PPA2 and autoimmune disease: Especially, we identified a total of 11 common hub genes expressed both in air pollutants and autoimmune diseases, including BEND3, PPA2, PSMG2, RNF40, ZMYM1, ZNF780A, SFR1, NDST2, SLC35A1, OLIG1, and PI4KB (Table 3 and Additional file 1: Fig. S3), which will provide a reliable theoretical basis for exploring the pathological mechanisms of air pollutants molecules in the occurrence and development of autoimmune diseases.