Heterogeneity within medullary-type TCRαβ+CD3+CD4-CD8 + thymocytes in normal mouse thymus

Abstract

The functional maturation process of medullary-type CD4-CD8+ [CD8 single-positive (SP)] thymocytes remains largely uncharacterized. We describe a phenotypic analysis of CD8 SP medullary-type thymocytes and find a remarkable heterogeneity within this thymic cell population. While mature CD8+ T cells in the periphery are relatively homogenous (TCRαβ+CD3+Qa-2+ HSA-3G11-6C10-CD69-), CD8 SP medullary-type thymocytes contain discrete subpopulations that can be identified by differential expression of several cell-surface markers. We have identified at least six discrete subpopulations in the subset of TCRαβ+CD3+ CD8 SP cells in the thymus. According to the expressed phenotypes, a linear developmental pathway is predicted among these CD8 SP subpopulations as follows: 6C10+CD69+ HSAhi3G11+Qa-2 → 6C10- CD69+HSAhi/int3G11+Qa-2- → 6C10-CD69-HSAInt3G11 +Qa-2- → 6C10-CD69-HSAIo3G11 + Qa-2- → 6C10-CD69-HSA-/Io3G11- Qa-2- → 6C10-CD69-HSA-/Io3G11- Qa-2+. This study provides a framework for understanding CD8 SP T cell maturation in the thymic medulla.