Histological Distribution of MHC Class II‒expressing Cells Responsible for Ingestion of Blood‒borne Exogenous Particles in Japanese Flounder Paralichthys olivaceus

This study investigated the ability of MHC class II‒expressing cells to ingest blood-borne exogenous particles and their tissue distribution in Japanese flounder Paralichthys olivaceus. ​Carbon particles were injected into a blood vessel in the caudal peduncle. ​After 3 h, carbon-laden MHC class II‒expressing cells were found in the spleen and the kidney, and localised in ellipsoids, splenic cords, peritubular sinuses and interstitial veins of the kidney. ​Additionally, the percentage of these cells was significantly higher in the spleen than the kidney. ​These results suggest that the spleen is the main organ that plays a role in the ingestion of blood‒borne exogenous particles for antigen presentation.