Antitoxin

An antibody capable of destroying microorganisms including viruses and bacteria.

An antitoxin provides passive immunity.

For example, if a child gets whooping cough (diphtheria), an antitoxin prepared in horses against diphtheria may be useful in treatment.

The antitoxin can only be of short-term value because the antibodies against diphtheria were made by the horse and the child is just the passive recipient of the antibodies.

The antitoxin is directed against a toxin, one of a number of poisons produced by certain plants, animals, and bacteria.

The term 'toxin' is frequently used to refer specifically to a particular protein produced by some higher plants, animals and pathogenic (disease-causing) bacteria.

A toxin typically has a high molecular weight (as compared to a simple chemical poison), is antigenic (elicits an antibody response), and is highly poisonous to living creatures.

The word 'toxin' comes from the Greek 'toxikon' = arrow poison.