ONTOGENY OF THE IMMUNE-SYSTEM - GAMMA DELTA AND ALPHA/BETA T-CELLS MIGRATE FROM THYMUS TO THE PERIPHERY IN ALTERNATING WAVES/

The embryonic thymus is colonized by the influx of hemopoietic progeni tors in waves. To characterize the T cell progeny of the initial colon ization waves, we used intravenous adoptive transfer of bone marrow pr ogenitors into congenic embryos. The experiments were performed in bir ds because intravenous cell infusions can be performed more efficientl y in avian than in mammalian embryos. Progenitor cells, which entered the vascularized thymus via interlobular venules in the capsular regio n and capillaries located at the corticomedullary junction, homed to t he outer cortex to begin thymocyte differentiation. The kinetics of di fferentiation and emigration of the T cell progeny were analyzed for t he first three waves of progenitors. Each progenitor wave gave rise to gamma/delta T cells 3 d earlier than alpha/beta T cells. Although the flow of T cell migration from the thymus was uninterrupted, distinct colonization and differentiation kinetics defined three successive wav es of gamma/delta and alpha/beta T cells that depart sequentially the thymus en route to the periphery. Each wave of precursors rearranged a ll three TCR V gamma but displayed a variable repertoire. The data ind icate a complex pattern of repertoire diversification by the progeny o f founder thymocyte progenitors.