Receptor-mediated endocytosis of immune complexes in rat... : Hepatology (original) (raw)

Liver Biology/Pathobiology

Receptor-mediated endocytosis of immune complexes in rat liver sinusoidal endothelial cells is mediated by FcγRIIb2

Mousavi, Seyed Ali1; Sporstφl, Marita1; Fladeby, Cathrine1; Kjeken, Rune1; Barois, Nicolas1; Berg, Trond1*

1 Department of Molecular Biosciences, University of Oslo, Norway

* Department of Molecular Biosciences, University of Oslo, P.O. Box 1041, Blindern, 0316 Oslo, Norway

Email:[email protected]

Received 19 October 2006; Accepted 27 March 2007

Published online in Wiley InterScience (www.interscience.wiley.com).

Grant sponsor: Norwegian Cancer Society.

Potential conflict of interest: Nothing to report.

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Abstract

Liver sinusoidal endothelial cells (LSECs) display a number of receptors for efficient uptake of potentially injurious molecules. The receptors for the Fc portion of immunoglobulin G (IgG) antibodies (FcγRs) regulate a number of physiological and pathophysiological events. We used reverse transcription polymerase chain reaction (RT-PCR) and Western blotting to determine the expression of different types of FcγRs in LSECs. Biochemical approaches and immunoflorescence microscopy were used to characterize the FcγR-mediated endocytosis of immune complexes (ICs). FcγRIIb2 was identified as the main receptor for the efficient uptake of ICs in LSECs. The receptor was shown to use the clathrin pathway for IC uptake; however, the association with lipid rafts may slow the rate of its internalization. Moreover, despite trafficking through lysosomal integral membrane protein-II (LIMP-II)–containing compartments, the receptor was not degraded. Finally, it was shown that the receptor recycles to the cell surface both with and without IC. Conclusion: FcγRIIb2 is the main receptor for endocytosis of ICs in rat LSECs. Internalized ICs are degraded with slow kinetics, and IC internalization is not linked to receptor downregulation. After internalization, the receptor recycles to the cell surface both with and without ICs. Thus, FcγRIIb2 in rat LSECs is used as both a recycling receptor and a receptor for efficient IC clearance. (Hepatology 2007.)

**Abbreviations:**125I-TC, radiolabeled tyramine cellobiose; Ag, antigen; AP-3, adaptor protein 3; BSA, bovine serum albumin; BSA-DNP, dinitrophenylated bovine serum albumin; DRM, detergent-resistant membranes; EEA1, early endosomal auto-antigen 1; FcγRs, Fc gamma receptors; IC, immune complexes; IgG, immunoglobulin G; LIMP-II, lysosomal integral membrane protein-II; LSEC, liver sinusoidal endothelial cells; MHC, major histocompatibility complex; OVA, ovalbumin; PBS, phosphate-buffered saline; PCR, polymerase chain reaction; RT-PCR, reverse transcription polymerase chain reaction; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis; TCA, trichloracetic acid.