Fig. 6.

Quantification of the effects of TPO on P-selectin A) and VWF B) expression at different stages of maturation in the spleen of WT and Gata1^low mice. Representative semithin sections from the spleens of WT and Gata1^low mice were immunostained for P-selectin (Fig. 4) and VWF (Fig. 5) and numbers of gold particles within each MK determined, before and on day 7 of TPO-treatment. MKs were classified as immature (stage I/II), immature (stage III/IV) or heavy electron dense (H) and numbers of P-selectin and VWF gold particles per MK in each group determined. Results are presented as the mean6SD of determinations in eight MKs for each experimental group except for stage I/II MKs in untreated WT mice for which only two MKs were available. As seen in the upper left panel, TPO-treatment did not induce a statistically significant difference in P-selectin expression in MKs from the spleen of WT mice. The upper right panel shows that significantly more P-selectin gold particles were observed in the mature MKs in the spleen of TPO-treated Gata1^low mice than in the immature MKs of untreated Gata1^low mice (p = 0.003). As seen in the lower left panel, immature MKs in the spleen from TPO-treated WT mice expressed significantly fewer VWF-gold particles than mature MKs from untreated WT mice (p < 0.001). As seen in the lower right panel, TPO did not significantly alter the expression of VWF in MKs from the spleen of Gata1^low mice.