PECAM1 and Thrombocytopenia: In addition to the virus-induced thrombocytopenia in infected HuPBL-NCG mice, we observed disorganization of vascular endothelium in sacrificed mouse lung sections by immunostaining with anti–platelet cell adhesion molecule 1 (PECAM-1; CD31) antibody and H&E staining (Figs 5A and S4).