Hybridoma cell. Coloured transmission electron micrograph (TEM) of mouse leukaemia particles (pink) in a hybridoma cell. This 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. Magnification: x19,000 when printed 10 centimetres wide.