Active macrophages. Immunofluorescent light micrograph of active macrophage white blood cells producing enzymes. The enzymes, inducible nitric oxide synthetase (iNOS, green) and cyclo-oxygenase 2 (COX-2, red) are both involved in promoting inflammation. Cell nuclei are purple/blue. The enzyme iNOS converts the amino acid arginine into nitric oxide, an important signalling molecule that in this case is regulating and mediating the immune system. The macrophages have been activated by exposure to a mock bacterial infection. Macrophages help to kill invading organisms. Magnification: x200 at 5x7cm size.

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