title: Structure-function studies for in vitro chemical inhibition of Fc gamma receptor-mediated phagocytosis.
abstract: BACKGROUND
  Previous studies [Transfusion 2005;45:384] showed that certain chemical compounds containing sulfur-reactive groups can inhibit Fcgamma receptor (FcgammaR)-mediated phagocytosis in vitro. These studies, however, did not prove that only sulfur functionality-induced reactivity was efficacious. In an effort to develop a drug-based approach for the future treatment of immune-mediated cytopenias, these earlier findings have now been extended and this chemically induced interference with FcgammaR-mediated phagocytosis of anti-D-coated red cells (RBCs) was examined to assess the optimal structural requirements for the inhibitory effect.
  
  
  METHODS
  Chemical compounds were purchased or synthesized and used for the assessment of which chemical moiety(-ies) were required for successful inhibition of in vitro phagocytosis of anti-D-coated RBCs with a monocyte monolayer assay.
  
  
  RESULTS
  Using compounds having similar structures but differences in reactive moieties, it was proved that the only chemical moiety that was required for inhibition of FcgammaR-mediated phagocytosis in vitro was a disulfide bond. It is also shown, however, that a p-nitrophenyl group provides significant enhancement to the inhibitory effect of disulfide-containing compounds. Involvement of carbonyl and hydroxyl functional groups was also able to be ruled out.
  
  
  CONCLUSIONS
  Our results confirm and extend previous studies that suggested that only those compounds that target free sulfhydryl groups on the monocyte-macrophage are most effective at blocking phagocytosis of antibody-coated RBCs in vitro. It is also shown that p-nitrophenyl substituent groups have an enhancing effect on the efficacy of disulfide bond-containing compounds. These findings should aid in the design of a drug-based approach for the future treatment of immune cytopenias.
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, The Division of Cell and Molecular Biology, Toronto General Research Institute, Canadian Blood Services, Toronto, Ontario, Canada.
authors.forename: Alison H
authors.initials: AH
authors.lastname: Foo
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Fletcher
authors.forename: Richard F
authors.initials: RF
authors.lastname: Langler
authors.forename: Charlotte H
authors.initials: CH
authors.lastname: Porter
authors.forename: Donald R
authors.initials: DR
authors.lastname: Branch
mesh_terms: D000906:Antibodies / Q000276:immunology; D004220:Disulfides / Q000737:chemistry* / Q000494:pharmacology*; D004912:Erythrocytes / Q000276:immunology; D006801:Humans; D066298:In Vitro Techniques; D008264:Macrophages / Q000187:drug effects* / Q000276:immunology; D009578:Nitrobenzenes / Q000737:chemistry / Q000494:pharmacology; D009596:Nitrophenols / Q000737:chemistry / Q000494:pharmacology; D010587:Phagocytosis / Q000187:drug effects* / Q000276:immunology; D017452:Receptors, IgG / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000276:immunology; D013329:Structure-Activity Relationship; D013438:Sulfhydryl Compounds / Q000737:chemistry / Q000494:pharmacology
chemical_list: D000906:Antibodies; D004220:Disulfides; D009578:Nitrobenzenes; D009596:Nitrophenols; D017452:Receptors, IgG; D013438:Sulfhydryl Compounds; C024836:4-nitrophenol