Internalization of large particles by turbot (Scophthalmus maximus) IgM+ B cells mainly depends on macropinocytosis

Increasing evidence has demonstrated support for the endocytic capacities of teleost B cells. In the present study, the ability of turbot IgM(+) B cells to ingest microspheres of different sizes and the corresponding internalization pathways were investigated. The results showed that IgM(+) B cells exhibited relatively high endocytic capacities for 0.5 mu m and 1 mu m latex beads, and that different mechanisms were employed for IgM(+) and IgM(-) cells to uptake 0.5 gm and 1 gm beads. For 0.5 gm beads, IgM(+) B cells apparently employed macropinocytosis-dependent endocytic pathway, whereas IgM(-) cells utilized a different process involving both clathrin-and caveolae-mediated pathways. For the uptake of 1 mu m beads, IgM(+) cells relied mainly on macropinocytosis and partially on caveolae-mediated pathway, while IgM(-) cells utilized the routes similar to that of internalizing 0.5 mu m beads. Consistently, the internalized microspheres were co-localized with high-molecular-mass dextran in IgM(+) phagocytic cells. In addition to latex beads, IgM(+) B cells could also ingest inactivated bacteria predominately through macropinocytosis and caveolae-mediated endocytosis. These results collectively indicated that macropinocytosis is principally responsible for particle uptake by turbot IgM(+) B cells. (C) 2018 Elsevier Ltd. All rights reserved.