Taking as an inspiration the classical painting by Paolo Uccello, the knight is the killer T cell in shining armour, here seen attacking a cancer cell. Like Uccello’s pestilent dragon, this cancer cell is complex and disorganized. The red granules are the T cell’s killing weapon, they are able to disturb the permeability of the cancer cell membrane therefore killing it. The cancer cell loses this battle.
Wellcome Images wrote a very nice blog post about this image. You can read it here.