The first part of the diagram shows an antibody molecule binding to the virus and preventing it from entering the cell. The next part shows a virus entering and multiplying within a cell, causing the cell to release interferon. When the interferon reaches a neighbouring uninfected cell, it makes that cell resistant to infection. Also shown are a natural killer cell and a cytotoxic T cell. Either of these can bind to an infected cell via specific receptors on the cell surface, and kill that cell.