PECAM1 and Thrombocytopenia: On the first day of regenerative thrombocytopenia when the proportion of immature platelets was highest, the expression levels of almost all surface markers (CD41, CD61, CD31, CD9, TLR2, and TLR9) was significantly higher in immature platelets than mature platelets expect for TLR4 expression (Figure 4A), which mirrored the results obtained in the PF4 iDTR mice.