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.