Genetic Aspects of Resistance to Friend Leukemia Virus. ∗

Abstract

Resistance of inbred C57BL mice to Friend's leukemic agent has been documented in a number of studies( 1 , 2 , 3 ). Analysis of F2 and backcross progeny from RF X C57BL crosses suggested that resistance is a simple recessive character ( 4 ). In an attempt to differentiate susceptibility in the CFW and DBA2 strains from C57BL-resistance by-standard mendelian methods, an alternate form of gene expression was suggested by our findings. These observations are described here.

Materials and methods. Mice. C57BL/ Crgl and DBA2/Crgl mice were obtained from the Cancer Research Genetics Laboratory, University of California, Berkeley. Inbred CFW mice were obtained from the Lobund Laboratory, University of Notre Dame, Notre Dame, Ind. Virus. BALB/c-adapted Friend virus was obtained from Dr. W. Bostick, California College of Medicine, Los Angeles. It was specifically adapted to DBA and CFW mice by serial passage. After 7 passes in each respective strain, 2 pools of virus were prepared from spleen homogenates in the manner described by Fieldsteel et al ( 2 ). Virus titers of DBA-derived preparations were determined in DBA and CFW mice respectively as described by Friend( 1 ). A similar reciprocal titration was made with CFW-derived virus. The results summarized in Table I indicate negligible differences. Passage history appeared to have little or none of the effects previously described ( 1 , 2 ). Stock virus for subsequent experiments consisted exclusively of DBA-derived preparations. Inoculation and subsequent animal observations. Cell-free preparations containing approximately 20 ID₅₀ of virus were inoculated intraperitoneally in 35-40 day old test mice. Simultaneous inoculation of indicator DBA mice with 5 ID₅₀ of virus provided a check on the efficacy of this procedure. Twenty-one days after inoculation, mice were killed by cervical dislocation, and their spleens removed and weighed. Spleen weight frequencydistributions were plotted on a 0.05 g scale in an attempt to detect genetic variance.