title: CD200-dependent and nonCD200-dependent pathways of NK cell suppression by human IVIG.
abstract: OBJECTIVE
  Intravenous immunoglobulin (IVIG) has been used to suppress autoimmune and inflammatory disorders by a variety of mechanisms. Recently, the CD200 tolerance-promoting signal has been found to play a role in IVIG suppression of blood natural killer (NK) cells. Further, different types of IVIG have been reported to differ in this activity, and that has been related to efficacy (and inefficacy) of treatment of women with pregnancy failure. CD200 acts by binding to CD200 receptors (C200R). The objective of this study was to determine if CD200-dependent NK suppression by IVIG involved direct binding of IVIG-associated CD200 molecules to CD200R on NK cells.
  
  
  METHODS
  Peripheral Blood Lymphocytes isolated from human blood were used as a source of NK cells to lyse Cr(51)-labelled K562 target cells in vitro in 18 and 4 h assays, and three different types of IVIG were tested for suppressive activity in the presence or absence of specific monoclonal anti-huCD200. In some experiments, CD56(+) NK cells were purified using anti-CD56 magnetic beads. Western blotting of IVIG using a specific anti-huCD200 antibody was done. Enzyme-Linked ImmunoSorbent Assays were used to measure cytokine production in NK assays.
  
  
  RESULTS
  Different IVIGs showed significant differences in potency in suppressing NK cytolytic activity in vitro (mg/ml for 60% suppression, Gammagard 4.1, Gamunex 14.1, Gamimmune 20.2). For CD200-dependent suppression, Gammagard was twice as potent as Gamimmune, but equivalent to Gamunex. The presence of suppression in 4 hour assays indicated stimulation of cytokine synthesis was unlikely to explain CD200-dependent suppression. Purification of NK cells led to loss of the CD200-dependent component. Western blotting confirmed that material reactive with anti-CD200 antibody was present in Immunoglobulin G (IgG) preparations, and at a lower level in human serum that contains IgG.
  
  
  CONCLUSIONS
  IVIGs are not all equipotent in suppressing NK cell cytolytic activity. CD200 associated with IVIG is an important component of suppression. CD200-dependent suppression appears to be mediated by a non-NK population that then acts on NK cells by direct contact rather than indirectly through release of immunosuppressive cytokines.
authors.affiliation: Department of Medicine, McMaster University, 1200 Main St. West., Hamilton, ON L8N 3Z5, Canada. clarkd@mcmaster.ca
authors.forename: David A
authors.initials: DA
authors.lastname: Clark
authors.forename: Karrie
authors.initials: K
authors.lastname: Wong
authors.forename: Daljeet
authors.initials: D
authors.lastname: Banwatt
authors.forename: Ziqhi
authors.initials: Z
authors.lastname: Chen
authors.forename: Jian
authors.initials: J
authors.lastname: Liu
authors.forename: Lydia
authors.initials: L
authors.lastname: Lee
authors.forename: Reginald M
authors.initials: RM
authors.lastname: Gorczynski
authors.forename: Morris A
authors.initials: MA
authors.lastname: Blajchman
mesh_terms: D015703:Antigens, CD / Q000502:physiology*; D002460:Cell Line; D002469:Cell Separation; D005260:Female; D006801:Humans; D016756:Immunoglobulins, Intravenous / Q000145:classification / Q000627:therapeutic use*; D007165:Immunosuppression Therapy; D007694:Killer Cells, Natural / Q000166:cytology / Q000276:immunology*; D011247:Pregnancy; D015398:Signal Transduction / Q000276:immunology*
chemical_list: D015703:Antigens, CD; D016756:Immunoglobulins, Intravenous; C042739:antigens, CD200