Enzyme-linked immunosorbent assay (ELISA)
We measured the levels of interleukin 6 (IL-6), tumour necrosis factor-α (TNF-α), tyrosinase (TYR), monoamine oxidase (MAO), and malondialdehyde (MDA) in the mouse or guinea pig sera using specific ELISA kits (NJJCBIO Co., Nanjing, China; Elabscience Biotechnology, China) according to the manufacturers’ instructions. The absorbance at 450 nm was measured using a Spectra Max M5 microplate reader (Molecular Devices, San Diego, CA, USA).