*4.7. Determination of ROS*

In brief, after being treated with the indicated concentrations of astaxanthin or astaxanthin plus LPS (100 ng/mL) for 24 h, DCs were collected and incubated with 10 μM DCFH-DA (Beyotime, Shanghai, China) for 20 min at 37 ◦C. After being washed three times with PBS, ROS generation was analyzed by FCM.

#### *4.8. Determination of the Lipid Peroxidation*

MDA is the marker of lipid peroxidation [63]. In vitro, after stimulation for 24 h with astaxanthin or astaxanthin plus LPS, DCs were collected and lysed with RIPA buffer. The MDA content in the cell lysate supernatants or serum specimens was measured with thiobarbituric acid (TBA) according to the manufacturer's instructions (NJBC, Nanjing, China). Briefly, 100 μL samples were mixed with 1 ml of TBA working solution. After being heated for 40 min at 95 ◦C and cooled to room temperature, the absorbance of the organic layer was determined at 530 nm.

#### *4.9. Determination of the GSH and GSSG*

In vitro, after stimulation for 24 h with astaxanthin or astaxanthin plus LPS, DCs were lysed by sonication in ice-cold 5% metaphosphoric acid and centrifuged at 10,000× *g* for 20 min to remove debris. The total glutathione (T-GSH) content and GSSG content in the cell lysate supernatants were measured by T-GSH/GSSG kits (NJBC, Nanjing, China) according to the manufacturer's instructions. The GSH content was obtained by subtracting the 2 × GSSG values from the T-GSH values.
