What is Clonal Selection?

Clonal selection is an important immunological process that determines which B and T lymphocytes, types of white blood cells, will be produced in large quantities. It is through this process that our bodies combat antigens—substances it considers to be harmful to it. Niels Jerne, a Danish immunologist, provided the basis for the clonal selection theory in 1955. Prior to Jerne's theory, it was a commonly held belief that our bodies were stimulated to produce a specific antibody when a foreign substance entered it.

Jerne proposed that humans are born with the necessary templates for all the antibodies the immune system would ever need to make. Each person's entire immunological repertoire of antibodies is developed while in the womb. David Talmage and F. McFarlane Burnet independently outlined the clonal selection process in 1957.

Each lymphocyte has a unique antibody on its surface. Antibodies are proteins that bind with harmful antigens to neutralize them. If the immature cells have antigen receptors that match any of the bodies own tissues, then those particular cells are destroyed.

Clonal selection is part of the primary immune response. A primary immune response is provoked when a new antigen invades the body. Traveling through the circulatory system, the antigen will inevitably meet up with the lymphocyte that has the correct antibody pattern.

When the lymphocyte and antigen connect, a chemical change is triggered. The lymphocyte is activated, causing it to rapidly multiply and create many clones of itself. This is how the process came to be called clonal selection. The body will keep producing prolific amounts of the selected lymphocyte cells in an effort to inhibit and prevent infection.

While multiplying, the lymphocyte creates two main types of cells: effector and memory cells. Effector cells, or B and T lymphocytes, are short lived cells created for immediate immunological defense. Memory cells are not active during the primary immune response, but will play an important part during a secondary immune response.

Effector cells are cells that are produced to perform a specific function in response to a particular stimulus. In this case, cells are produced in response to a specific antigen. Effector B cells are responsible for antibody production.

T cells are divided into helper T cells and cytotoxic cells. Helper cells produce cytokines. Cytokines are protein molecules that are produced when an antigen is detected to aid in cell to cell communication and immune response. Cytotoxic T cells destroy cells that have become infected with the antigen in question.

Some of the B and T cells created will become memory cells. The second time an antigen enters the body it triggers a secondary immune response. Memory cells created during clonal selection reactivate and mount a response. Each time an immune system is exposed to an antigen, the number of memory cells created becomes greater and greater, thereby reducing the effects of an antigen.