What is the third line of defense in the immune system?
Lymphocytes like B- and T-cells
Physical barriers like the skin and antiviral compounds it produces
Macrophages and dendrites
Interferon proteins that induce fever
As learnt in Immune Response & Lines of Defence -
There are three lines of defence in the body:
Since, B- and T-cells are the components of acquired immunity, they form the third line of defence.
Hence, the correct answer is option a.