About 50 years ago, flow cytometry revolutionized biology and medicine in general, and immunology in particular, by making possible the distinction of individual cells by their antigenic spectra. Unlike lymphocytes, viruses themselves are still characterized predominantly in bulk, in spite of the fact that viral particles are probably not less individual than lymphocytes. We developed a new technology, “flow virometry”, which allows antigen detection on individual virions. Antibody-stained HIV-1 virions immobilized on magnetic nanoparticles were isolated and analyzed with a flow cytometer. HIV-1 antigenic variability stems not only from the high mutagenicity of its genome but also from virus ability to include various cellular molecules, which may significantly alter viral properties. We used flow cytometry to study the distribution of antigens that HIV-1 acquires from infected cells. We found that cellular anigens HLA-DR and LFA-1 are not present on each virion and are not equally distributed among them. Some viral particles carry one of these two antigens, while others carry both. Moreover, the antigenic makeup is determined both by HIV-1 genotype and by the cells from which the virus originates, and the latter determinant seems to predominate. Different virions of a single HIV-1 variant originating from cells of two different types have different spectra of two cellular antigens, whereas two genotypically different viruses (one using CCR5 and another CXCR4 as coreceptor) but originating from the same cells become similar in their cellular antigen composition. Analysis of individual virions will give new insights into basic mechanisms of viral infection much as flow cytometry produced new insight into basic mechanisms of immunity.
© 2013 Lippincott Williams & Wilkins, Inc.