The Opsonic Effect of Lectin on Phagocytosis by Hemocytes of Kuruma Prawn, Penaeus japonicus

Abstract

Three morphologically distinct populations of hemocytes (hyaline, semigranular and granular cells) were isolated from the blood of the kuruma prawn, Penaeus japonicus, by Percoll continuous gradient centrifugation. All three types of hemocytes ingested glutaraldehydefixed sheep red blood cells (SRBC^f), and the phagocytic activity of semigranular cells and granular cells was significantly higher than that of hyaline cells. Phagocytosis of SRBC^f by the hemocytes was greatly enhanced by the opsonization of SRBC^f with kuruma prawn serum (KPS), but this opsonic activity of KPS was inhibited by N-acetylglucosamine (GlcNAc). Lectin was eluted from KPS-opsonized SRBC^f using 100 mM GlcNAc solution. The lectin which showed a strong opsonic activity had a molecular weight of 330 kDa and consisted of identical subunits of 33 kDa. The opsonic activity of the lectin was inhibited by GlcNAc, but not by heating (60°C, 15 min) nor by EDTA treatment. We therefore conclude that the opsonic activity of KPS on phagocytosis is dependent on the lectin in the serum.