Gameplay

Cellular Migration
In cellular migration, the player navigates through the circulation, trying to find the target cells for infection. The player can only move up and down and from left to right, because the blood flow makes any movement along the "z" access impossible. As the player tries to locate the cells for attack, she must avoid the B lymphocytes and monocytes, which appear in the circulation and increase in number as the immune system responds. Clusters of neutrophils get stuck to the inner endothelium of blood vessels creating a menacing obstruction for the player to negotiate past. Large clusters of neutrophils in a narrow vessel spells trouble, but the player must pass through in order to reach the cells.

As the player successfully infects the host, the host organism reacts. Infected organs fill with macrophages that engulf pathogens with deadly pseudopods. Antibodies proliferate in their millions. Neutrophils also predominate in early stages. Later, Cytotoxic Killer T Cells reign and attack infected cells. If a player (virion) is destroyed during either phase, she switches to another free, available virion in the vicinity, and takes control. The number of virions and viruses in the body at any given time rises and falls in direct proportion to the player's success or failure. This allows the player to control millions of viruses by 'operating' only one at a time.

Cellular Attack
Once the player successfully navigates to a cell, she must enter the cell and replicate. First, she must choose the proper method for entering the cell, depending upon the type of virus she plays. If she is a virus with a lipid membrane, she will need to skim the coat until she finds an appropriate receptor. Other virions bind to the cell surface with receptors and are internalized into the cell, by the cell.

The virus is now inside the cell and needs to replicate before the Killer T Cells or the macrophages destroy the infected cell. A countdown begins, based on the amount of time available before a Killer T cell or a macrophage arrives. This period of time becomes progressively shorter as the game proceeds and as the number of phagocytes increase and recognize the attack.

The player is now in control of the nucleic acid of the virus. In the case of Type VII viruses, the player controls one fragment of the virus DNA released into the cell. The player needs to move around the cell to gather the components necessary to synthesize progeny viruses. Most of the cell is cytoplasm and the player cannot leave via the exterior cell membrane. Close to the center of the cell is the nucleus, into which the player can enter and leave by finding one-way intracellular transport structures, resembling translucent pipes in the cell. In effect, the player is engaged in a free-roaming, spherical navigation game of chutes and ladders.

The player collects components simply by moving over them. The game will not pick up components that are not necessary. Several types of viruses will automatically begin replicating when the player collects enough enzymes or proteins so that beginning players will have less difficulty with Cellular Attack. These viruses do not yield good scores for replication. Others will require the player to press the ‘A’ button to activate the collected components, and Type VII viruses need to collect all the fragments of viral DNA before it can even begin to synthesize progeny. Type VI retroviruses require the player to press ‘A’ inside the nucleus in order to synthesize progeny.

For more information on gameplay, see the full documentation.

Copyright 2002, MIT.