Atomic force microscopy imaging of retroviruses: human immunodeficiency virus and murine leukemia virus

Retroviruses are membrane-enveloped, RNA-containing viruses that produce a wide range of threatening diseases in higher animals. Among these are human immunodeficiency virus (HIV), which produces acquired immune deficiency syndrome (AIDS) in humans, and murine leukemia virus (MuLV), which produces leukemias in rodents. We have obtained the first atomic force microscopy (AFM) images of these two retroviruses, both isolated from culture media and emerging from infected cell surfaces. The HIV virions are 127 nm diameter on average, and those of MuLV are 145 nm, although there are wide distributions about the means. The AFM images show the arrangement of the envelope protein, responsible for host cell entry, on the surfaces of both virions. Disruption of the viruses using detergents or physical means allowed us to visualize interior structures, including the outer shells of both MuLV and HIV, the cores of MuLV, and the nucleic acid of HIV complexed with core proteins. Using immunolabeling techniques borrowed from electron microscopy, we were able to demonstrate the binding of gold-labeled antibodies directed against the envelope protein of MuLV. The AFM images are revealing, not only in terms of surface topology, but in terms of interior features as well, and they reveal the eccentricities and uniqueness of individual virus particles rather than yielding the average member of the population. Further application of AFM to viruses associated with other pathologies may ultimately have a significant impact on the diagnosis and treatment of virus-promoted diseases.