Lesson 7 of 13 · 6 min
Active and passive immunity
NCERT §7.2.3, §7.2.4
Two emergencies reach the casualty ward on Thursday: a boy with a deep, dirty nail wound, and a farm worker bitten by a snake. Neither can wait weeks for the body to make its own antibodies.
The lesson in notes
In short
Active immunity: the host is exposed to antigens (living or dead microbes or other proteins) and makes its own antibodies. It is slow and takes time to reach full effect.
Active immunity follows either deliberate immunisation or natural infection.
Passive immunity: ready-made antibodies are given directly to protect the body.
Colostrum, the yellowish fluid a mother secretes in the first days of lactation, is rich in IgA antibodies that protect the infant; the foetus also receives antibodies across the placenta. Both are passive immunity.
Vaccination rests on immune memory. A vaccine (antigenic proteins of a pathogen, or the pathogen inactivated or weakened) makes the body produce antibodies that neutralise the real pathogen later, and memory B and T cells that recognise it quickly and flood it with antibodies.
When a quick response is needed against a deadly microbe, as in tetanus, preformed antibodies or an antitoxin (antibodies against the toxin) are injected. The snakebite injection likewise carries preformed antibodies against the venom. This is passive immunisation.
Recombinant DNA technology makes a pathogen's antigenic polypeptides in bacteria or yeast, allowing large-scale production of vaccines, for example the hepatitis B vaccine made from yeast.