Total thymectomy in the early chick embryo.

A new microsurgical procedure is described through which the thymus can be completely removed bilaterally prior to its seeding by lymphoid precursor cells in the chick embryo. 53% of the embryos operated at 5 days of incubation and sacrificed either before or after hatching were totally thymectomized as controlled on serial sections of the neck. Hatchability is low, as it normally is when operations are performed on embryos in ovo. However totally thymectomized viable chicken could be recovered. In certain series of experiments, the graft of a 5-day quail embryonic thymus was performed into the site of excision of the chick thymus. The quail thymic rudiment then became colonized by chick lymphoid precursor cells and developed normally. The possibility of using this excision-graft technique is suggested to study the role of MHC gene products in T-cell differentiation.