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 grey/blue 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.