Mutation of PIRB causes mild thrombocythemia. (A) The expression of LILRB2 in human peripheral leukocytes (H-Leu) and human platelets (H-Plt). (B) The expression of PIRB in mouse peripheral leukocytes (M-Leu) and mouse platelets (M-Plt). (C) The expression of PIRB in WT mouse leukocytes (M-Leu) and platelets (M-Plt). Washed WT or PIRB-TM platelets at a concentration of 3 × 10⁷/mL were incubated with PerCP-conjugated rat anti-mouse PIRB monoclonal antibody or PerCP-conjugated rat IgG control at 25°C for 30 minutes. The expression of PIRB on WT and PIRB-TM platelets was analyzed using flow cytometer. (D) The platelet counts in the peripheral blood of WT and PIRB-TM mice (WT, n = 10; PIRB-TM, n = 10; mean ± standard error of the mean [SEM]; **P < .01). (E) The percentage of CD41b-positive cells in WT and PIRB-TM mice bone marrow (BM) (WT, n = 5; PIRB-TM, n = 5; mean ± SEM; **P < .01).