**6. Conclusions**

Extracellular vesicles are small phospholipid bilayer particles that carry various biologically active molecules, such as proteins, lipids and nucleic acids. Their key biological function is cell–cell communication and the transfer of cargo. EVs normally circulate in the bloodstream of healthy individuals, but their levels are elevated in various pathological conditions, including APS. The classification, isolation and characterization of EVs has been developing in an accelerated manner over the last 20 years. Nevertheless, terms such as exosomes and microparticles are still present in the literature, but it is important to note that this classification is based on biogenesis, which is rather difficult to assess. It is therefore more optimal to classify EVs based on their other characteristics, such as size, density, origin etc. Each isolation and characterization techniques have their advantages and disadvantages and influences the properties of the EVs studied. Choosing the best combination, albeit of different isolation techniques, along with the characterization of EVs, is of utmost importance to achieve good data quality. In addition, the limitations of the methods used in both isolation and characterization must be considered. In the rapidly developing field of EVs research, variations of existing methods, as well as new technologies, are emerging that enable more precise isolation and characterization of EVs. EVs from platelets, monocytes and endothelial cells play a crucial role in vascular dysfunction, which is a causal factor in the disturbance of hemostasis and the development of thrombosis. Platelet and monocyte EVs are involved in the increased adhesiveness of endothelial cells and the increased interaction of leukocytes with the endothelium. Platelet, monocyte and endothelial EVs carry procoagulant molecules, such as TF, and modulate the expression of coagulation molecules in endothelial cells. Research on EVs in APS is very heterogeneous, due to the lack of standardization of isolation and characterization methods, all of which limits solid findings and conclusions. In addition to the technological challenges, EVs in APS are difficult to study because of the puzzling nature of APS. It is a chronic disease with a complex clinical spectrum due to many different features and symptoms (e.g. hypertension, thrombocytopenia). Patients with APS receive lifelong treatment with anticoagulants, and the actual acute phase is practically impossible to monitor. However, in view of the data on EVs in APS, a trend towards elevated total endothelial and platelet EV levels can be observed, suggesting an activated endothelium, even in the absence of an acute event. The results of the study of sEVs suggest that smaller vesicle populations may also play a role in the pathogenesis of APS. It appears that in patients with APS, levels of sEVs and different medium/large EVs are elevated. Further research is needed to confirm this in a larger number of patients as well as determine their functionality in APS. Data on increased levels of endothelial EVs in APS is supported by *in vitro* studies showing elevated levels of endothelial EVs following stimulation of endothelial cells with aPL. Studies investigating the role of aPL in vesicular release and its effects on the original cells also suggest that both small and medium/large EVs may play an important role in endothelial dysfunction in APS. However, future studies are needed to obtain a clearer picture of the signaling pathways and key molecules involved in interactions of EVs with the target cells.

*Antiphospholipid Syndrome - Recent Advances in Clinical and Basic Aspects*
