Do bursa-derived T cells exist?

In order to study the bursal origin of T cells, 18-d chromosomally-marked bursa cells were transplanted into 18-d chick embryos treated with cyclophosphamide (CY). Transfer of bursa cells restored not only the humoral immune functions but also the mitogenic responses of peripheral blood lymphocytes against phytohaemagglutinin and concanavalin A (Con A). Transplanted bursa cells proliferated primarily in the recipients' bursa. Only 8 out of 209 Con A responsive spleen cells were of donor origin, but no donor-derived cells were observed in the thymus. These findings suggest that cells in the 18-d embryonic bursa are already committed to the B cell lineage, and are not capable of migrating into thymus and of developing into mature T cells.