What does alexin mean?
Alexin is a noun denoting a protective substance found naturally in the blood serum of humans and animals, first described by late-nineteenth-century immunologists as the agent responsible for destroying bacteria and other foreign cells. The term derives from the Greek verb alexein, meaning 'to ward off' or 'to defend,' reflecting its role as the body's intrinsic line of defense. In classic experiments, researchers showed that fresh serum could kill bacteria but that heating destroyed this capacity, revealing that alexin was a heat-labile component later identified with the complement system — a cascade of proteins central to immune defense. Today the word is largely of historical interest, having been replaced in modern immunology by the term 'complement,' though it persists in older scientific texts and remains a useful illustration of how immunological vocabulary evolved alongside the science itself.
nounA protective substance present in normal blood serum that destroys bacteria and other foreign cells; now understood to be identical with the proteins of the complement system.
- A bactericidal substance normally present in blood serum that destroys foreign cells, identified historically with the complement system of immunity.
"The scientist demonstrated that fresh serum contained an alexin capable of destroying the bacteria within minutes."
"Heated serum lost its alexin, and the bacteria survived undisturbed in the culture."
"Early immunologists measured the alexin content of serum to gauge a patient's resistance to infection."
Rarely pluralized in practice; the singular is standard even when discussing multiple serum components.
"The paper compared the alexins present in the sera of several mammalian species."
Named from the Greek word for 'to ward off,' alexin was the late-19th-century name for what immunology now calls complement — your blood's built-in bacterial demolition crew.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of alexin
Alexin comes from the Greek verb alexein, meaning 'to ward off' or 'to defend,' adopted into scientific Latinized usage in the late nineteenth century when immunologists such as Hans Buchner and Jules Bordet identified heat-labile substances in serum that destroyed bacteria. The same Greek root produced related terms such as alexipharmic and alexiteric, used for antidotes against poison. As understanding deepened, alexin was recognized to be identical with the complement system, and modern usage has largely abandoned the name.
How alexin is actually used
A technical term of historical immunology and serology, now largely superseded by 'complement' in modern scientific usage; it survives mainly in older textbooks and literature.
Easily confused with alexin
An alexin is a defensive serum substance that destroys harmful cells, whereas a toxin is a poisonous substance produced by living organisms.
An antitoxin specifically neutralizes a particular toxin, while an alexin is a general bacterium-destroying component of normal serum.