Construction of chimeric thymuses in the mouse fetus by in utero surgery.

Normal thymuses develop in the coelomic cavity of mice following grafts carried out in utero into embryonic day 16 to 17 fetuses of the third branchial arch region removed from 10-day embryos. The recipients were killed at various times (up to 29 days after birth) and the thymic lobes which developed from the graft were recovered. Microscopical examination and immunocytochemistry revealed that these thymuses developed normally whether the grafts involved syngeneic or allogeneic (between BALB/c and C3H) strain combinations. Two major populations of class II-expressing cells could be recognized by the Ia allotype they expressed: epithelial cells of donor type and accessory cells of host origin.