In vitro studies of the effect of RAP and anti-LRP1 antibodies on megakaryopoiesis. (A) The effect of RAP on megakaryocyte colony formation. GST indicates empty GST without conjugated RAP. Graphed is the mean percentage of megakaryocytes per well plus 1 SD. Number of experiments, each performed in duplicate, is indicated in each bar. *P = .004 versus WT cultures without PF4; **P < .003 compared with WT culture with PF4. (B) The effect of anti-LRP1 antibody (MA5A6). Ig is isoimmune control for the anti-LRP1 antibody. Mean percentage of megakaryocytes per well plus 1 SD is graphed. Number of experiments done in duplicate is indicated in each bar. *P = .004 compared with WT without PF4; **P < .003 compared with WT with PF4; ***P = .04 compared with WT without PF4.