Question

What is the basic principle of vaccination? How do vaccines prevent microbial infections? Name the organism from which hepatitis B Vaccine is produced.

Answer 1

Definition

The introduction of attenuated or weakened pathogens or toxoids into the body to confer resistance against those antigens is called vaccination.

Principle

Vaccination is based on the property of memory exhibited by the immune system where the body is able to recognise an antigen that it has previously encountered. As a result of this immunological memory, the body's response to the subsequent exposure of the same antigen is heightened and quick, thus preventing illness.

Mechanism of prevention

• The first contact with an antigen causes the production of effector T cells (helper T cells and cytotoxic T cells) and B cells (plasma cells).
• Memory T cells and B are also produced at the same time.
• These memory cells and antibodies produced stay in the body for a long time. This is called primary immune response.
• On second exposure with the same antigen, the memory cells recognise the antigen quickly, differentiate into effector cells to neutralise the invader. The response is faster and effective, preventing the body from falling prey to the disease. This is called a secondary immune response.

Hepatitis B vaccine

Hepatitis vaccine contains antigens and is obtained from yeast (Saccharomyces cerevisiae) through recombinant DNA technology.