The stages of T cell development are marked by changes in cell-surface molecules
Progenitor cells form bone marrow: No T-specific surface molecules Receptor genes are not rearranged
major
           minor
~20% DN
~20% DN NKT
(not shown)
Interaction with thymic stroma trigger initial phaseè cell proliferation and expression of first surface molecules (eg, Thy1/CD2)but not CD3, CD4,
or CD8
Several proliferation cycles