Journal zyxwvuts of Immunogenetics zyxwvut (1978) 5, 255-260. HISTOCOMPATIBILITY DIFFERENCE BETWEEN C3HfeB/HeN AND C3H/HeN MICE: TUMOUR INDUCED IN C3HfeB/HeN MICE EXPRESSES C3H/HeN-ASSOCIATED ALLOANTIGEN zy W. J. MARTIN, T. G. GIPSON, M. A. CONLIFFE, W. G. COTTON,* L. F. DOVE* AND J. M. RICE* Division of Virology, Bureau of Biologics, Food and zyxwv Drug Administration, and *Experimental Pathology Branch, National Cancer Institute, Bethesda, Maryland, USA. (Received 28 January zyxwvu 1978) SUMMARY A transplacentally induced lung tumour of C3HfeB/HeN mouse origin expresses, as a tumour-associated antigen, a normal tissue component of strain A mice. The genetic locus coding for this alloantigen has been shown to be linked to the H-2 major histocompatibility complex. In the present study we demonstrate that this antigen is also expressed on normal tissues of C3H/HeN mice. Skin grafts exchanged between C3HfeB/HeN and C3H/HeN mice are reciprocally rejected at approximately 3 weeks after grafting. C3HfeB/HeN mice were derived from C3H/HeN mice in 1945. These strains have apparently deviated since then in their genetic regulation of the expression of the MHC- linked genetic locus. The finding of the C3H/HeN-associated antigen on a C3HfeB/HeN mouse-derived lung tumour indicates that this deviation is reversible. INTRODUCTION Highly malignant lung tumours can be induced in most strains of mice by the transplacental administration of the carcinogen 1-ethyl- 1-nitrosourea (ENU) between days 13-16 of gestation (Rice, 1969). Although these tumours may grow progressively and cause death of their primary host, many of them grow poorly when transplanted to normal syngeneic recipients (Martin et al., 1977a, and unpublished observations). Several transplacentally induced lung tumours of C3HfeB/HeN mice have been observed to grow much more rapidly when transplanted to (C3Hf x A)F, hybrid mice compared to C3Hf mice (Martin et al., 1977b). The preferential growth of these tumours is due to the expression by the tumours of an antigen which is present in normal tissues of A mice (Martin et al., 1973). Genetic studies reported elsewhere (Martin et al., 1976) indicated Correspondence: Dr W. J. Martin, Division of Virology, Bureau of Biologics, Food and Drug Administration, 8800 Rockville Pike, Bethesda, Maryland 20014, U.S.A. 0305-18 1 1/78/0800-0255SO2.00 01978 Blackwell Scientific Publications zyx 255