Thrombin-cleaved Opn but not intact Opn significantly inhibits hematopoiesis in the presence of 6-factor stimulation. (A) Sorted CD34⁺CD38^– HSCs (384 per well) were plated in serum-deprived media (SDM) supplemented with 6 factors (▦) and intact bovine Opn (bOPN; ▪), hyaluronic acid binding protein (HABP; ▥), tcOpn (□), or the thrombin control (▤). After 6 days there was significant inhibition of cell proliferation in the presence of HABP and tcOpn. Data are the mean ± SEM of quadruplicate wells and are representative of 6 independent experiments. *P < .05 compared with SDM following analysis by one-way ANOVA and a means comparison using Tukey test. (B) Sorted CD34⁺CD38^– HSCs (384 per well) were plated in the presence of SDM supplemented with 6 factors (▦), HABP (▥), or limiting doses of tcOpn (□) for 6 days. Data demonstrate a significant dose response with a maximal effect with 15μg/mL tcOpn. Data are the mean ± SEM of quadruplicate wells from 3 independent experiments. *P < .05 compared with SDM following analysis by one-way ANOVA and a means comparison using Tukey test. (C) After 6 days of culture, cells in panel B were analyzed for myeloid differentiation by the presence of CD15. In the presence of HABP or tcOpn there was a significant reduction in differentiation into myeloid cells. *P < .05 compared with SDM following analysis by one-way ANOVA and a means comparison using Tukey test.