Immune Defense

An immune response is a relay among cells too small to see, so it is easy to learn their names and miss what they pass along. This game puts you inside that relay during an airway infection, where many handoffs need two cells to touch. A dendritic cell engulfs a virus, displays pieces of it and activates a helper T cell. That helper T cell helps activate killer T cells, which destroy infected cells before they burst. It also helps B cells become plasma cells, whose antibodies keep the virus out of cells and tag it for phagocytes. Later levels bring cancer that switches killer T cells off, HIV that infects helper T cells, and a microbe that mimics a self protein, turning the response on healthy cells.