Our body can protect itself by many mechanisms that involve the immune system. The first barrier is our skin, hair and mucous membranes that prevent antigens to enter the body. If this happens, different cells from the immune system help to identify and kill the antigen. These cells are: the lymphocytes (T-cells, B-cells and NK cells), neutrophils, and monocytes/macrophages; which are all different types of white blood cells.