Fig. 1.
Two models for timing and location of progenitor commitment to the thymic B cell lineage. This figure shows two possible pathways for how cells might undergo B lineage restriction within the thymus. 1) Circulating progenitors (such as the CLP-2 and CTP described in the text) enter the thymus already partially restricted to the T or B cell lineage, and 2) Lineage decision occurs intrathymically from multipotent progenitors.