The study of DNA polymerase in resistant and susceptible macrophages infected with vaccinia virus.

Abstract

Studies have demonstrated that mouse peritoneal macrophages restrict vaccinia virus replication in yitro whereas rabbit peritoneal macrophages do not. Because this in vitro pattern parrallels the resistance and susceptibility to vaccinia infection by the respective macrophage donors, it is reasonable to assume that information concerning the intracellular mechanisms which account for these differences would be valuable to the understanding of innate host resistance. Previous studies revealed that although there is no difference in the phagocytosis, first stage uncoating, and the second stage uncoating of vaccinia in mouse and rabbit macrophages, there was a difference in viral induced DNA synthesis. DNA syntheses occurred in rabbit macrophages but was not found in mouse rnacrophages (Ward, 1980; Milligan, 1983; Kashanchi, 1986). These findings indicated that the inhibition of vaccinia by mouse macrophages took place after second stage uncoating but before viral DNA synthesis. Mpwo (1989) investigated the question of whether vaccinia virus induced protein synthesis occurred. He used as a marker of early protein synthesis the enzyme, thymidine kinase. His studies revealed no thymidine phosphorylating activity in mouse macrophages. The present study was undertaken in order to extend the findings of intracellular mechanisms involved in the innate resistance of mouse macrophages to vaccinia virus. It was important to determine if another early enzyme, DNA polymerase was made. This enzyme is directly involved with DNA synthesis. Biochemical studies revealed no DNA polymerase activity in mouse macrophages in comparison to rabbit macrophages and mouse fibroblasts. Studies concerning the second stage uncoating revealed no occurrence of second stage uncoating in the mouse macrophages treated with the protein synthesis inhibitor Streptovitacin A. This study indicated that the host must synthesize protein at the time of infection for the release of viral DNA. This evidence suggests that the enzyme responsible for second stage uncoating is being synthesized in the mouse macrophages and the second stage uncoating is viral induced. The two early enzymes responsible for DNA synthesis are not produced. Therefore, mouse peritoneal macrophages express innate resistance against vaccinia by suppressing the synthesis of early enzymes thymidine kinase and DNA polymerase which leads to suppression of DNA synthesis.