Now, let's move on to number two. In number two, let's suppose we have some type of cell that was infected by our viral agent. Now, once the cell is infected, that infected cell releases some type of pathogenic antigen and places it onto the MHC class one complex. Remember, MHC is the major histocompatibility complex that our cells use to basically differentiate healthy cells from our infected cells. And once the pathogenic antigen is found on the MHC class one complex, some type of white blood cell, a macrophage, a neutrophil, or our cytotoxic T cell, a special type of T lymphocytes, can basically approach this infected cell. And if it contains the specific type of antibody that reflects this specific type of antigen, they can basically bind.