The immune system has two major components. The innate response, a first line of defense, is made up of cellular proteins and killer cells. The adaptive response is based on immune system cells’ ability to recognize and attach to specific antigens on the surface of infected cells and tumor cells.
The immune system is made up of various types of white blood cells (WBC). All blood cells derive from blood-cell making (“hematopoietic”) stem cells in the bone marrow. These stem cells can make white blood cells (leukocytes), red blood cells (erythrocytes), or platelets (thrombocytes), depending upon the body’s needs. White blood cells circulate in the bloodstream and in the lymphatic system.