To identify the existence and composition of the blood–spleen barrier (BSB) in chickens, the microanatomical
features of the spleen were investigated by light and transmission electron microscopy, intravenous
injection of ink, acid phosphatase reaction, and silver impregnation. The results showed that the white
pulp in chicken spleen consists of lymphoid nodules, periarteriolar lymphatic sheaths (PALS) and
periellipsoidal lymphatic sheaths (PELS). There was no evidence for the presence of a marginal zone.
The splenic ellipsoid was a unique structure, which functioned as a barrier for filtering and phagocytosis.
Uptake of carbon particles was limited to the ellipsoid and PELS, 60 min after injection of carbon
particles. Reticular fibres were densely distributed in the ellipsoid and extended into the PELS. Ellipsoidassociated
cells (EACs), reticular cells and macrophages were acid phosphatase positive. The sheathed
capillaries, surrounded by the ellipsoid, were similar to high endothelial venules (HEVs). These findings
suggest that the BSB of chickens is present in the ellipsoid and PELS, protecting the spleen from invasion
from circulating pathogens. The BSB was a reticular framework, between the arterial and venous
vessels, which included cuboidal-shaped endothelial cells, supporting cells, EACs, macrophages, reticular
cells and fibres. Lymphocyte migration into the spleen parenchyma is most likely via the HEV-like
vessels. These research findings contribute to better understanding of avian immunology and provide
an insight into evolutionary differences in the immune system.
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