The distribution of serum HMGB1 and anti-HMGB1 antibodies concentrations of the 92 FUO patients diagnosed with definitive etiologies (subtypes) was shown in the two-dimensional scatter plot (Fig. 2a), which showed the ratio of serum HMGB1/anti-HMGB1 antibodies had a good diagnostic value in the differential diagnosis of different subtypes of FUO, especially in the subgroups of infectious diseases and autoimmune diseases. Here, HMGB1 is linked to autoimmune disease.