Human endogenous retrovirus and a cell, illustration. The human endogenous retrovirus (HERV) and its viral mRNA is at centre (green) along with the host cell's chromosomes (X-shaped). The oncogene (red) that is being activated here is at upper right. Retroviruses are RNA viruses that copy their genome into the DNA of the host cell. This can then lie dormant and be passed on through the generations, when it is known as an endogenous retrovirus. If it then reactivates, it may cause diseases such as cancer, although the link is not yet certain. At upper left are interferons and pro-inflammatory cytokines, with an RNA sensor protein and ribosomes (purple) at centre left. Viral proteins (green) are seen exiting the cell at lower left.