title: Fc gamma receptor IIb on GM-CSF macrophages controls immune complex mediated inhibition of inflammatory signals.
abstract: BACKGROUND
  In rheumatoid arthritis (RA) macrophages play a major role in amplifying synovial inflammation. Important activating signals are those induced by Toll-like receptor (TLR) ligands and by activated T cells. The balance between activating and inhibitory Fc gamma receptors (FcγRs) on macrophages might be crucial in modulating these inflammatory responses. The purpose of this study was to determine FcγR expression on pro- and anti-inflammatory macrophages (gmMφ and mMφ, respectively) and identify functional consequences on immune complex uptake and macrophage activation.
  
  
  METHODS
  Human monocytes were isolated and differentiated into gmMφ and mMφ. A full FcγR characterization of both macrophage subtypes was performed and uptake of fluorescent immune complexes (ICs) was determined. FcγRIIb isoforms were determined by qPCR. Macrophages were stimulated via different TLRs or cytokine activated T cells in the presence or absence of ICs and cytokine production was determined. Blocking studies were performed to look into the pathways involved.
  
  
  RESULTS
  mMφ expressed high levels of the activating FcγRIIa and FcγRIII and low levels of the inhibitory FcγRIIb, while the FcγR balance on gmMφ was shifted towards the inhibitory FcγRIIb. This was accompanied by a clear increase in FcγRIIb1 mRNA expression in gmMφ. This resulted in higher IC uptake by mMφ compared to gmMφ. Furthermore, FcγR-mediated stimulation of gmMφ inhibited TLR2, 3, 4 and 7/8 mediated cytokine production via FcγRIIb and PI3K signaling. In addition, gmMφ but not mMφ produced TNFα upon co-culture with cytokine activated T cells, which was reduced by IC binding to FcγRIIb. The latter was dependent on PI3K signaling and COX2.
  
  
  CONCLUSIONS
  FcγR expression patterns on gmMφ and mMφ are significantly different, which translates in clear functional differences further substantiating FcγRIIb as an interesting target for inflammation control in RA and other autoimmune/inflammatory diseases.
authors.affiliation: Department of Rheumatology & Clinical Immunology, University Medical Center Utrecht, Utrecht, the Netherlands; Laboratory of Translational Immunology, Department of Immunology, University Medical Center Utrecht, Utrecht, the Netherlands; Department of Rheumatology, Radboud university medical center, Nijmegen, the Netherlands.
authors.forename: Kim C M
authors.initials: KC
authors.lastname: Santegoets
authors.affiliation: Department of Rheumatology & Clinical Immunology, University Medical Center Utrecht, Utrecht, the Netherlands; Laboratory of Translational Immunology, Department of Immunology, University Medical Center Utrecht, Utrecht, the Netherlands; Department of Rheumatology, Radboud university medical center, Nijmegen, the Netherlands.
authors.forename: Mark H
authors.initials: MH
authors.lastname: Wenink
authors.affiliation: Department of Rheumatology, Radboud university medical center, Nijmegen, the Netherlands.
authors.forename: Wim B
authors.initials: WB
authors.lastname: van den Berg
authors.affiliation: Department of Rheumatology & Clinical Immunology, University Medical Center Utrecht, Utrecht, the Netherlands; Laboratory of Translational Immunology, Department of Immunology, University Medical Center Utrecht, Utrecht, the Netherlands; Department of Rheumatology, Radboud university medical center, Nijmegen, the Netherlands.
authors.forename: Timothy R D J
authors.initials: TR
authors.lastname: Radstake
mesh_terms: D000936:Antigen-Antibody Complex / Q000276:immunology; D018920:Coculture Techniques; D016207:Cytokines / Q000378:metabolism; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism*; D006801:Humans; D007249:Inflammation / Q000378:metabolism*; D016753:Interleukin-10 / Q000378:metabolism; D008024:Ligands; D008213:Lymphocyte Activation; D008264:Macrophages / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009000:Monocytes / Q000166:cytology / Q000378:metabolism; D010587:Phagocytosis; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011485:Protein Binding; D017452:Receptors, IgG / Q000378:metabolism*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000166:cytology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D000936:Antigen-Antibody Complex; D016207:Cytokines; C080571:Fc gamma receptor IIB; D008024:Ligands; D017452:Receptors, IgG; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D019869:Phosphatidylinositol 3-Kinases