title: Platelets convert peripheral blood circulating monocytes to regulatory cells via immunoglobulin G and activating-type Fcγ receptors.
abstract: BACKGROUND
  Monocytes and macrophages produce interleukin (IL)-10, an immunoregulatory cytokine and a potent therapeutic tool for immune disorders. Augmentation of IL-10 production with a concomitant reduction of proinflammatory cytokines in macrophages in vitro is attained by doubly stimulating the cells with a toll-like receptor ligand and immunoglobulin (Ig)G immune complexes, a response known as that of regulatory (or alternatively activated/M2) macrophages. However, it has not been explored sufficiently how such a regulatory response could be exploited for anti-inflammation. Our objective is to find a potential way or condition for augmenting IL-10 by monocytes/macrophages in vivo and in vitro.
  
  
  RESULTS
  We show that platelets, when they are opsonized with IgG, can convert human peripheral blood circulating monocytes to IL-10-producing regulatory monocytes in vitro and also in a murine in vivo model. Co-culturing of platelets and monocytes in the presence of anti-integrin IgG and a bacterial lipopolysaccharide augmented IL-10 production via a direct interaction between platelets and monocytes. This novel way of enhancing IL-10 was mediated by activating-type Fc receptors for IgG.
  
  
  CONCLUSIONS
  These findings indicate that the IgG-bound platelet-induced conversion of monocytes to regulatory cells might provide a novel strategy for controlling inflammation.
authors.affiliation: Department of Experimental Immunology, Institute of Development, Aging and Cancer, Tohoku University, 4-1 Seiryo-machi, Aoba-ku, Sendai, 980-8575, Japan. inui@idac.tohoku.ac.jp.
authors.forename: Masanori
authors.initials: M
authors.lastname: Inui
authors.affiliation: Department of Experimental Immunology, Institute of Development, Aging and Cancer, Tohoku University, 4-1 Seiryo-machi, Aoba-ku, Sendai, 980-8575, Japan. tazawa@idac.tohoku.ac.jp.
authors.forename: Kino
authors.initials: K
authors.lastname: Tazawa
authors.affiliation: Medical & Biological Laboratories, Co., Ltd., 4-5-3, Sakae, Naka-ku, Nagoya, 460-0008, Japan. kishi.yoshiro@mbl.co.jp.
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Kishi
authors.affiliation: Department of Experimental Immunology, Institute of Development, Aging and Cancer, Tohoku University, 4-1 Seiryo-machi, Aoba-ku, Sendai, 980-8575, Japan. tostakai@idac.tohoku.ac.jp.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Takai
mesh_terms: D019138:Antibodies, Blocking / Q000494:pharmacology; D001775:Blood Circulation; D001792:Blood Platelets / Q000187:drug effects / Q000276:immunology*; D002450:Cell Communication / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D018920:Coculture Techniques; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism*; D056747:Immunomodulation; D016023:Integrins / Q000276:immunology / Q000378:metabolism; D016753:Interleukin-10 / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism; D009000:Monocytes / Q000187:drug effects / Q000276:immunology*; D017452:Receptors, IgG / Q000378:metabolism*
chemical_list: D019138:Antibodies, Blocking; D007074:Immunoglobulin G; D016023:Integrins; D008070:Lipopolysaccharides; D017452:Receptors, IgG; D016753:Interleukin-10