Differential response of Friend leukemia virus and lactate dehydrogenase virus to chemotherapy and in vitro neutralization.

Preparations of pooled Friend virus used in this laboratory were found to contain lactate dehydrogenase (LDH) virus. Interrelationships between these viruses and the effects of drug treatment i~ vivo and virus neutralization in vitro were studied. Both 6-mercaptopurine and streptonigrin administered to Friend virus-infected mice delayed the onset of the 10to 100-fold normal elev,%tion of plasma LDH seen in untreated animals. The suppressed LDII levels in the treated mice were accompanied by a three to four log reduction in Friend virus titer. Drug treatment (lid not reduce the titer of Friend virus-associated LDH virus in mice nor was it effective against a preparation of Riley's LDH virus. A preparation of Friend virus neutralizing antibody was tested for its ability to modify the typical Friend virus LDH response in vivo. A neutralized Friend virus preparation produced LDH levels identical to those of mice inoculated with LDH virus alone, whereas mice receiving non-neutralized Friend virus showed a 90-fold normal elevation of plasma LDIt after 14 days. The Friend virus neutralizing 'mtibody preparation, though effective against Friend virus, did not significantly reduce the titer of the LDH virus. The results suggest that chemotherapy and virus neutralization i)rocedures delay or prevent Friend virus replic%tion, but are ineffective against LDH virus. Friend virus was unable to modify the infectivity of the LDH virus.