We have cell mediated immunity, also known as T cell immunity. And we also have antibody mediated immunity, also known as B cell immunity or humoral immunity. So the major difference between these two types of divisions of the quiet immunity is one uses a type of cell known as a T lymphocyte or a T cell. And the second type uses a type of cell known as a B lymphocyte or a B cell. And number two, this uses a special type of biological molecule known as an antibody. And we'll see what that is in just a moment.