Mechanism of lactate dehydrogenase (LDH) elevation in virus-infected hosts

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.

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.

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. 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.