involves mainly T cells and leads to the destruction of cells that are infected with viruses 2. involves mainly B cells and takes place in blood and lymph 3. being able to resist a pathogen that infected the body in the past 4. the deliberate exposure of a person to a pathogen in order to provoke an immune response 5. part of the immune system that produces lymphocytes 6. results when antibodies are transferred to a person who has never been exposed to the pathogen 7. the third line of de