Microarray analysis and bioinformatics
The spleens of mice in the 10 mg/kg/day group at week 3 were used for microarray analysis. Total RNA was extracted using the Trizol reagent (Invitrogen, Carlsbad, CA, USA). The Agilent 2100 Bioanalyzer System (Agilent Technologies, Inc., Waldbronn, Germany) was used to assess the quality and quantity of purified total RNA. Only the samples that passed the RNA quality test were used in the subsequent assays. 

1 week measurement

Male BALB/c mice (4-5 weeks of age) were purchased from the Department of Laboratory Animal Science, Peking University (Beijing, China) and bred and housed under pathogen-free conditions at the animal care facility. All of the animal experiments conformed to the principles of care and use of laboratory animals and were approved by the Institutional Animal Care and Use Committee of Peking University. The mice were randomly distributed into four groups, with each group consisting of 28 mice. The four groups of mice were orally exposed to 0, 2.5, 5, and 10 mg/kg/day PFOS, respectively, via gastric gavage, and the vehicle control group (0 mg/kg/day) was treated with an equal volume of ddH2O (with 0.5% Tween-20). The treatment continued for 3 weeks,  followed by a one-week recovery period. The mice in each group were sacrificed by cervical dislocation every 7 days and the spleens were immediately isolated, weighed, and divided into three portions for the following treatments: one portion was fixed in 4% paraformaldehyde for histological examination (see in Supplementary materials.), the second portion was frozen and stored at 80 C for RNA and protein extraction, and the third was immediately made into a single-cell suspension and red blood cells were lysed for lymphocyte phenotyping and lymphoproliferation analyses. Additionally, a hemocytometer was used to count the number of splenocytes in cell suspension and Trypan blue exclusion was used to assess cell viability, which was always >90%.