The immune responses may be primary or secondary (Table 8.3).
The primary immune response occurs when a pathogen comes in contact with the immune system for the first time.
During this, the immune system has to learn to recognize the antigen, produce antibody against it and eventually produce memory lymphocytes. The primary immune response is slow and short-lived.
The secondary immune response occurs when a person is exposed to the same antigen again. During this time, immunological memory has been established and the immune system can start producing antibodies immediately.
Within hours after recognition of the antigen, a new army of plasma cells are generated. Within 2 to 3 days, the antibody concentration in the blood rises steeply to reach much higher level than primary response. This is also called as “booster response”.
Primary Immune Response
1. It occurs as a result of primary contact with an antigen.
2. Antibody level reaches peak in 7 to 10 days.
3. Prolonged period is required to establish immunity.
4. There is rapid decline in antibody level.
5. It appears mainly in the lymph nodes and spleen.
Secondary Immune Response
1. It occurs as a result of second and subsequent contacts with the same antigen.
2. Antibody level reaches peak in 3 to 5 days.
3. It establishes immunity in a short time.
4. Antibody level remains high for longer period.
5. It appears mainly in the bone marrow, followed by the spleen and lymph nodes.