PLASMA ENZYME LEVELS IN VIRUS-INFECTED MICE

A tumor-associated lactic dehydrogenase virus suppresses the host resistance to infection with Listeria monocytogenes

Infection of mice with lactic dehydrogenase virus (LDV) causes a lifelong chronic infection which is followed by alterations in immune responses during the acute phase of the infection. LDV was found to impair many functions of the reticuloendothelial system and to suppress macrophage-dependent immune responses. We tested the effect of acute infection with LDV in mice on the macrophage-mediated resistance to infection with a virulent bacterium. We found that LDV reduces the host's capacity to resist infection with Listeria monocytogenes. Many tumor lines which are transferred in mice are infected with LDV, and their growth rate is affected by the presence of the virus. It is therefore important to distinguish between immune alterations in tumor-bearing mice which are caused by the progressive growth of the tumor and those which are secondary to the viral infection. We tested whether LDV and a circulatory factor from tumor-bearing mice with similar suppressive effects on anti-Listeria immunity are two different entities or whether they are similar. We found that the factor is associated with LDV-infected tumor cells and is absent in LDV-free tumor cells. Other biological and physical characteristics supported the assumption that the tumor-associated factor is the LDV.

Lactate dehydrogenase-elevating agent is responsible for interferon induction and enhancement of natural killer cell activity by inoculation of Ehrlich ascites carcinoma cells into mice

Inoculation of Ehrlich ascites carcinoma cells (EAC) into the peritoneal cavities of outbred ddY mice induced interferon (IFN) in the circulation. The maximum titer (1,280 U) was obtained at 24 hr after inoculation. This induced IFN had the characteristics of type I IFN, i.e., stability at pH2 and lability at 56 C. An increase in natural killer cell (NK) activity was also observed for the first 3 days after inoculation. In addition, plasma lactate dehydrogenase (LDH) activity was elevated in these mice. Inoculation of ascitic fluid or serum of EAC-bearing mice into normal mice increased plasma LDH activity six- to sevenfold over normal levels and elevated activities persisted throughout the life of the mice. These results suggest that the LDH-elevating agent was responsible for IFN induction and for enhancing NK activity. Because lactate dehydrogenase-elevating virus (LDV) can be eliminated from tumor cells by passage in vitro, we attempted to grow EAC in tissue culture for several months and re-examined whether the inoculation of such cells could elevate plasma LDH activity induce IFN and enhance NK activity. The results showed that inoculation of the passaged cells had no effect on these activities in normal mice. Therefore, we concluded that the IFN inducer was LDV which contaminated the EAC and then enhanced the NK activity. N-tropic murine leukemia virus also contaminated EAC, but this virus was not responsible because cultured cells of EAC still shed this virus.

Impaired resistance to bacterial infection after tumor implant is traced to lactic dehydrogenase virus

A BALB/c mouse-passaged methylcholanthrene-induced fibrosarcoma tumor caused severe impairment of resistance to systemic listeriosis. Depressed resistance expressed immediately after tumor implantation was traced to inadvertent association of tumor with lactic dehydrogenase virus. Tumor cured of virus was totally inactive.

Absorption of lactulose from mammalian gastrointestinal tract

1. The disaccharide lactulose (galactosyl-beta-1,4-fructose) was poorly absorbed from rat small intestine in vitro and human mouth in vivo. 2. These results confirm indirect clinical evidence of poor absorption from the intestine. 3. The presence of calcium ions, or absence of sodium ions, had no effect on lactulose absorption from buccal cavity. 4. The presence of ouabain, or absence of Na+, did not increase the absorption of lactulose from small intestine. 5. It is thought that the mode of transport, in both instances, is by passive diffusion with the concentration gradient.

The effects of different bile salts on the absorption of fluid, electrolytes, and monosaccharides in the small intestine of the rat in vivo

The effects of different bile salts on the absorption of fluid, electrolytes, and monosaccharides have been investigated in the rat small intestine in vivo. In the jejunum, deoxycholate (1 mM) impaired absorption of water and potassium, but not of sodium or glucose; at higher concentrations (2.5 and 5 mM) secretion of fluid and electrolytes occurred, and glucose and fructose absorption was impaired. By contrast, in the ileum, 1 mM deoxycholate failed to inhibit fluid and electrolyte absorption, and a concentration of 10 mM was required completely to inhibit absorption; secretion was not observed in the ileum. Chenodeoxycholate (5 mM) produced a similar effect to deoxycholate on fluid and electrolyte absorption in both jejunum and ileum, but taurocholate (5 mM) and taurodeoxycholate (5 mM) were ineffective.In jejunum, cholate, taurocholate, and taurodeoxycholate, each at a concentration of 5 mM, were less effective inhibitors of glucose transport than deoxycholate; chenodeoxycholate failed to inhibit glucose absorption. Deoxycholate produced histological damage at 5 mM, but not at lower concentrations. The functional and structural abnormalities were shown to be reversible phenomena. These findings may be relevant to the pathogenesis of diarrhoea in patients with bacterial overgrowth in the small intestine.

Effect of Friend leukemia virus and Rowson-Parr virus on immunological maturation of mice

The effect of neonatal infection with Friend virus (FV) and Rowson-Parr virus (RPV) on the maturation of the capacity to respond to sheep red cells, as measured by the numbers of hemolytic plaque-forming cells in the spleen, was investigated in BALB/c mice. Both viruses affected immunological maturation but there were significant differences between their effects. The development with age of the ability to produce plaque-forming cells in response to antigen was virtually abolished by FV and only slightly impaired by RPV. Furthermore, FV also suppressed the development of background plaque-forming cells, whereas RPV did not.

Enzyme and isoenzyme alterations in Friend disease

The activities of certain enzymes in the tissus of mice infected with Friend virus have been studied. Progressive increases in LDH, G6PDH and 6PGDH have been observed in the spleen and liver concomitant with malignant transformation. Plasma LDH activity was also observed to increase over the period of study, but changes in the isoenzyme distribution probably resulted from contamination of the Friend virus preparation with lactic dehydrogenase virus. The tissue enzyme changes are similar to those observed in human malignancies.

Spontaneous mammary tumors: decrease of incidence in mice infected with an enzyme-elevating virus

Mice infected with a virus which causes increased activity of lactate dehydrogenase, and of other enzymes in blood plasma, had a significantly lower incidence of spontaneous mammary carcinoma than did controls. When the experiment was terminated at 18 months, the incidence of mammary tumors in controls was 90 percent, and in infected mice, 53 percent.

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.

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.