title: Immunotoxicity of silver nanoparticles in an intravenous 28-day repeated-dose toxicity study in rats.
abstract: BACKGROUND
  Nanosilver is used in a variety of medical and consumer products because of its antibacterial activity. This wide application results in an increased human exposure. Knowledge on the systemic toxicity of nanosilver is, however, relatively scarce. In a previous study, the systemic toxicity of 20 nm silver nanoparticles (Ag-NP) was studied in a 28-day repeated-dose toxicity study in rats. Ag-NP were intravenously administered with a maximum dose of 6 mg/kg body weight (bw)/day. Several immune parameters were affected: reduced thymus weight, increased spleen weight and spleen cell number, a strongly reduced NK cell activity, and reduced IFN-γ production were observed.
  
  
  METHODS
  Prompted by these affected immune parameters, we wished to assess exposure effects on the functional immune system. Therefore, in the present study the T-cell dependent antibody response (TDAR) to keyhole limpet hemocyanin (KLH) was measured in a similar 28-day intravenous repeated-dose toxicity study. In addition, a range of immunological parameters was measured. Data obtained using the benchmark dose (BMD) approach were analyzed by fitting dose-response models to the parameters measured.
  
  
  RESULTS
  A reduction in KLH-specific IgG was seen, with a lowest 5% lower confidence bound of the BMD (BMDL) of 0.40 mg/kg bw/day. This suggests that Ag-NP induce suppression of the functional immune system. Other parameters sensitive to Ag-NP exposure were in line with our previous study: a reduced thymus weight with a BMDL of 0.76 mg/kg bw/day, and an increased spleen weight, spleen cell number, and spleen cell subsets, with BMDLs between 0.36 and 1.11 mg/kg bw/day. Because the effects on the spleen are not reflected by increased KLH-specific IgG, they, however, do not suggest immune stimulation.
  
  
  CONCLUSIONS
  Intravenous Ag-NP administration in a 28-day repeated-dose toxicity study induces suppression of the functional immune system. This finding underscores the importance to study the TDAR to evaluate immunotoxicity and not to rely solely on measuring immune cell subsets.
authors.affiliation: Centre for Health Protection, National Institute for Public Health and the Environment, PO BOX 1, Bilthoven, BA 3720, The Netherlands. rob.vandebriel@rivm.nl.
authors.forename: Rob J
authors.initials: RJ
authors.lastname: Vandebriel
authors.forename: Elisa Cm
authors.initials: EC
authors.lastname: Tonk
authors.forename: Liset J
authors.initials: LJ
authors.lastname: de la Fonteyne-Blankestijn
authors.forename: Eric R
authors.initials: ER
authors.lastname: Gremmer
authors.forename: Henny W
authors.initials: HW
authors.lastname: Verharen
authors.forename: Leo T
authors.initials: LT
authors.lastname: van der Ven
authors.forename: Henk
authors.initials: H
authors.lastname: van Loveren
authors.forename: Wim H
authors.initials: WH
authors.lastname: de Jong
mesh_terms: D000818:Animals; D000917:Antibody Formation / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D001854:Bone Marrow Cells / Q000187:drug effects; D016207:Cytokines / Q000096:biosynthesis; D003601:Cytotoxicity Tests, Immunologic; D004305:Dose-Response Relationship, Drug; D004912:Erythrocytes / Q000378:metabolism; D006433:Hemocyanins; D006454:Hemoglobins / Q000378:metabolism; D007275:Injections, Intravenous; D007962:Leukocytes / Q000187:drug effects / Q000276:immunology; D008297:Male; D053768:Metal Nanoparticles / Q000633:toxicity*; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D012834:Silver / Q000276:immunology* / Q000633:toxicity*; D013154:Spleen / Q000166:cytology / Q000187:drug effects; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology
chemical_list: D016207:Cytokines; D006454:Hemoglobins; D012834:Silver; D006433:Hemocyanins; C032808:keyhole-limpet hemocyanin