;'e;'iew 2" Dang, .N H, Tormlort), "~.,buglta, K et dl. 11990) I lmmunol. 14q, 3963--~9-1 28 Tornn~to, Y, Dang, N.H., \'l~ wr, E., Tan,~ka, T., ~chlo,,sman. S.F and \lortmoto, C.. ( 1991 ~[ Immuno! 14-, _314-_~ 1- 29 \lattern, T., Ansorgc, ~., Had, HD. and Ulmer, A.J. I q93 ~ lmmunobu)loga' 188, 36-50 30 Kameoka, J., Tanaka, T., Noltma, ~t.. Schlossman, S.E and Monmoto, C. 119931 Scwnce ".61,466-469 31 Mornson, M.E., \'lla.~asaradh, S., Engdstem, D, Albino, A.P and Houghton, A N. 110931 ]. Exp. Med. 177, 1135-1143 32 Piazza, G.A, Callanan, H M., Mower~, J. and Hixson, D C. ~19S9} Btocl,em.J. 262, ~}_ -,},}4 33 Hanskl, C., Huhlc, T. :-d Ret fret, xw , ! 08~ Bro! CI, em, Hoppe-So'ler 366, 1169-1176 34 Bau~ols, B. ~19881Btocbem. ]. 252, 723-731 ~,5 Dang, N.H., Tonmoto, Y., Schlossman S E and Monmt~to, C. 119901 ]. Exp. Med. 172, 649-652 36 Flentke, G.R., Munoz, E., Huber, B T., Plaut, A.G., Kettner, C A. and Bachovchm, W.W. ( 1991 ) Proc. Natl Acad. Sct USA 88, 1556-1559 37 Schon, E., Jahn, S., Klesstg, S.T. et aL (1987) Eur.J hnmunol. 17, 1821-1826 38 Kubota, T., Flentke, G.R., Bachovchm, W.W and Stollar, B.D. (1992) Chn. Exp. Immunol. 89, 192-197 39 Hegen, M., Mmrucker, H-W., Hug, R. et al. (1993) Immtmobtolog3' 189, 483-493 40 Tanaka, T, Kameoka, J., Yaron, A. Schlossman, S.E and Monmoto, C. (1993) Proc. Natl Acad. Scl. USA 90, 4586-4590 41 Blasquez, M.V., Madueno, J.A., Gonzalez, R. et aL 11992) J. ImmunoL 149, 3073-3077 42 Viscid1, R.P., Mayur, K.. Ledermann, M.M. and Frankel, A.D. (1989) Scwncc 246, 1606-1609 43 Subramanvam, M., Guthed, W.G., Bachown, W.M. and Huber, B.T. (1993)J. lmmunoL 150, 2544-2553 44 Callebant, C., Krust, B., Jacotot, E. and Hovanesstan, A G 11993) Sclerrce 262, 2045-2050 45 Baiter, M. 11993) Science 262, 843-844 Superantigens and retroviral infection: insights from mouse mammary tumor virus Werner Held, Hans Acha-Orbea, H. Robson MacDonald and Gary A. Waanders Superanttgens reduce :. t%orous immune response by stimulating T cells that express parucular T-cell receptor VI~ chains. Mouse mammary tumo; virus ts a nulk-transnutted retro',trus that encodes such a superanttgen. Paradoxwall); as d~scussed by Werner Held and colleagues, the stro;;g superanttgen-induced ,mmune response permits the survival of the virus via T-cell dependent clonal expansion of infected B cells. Mouse mammary tumor virus ~MMTV), a rephcatlon- competent B-type retrovlrus, was ~JlSCovered more than 50 years ago as a mdk-borne "enuty' that Induces mammao carcinomas in mice I The predominant cell t3.pe permlsswe for efficient replication of MMTV is the alveolar eptthehal cell of the mammary gland (revJewed in Ref. 2). During lactation, the expression of MMTV markedly increases under the mflaence of steroid hormones. This property largely determines the life cycle of the virus, whereby MMTV IS secreted m mothers' mdk and Is transmitted to the offspring, probably through the gut epithelium. Infectloo of the mammary gland requires a functional immune s)~-rem~ and it Is now known that the immune system pla), a central role :n the MMTV hfe cycle. The long latency period m the development uf mam- mary tumors after MMTV infection suggests that MMTV does not contain an oncogene. Instead, upon '~f~uon of ma,amary epithelial cells, tumors arise as the result of the integration of provirus into the genome, m the proximity of either the rot-1 and mr-2 genes or other, as yet undefined, genes. This msertion event leads to gene actwauon l,ta enhancer activity of the glucocorttcoLd-response element in the MMTV ':,ng terminal repeat (LTR) (Ref. 4). In addmon, infec- tious MMTV occasionally integrates m germ cells, to the extent that MMTV-related sequences are present m the germhne of all inbred strains of mice and most wild mice. Many germ-hne transmitted MMTV loci (Mtv) have now been identified, with most mouse strams harboring from two to eight distinct provlral integrations 5. MMTV encodes a superantigen The MMTV genome, like that of other retrowruses, encodes the core proteins (gag), reverse transcriptase (pol) and the envelope proteins (env) (Fig. 1). After reverse transcription repeated sequences known as LTRs are found at the 3' ,,nd 5' ends. It has been known for some time that the YLTR of MMTV © 1994. Elsevier ~,clenLeLid 0167-5699/94/$07 fl0 ;.,.,unotogy Today 1 8 4 Vo;. !5 No. 4 1994