Zoology · Ch 8 — Immunology
Immune responses
Immune responses
When a pathogen meets the immune system for the very first time, the resulting primary immune response is comparatively slow: the system must first learn to recognise the antigen, then mount antibody production and, in the process, generate memory lymphocytes for future defence. Antibody levels rise gradually, peak only after roughly 7 to 10 days, and then decline rapidly, and the response is centred mainly in the lymph nodes and spleen — overall it is a short-lived, hard-won victory.
When the same antigen is encountered again, immunological memory from the first exposure kicks in and the secondary immune response unfolds very differently. A fresh army of plasma cells is mobilised within hours, and by 2–3 days the antibody concentration in the blood shoots up to levels far exceeding the primary response's peak — earning it the nickname 'booster response.' Antibody levels here reach their peak faster (in about 3–5 days), stay elevated for much longer, establish protection more quickly, and this time the response is c …
| Sl.No | Primary Immune Response | Secondary Immune Response |
|---|---|---|
| 1 | It occurs as a result of primary contact with an antigen. | It occurs as a result of second and subsequent contacts with the same antigen. |
| 2 | Antibody level reaches peak in 7 to 10 days. | Antibody level reaches peak in 3 to 5 days. |
| 3 | Prolonged period is required to establish immunity. | It establishes immunity in a short time. |
| 4 | There is rapid decline in antibody level. | Antibody level remains high for longer period. |