Adenoviruses. Coloured transmission electron micrograph of a cell infected by adenoviruses. The red dots in the cell nucleus (outlined in red) are new viruses produced by the cell. The uniform green areas in the nucleus are crystalline inclusions produced as a result of infection. Adenoviruses are common in humans, causing symptoms similar to a cold. They are also thought able to trigger cancer by interfering with the expression of genes in the host cell. Some adenoviruses can introduce genes into host cells, making them a potential vector in gene therapy. The cell is a HeLa cell, a cultured human cancer cell. Magnification x2000 at 6x6cm.