All of these elements can be recognized by the host as foreign material, and will provoke an immune response. Viruses have an advantage if they are able to penetrate host cell walls in that they are then capable of masquerading as host cells. The immune system must then counter by killing off host cells it recognizes as infected. | All of these elements can be recognized by the host as foreign material, and will provoke an immune response. Viruses have an advantage if they are able to penetrate host cell walls in that they are then capable of masquerading as host cells. The immune system must then counter by killing off host cells it recognizes as infected. |