Sequential analysis of the thymocyte differentiation in fully allogeneic bone marrow chimera in mice. II. Further characterization of the CD4+ or CD8+ single positive thymocytes.

Differentiation of CD4+8- and CD4-8+ single-positive (SP) thymocytes in fully allogeneic bone marrow chimeras were investigated using multicolor cytometric analysis. The proportion of CD3+ cells in CD4+ SP population derived from donor mice considerably increased between day 12 and 14 after bone marrow transplantation (BMT), and gradually increased thereafter. The proportion of V beta 8+ cells in the CD3+CD4+ population remained constant (around 20%) at each period, suggesting that alpha and beta chains were used as TCR. The proportion of J11d+ cells in the CD4+ SP thymocytes transiently increased from day 12 to 14 and decreased thereafter, even though almost half of CD4+ SP cells were still dull J11d+ at day 35 after BMT. When CD8+ SP populations were analyzed, the proportion of CD3+ cells was very small until day 18. Thereafter, the proportion considerably increased and reached a maximum (83.2%) at day 21. The proportion of V beta 8+ cells in the CD3+ CD8+ SP population fell within range between 20 and 30%. However, before day 18, most of the V beta 8+ cells were dull positive, while after day 21 the majority were bright V beta 8+. Further, CD8+ SP cells at day 12, 14 and 18 were largely bright J11d+. After day 21, however, the proportion of bright J11d+ cells rapidly decreased. Similar results were obtained when the sequence of appearance of CD4+ and CD8+ SP cells was compared among bright CD3+, bright V beta 8+ or J11d- mature populations. The CD4+ SP cells regularly appeared earlier than CD8+ SP cells in the mature populations. These findings indicate that a considerable heterogeneity exists within both CD4+ and CD8+ SP populations and that the differentiation process for CD4+ SP cells precedes that for CD8+ SP cells.