Peripheral blood fibrocytes contribute to the formation of the avian spleen

Abstract

Chick–quail chimeric studies were made to determine the origin of the cells of splenic ellipsoid. The ellipsoid is formed by supporting and phagocytic cells, which are embedded in a well‐organized extracellular matrix. Splenic and bursal anlage of 6‐ to 6.5‐day‐old quail embryos were transplanted into the coelomic cavity of 3‐day‐old chick embryos and further incubated for 17 days. CD45+ chicken hemopoietic cells colonized both organs. They formed the cells of the ellipsoid and the periellipsoidal white pulp of the transplanted quail spleen. Chicken‐specific collagen III was produced only in the donor quail spleen, but not in the bursa of Fabricius. The CD45+/collagen I+/collagen III+ cells are probably identical with the mammalian peripheral blood fibrocytes and contribute to the formation of supporting cells, whereas the CD45+/74.2+ ellipsoid‐associated macrophages are of monocytic origin. We provide, for the first time, experimental evidence that peripheral blood fibrocytes exist in the avian species; they are present in the circulation of the chicken embryo and contribute to the organogenesis of the spleen. Developmental Dynamics 232:55–66, 2005.