Human defence systems: antitoxin production.

The idea

Antitoxins are proteins produced by lymphocytes as part of the specific immune response. They bind to toxins released by pathogens, neutralising them so the toxin cannot damage cells. For example, in diphtheria the bacterium releases a toxin, and lymphocytes produce antitoxin molecules that lock onto it. Antitoxin production follows the same principle as antibody production: a lymphocyte recognises a specific toxin, divides, and releases matching antitoxin. Because the response is specific, antitoxins against one toxin do not neutralise another. Antitoxins do not kill the pathogen itself; they stop the harmful effect of its toxin while other defences destroy the pathogen.

What earns the marks

• Antitoxins are proteins produced by lymphocytes.
• Antitoxins bind to toxins released by pathogens and neutralise them.
• Neutralising a toxin prevents it from damaging cells or tissues.
• Antitoxin production is specific to the toxin's shape, so one antitoxin does not neutralise a different toxin.
• Antitoxins act against toxins, not directly against the pathogen itself.

Common mistakes and how to put them right

• Saying antitoxins kill bacteria.

  Put it right: Antitoxins neutralise bacterial toxins, while other defences destroy the bacteria.

• Treating antitoxins and antibodies as identical.

  Put it right: Antibodies bind antigens on pathogens, whereas antitoxins bind and neutralise toxins.

• Claiming one antitoxin works against all toxins.

  Put it right: Binding is specific to the toxin's shape.

Exam tips

• State clearly that the target is a toxin, not the whole pathogen.
• Use 'neutralise' to describe what the antitoxin does to the toxin.
• Contrast antitoxin action with antibody action in one sentence to show precise understanding.