Differentiate between the roles of B-lymphocytes and T-lymphocytes in generating immune responses.
OR
Principle of vaccination is bassed on the property of "memory" of the immune system. Taking one suitable example, justify the statement.

Explanation

B-lymphocytes are produced in the bone marrow and they produce antibodies in response to antigen (pathogen) in blood stream. B-lymphocytes are responsible for humoral immunity.
T-lymphocytes gets mature in thymus. These lymphocytes are responsible for cell- mediated immunity. Helper T-cells stimulate B-cells to produce antibodies and killer T-cells migrate to site of infection.
OR
When an organism (pathogen) enters human body, B-lymphocyte starts produching antibodies and memory cells.
Memory cells gives faster response whenever in future new infection with the pathogen takes place. Same principle is used for the vaccination process. In vaccination process dead, weakened or inactivated micro-organism is introduced into human body either orally or injected, this generate immune response and formation of memory cells which take care of any future infection.