Morphological characterization of postembryonic development of blood–spleen barrier in duck

ABSTRACT The spleen is the largest peripheral lymphoid organ and an important site of immune response, in which the blood–spleen barrier (BSB) plays a significant role to resist various pathogens. The BSB structure of duck spleen is different from that of chicken and mammals. However, no information about the development of BSB after postembryonic age has been reported in ducks. The current study investigated the spleen of ducks at 1, 7, 14, 21, 35, and 60 days old by light and electron microscopy to provide the cellular structural development. The results showed the spleen index was significantly increased from 1 to 14-day-old ducks. During the early age of ducks, the spleen showed no definite zone of white and red pulp, but the area of the white pulp was large compared to red pulp. The diameter of ellipsoid was remarkedly increased up to 35-day-old duck spleen, while periellipsoidal lymphatic sheath (PELS) and periarterial lymphatic sheath (PALS) continuously developed after 1 d. The reticular fibers developed with age; their branching reached to the ellipsoidal wall to show a developed framework in 14-day-old ducks’ BSB. After 7 d, the endothelial cells of the sheathed capillary showed a typical cuboidal shape; between these cells, the gaps increased as age advanced, while thick basement membrane and collagen fibers were increased in 35-day-old ducks. The mechanical filtration function of BSB by intravenous injection showed one ring layer of carbon particle was restricted in the white pulp in day-old duck spleen, however, in 14–60 days, these particles were restricted in the ellipsoid and PELS, forming two ring layers of carbon particle. Collectively, the cellular features of the duck BSB developed up to 35 days post-embryonic age to perform their immunity role.