Identification of Blood Flow Type and Position of Blood Barrier in the Fruit Bat Spleen

The blood-spleen barrier (BSB) is essential for filtering blood-borne particles, removing damaged erythrocytes, and initiating immune responses. Therefore, this study aimed to investigate the location, structural components, and functional implications of the BSB in fruit bats (Cynopterus titthaecheilus and Rousettus leschenaultii) using intravenous India ink injection as a tracer. A total of seven wild-caught bats were examined histologically after splenic sampling and staining with haematoxylin-eosin, toluidine blue, and Masson's trichrome. Carbon particles were distributed in several splenic compartments, but the highest accumulation occurred in the marginal zone, ellipsoid, and periellipsoidal lymphoid sheaths, suggesting these regions as the principal BSB sites. Additional deposits in the splenic cord and sinus reported further downstream filtration within the red pulp. Carbon residues were also observed in the white and red pulp, suggesting continued inclusion in specific immune induction and phagocytic clearance after primary filtration. The splenic microcirculation of both species comprised open and closed pathways. The results showed that fruit bat spleen possessed a well-developed BSB centered in the marginal zone ellipsoid-PELS complex, with subsequent processing in red pulp structures, supporting integrated innate and adaptive immune defence against blood-borne material. The understanding of splenic filtration architecture was also refined in chiropteran mammals.