The animal care and use protocol was reviewed, and the experiments were approved by the Institutional Animal Care and Use Committee (IACUC) at Korea National Institute of Health (KNIH) (Approval Nos. NIH-06-15, NIH-07-16 and NIH-08-19). The experiments were approved by the Committee on the Ethics of Animal Experiments of the Korean Centers for Disease Control and Prevention (KCDC) (Korean Laboratory Animal Act No. KCDC-122-14-2A). The use of experimental animals was maintained and handled in strict accordance with institutional guidelines at KCDC. The serum samples were collected from experimental rats.