In vivo competition between AKR/J and B10.BR thymocytes. BM chimeras were constructed by injecting different ratio of BM cells isolated from 2-month-old AKR/J (Thy1.1) together with control B10.BR or CBA/J (Thy1.2) mice into irradiated Rag-1–deficient hosts. Graph (A) represents numbers of total thymocytes at 3, 5, 7, and 9 weeks after transfer. Dashed line represents results from control single BM chimeras reconstituted with 100% AKR/J cells, solid thick line represents results from control single BM chimeras reconstituted with 100% B10.BR cells, and solid thin lines represent results from mixed BM chimeras. Graph (B) represents the frequency of the control donor-derived thymocytes as a function of the control BM inoculum. Values indicate the frequency of B10.BR (▪) or CBA/J (□) Thy1.2⁺ donor-derived thymocytes at 3 (solid) and 9 (dashed) weeks after transfer. Results are representative of 5 experiments with n = 3 mice per group of B10.BR-AKR/J and 2 experiments with n = 5 of CBA/J-AKR/J chimeras. Graph (C) shows marrow chimerism of CBA/J versus AKR/J at 3 and 9 weeks after transfer. Results show DNA polymorphism in the chromosome 1 with specific PCR product for AKR/J (131 bp) and CBA/J (109 bp). Data are from a pool of 5 BM chimeras generated either with 0%, 10%, 90%, or 100% AKR/J donor cells. Graph (D) represents second transfer of BM cells isolated from 9-week-old chimeras generated originally with 90% B10.BR (▪) or 90% CBA/J (□) inoculum. Results indicate the percentages of Thy1.2⁺ thymocytes at 3 and 9 weeks after second transfer. Values represent the mean of n = 5 mice per group.