Early dominance of irradiated host cells in the responder profiles of thymocytes from P leads to F1 radiation chimeras.

The number of cells in the thymus of [k leads to (b X k)F1] radiation (100 rad) chimeras increases approximately 10-fold between 7 and 14 days after reconstitution with bone marrow. At least 50% of the cells in thymus on day 14 are of host origin and respond to virus presented in the context of both H-2k and H-2b when primed in irradiated, virus-infected (b X k)F1 recipients. Strong CTL responses can be generated from thymocytes of donor origin on day 21. All evidence of a significant host thymocyte component has disappeared by day 28. The responsiveness of 14-day thymocytes is not abrogated by pretreatment of the mice used to make the chimeras with anti-thymocyte serum or by using doses of irradiation as high as 1200 rads to eliminate host components.