Reovirus naturally infects the lining of the lungs and the bowels of humans from time to time. For example, the small intestine is a natural place for reovirus to survive and proliferate as new cells are constantly being regenerated and shed.

Reovirus naturally grows in ... "the lining of the lungs and the bowel where the cells are bathed in EGF and they are in sort of a pseudo state of Ras activation. The reason these isn't a pathology associated with that is that those cells die, they self-destruct within 24-36 hours after division anyway and so it is about the same time that the virus will actually kill the cell population. It's the natural reservoir for these viruses" - Dr. Brad Thompson, April 2005. Putative stem cells (dark blue) reside immediately above the Paneth cells (yellow) near the crypt bottom. Proliferating progenitor cells occupy the remainder of the crypt. Differentiated cells (green) populate the villus, and include goblet cells, enterocytes and entero-endocrine cells. Source of picture: Wnt signalling in stem cells and cancer - Tannishtha Reya and Hans Clevers

Reovirus depends on the cells it infects to produce the proteins it needs to make more copies of itself. Reovirus does not command the nucleus of the host cell to produce its mRNA as many other viruses do, but produces its own mRNA from the reovirus core. A thick cloud called a viral factory forms inside the cell where the proteins are assembled back into reovirus particles.

Source of Picture: Parker Lab

Cells have natural defenses against reovirus.

• Some cells that are penetrated by a reovirus particle react by killing themselves off by entering an apoptotic state and are devoured by the immune system.
• Some immune cells simply kill the virus and use it as a marker to kill other cells that display the same markers (dendritic cells).
• Other immune cells create small antibodies to the virus that attach to the virus outer proteins and mark it for distruction even before the virus enters a cell.
• Most normal cells will automatically prevent the mRNA from generating more reovirus particles because of a molecule called PKR circulating within the cell.

Cells in certain unusual states (as cancerous cells often are) appear to be especially poor at stopping the reovirus from replicating. In fact, in many cancerous cells, reovirus is able to replicate and produce 1000's of prodigy virus out of that one cell before exploding out of the cell in a process called cell lysis.