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Thymic Hormone Modulation of Leukemogenic Virus Replication¹

Department of Microbiology, Harvard School of Public Health, Boston, Massachusetts 02115

The effect of purified calf thymus extract, thymosin, on infection with murine leukemia virus (MuLV) (Rauscher) was studied in adult thymectomized BALB/c mice. The course of infection was determined by virus titer in the blood plasma, by enumeration of spleen cells replicating MuLV (i.e., infectious centers), and by the examination of cells for expression of virus-induced cell membrane antigen. Thymectomy (performed 1 week prior to the virus injection) decreased MuLV infection by all three parameters. However, administration of thymosin (500 µg, given in equal doses 2 days before and at the time of injection of virus) caused a marked increase of plasma titer of virus, as well as an increased number of spleen cells generating MuLV as compared to controls treated either with purified spleen fraction or with diluent (buffered salt solution). More than two doses of thymic extract (up to nine, given every 2 days after infection) had no further effect on plasma virus titer or number of splenic infectious centers. Furthermore, treatment of mice with either thymic or splenic extracts increased the incidence of virus-related membrane antigen appearing on the surface of spleen cells, as compared to diluent-treated control animals. These results indicate that thymosin may enhance infection by or replication of murine oncornaviruses.

¹ This work was supported by the American Cancer Society and USPHS Grants CA-15277 and CA-14922.

² Supported by USPHS Training Grant 2 T01 AI 000 14-17.

Received 1/ 9/76. Accepted 2/25/76.