9 min readPathway sheet1-mark MCQ on colostrum or antitoxin, a 2 or 3-mark question on active vs passive immunity or the principle of vaccination; also a NEET favourite

Active and passive immunity; vaccination and immunisation

Making your own antibodies is active immunity (slow, lasting); receiving ready-made antibodies is passive immunity (quick, short). Vaccines work through the immune system's memory.

Active immunityThe host makes its own antibodies after exposure to antigens; slow to develop

Passive immunityReady-made antibodies are given directly; quick protection

ColostrumFirst milk of the mother; rich in IgA antibodies that protect the infant

Recombinant vaccineHepatitis B vaccine, made from yeast by recombinant DNA technology

Active vs passive immunity

Active immunityThe body 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, but it lasts long because memory cells form. Comes from natural infection or from deliberate immunisation with a vaccine.

Passive immunityReady-made antibodies are given to the body. Protection is immediate but short-lived, since no memory cells form. Examples: IgA in colostrum, antibodies passing from mother to foetus through the placenta, and injections of antitoxin or antivenom.

Four kinds of acquired protection

Kind	How it is gained	Example
Natural active	Catching an infection	Recovering from chickenpox
Artificial active	Vaccination	Polio drops, hepatitis B vaccine
Natural passive	Antibodies from the mother	IgA in colostrum; antibodies through the placenta
Artificial passive	Injection of preformed antibodies	Tetanus antitoxin, snake antivenom

How vaccination works

The principle of vaccination is the **memory** of the immune system.

1
A vaccine is given: antigenic proteins of a pathogen, or an inactivated or weakened pathogen.
2
The body treats it as foreign and makes antibodies against these antigens (a primary response).
3★
Memory B and T cells form and stay in the body.
4
During a real infection later, memory cells recognise the pathogen quickly.
5
A massive production of antibodies overwhelms and neutralises the invaders before disease develops.

★ key step

Passive immunisation and new vaccines

Some infections need protection at once, faster than the body can make antibodies. For tetanus, doctors inject preformed antibodies or an antitoxin (a preparation of antibodies against the toxin). For a snakebite, the injection contains preformed antibodies against the snake venom. This is passive immunisation. Recombinant DNA technology now lets us make the antigenic polypeptides of a pathogen in bacteria or yeast. So vaccines can be produced on a large scale; for example, the hepatitis B vaccine is made from yeast.

In real life

Health workers in India advise mothers to breastfeed within the first hour so the baby gets colostrum, rich in IgA. The child's immunisation card of free government vaccines builds active immunity against diseases like polio, measles and tetanus.

Exam angle

2 marks: “Why is colostrum important for a newborn? Name the antibody it contains and the type of immunity it gives.” It contains abundant antibodies that protect the infant; the antibody is IgA. It gives passive immunity.

3 marks: “Explain the principle of vaccination. Why is a snakebite victim given antivenom rather than a vaccine?” Vaccine (antigens or weakened pathogen) makes the body produce antibodies and memory B and T cells; on real infection memory gives quick massive response. Snakebite needs immediate action, so preformed antibodies (passive immunisation) are injected.

Remember it

Active = Antibodies made At home (slow, long). Passive = Pre-made antibodies (fast, short).