions are fundamental for the demonstration and interpretation of stress-related phenomena. Technical prerequisites include protective animal facilities, special handling procedures, the use of nontraumatic stressors, and the recognition of vital psychosocial, coping and timing factors. Various biologic factors, such as sex, genetic substrain differences and common interfering viral infections, must also be controlled or taken into consideration.

Lactic dehydrogenase virus (LDV) impairs the antigen-presenting capacity of macrophages yet fails to affect their phagocytic activity

The effect of acute infection of mice with lactic dehydrogenase virus (LDV) on two major functions of peritoneal macrophages was tested. Using a macrophage-dependent T cell proliferative assay to test the antigen-presenting capacity of LDV-infected macrophages we found that LDV impairs the capacity of antigen-presenting cells to trigger memory T lymphocytes. Endocytosis of antigen by LDV-infected macrophages was similar to that of uninfected cells. In addition, the proportion of intracellular antigen versus membrane-bound antigen in LDV-infected cells were similar to that observed in uninfected mice. It appears therefore, that the impaired immunogenic effect of LDV-infected macrophages results from reduced immunogenicity of the membrane-bound antigen. Testing the phagocytic activity of peritoneal macrophages we found that the uptake of radiolabeled antibody-coated sheep erythrocytes or bacteria (E. coli) by infected cells was similar to that by uninfected macrophages. In addition, LDV failed to affect the ability of peritoneal macrophages in a nitroblue tetrazolium reduction reaction which serves as an alternative parameter for measuring phagocytic activity. Our results support the assumption that LDV, which probably propagates in the cells of the reticuloendothelial system, impairs some of the immunogenic functions of macrophages and thereby affects macrophage-dependent immune responses.

Studies on the mechanism of action of Riley virus. IV. The reticuloendothelial system and impaired plasma enzyme clearance in infected mice

The plasma clearance of intravenously injected rabbit muscle LDH was studied. In normal mice the clearance followed a biphasic exponential curve comprising an initial fast and subsequent slow phase. Riley virus-infected mice showed only the slow phase of enzyme clearance. The change from fast to slow clearance rate in normal mice appeared to depend upon the level of plasma enzyme activity rather than on the amount of enzyme cleared. Treatment of mice with RES-blocking agents (cholesterol oleate and carbon) inhibited the fast clearance phase, whereas an RES-stimulating agent (stilbestrol) caused an accelerated rate of enzyme clearance. Riley virus infection was found to inhibit the clearance of phosphoglucose isomerase, but had no effect on the clearance of alanine transaminase. The activity of the former enzyme is raised in the plasma of infected mice, whereas the activity of the latter enzyme is unaltered.

Elevated gamma-globulin and increased antibody production in mice infected with lactic dehydrogenase virus

Infection of mice with the lactic dehydrogenase virus (LDV) resulted in an elevated level of gamma-globulin. Histologic examination of the spleen and lymph nodes revealed that the number of germinal centers was greatly increased. Immunization with human gamma-globulin showed that the capacity of the virus-infected animal to produce anti-human gamma-globulin was greatly enhanced and that the virus acted as an adjuvant. From these experiments it is concluded that a virus infection (LDV) can affect the immunologic response of the host to a heterologous antigen.

Studies on the mechanism of action of Riley virus. I. Action of substances affecting the reticuloendothelial system on plasma enzyme levels in mice

Plasma LDH levels were determined in normal and Riley virus-infected mice following treatment with various drugs known to alter the activity of the RES. The rise in plasma LDH level after Riley virus infection was considerably enhanced by previous treatment with thorotrast (to produce blockade of the RES), and decreased by previous treatment with stilboestrol (to stimulate the RES). A dose of 2000 r whole-body x-irradiation, lethal within 3 to 4 days, did not alter the phagocytic activity of the RES, and was without effect on plasma LDH activity in normal mice, or on the rise in plasma LDH level following infection with Riley virus. Blockade of the RES with cholesterol oleate, thorotrast, or zymosan, resulted in a 2- to 3-fold rise in plasma LDH level within a few hours. The level returned to normal by 1 to 3 days. Stimulation of the RES with stilboestrol resulted in a decrease in plasma LDH level by 1 to 2 days in both normal and infected mice, with a return to normal by about a week. Blockade of the RES in uninfected mice with thorotrast or cholesterol oleate, besides increasing the plasma LDH level caused a rise in plasma phosphoglucose isomerase level, but no significant alterations in plasma aldolase or alanine transaminase levels, studied up to 10 days. Riley virus causes a similar pattern of enzyme elevation. It is suggested that the increased levels of certain plasma enzymes in Riley virus-infected mice may be due to competitive inhibition by virus particles of plasma enzyme clearance by the RES.

Studies on the mechanism of action of Riley virus. II. Action of substances affecting the reticuloendothelial sysem on the level of viraemia

The level of viraemia was determined in serial blood samples obtained from 2 mice after the injection of Riley virus. The plasma virus titre rose rapidly to a peak value of 10(9) to 10(10)ID(50) per ml by 24 hours after infection, and then fell slowly to a level of 10(5) to 10(6)ID(50) per ml by the 10th day after infection, where it remained relatively stable. Neither blockade of the RES with thorotrast, zymosan, or carbon, nor stimulation of the RES with stilboestrol or zymosan, before the injection of Riley virus, produced any observable alteration in the level of viraemia attained 24 hours after infection. However 10 days or more after infection with Riley virus blockade of the RES with thorotrast caused a transitory rise, and stimulation of the RES with stilboestrol caused a slight but prolonged fall, in the level of viraemia. Zymosan injection at this period of infection caused an initial rise, followed by a fall, in the level of viraemia; these changes correlated with the initial period of blockade and the subsequent period of stimulation of the RES observed in carbon clearance studies. The clearance of injected Riley virus particles from the plasma over a period of 3 hours after injection was measured in previously uninfected mice and mice which had been infected with Riley virus for 3 weeks. The mice which had been infected 3 weeks before the test cleared rather more of the injected virus than the previously uninfected mice. It is concluded that although the activity of the RES affects, and may determine, the level of viraemia, the permanence of the viraemia in Riley virus-infected mice does not appear to be due to a failure of the RES to clear virus particles from the plasma.

Studies on the mechanism of action of Riley virus. 3. Replication of Riley's plasma enzyme-elevating virus in vitro

A study was made of the replication of Riley virus in various tissue cultures. It was observed that Riley virus replicated in primary mouse embryo cultures for 8 to 12 days. As they aged primary cultures became less susceptible to Riley virus infection, and subcultured cells were not susceptible. Suspensions of virus, in the absence of cells, were inactivated at 36.5 degrees C. Serial passage by transfer of supernatant fluids to fresh embryo cultures was not successful. Replication of the virus was more active in mouse embryo liver cultures than in the cultures of the embryo minus the livers. In cultures of mouse macrophages, the supernatants remained infective throughout the life of the cultures (21 days). The virus was passed 23 times through fresh macrophage cultures over a period of 80 days, during which the original inoculum (10(6.0)ID(50)/ml) was theoretically diluted to 10(-14). The possibility that the cells of the RES are involved in Riley virus replication is discussed.

Some properties of the lactic dehydrogenase agent of mice

The lactic dehydrogenase agent was obtained in quantities sufficient for purification studies by growing the virus in Ehrlich ascites tumor-bearing mice. A rapid method of titration of the agent is described. Subsequent to the standard procedure of concentration of virus by treatment with hyaluronidase and centrifugation, lipids were removed by extraction with PE, without major loss of infectivity. Electron microscopic sections of purified preparations contained particles consisting of a dense inner ring of about 25 mmicro and a less dense ring extending to about 50 mmicro. The particles occur frequently in single-membraned vesicles of varying size, and occasionally in large double-membraned bodies. The purified LDH agent did not stimulate the formation of neutralizing antibodies in rabbits and guinea pigs. The crude LDH agent was found to be a low interferon producer. Increased interferon, produced by secondary inoculation with Newcastle disease virus temporarily decreased the titer of the LDH agent. The results of others regarding the nature and the size of the LDH agent are interpreted in regard to the findings presented, and the role of interferon in permanently LDH agent infected mice is discussed.

Isoenzymic Specificity of Impaired Clearance in Mice Infected with Riley Virus

The clearance from the plasma of purified lactate dehydrogenase isoenzyme No. 5, which is increased in the plasma of mice infected with Riley virus, is impaired during the infection. That the clearance of purified isoenzyme No. 1 is unchanged by infection with Riley virus provides an explanation of why only the lactate dehydrogenase-5 isoenzyme activity is elevated in the plasma of infected mice.