Angiogenesis occurs exclusively in target organs and precedes leukocyte infiltration during GHVD. (A-C) Leukocyte infiltration: percentage of CD4-, CD8-, CD11b-, and Gr1-positive area in GVHD-target organs colon, skin, and liver of allogeneic (ALLO) compared with syngeneic transplanted mice (SYN) 2 days (d+2) after BMT. Vascular density: percentage of CD31-positive area in colon and skin and EC number in liver of SYN and ALLO mice at day+2 after BMT. (D) Time course of CD4⁺ and CD8⁺ lymphocyte infiltration. The red box marks first significant increase in CD4- and CD8-positive area in ALLO mice. Untreated (Naive) and only chemotherapy-conditioned (Chemo) mice served as control and showed no infiltration. (E) Vascular density in nonclassical target organs skeletal and cardiac muscle and joints at day+2, +7, and +15 after BMT. Untreated mice (Naive) served as control. Data pooled from 2 independent experiments (naive, chemo, n = 5 per group; SYN, ALLO, n = 10-12 per group). Error bars indicate mean ± SEM. *P < .05; **P < .01; ***P < .001; n.s., not significant by Student t test (2-tailed).