The entry of an antigen is sensed by the B-cells. The B-cells become active and synthesize specific protein molecule called the antibody, which is secreted into the plasma. Upon encountering the antigen, the antibodies bind with the antigen molecules and deactivate them. This whole process takes from days to weeks during first exposure but will be rapid upon second exposure due to the memory which was built up during first encounter with the pathogen. This phenomenon of recognizing an antigen is called as immunization and this lead to the basis of vaccination. 0.16 Vaccination is the process by which an individual's immune system is strengthened against a particular First exposure infectious agent.

The condition where immune system mistakes part of body like tissues, joints, skin, as foreign and attack them is:

Explanation

Autoimmunity: Autoimmunity is the disease when an immune system could not distinguish between self and non self antigens and attack self cells. E.g., Rheumatoid arthritis, Multiple sclerosis, Type 1 diabetes mellitus