Biological Activities of Murine Low-Affinity Fc Receptors for IgG |
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| Affiliation: | 1. International Tomography Center SB RAS, Institutskaya 3a, Novosibirsk 630090, Russia;2. Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russia;3. Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, Heidelberg 69120, Germany;4. Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, Berlin 14195, Germany;1. The State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, PR China;2. University of Chinese Academy of Sciences, Beijing 100049, PR China;3. Division of Magnetic Resonance, Korea Basic Science Institute Ochang Campus, Cheongwon-Gun, Ochang-Eup, Yangcheong-Ri 804-1, Chungcheongbuk-Do 363-883;4. Department of Bio-Analytical Science, University of Science and Technology, Daejon 305-333, South Korea;6. Department of Bioengineering, University of Washington, Seattle, Washington 98195;5. Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado 80523-1870 |
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| Abstract: | Murine low-affinity Fc receptors for IgG (FcγRIIbl, FcγRIIb2, and FcγRIII) bind the same IgG subclasses and are not distinguished by available anti-FcγRII/III mAbs (2.4G2). They trigger various biological activities, among which are the internalization of soluble and particulate immune complexes, cell activation, and its regulation. To determine the biological properties of the three murine receptors, each was expressed by stable transfection of corresponding cDNAs in two model cells: the murine lymphoma B cell IIA1.6 and the rat basophilic leukemia cell RBL-2H3. Biological activities of recombinant receptors were triggered with soluble immune complexes or 2.4G2 IgG in IIA1.6 cells, which express no FcγR, and with 2.4G2 Fab or F(ab′)2, cross-linked with mouse anti-rat F(ab′)2 in RBL, which express rat FcγR. Conditions for studying cell activation and endocytosis in both cell models are described, as are conditions for studying phagocytosis in RBL cells and antigen presentation or regulation of cell activation in IIA1.6 cells. Internalization of immune complexes was triggered by FcγRIIb2 and FcγRIII, but not by FcγRIIb1. Intracytoplasmic sequences required for phagocytosis and endocytosis could be distinguished in FcγRIIb2, but not in FcγRIII. Cell activation was restricted to FcγRIII. FcγRIII-mediated endocytosis, phagocytosis, and cell activation involved the consensus tyrosine-containing activation motif found in the intracytoplasmic domain of the γ subunit. Regulation of cell activation was induced by both FcγRII isoforms and depended on the same sequence as endocytosis. As a consequence, a single motif can determine more than one biological response of the cell, and a given response may be triggered by several motifs, borne by different FcγR. |
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