Multiple enzyme changes in the plasma of normal and tumor-bearing mice following infection with the lactic dehydrogenase agent

Studies on the multiplication and the properties of the lactic dehydrogenase agent

The procedure used to determine the infective titer of the LDH agent, the reproducibility of this assay, and the relationship between virus dose and plasma enzyme activity were described. Multiplication of the LDH agent began within 6 hours after infection and reached 10^10.8 ID₅₀/ml of plasma within 24 hours. The titer rapidly decreased over the next 72 hours but viremia persisted for at least 16 months with titers as high as 10^5.2 ID₅₀/ml. The appearance of the LDH agent in the circulation preceded the first noticeable rise in plasma LDH activity by close to 24 hours. After 10 months, when the plasma titer of the LDH agent had decreased nearly one millionfold, the plasma enzyme LDH had decreased by less than 50 per cent. The LDH agent is inactivated by ether but withstands lyophilization, and freezing and thawing. It is stable at low temperatures. Ultracentrifugation at 105,000 G for 2 hours leaves less than 0.1 per cent of the LDH agent in the supernatant fluid and filtration through gradocol membranes suggesst that the upper size of the LDH agent is about 55 mµ. Spread of the LDH agent from infected to uninfected mice kept in the same cage and transmission from mothers (infected prior to mating) to their offspring was relatively low.

Studies on the transmission and excretion of the lactic dehydrogenase agent

The lactic dehydrogenase agent (LDH agent) was found in the urine, feces, and saliva of mice within 24 hours after inoculation. The titer of virus in these materials appears to be directly related to the titer in the plasma. Infection by the oral route occurred only when a high concentration of virus was used. Animals infected prior to mating rarely transmitted the LDH agent to their progeny. However, 91.2 per cent of the progeny of mothers infected during gestation and 51.5 per cent of the progeny of mothers infected within 48 hours after giving birth became infected with the LDH agent. Evidence is discussed which suggests that the transmission of the LDH agent from the infected mother to her offspring is related to the titer of the LDH agent in the maternal circulation.

Detection of lactate dehydrogenase-elevating virus in transplantable mouse tumors by biological assay and RT-PCR assays and its removal from the tumor cell

It is known that lactate dehydrogenase-elevating virus (LDV) of mice is a common contaminant of transplantable tumors of both murine and human origin. It is imperative that tumors that are maintained by transplantation in mice are examined for LDV and freed of the virus, when present, before use in experimental studies, because an LDV infection of mice exerts considerable effects on lymphoid cell populations and cytokine production and other effects. Methods for LDV detection are described using a biological assay and reverse transcription (RT)-polymerase chain reaction (PCR) technology and their application is illustrated. A differential RT-PCR method that distinguishes between three quasispecies of LDV is also described and applied to an examination of LDVs isolated from a number of different tumors. Each of the LDV isolates was found to contain at least two different quasispecies, generally in different concentrations.

Macrophage function in the acute phase of lactic dehydrogenase virus-infection of mice: suppression of superoxide anion production in normal mouse peritoneal macrophages by interferon-alpha in vitro

The effect of interferon (IFN)-alpha on the release of superoxide anions (O2-) by normal mouse macrophages (PEM) was examined. Sera from LDV-infected mice at 1 day, but not at 7 days post-infection, suppressed the O2- release by PEM. When PEM were exposed in vitro for 24 h to IFN-alpha, their capacity to release O2- was significantly suppressed. Progressive suppression of O2- release with increasing IFN-alpha concentration was observed. These results suggest that IFN-alpha in the circulation may be one of several suppressive factors on macrophage function in the early phase of infection and IFN-alpha may play a modulatory role in inflammation and immunity.

Decrease in neutrophil migration induced by endotoxin and suppression of interleukin-1 production by macrophages in lactic dehydrogenase virus-infected mice

Neutrophil (PMN) migration into the peritoneal cavity after intraperitoneal injection of lipopolysaccharide (LPS), chemotactic activity of PMN, interleukin-1 (IL-1) production by macrophages (M phi) and its ability to attract PMN in mice chronically infected with lactic dehydrogenase virus (LDV) were compared with those in uninfected control mice. PMN migration into the peritoneal cavity decreased in infected mice when LPS was injected intraperitoneally. PMN chemotactic activity did not show any difference following infection. To assess the mechanism of this decreased PMN migration, IL-1 production, which is responsible for PMN attraction, was studied in LDV-infected mice. IL-1 production by M phi derived from infected mice decreased and its ability to attract PMN was weak. IL-1 production by M phi from control and infected mice increased after treatment by indomethacin and LPS. PMN migration into the peritoneal cavity increased after treatment with indomethacin and LPS in both control and infected mice. However, the rate of increase of IL-1 production and PMN migration was greater in infected mice. These results suggest that the excess activation of cyclo-oxygenase-derived products (prostaglandins) in infected mice might be responsible for the suppression of IL-1 production by M phi, resulting in decreased PMN migration induced by endotoxin.

The 3'terminus of lactate dehydrogenase-elevating virus genome RNA does not contain togavirus or flavivirus conserved sequences

Lactate dehydrogenase-elevating virus (LDV) is currently considered to be an unclassified togavirus. The 3' terminus of the genome RNA of the C-strain of LDV was cloned and sequenced. A synthetic DNA oligomer complementary to the 3' portion of this cloned sequence was then used to prime dideoxy sequencing from the LDV-C genome RNA as well as from the genome RNAs of three additional LDV isolates. A high degree of sequence conservation was observed in the 3' terminal region among the four LDV isolates analyzed. Comparison of the LDV 3' sequence with those of the alpha togaviruses, rubella virus, and the flaviviruses showed that the LDV genome does not contain conserved 3' sequences characteristic of these viruses.

Regulation of enzyme levels in the blood. Influence of environmental and genetic factors on enzyme clearance

Since its discovery, lactic dehydrogenase virus (LDV) has remained unique as a model of long-term enzyme elevation due to impairment of enzyme clearance. The present study shows that mice inoculated with silica develop an increase in plasma lactate dehydrogenase (LDH) lasting for at least 6 months and that the enzyme elevation is due, at least in part, to impairment of clearance. The extent of the enzyme elevation is dependent on both the dose and route of silica administration and mice that had received both silica and LDV showed a more profound impairment of LDH clearance than mice that had received silica or LDV alone. Examination of the factors that regulate circulating enzyme levels in normal mice revealed that whereas there was no difference in resting enzyme levels among several inbred strains of mice (BALB/cAnN, NZBWF1/J,B10.D2/nSnN, and A/J mice), when mice were stressed by the administration of an enzyme load, certain inbred strains (BALB/cAnN) cleared the enzyme rapidly and others (B10.D2/nSnN) cleared the enzyme slowly. Moreover, in B10.D2/nSnN mice, enzyme clearance was age-related. When different strains of mice were infected with LDV, LDH levels were substantially higher in the circulation of slow enzyme clearers as compared to rapid enzyme clearers. It is concluded that both environmental and genetic factors influence the clearance of LDH and that impairment of enzyme clearance may be a more important factor than previously suspected in regulating enzyme levels in disease states.

Immune response to lactate dehydrogenase-elevating virus: serologically specific rabbit neutralizing antibody to the virus

A rabbit was immunized with large amounts of the lactate dehydrogenase-elevating virus (LDV) over a 9-month period. The plasma from this rabbit possessed an anti-LDV IgG titer of 1:80,000 as measured by the enzyme-linked immunosorbent assay (ELISA) method and a neutralizing titer of 1:1,000 for the homologous strain of LDV. LDV neutralization at 4 degrees C followed single-hit kinetics. In contrast, mouse anti-LDV IgG in plasma of chronically LDV-infected mice failed to neutralize LDV at 4 degrees C and neutralization at 37 degrees C was slow, biphasic, and inefficient compared with the neutralization caused by rabbit anti-LDV IgG, even though high levels of anti-LDV IgG were detectable in mouse plasma by the ELISA method. Rabbit anti-LDV IgG neutralized one heterologous strain of LDV as rapidly as it did the homologous strain, but failed to significantly neutralize five other strains of LDV, all of which were originally isolated from different mouse strains bearing transplantable tumors. The results indicate clear serological differences between LDV strains. Cross-reactions between the strains, however, were observed by ELISA, using the antibody induced during persistent infection of mice with each LDV strain. Immunoglobulin M (IgM) from mice infected for 15 days with the various strains bound equally to our LDV strain. IgG obtained from 2-month-infected mice also cross-reacted, but to a varying extent which partly correlated with the specificity detected by neutralization. Both rabbit and mouse anti-LDV IgG enhanced the infectivity of LDV at a low multiplicity of infection for primary cultures of peritoneal mouse macrophages.

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 Lactic Dehydrogenase Activity In Parasitic Helminths]

A series of experiments was performed to determine the lactic dehydrogenase activity of various parasitic helminths. The enzyme activity was determined by the modified method of Wroblewshi and LaDue (1955) using tissue homogenate of 16 kinds of worm parasites. The worms were mostly collected alive from local abattoir and removed from the organ or tissues of the naturally infected animal host and some materials were also obtained from the human host. They were thoroughly washed and homogenized in chilled glass tissue grinder, and then centrifuged. The supernatants were designated as enzyme preparations, and their enzyme activity was measured by spectrophotometry at the wave length of 340 millimicron. In order to know the effects of temperature and substrate concentration on the enzyme activity, the extinction of reduced Coenzyme I(NADH) was measured at the various conditions of incubation temperature and substrate concentration. The results of this experiments were as follows: 1. The lactic dehydrogenase activity occurred over all kinds of parasites used in this study. 2. Most worms of nematodes and trematodes displayed their maximum activity in the range of pH 2.7~3.5, and cestodes revealed their maximum activity in the ranges of both pH 2.7~3.5 and pH 7.4. 3. In nematodes and trematodes, the lactic dehydrogenase activity increased slowly as incubation temperature increases except in the case of Eurytrema pancreaticum, while the activity in cestodes decreased inversely. 4. The lactic dehydrogenase activity increased in proportion to the increase of substrate concentration in most of worm parasites.

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.

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.