SUMMARYMicroparticles (MPs) are small membrane vesicles released from activated cells and are associated with thrombosis and inflammation. Microparticles contain a unique subset of surface proteins derived from the parent cell and may be responsible for their diverse biological functions. To identify these proteins juvenile baboons (Papio anubis, n=4) underwent iliac vein thrombosis with six-hour balloon occlusion. Plasma samples were taken at baseline and at 2 days post thrombosis for MP analysis. Microparticles were extracted from platelet-poor plasma, digested separately with trypsin and tagged using iTRAQ reagents. The digests were subjected to 2-D LC separation followed by MALDI tandem mass spectrometry. Peak lists were generated and searched against all primate sequences. For protein identity, a minimum of two peptides at 95% confidence was required. Later, iTRAQ ratios were generated comparing relative protein level of day-2 to baseline. The proteomic analysis was performed twice for each blood sample, totaling 8 experiments. Proteins were considered elevated or depressed if the iTRAQ ratio deviated by 20% change from normal and a p-value less than 0.05. Significantly, 7 proteins were differentially expressed on day-2 compared to baseline, and appeared in at least two animals and regulated in at least 4 experiments, and appeared in at least three animals and regulated in at least four experiments. Among these 7 proteins, up-regulated proteins include various forms of fibrinogen and alpha-1-antichymotrypsin, and down-regulated proteins include immunoglobulins. These proteins influence thrombosis and inflammation through hemostatic plug formation (fibrinogen), inhibiting neutrophil adhesion (alpha-1-antichymoptrypsin), and immunoregulation (immunoglobulins). Further studies are needed to confirm the mechanistic role of these proteins in the pathogenesis of venous thrombosis.