BCG vaccine testing. Coloured transmission electron micrograph (TEM) of a section through BCG vaccine (black & red) infecting a human macrophage white blood cell (green). BCG vaccines are live but attenuated (weakened) Mycobacterium bovis bacteria used to immunize patients against tuberculosis (TB). The bacteria sensitise the immune system to TB, so the body is prepared if the bacteria is encountered. This culture models the effect of the vaccine in order to detect gene products from the macrophages it infects. It may be possible to use these products as a check of vaccination and to judge each vaccine's effective- ness. Magnification: x11,500 at 6x7cm size. x39,000 at 7.5x9.5 inch size.