Metchnikoff's discovery of phagocytosis

Ilya Metchnikoff (Mechnikov in the Nobel Prize records), born near Kharkov in 1845, was a zoologist who studied the embryos of invertebrates. In 1882 he resigned his professorship at Odessa over troubles at the university under the reactionary government that followed the assassination of Alexander II. He went to Messina in Sicily and set up a private laboratory to go on with his embryology.

The floating larvae of starfish there are transparent and can be watched alive under the microscope. Metchnikoff had seen in such small animals mobile cells that gathered wherever the body was injured, and he suspected they were a defense. To test the idea he pushed sharp splinters into the larvae; according to his Nobel biography they were thorns from a tangerine tree that had been decorated as a Christmas tree for his children. The next morning a thick layer of moving cells surrounded each splinter. He knew that during inflammation in animals with blood vessels, white blood cells leave the vessels, and it struck him that these cells might take up and digest bacteria that entered the body. A 2016 review notes that he later described the episode as the moment he turned from zoologist into pathologist.

On the way back to Odessa he explained the idea in Vienna to Claus, the professor of zoology there, who suggested the name phagocyte. Metchnikoff gave his first paper on phagocytosis at Odessa in 1883. He then found that the phagocytes of the water flea Daphnia attacked the fungal spores that infected it, and that phagocytes attacked the weaker strains of anthrax bacilli but not the more virulent ones.

His theory of cellular immunity met considerable hostility. In 1888 he went to Paris, where Pasteur gave him a laboratory at the Pasteur Institute, and he stayed there for the rest of his life; his treatise Immunity in Infectious Diseases appeared in 1901. In 1908 he shared the Nobel Prize in Physiology or Medicine with Paul Ehrlich, in recognition of their work on immunity. The two are counted as pioneers of cellular and humoral immunology respectively.