Figure 2:

Schematic of T-cell development with emphasis on stages when multipotency is narrowed and then relinquished. Blue vertical arrows indicate the stages at which Notch pathway signaling within the thymus is required for progression. Labels above the cell cartoons depict common names for the stages. For prethymic cells: MPP, multipotent progenitor; LMPP, lymphoid-primed multipotent progenitor; CLP, common lymphoid progenitor. For intrathymic cells, DN = CD4-CD8-TCR-stages; substages (DN1, 2a, 2b, etc.) are distinguished by expression of Kit, CD25, CD44, and other markers including CD27 and CD28. ETP, early T-cell precursor, same as Kit-high DN1. β-Selection indicates first stage when proliferation and survival depend on expression of a part of the T-cell receptor complex, a phase of rapid proliferation and differentiation triggered by the successful rearrangement of the TCRβ chain gene. DP = CD4+ CD8+ TCRβ⁺ cells. DC = dendritic cell potential; myel = myeloid (macrophage and/or granulocyte) potential; eryth = erythrocyte potential; NK = natural killer potential. For explanation, see text.