PECAM1 and Thrombocytopenia: Investigations of immature and mature platelets in mouse models of regenerative thrombocytopenia suggest that cellular aging affects the surface expression of certain receptors including CD41, CD61, CD31, CD36, CD9, TLR2, TLR9, CD62P, CD63, and CD107a (and CD40L in the R300 mouse model) on platelets.