[Alkaline phosphatase activity of the bursa of Fabricius: histochemical study in the normal embryo and during allograft reactions].

Alkaline phosphatase activity allows a certain discrimination between lympho-inhibition following a direct action on the lymphoid stem cells or a modification of mesenchyme/epithelium interactions; in this study we have compared the evolution of this activity in untreated chick embryos and in chick embryos following graft-versus-host-reactions. The important decrease of mesenchyme alkaline phosphatase activity induced here, involves a localisation of allograft reaction in this tissue; this result does not agree with the former explanations about a direct action on the lymphoid stem cells.