Allantois as the bursa-equivalent in man.

This article proposes the hypothesis that allantois is the anatomical homologue of bursa of Fabricius in mammalia. This hypothesis is based on immunohistochemical study of sections from hematopoietic organs of three fetuses with cloacal exstrophy. In the complex maldevelopment of cloacal exstrophy the common features are absence of distal midgut and exstrophy of cloaca with an exstropic intervening intestinal band. It has been suggested that gut is of dual origin and in addition to the yolk sac, allantois, absent in this maldevelopment, is involved in the embryogenesis of intestines by developing into distal midgut. There was absence of B-lymphocyte in two of three fetuses with rudimentary midgut and aplastic allantois. Meanwhile, B-cells were identified in the hematopoietic tissues and the prominent Peyer's patches of the more developed exstrophic allantois in the third case presented here. Therefore, it is concluded that allantois as the origin of distal midgut and lymphatic-rich ileocecal portion of digestive system is directly involved in the B-cell formation and represents the bursa of Fabricius in man.