Identification of proteasome-containing PEVs under physiological and pathological conditions. (A) Proteasome-containing PEVs detected by hs-FCM are found in PFP from platelet concentrates that caused ATRs in recipients and in control concentrates that did not induce ATRs. The total number of proteasome-containing PEVs (containing mitochondria [mito] or not; proteasome+mito+ PEVs or proteasome+mito− PEVs) did not significantly differ between control and ATR, whereas proteasome−mito+ PEVs increased in ATR (no ATR group [n = 33] vs the ATR reaction group [n = 34], matched in duration of storage; data are the mean ± standard error of the mean [SEM]; ****P < .0001 (Student t test). NS, nonsignificant. (B) Proteasome-containing PEVs detected by hs-FCM are found in bronchoalveolar lavage fluid from mice after induction of transfusion-related acute lung injury (TRALI) with the 34-1-2s and AF6-88.5.5.3 antibodies and in control mice (n = 5) Data are the mean ± SEM; Student t test. NS, nonsignificant. (C) Proteasome-containing PEVs were detected at significantly higher levels in mice 1 hour after IV injection of HA-IgG vs control (diluent) mice (n = 3). Data are the mean ± SEM. **P< .01 (Student t test). PFP, platelet-free plasma.