In Immune response shown in the image, ‘1’ is due to ?
A. Increase in the amount of exposure of Antigens
B. Primary exposure to the Antigen
C. Secondary exposure to the Antigen
D. A and B
Ans:C. Secondary exposure to the Antigen
Primary and Secondary Immune Responses
1° Immune Response
- Following the first exposure to a foreign antigen, a lag phase occurs in which no antibody is produced, but activated B cells are differentiating into plasma cells. The lag phase(marked in the figure by ‘4’) can be as short as 2-3 days, but often is longer, sometimes as long as weeks or months.
- The amount of antibody produced is usually relatively low.
- Over time, antibody level declines to the point where it may be undetectable.
- The first antibody produced is manily IgM (although small amounts of IgG are usually also produced).
2° Immune Response
- If a second dose of the same antigen is given days or even years later, an accelerated 2° or anamnestic immune response (IR) occurs(marked in the figure by ‘1’).
- This lag phase is usually very short (e.g. 3 or 4 days) due to the presence of memory cells.
- The amount of antibody produced rises to a high level.
- Antibody level tends to remain high for longer.
- The main type of antibody produced is IgG (although small amounts of IgM are sometimes produced).