The expression of ICOS in SGs tested by RT-qPCR was found to be positively related to ESSDAI scores and positively associated with the grade of lymphocytic infiltration and hyperimmunoglobulin in pSS (Figures 6E–G), while there was no significant association was found with anti-SSA positivity, increased ESR, reduced C3, and keratoconjunctivitis sicca (Supplementary Figures 5H–K). Here, C3 is linked to Keratoconjunctivitis sicca.