Explain unique features of acquired immunity.

Answer: Acquired (adaptive) immunity develops during life after exposure to an antigen. Its unique features are:

1. Specificity: it acts against a particular antigen; a specific antibody or T-cell reacts only with the antigen that induced it.
2. Diversity: it can recognise a vast variety (millions) of different foreign molecules/antigens.
3. Discrimination between self and non-self: it responds to foreign (non-self) molecules but normally not to the body’s own (self) molecules.
4. Memory: after the first (primary) response, memory B and T cells are formed; a second exposure to the same antigen produces a quicker and stronger (secondary or anamnestic) response.