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A virus is a small infectious agent that enters a host cell and uses the cellular machinery to replicate its genome. In order for the host to fight the viral infection, it uses components from the adaptive immune system. Cells involved in the adaptive immune response include CD4+ T cells, CD8+ T cells, and B cells. CD4+ T cells are termed helper T cells, and work by activating and recruiting other immune cells to fight the infection. CD8+ T cells can recognize specific antigens being presented on the surface of the infected cell, and directly kill the cell. B cells produce special proteins called antibodies. The antibody recognizes specific antigens, and targets the antigen for killing by other immune cells.

Antibodies produced by B cells have been an important tool in biological research. Antibodies against specific markers on cells can be used to help determine the number and percentage of specific cell types in a population, and to determine what functions theses cells have. The antibodies used in these applications are labeled with a type of marker, or can be detected with a secondary antibody that is conjugated to a marker. The marker is used for detection of the antibody. The antibodies are used in a variety of assays, to detect proteins, cell surface markers, and other organic molecules. This approach is very valuable in many types of research, and can even be used to separate different cell types from large, mixed populations. Antibodies are currently the best tool scientists have for isolating cells, viruses, and other large molecules for study. In addition, antibodies are used in imaging studies to label cells and parts of the cell. The antibodies are generally conjugated to a fluorescent molecule, which can be detected as different colors by the microscope.

While antibodies are an effective tool for these studies, they have some drawbacks. First, antibodies can be difficult and time consuming to produce. Antibodies for scientific research must be developed by inoculating a producer animal with an antigen in order to activate the B cells. This inoculation also generally requires the use of an adjuvant, to increase the immune response. Once the animal has developed a strong immune response to the antigen, B cells must be isolated from the blood. B cells producing antibody that recognizes the specific antigen are isolated from other B cells, and individually seeded into plates. The B cells are generally hybridized with a tumor cell, so that the B cell can live indefinitely and continue to produce large quantities of antibody. This is called a hybridoma. Each hybridoma is tested to determine which has the optimum antibody for the application. Once the hybridoma has been selected, it can be grown, and antibody can finally be isolated.

The antibody must be purified, and for many research projects, it must be conjugated to another molecule, such as a fluorophore or enzyme, to assist with detection. Once the antibody has been produced, it may be unstable, and will generally require specific storage conditions. In addition, antibodies are fairly large proteins. Some isotypes of antibodies are arranged as five antibody molecules. The large size of the antibody may make it inappropriate for use in certain studies. Smaller materials would be better for studies involving small molecules, and for many imaging applications. If synthetic material could be developed that directly incorporate fluorescent properties, this could provide a big step forward to imaging small molecules on and within the cell.

Synthetic materials could be easier to produce, cheaper, and more stable than antibodies. The problem has been developing synthetic materials that can recognize molecules as specifically and efficiently as antibody does. Recently, researchers in Switzerland were able to produce synthetic nanoparticles capable of specifically recognizing a family of viruses. The viruses were bound to silica nanoparticles. Then, a layer of carbon and silicone containing compounds, called organosilanes, was grown around the viruses. When the viruses were removed, the oragnosilanes still maintained the shape of the viruses. They were also able to recognize the chemical properties of the virus. The organosilanes could specifically bind to the template virus, but not to other similarly structured viruses. This technology could be adapted to recognize not only virus particles, but cells and other organic molecules as well.



References:

http://www.sciencenews.org/view/generic/...ze_viruses