Murad Vagida

Flow Virometry to Analyze Antigenic Spectra of Virions and Extracellular Vesicles

Cells release small extracellular vesicles (EVs) into the surrounding media. Upon virus infection cells also release virions that have the same size of some of the EVs. Both virions and EVs carry proteins of the cells that generated them and are antigenically heterogeneous. In spite of their diversity, both viruses and EVs were characterized predominantly by bulk analysis. Here, we describe an original nanotechnology-based high throughput method that allows the characterization of antigens on individual small particles using regular flow cytometers. Viruses or extracellular vesicles were immunocaptured with 15 nm magnetic nanoparticles (MNPs) coupled to antibodies recognizing one of the surface antigens. The captured virions or vesicles were incubated with fluorescent antibodies against other surface antigens. The resultant complexes were separated on magnetic columns from unbound antibodies and analyzed with conventional flow cytometers triggered on fluorescence. This method has wide applications and can be used to characterize the antigenic composition of any viral- and non-viral small particles generated by cells in vivo and in vitro. Here, we provide examples of the usage of this method to evaluate the distribution of host cell markers on individual HIV-1 particles, to study the maturation of individual Dengue virions (DENV), and to investigate extracellular vesicles released into the bloodstream.

Monocytes of Different Subsets in Complexes with Platelets in Patients with Myocardial Infarction

Acute myocardial infarction (AMI) is associated with activation of various cells, including platelets that form monocyte-platelet complexes (MPCs). Here, we analysed MPC in vivo and in vitro and investigated the abilities of different monocyte subclasses to form MPC, the characteristics of the cells involved in MPC formation and MPC changes in AMI. We identified MPC by co-staining for platelet antigen CD41a and monocyte antigens CD14 and CD16. Platelet activation was evaluated from expression of phosphatidylserine as revealed by annexin V. Our results confirm published data and provide new information regarding the patterns of MPC in AMI patients. We found that the patterns of platelet aggregation with monocytes were different in AMI patients and controls: (1) in AMI patients, MPC formed by intermediate monocytes carry more platelets whereas in healthy controls more platelets aggregated with classical monocytes; (2) the numbers of MPC in AMI patients, being already higher than in controls, were further increased if these patients suffered various in-hospital complications; (3) on the basis of the CD41a fluorescence of the antibody-stained MPC, some of the aggregates seem to consist of monocytes and platelet-derived extracellular vesicles (EVs); (4) aggregation of monocytes with platelet EV occurred in in vitro experiments; and (5) these experiments demonstrated that monocytes from AMI patients aggregate with both platelets and platelet EVs more efficiently than do monocytes from controls. MPC in AMI patients may play an important role in this pathology.

Addition of thrombin reduces the recovery of extracellular vesicles from blood plasma

Extracellular vesicles (EVs) are widely studied as a system of intercellular communication, as markers of various diseases, as well as a vehicle for delivery of various bioactive molecules to various cells. Investigation of EVs’ structure and function requires their isolation and precise quantification. However, in the current literature, there are significant discrepancies in the estimated numbers of EVs in different body fluids. In part, this discrepancy is due to the difference in EVs isolation protocols used by different investigators. A common protocol that includes ExoQuick™ is often used to isolate EVs from body fluids and culture medium. Here, we show that in the case of isolation of EVs from blood, thrombin should be omitted from the protocol as clots formed due to the thrombin-triggered coagulation may entrap many EVs thus leading to the underestimation of their numbers.