HS is elevated in serum samples of human allo-HSCT recipients with GVHD. (A) Serum samples from allo-HSCT recipients were tested for HS by ELISA. Patients were divided into 3 groups: no GVHD (grade 0; n = 8), mild GVHD (grade 1-2; n = 17), and moderate to severe GVHD (grade 3-4; n = 11; *P = .003, **P = .0009, ***P = .01). (B) Serum HS levels relative to time of diagnosis of GVHD in patients with grades 1 to 2 and grade 3 to 4 GVHD. Average ± SEM plotted (*P = .01).