IL15 and Parkinson disease: In serum, only 4 markers (of 27 reliably assayed markers; Supporting Information Table S3; Supporting Information Fig. S2) showed PD‐related changes with P < 0.05 (Fig. 3L–S): VCAM‐1 was increased in patients' serum, and IL‐15 and VEGF‐D were both increased in late versus early PD (Fig. 3L,R–S), whereas VEGF‐C was decreased in all patients (Fig. 3M).