Neutrophils – Definition, structure, count, range, functions


Neutrophils are a type of white blood cell that play a vital role in the immune system. They are the most abundant and the first to arrive at the site of infection, where they engulf and destroy bacteria and other foreign invaders. Neutrophils are also involved in inflammation, wound healing and tissue remodeling.

Neutrophils are classified as granulocytes because they have granules in their cytoplasm that contain enzymes and proteins that help them fight infection. They are also called polymorphonuclear leukocytes (PMNs) because they have a nucleus with multiple lobes.

Neutrophils are produced in the bone marrow from stem cells and circulate in the blood for a few hours before migrating into the tissues. They have a short lifespan of only a few days, after which they die by a process called apoptosis or programmed cell death.

Neutrophils can be divided into two subtypes: neutrophil-killers and neutrophil-cagers. Neutrophil-killers are the ones that directly attack and kill bacteria by phagocytosis (cell eating) and secretion of antimicrobial substances. Neutrophil-cagers are the ones that transport bacteria to the site of infection and trap them in extracellular traps called neutrophil extracellular traps (NETs).

Neutrophils are part of the innate immune system, which means they can recognize and respond to common pathogens without prior exposure or memory. They can also interact with other cells of the immune system, such as macrophages, dendritic cells and lymphocytes, to coordinate a more effective immune response.

Neutrophils are essential for fighting infection and maintaining health, but they can also cause damage to the host tissues if they are activated inappropriately or excessively. Disorders of neutrophil function can result in increased susceptibility to infection (neutropenia) or chronic inflammation (neutrophilia).

In this article, we will discuss the structure, count, range and functions of neutrophils in more detail. We will also look at some of the causes and consequences of abnormal neutrophil levels in the blood. Finally, we will watch a video lecture by Thomas Underhill on the mechanisms of neutrophil action.