MOUSE MAMMARY-TUMOR VIRUS PRODUCTION BY THYMIC EPITHELIAL-CELLS IN-VIVO

Exogenous mouse mammary tumor viruses (MMTV) replicate in the mammary glands of infected females, and so infect the suckling pups. We have p reviously shown that the virus is rapidly disseminated to all the lymp hoid organs, including the thymus. The present electron microscope imm unohistochemical study describes the viral production site in the thym us. Viral buds and viral proteins were restricted to the thymus medull ary epithelial cells. MMTV-encoded proteins were identified on the fre e viral particles and on the budding ones, the ribosomes, the membrane of the endoplasmic reticulum, and on the membrane of the medullary ty pe II epithelial cell vacuolar network. The thymus medullary epithelia l cells can thus integrate the virus and allow viral replication. The results support earlier results indicating that in some experimental c onditions, epithelial cells may be involved in MMTV-induced negative s election by showing that thymic epithelial cells do express MMTV-encod ed proteins.