Flow Virometry for Characterizing the Size, Concentration, and Surface Antigens of Viruses.

Application of flow cytometry principles for the analysis of viruses has been referred to as flow virometry (FVM). FVM is a multiparametric, high-throughput, and sensitive technique that allows viral particles to be detected, quantified, and characterized based on the biophysical properties of the virus and the expression of proteins on their surface. More specifically, by calibrating the flow cytometer with reference materials, it is possible to measure the concentration of intact viral particles in a sample, the abundance of a target antigen on the surface of the virus, and the relative diameter of the virus. Here, we describe a comprehensive overview of procedures used to stain, detect, and quantify viral and host-derived proteins located on the surface of retroviruses. These outlined techniques can be applied for the rapid phenotypic characterization of retroviruses, other enveloped viruses, and generally most viruses at the single-particle level through the direct staining of viruses collected from the supernatant of infected cells, without the need for enrichment or purification. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Virus production Basic Protocol 2: Instrument setup, standardization, and quality control for fluorescence quantification Basic Protocol 3: Flow virometry analysis Basic Protocol 4: Viral surface antigen staining and fluorescence quantification Support Protocol: Determination of the optimal antibody concentration for virus staining Basic Protocol 5: Gain configuration optimization.