Effect of PF4 and various peptides (p47-55, p47-58, p47-70, and p58-70) of PF4 on the formation CFU-MK. Values are expressed as mean ± SEM of triplicate determination obtained from three separate experiments. *P < .01 as compared with control value determined by the Student's t-test. One hundred percent (100%) corresponds to the number of megakaryocyte colonies (75 colonies/mL) in control cultures.