The Theory of Phagocytosis 1882 – Phagocytosis and Immunity

Our bodies have an extraordinarily complex immune system that protects us from various diseases. Through his work with starfish larvae, the Russian biologist Ilya Mechnikov became the first person to discover how one component of this system works.

In 1882, he observed certain cells moving toward a thorn he had placed in a larva's body. These cells would soon be associated with the meaning “engulfing” from the Greek word “phagein” and become known as phagocytes (engulfing cells). These cells acted like single-celled organisms that engulf and destroy smaller particles as part of their normal digestive processes. 

• Later, while studying water-flea shells, Mechnikov discovered that their mobile phagocytes destroyed fungal spores inside their bodies. 
• He also observed mammalian phagocytes engulfing and destroying anthrax bacteria. 

Mechnikov proposed that phagocytes are an important defense against invading organisms such as bacteria and that the process probably evolved from the simple digestive processes of single-celled organisms such as amoebae. Mechnikov compared the behavior of phagocytes in the body to an army fighting an infection.

Many scientists of Mechnikov's time argued that these cells actually helped spread pathogens through the body rather than destroying them. Because of these prevailing theories, they resisted the idea of phagocytosis as a defense mechanism. However, Mechnikov won the Nobel Prize in 1908. 

Today, we know that the phagocytes Mechnikov studied were most likely monocytes and neutrophils. These cells are just two types of leukocytes (white blood cells), part of the immune system, produced in the bone marrow. During infection, chemical signals attract phagocytes to invaded areas. Phagocytes also help the body remove dead or dying cells each day. The blood leukocyte count can indicate certain diseases, including infections.

About the Article Image: Scanning electron micrographs of a neutrophil, a phagocyte (colored yellow), engulfing rod-shaped anthrax bacteria (orange). Neutrophils are the most abundant white blood cells in the blood and the body's first line of defense against microbes. Ilya Ilyich Mechnikov is shown on the right.

Historical Figures Mentioned in the Article: Ilya Ilyich Mechnikov (1845–1916)

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