Clonal selection theory is a scientific theory in immunology that explains the functions of cells (lymphocytes) of the immune system in response to specific antigens invading the body.

1. CLONAL SELECTION

2. History
• In 1900, Paul Ehrlich proposed the so-called side chain
theory of antibody production.
• In 1955, Danish immunologist Niels Jerne put forward a
hypothesis that there is already a vast array of soluble
antibodies in the serum prior to any infection. The
entrance of an antigen into the body results in the
selection of only one type of antibody to match it.
• In 1957, Frank Macfarlane Burnet published a paper
titled ‘A modification of Jerne's theory of antibody
production using the concept of clonal selection’ in a
rather obscure Australian Journal of Science. In it
Burnet expanded the ideas of Talmage and named it
"clonal selection theory

3. B lymphocytes (b cells)
• Lymphocytes respond specifically to antigens on
foreign cells, cells infected by pathogens and
toxins released by pathogens.
• AN ANTIGEN IS A COMPLEX
MOLECULE – RECOGNISABLE AS
SELF OR FOREIGN/ NON-SELF
• ANTIGEN TRIGGERS PRODUCTION
OF ANTIBODIES
• ANTIBODY IS A Y-SHAPED
MOLECULE WITH A SPECIFIC
RECEPTOR (BINDING SITE)

4. Memory cells
• Some T and B lymphocytes
produced in response to
antigens by clonal selection
survive long term as memory
cells.
• A secondary exposure to the
same antigen rapidly gives rise
to a new clone of lymphocytes
producing a rapid and greater
immunological response.

5. How Do B Cells Produce Antibodies?
– B cells develop from stem cells in the bone marrow
of adults (liver of fetuses).
– After maturation B cells migrate to lymphoid organs
(lymph node or spleen).
– Clonal Selection: When a B cell encounters an
antigen it recognizes, it is stimulated and divides
into many clones called plasma cells, which actively
secrete antibodies.
– Each B cell produces antibodies that will recognize
only one antigenic determinant.

6. Clonal Selection of B Cells is Caused by
Antigenic Stimulation

7. Types of Immune Response
• Primary Immune Response
– This is a response to an invader the First time the invader
infects the body.
• No measurable immune response for first few days.
• Next 10 – 15 days antibody production grows steadily
• Secondary Immune Response
– A more rapid response to an invader the 2nd time it invades
the body.
• Antibody production increases dramatically and in a much shorter
time period..

8. 8
Primary – establishes immunological
memory

9. Consequences of Antibody Binding