The human body has an amazing protection mechanism called the immune system. It offers protection and defense against agents of infection. There are vast amounts of leukocytes in the human body to protect us from pathogens, but where do they go when they are done and what happens to them?

Researchers at Centro Nacional de Investigaciones Cardiovasculares (CNIC) in Madrid, Spain have discovered the fate of one leukocyte, the neutrophil, after it has come in contact with a pathogen. There is great interest in studying the fate of neutrophils due to their nature of releasing toxic substances after fighting pathogens. Neutrophils cause inflammation to blood vessels and tissue as a response to pathogens; this response can lead to serious injury. Fortunately, our body regulates the migration of neutrophils and prevents this.

CNIC researchers have concluded that the clearance of neutrophils lead to the production of hematopoietic stem cells. This is due to the regulation of neutrophils. The leukocytes are taken to the bone marrow and eliminated by macrophages through specialized phagocytosis.  A chain reaction takes place wherein the macrophages that ingest the neutrophils undergo a change. This change causes a decrease in bone marrow macrophages retaining the hematopoietic stem cells in bone marrow.  This process circulates hematopoietic cells throughout the bloodstream allowing the cells to differentiate into cells that are necessary in other regions of the body i.e. neutrophils. Researchers also found that the aging of neutrophils undergo the same rhythmic cycle as the circadian cycle.