The immune system is a network of highly specialized cells, organs, and tissues, which shield the body from pathogenic foreign microorganisms, such as bacteria and parasites, as well as from viruses and cancer cells. When the body is well nourished and physiologically balanced, it prevents infectious diseases and tumors from breaking out.
The main pillar of the immune system is made up of white blood cells, or leukocytes, which are highly-specialized cells that move in the bloodstream through arteries and lymphatic vessels, reaching every organ and tissue of the body. They constitute the immune response, which is the white blood cell reaction to the presence of foreign microorganisms, abnormal cells and cellular debris. They are composed of three types of cells: 1) granulocytes, which comprise neutrophils, eosinophils, and basophils; 2) lymphocytes, which include T and B-lymphocytes; 3) monocytes, which develops into macrophages or phagocytic cells.
Granulocytes protect the body from bacteria and parasites, while lymphocytes are active against viruses and cancer cells. Monocytes, on the other hand, engulf and destroy pathogenic microorganisms and cancer cells. All these white blood cells originate in the red bone marrow from stem cells. Then they travel in the bloodstream into the spleen and thymus where they mature into active leukocytes, that protect us from diseases.
When the immune system does not work properly, it is said that that someone is immunodeficient. This means, the the patient lacks enough mature white blood cells to protect him/her from pathogenic microorganisms and viruses. This imbalance of the immune system can be caused by 1) malnutrition, as when we do not eat enough proteins, which contain the twelve essential amino acids; 2) diabetes, which causes comorbidity; 3) viruses that weakens the immune system, such as HIV; 4) cancer and chemotherapy; 5) second and third degree burns.
Below, the three types of white blood cells that are essential part of the immune system.
