Clonal selection and primary/secondary immune responses

This section deals with:

• Clonal selection (memory and efector cells)
• primary and secondary immune reponses

Clonal Selection

Clonal selection is the activation of a tiny fraction of cells in a lymphocyte due to an antigen binding to a recepto site. These activated cells clone themselves into effector and memory cells.

Effector cells

• Are short-lived
• combat the antigen that was binded
• the nature and function of the effector cell depends on whether the lymphocyte selected was a helper T cell, B cell, or cytotoxic T cell

Memory cells

• are longed-lived
• bear receptors specific for the same inducing antigen
• formed in primary immune response and lead the attack in the secondary immune response

As you can see, effector cells live only a short period of time and immediately attack the antigen and its mircobe. Memory cells on the other hand live a long time and while tehy do not fight, they remember the antigen and thus mount a successful attack if it ever shows up again.

Primary and secondary immune response

Primary response

The primary response is represented by the selective proliferation and differentiation of lymphocytes that occur s the first time a body is exposed to an antigen. It peeksabout 10 to 17 days after the inital exposure.

During this time:

• Plasma cells (effector b cells) are created
• seleted T cells are activated

The individual is sick during this time but after the defense is prepared, the antigen is cleared from the body by the effector and T cells. Memory B cells are created that rememer the antigen.

Secondary Immune Response

After the primary response, the body may be invaded by a pathogen with the same antigen again. Memory cells amde duing primari response quickly gather up the necessary effectr cells and get rid of the antigen.

In secondary response:

• There are more antibodies than in primary response
• they have a greater affinity for the antigen than the primary respnse one

                              Comparison of primary and secondary responses

Immunological memory

Immunological memory relies on memory T and B cells made after the first exposure to an antigen. When the antigen appears again, the memory cells proliferate and differentiate rapidly.