title: The rs1143679 (R77H) lupus associated variant of ITGAM (CD11b) impairs complement receptor 3 mediated functions in human monocytes.
abstract: OBJECTIVE
  The rs1143679 variant of ITGAM, encoding the R77H variant of CD11b (part of complement receptor 3; CR3), is among the strongest genetic susceptibility effects in human systemic lupus erythematosus (SLE). The authors aimed to demonstrate R77H function in ex-vivo human cells.
  
  
  METHODS
  Monocytes/monocyte-derived macrophages from healthy volunteers homozygous for either wild type (WT) or 77H CD11b were studied. The genotype-specific expression of CD11b, and CD11b activation using conformation-specific antibodies were measured. Genotype-specific differences in iC3b-mediated phagocytosis, adhesion to a range of ligands and the secretion of cytokines following CR3 ligation were studied. The functionality of R77H was confirmed by replicating findings in COS7 cells expressing variant-specific CD11b.
  
  
  RESULTS
  No genotype-specific difference in CD11b expression or in the expression of CD11b activation epitopes was observed. A 31% reduction was observed in the phagocytosis of iC3b opsonised sheep erythrocytes (sRBC(iC3b)) by 77H cells (p=0.003) and reduced adhesion to a range of ligands: notably a 24% reduction in adhesion to iC3b (p=0.014). In transfected COS7 cells, a 42% reduction was observed in phagocytosis by CD11b (77H)-expressing cells (p=0.004). A significant inhibition was seen in the release of Toll-like receptor 7/8-induced pro-inflammatory cytokines from WT monocytes when CR3 was pre-engaged using sRBC(iC3b), but no inhibition in 77H monocytes resulting in a significant difference between genotypes (interleukin (IL)-1β p=0.030; IL-6 p=0.029; tumour necrosis factor alpha p=0.027).
  
  
  CONCLUSIONS
  The R77H variant impairs a broad range of CR3 effector functions in human monocytes. This study discusses how perturbation of this pathway may predispose to SLE.
authors.affiliation: Genetics and Molecular Medicine and Immunology, Infection and Inflammatory Disease, King’s College London, London, UK.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Rhodes
authors.forename: Barbara G
authors.initials: BG
authors.lastname: Fürnrohr
authors.forename: Amy L
authors.initials: AL
authors.lastname: Roberts
authors.forename: George
authors.initials: G
authors.lastname: Tzircotis
authors.forename: Georg
authors.initials: G
authors.lastname: Schett
authors.forename: Tim D
authors.initials: TD
authors.lastname: Spector
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Vyse
mesh_terms: D000328:Adult; D000818:Animals; D039481:CD11b Antigen / Q000737:chemistry / Q000235:genetics* / Q000276:immunology*; D019556:COS Cells; D002448:Cell Adhesion / Q000276:immunology; D002522:Chlorocebus aethiops; D016207:Cytokines / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology; D015870:Gene Expression / Q000276:immunology; D020022:Genetic Predisposition to Disease / Q000235:genetics; D014644:Genetic Variation; D005838:Genotype; D006720:Homozygote; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000235:genetics* / Q000276:immunology*; D016177:Macrophage-1 Antigen / Q000737:chemistry / Q000276:immunology*; D008264:Macrophages / Q000166:cytology / Q000276:immunology; D009000:Monocytes / Q000166:cytology / Q000276:immunology*; D010587:Phagocytosis / Q000276:immunology; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
chemical_list: D039481:CD11b Antigen; D016207:Cytokines; C509295:ITGAM protein, human; D016177:Macrophage-1 Antigen