Hybridoma cell. Coloured transmission electron micrograph (TEM) of mouse leukaemia virus particles (bluedots) inside and outside a hybridoma cell. The cell is a man-made hybrid cell used in the production of monoclonal antibodies. Hybridomas are produced after injecting a mouse with a foreign substance (antigen), harvesting its antibody-producing white blood cells (plasma cells) and fusing them with myeloma cells (cancerous plasma cells). Fusing plasma and myeloma cells allows hybridomas to grow indefinitely in culture. The hybridoma cells are cloned and tested for the desired antibody. The desired clones are grown in culture and their antibodies harvested. Murine leukaemia virus infection of mice is common so mouse cells and their cultures may be infected. Magnification: x3000 at 10 cm wide