Question

Describe the graph of the primary and secondary response to an antigen by the human humoral (B cell mediated) immune system over time. What is happening in each response (particularly IgM and IgG levels), how are the responses similar and how do they differ? Why is this significant for medicine and human health?

Answer 1

Answer)

I would like to explain the answer using the images below.

Image1.Picture source: https://microbenotes.com/differences-between-primary-and-secondary-immune-response/

Image 2 Picture source: https://microbenotes.com/differences-between-primary-and-secondary-immune-response/

From the graph below points are noted as important differences.

	Primary response	Secondary response
Lag phase	5- 10 days and long	1-3 days and short
Peak response	smaller	larger
First Antibody isotype	Ig M	Ig G
Antbody affinity	relatively low	relatively higher
Response	slow	rapid

Reasons behind these differences :

1. Lag phase: It is time from which antigen entered the body or patients showing signs of infection to the first appearance of antibodies. As we can see in the image 2 it takes nearly 5-10 days for the antibody response in primary whereas in secondary nearly 3 days antibodies are produced.

The primary response has a long lag phase due to the fact that the development of B lymphocytes and production of an antibody that best fits the antigen(clonal selection) is a time taking process. Whereas in the secondary response body is already equipped against the antigen with memory plasma cells. It takes less time form memory plasma cells to differentiate to plasma cells and produce antibodies.

2. Primary antibody type: In primary response, we can see that IgM is preferred because IgM is a pentameric molecule. Initially, this has an efficient rate to detect antigen. Whereas in the secondary response IgG is produced immediately to antigen entry. This occurs due to class switching in the B cells, a process in which class of the antibody molecules change. from IgM to A, G, D,E.

3. Antibody affinity: In primary response antibody affinity is low whereas in secondary it is high, this due to the fact that the cells in the secondary response have undergone affinity maturation. A process that increases the affinity of the antibody.

These responses are familiar with the fact that they both are antibody-mediated immune responses.

Significance: This concept is applied to develop vaccines. For primary response, the person is administered with inactivated virus or bacteria. This develops immunity against that specific type and protects him/her when a real antigen attacks the body.