CLONAL SELECTION

Presented by- Rahul Kumar Thaosen

M.Sc Life Science Sem III , BBAU

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

Non specific immunity

Specific immunity

Immunological surveillance

Clonal Selection theory

T cellsB cells

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)

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.

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.

Clonal Selection of B Cells is Caused by Antigenic Stimulation

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..

9Primary – establishes immunologicalmemory

Consequences of Antibody Binding

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