4.1.9 Primary and Secondary Immune Responses

Question 1

What are the two types of immune responses?

Answer 1

During clonal expansion T and B cells form memory cells

Memory cells form the basis of immunological memory – the cells can last for many years and often a lifetime

There are two types of immune response:
Primary immune response (responding to a newly encountered antigen)
Secondary immune response (responding to a previously encountered antigen)

Question 2

Describe the primary immune response?

Answer 2

The primary immune response has a considerate time delay
It takes considerable energy and time for:
The clonal selection and expansion of specific T cells and B cells
The synthesis of antibodies
Antibodies do not begin to appear in the blood until roughly 10 to 17 days after the foreign antigen first entered the body

This time delay is why we often experience symptoms of a disease when we are first exposed to a pathogen

Some of the B cells differentiate during clonal expansion to become plasma cells and memory cells
Plasma cells are short-lived

A portion of the selected T cells also differentiate into memory cells

Memory cells remain circulating in the blood for a long time and allow for a rapid secondary immune response

Question 3

Describe the role of B memory cells and the secondary immune response.

Answer 3

If the same foreign antigen is found in the body a second time, the B memory cells recognise the antigen

B memory cells divide very quickly and differentiate into plasma cells (to produce antibodies) and more memory cells

This response is very quick, meaning that the infection can be destroyed and removed before the pathogen population increases too much and symptoms of the disease develop

This response to a previously encountered pathogen is, relative to the primary immune response, extremely fast
The response is quicker because there are more memory cells present to be selected than there were cells within the original clone (that existed prior to the first infection)
More memory cells can be selected and so more antibodies are produced within a short time period

Question 4

Describe the role of T memory cells and the secondary immune response.

Answer 4

T-lymphocytes also play a part in the secondary immune response

They differentiate into memory cells, producing two main types:
Memory helper T cells
Memory killer T cells

Just like the memory cells formed from B-lymphocytes, these memory T cells remain in the body for a long time and provide long-term immunity

If the same antigen is found in the body a second time, these memory T cells become active very quickly