T cells strike at and destroy diseased cells - i.e. cells that they recognize as being infected by a pathogen. They can recognize these cells because infected cells display foreign proteins called antigens. The Intelligence Officers B cells , also a special kind of white blood cell, are not themselves a defensive force as such. They do not actively neutralize or destroy pathogens. But they serve a crucial function in identifying particular pathogens and releasing the appropriate antibodies.
Antibodies are molecules that attach themselves to cells infected by a specific pathogen.
In doing so, they mark the infected cell for destruction by other immune cells, including non-specific white blood cells and T cells.