1184 GENETIC REGULATION OF XENOTROPIC MURINE LEUKEMIA EXPRESSION Typing

Rabbi t antisera raised against rabbit corneal (SIRC) cells infected with xenotropic murine leukemia virus (MuLV) 1 contain antibodies specific for antigens related to the major glycoproteins (gp70) o f the xenotropic M u L V envelope (1). These antigens appear to be normal constituents of the cell surface o f lymphoeytes of all inbred mice and have been termed XenCSA-xenotropic M u L V envelope-related cell-surface antigens (1). T he amoun t of X e n C S A expressed on lymphocytes from various inbred strains differs greatly. Some strains, such as NZB, NZW, and DBA/2 , express high levels o f X e n C S A on both thymocytes and spleen cells whereas others, such as C57BL/6 , NFS, and MA, express comparat ively low levels of the antigen on both types of cells (1). To determine if quant i ta t ive expression of X e n C S A is under genetic control, we have evaluated X e n C S A levels in 24 recombinant inbred (RI) strains derived from crosses between D B A / 2 and C57BL / 6 (2-7) as well as backcrosses o f Fls to both parental strains. The results indicate that in this cross, Fv-I or a closely linked gene on chromosome 4 has a major influence on X e n C S A levels.