pSS vs. HC: 58 proteins were ↑ and 46 were ↓. IFN-pos. and IFN-neg. pSS patients: ↑ IgG levels, higher frequency of anti-SSA and -SSB and ↓ levels of C3 complement in IFN-pos. pSS patients. 22 fatigued vs. 23 non-fatigued pSS patients: 14 serum proteins were ↑ including SNAP-25, ENO1, UCHL1 and 2 serum proteins were ↓ in fatigued. IL36a and several complement factors were upregulated in fatigued pSS patients compared to non-fatigued. Here, UCHL1 is linked to peeling skin syndrome.