Carboxyfluorescein succinimidyl ester (CFSE) assay
For cell proliferation assay, CD4 cells were incubated with 5 μM CFSE (CellTrace™ CFSE Cell Proliferation Kit, Invitrogen/Thermo Fisher Scientific, Waltham, MA) at 37°C for 10 min. After PBS washing, the CFSE-labeled CD4+ cells were seeded onto anti-CD3- and anti-CD28-coated plates, and cocultured with Fut1 KO or C57BL/6 WT splenocytes as described above. The CFSE fluorescence was measured using a flow cytometer (Cytek Aurora Flow Cytometer, Cytek biosciences, Fremont, CA).