Chimaerism in lymph nodes of F1 into irradiated parental recipient chimaeras rejecting skin allografts from the other parent.

Mice of the C57BL strain were irradiated with 800 R over the whole body. The next day they received i.v. a mixture of 50 x 10(6) spleen and bone marrow cells from (C57BL x CBA-T6T6)F1 hybrid mice, and were challenged with CBA-T6T6 skin grafts later on. About 20% of the recipients rejected the CBA-T6T6 skin, whereas the others were completely tolerant for more than 200 days. By using the cytotoxic test, we found that both tolerant and nontolerant recipients were complete chimaeras, i.e., had only (C57BL x CBA-T6T6)F1 cells in their lymph nodes. However, analysis of the same mice by the chromosome marker technique disclosed a proportion of host (C57BL) cells in lymph nodes of both tolerant and nontolerant chimaeras. The percentage of host metaphases in nontolerant chimeras was significantly higher than that in tolerant chimaeras (P less than 0.01). It is possible therefore that the CBA-T6T6 skin grafts were rejected by residual host (C57BL) cells rather than (C57BL x CBA-T6T6)F1 cells reacting against skin-specific transplantation antigen(s) of the parental graft.