title: Induction of tumor necrosis factor alpha production by adhered human monocytes: a key role for Fcgamma receptor type IIIa in rheumatoid arthritis.
abstract: OBJECTIVE
  Small IgG rheumatoid factor immune complexes may provide the trigger for macrophage-derived tumor necrosis factor alpha (TNFalpha) production in rheumatoid arthritis. Immune complexes may bind to any of 3 IgG Fc receptors (FcgammaR). Therefore, the ability of monocyte-derived macrophages to produce TNFalpha was examined following ligation of each of the 3 human FcgammaR, using murine monoclonal antibodies (mAb) to each receptor as a model for small immune complexes.
  
  
  METHODS
  Adhered human monocytes expressing all 3 FcgammaR were incubated with murine anti-FcgammaR mAb directed against FcgammaRI, FcgammaRII, or FcgammaRIII. Supernatants were collected at various time points and tested for the presence of TNFalpha and interleukin-1alpha (IL-1alpha) by enzyme-linked immunosorbent assay.
  
  
  RESULTS
  The anti-FcgammaRIII mAb induced adhered human monocytes to release TNFalpha. However, F(ab)2 and Fab fragments of the anti-FcgammaRIII mAb failed to induce TNFalpha production. TNFalpha was undetectable following incubation with the anti-FcgammaRI or anti-FcgammaRII mAb. Furthermore, blocking FcgammaRI or FcgammaRII had no effect on the levels of TNFalpha released in response to the anti-FcgammaRIII mAb. Of the 3 anti-FcgammaR mAb, only anti-FcgammaRIII induced IL-1alpha production from adhered human monocytes, and this was inhibited by the presence of a neutralizing anti-TNFalpha mAb.
  
  
  CONCLUSIONS
  This study suggests a dominant role for FcgammaRIIIA in the induction of both TNFalpha and IL-1alpha production by human macrophages in rheumatoid arthritis following receptor ligation by small immune complexes. The signaling of TNFalpha production may require the ligation of either 3 FcgammaRIIIA receptors or only 2 FcgammaRIIIA receptors, where one interaction must involve binding via an Fc domain. In addition, IL-1alpha production following FcgammaRIIIA ligation appears to be dependent on the presence of TNFalpha.
authors.affiliation: University College London, UK.
authors.forename: V M
authors.initials: VM
authors.lastname: Abrahams
authors.forename: G
authors.initials: G
authors.lastname: Cambridge
authors.forename: P M
authors.initials: PM
authors.lastname: Lydyard
authors.forename: J C
authors.initials: JC
authors.lastname: Edwards
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000503:physiopathology*; D002448:Cell Adhesion / Q000502:physiology; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D009000:Monocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017452:Receptors, IgG / Q000276:immunology / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D007140:Immunoglobulin Fab Fragments; D017452:Receptors, IgG; D014409:Tumor Necrosis Factor-alpha