Persistence of the irradiated host component in thymocyte populations from bone marrow radiation chimeras infected with lymphocytic choriomeningitis virus

The thymus of chimeras made using T cell-depleted donor bone marrow from Thy 1.1⁺ mice and 950 rad Thy 1.2⁺ recipients is dominated initially by cells expressing the Thy 1.2⁺ phenotype of the irradiated host. The thymocyte population recovered at 2 weeks after reconstitution comprises 80% Thy 1.2⁺ cells (host), the remainder being Thy 1.1⁺ (donor). This situation is normally reversed within a further week, with the host Thy1.2⁺ thymocytes being present at a frequency of less than 5% from Week 4. Infection with lymphocytic choriomeningitis virus (LCMV) at 1 week after reconstitution with bone marrow causes a profound and persistent drop in the total number of thymocytes. The decline is equivalent for all categories of donor-derived thymocytes defined by two-color flow microfluorometric analysis for CD4 and CD8. However, there is a partial compensation by the retention of cells originating from the Thy1.2⁺ host, which constitute 30-40% of the total thymocyte pool as late as 8 weeks after administration of bone marrow in the LCMV-infected chimeras. These radiation-resistant precursors give rise to CD4^-8^-, CD4^-8⁺, CD4⁺8^-, and CD4⁺8⁺ thymocytes, with the latter category being present at increased frequency. The potential skewing of the mature T cell repertoire as a consequence of persistent virus infection is discussed.