Cytomegalovirus infected cells. Immunofluorescent light micrograph of human fibroblast culture cells infected with cytomegaloviruses. The infected cells are shown by the presence of the virus- specific protein UL37 (orange). Cell nuclei are blue, with mitochondria red. UL37 localizes to the mitochondria, keeping the cells alive for longer and enabling them to produce more viruses. Fibroblasts are found in human connective tissue. They are involved in, among other things, making the fibrous structural protein collagen. In immunofluorescence, fluorescent dyes are attached to specific tissues using antibodies. Magnification: x80 at 5x7cm size.