When the virulent version of an agent is encountered , the body recognizes the protein coat on the virus , and thus is prepared to respond , by ( 1 ) neutralizing the target agent before it can enter cells , and ( 2 ) recognizing and destroying infected cells before that agent can multiply to vast numbers .
When the virulent version of an agent comes along the body recognizes the protein coat on the virus , and thus is prepared to respond , by ( 1 ) neutralizing the target agent before it can enter cells , and ( 2 ) by recognizing and destroying infected cells before that agent can multiply to vast numbers .