4. INTRODUCION
â–Ş Clonal selection theory is a scientific theory in
immunology that explains the functions of cells of the
immune system (lymphocytes) in response to specific
antigens invading the body.
â–Ş Each B cell has a specific antibody as a cell surface
receptor.
â–Ş The arrangement and generation of antibody genes
occurs prior to any exposure to antigen.
5. â–Ş When a soluble antigen is present, it binds to the
antibody on the surface of B cells that have the
correct specificity.
â–Ş These B cell clones develop into antibody producing
plasma cells or memory.
â–Ş Only B cells, which are antigen-specific, are capable
of secreting antibodies.
6.
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
8. Secondary Response
Amore rapid response to an invader the 2nd time it invades the
body.
Antibody production increases dramatically and in a much
shorter time period
9. B lymphocytes (b cells)
â–Ş 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
â–Ş ANTIGEN TRIGGERS PRODUCTION OF
ANTIBODIES
â–Ş ANTIBODY IS A Y-SHAPED MOLECULE WITH
A SPECIFIC RECEPTOR (BINDING SITE)
10. Memory cells
â–Ş Some T and B lymphocytes produced in response to
antigens by clonal selection survive long term as memory
cells.
â–Ş A secondary exposure to the same antigen rapidly gives rise
to a new clone of lymphocytes producing a rapid and
greater immunological response.
12. How Do B Cells Produce Antibodies?
â–Ş Bcells develop from stem cells in the bone marrow of
adults (liver of fetuses).
â–Ş After maturation B cells migrate to lymphoid organs
(lymph node or spleen).
13. Clonal Selection:
â–Ş When a B cell encounters an antigen it recognizes, it
is stimulated and divides into many clones called
plasma cells, which actively secrete antibodies.
â–Ş Each B cell produces antibodies that will recognize
only one antigenic determinant.
14.
15. BURNET’S CLONAL SELECTION THEORY
â–Ş 1959, F.M. Burnet proposed the
clonal selection theory of antibody
production.
â–Ş The clonal selection hypothesis
states that an individual B cell
expresses receptors specific to the
distinct antigen, determined before
the antibody ever encounters the
antigen.
Sir Macfarlane Burnet
16. â–Ş The clonal selection hypothesis has become
a widely accepted model for how the immune
system responds to infection and how certain
types of B and T lymphocytes are selected
for destruction of specific antigens
17. According to clonal selection
hypothesis:
â–Ş The lymphoid stem cells differentiate randomly to produce
different mature lymphocyte each carrying an Ag binding
receptor.
â–Ş Each lymphocyte bears a unique type of receptor with a
unique specificity (derived by V(D)J recombination),
determined before the antibody ever encounters the antigen
18.
19. â–Ş The occupation of a receptor by an antigen (epitope) is required
for cell activation (clonal selection), which is followed by
proliferation (clonal expansion) of this cell to form clones.
â–Ş The activated cells of a clone differentiate into Ab producing
cells, effector cells & memory cells.
â–Ş The differentiated effector cells derived from an activated
lymphocyte clone will bear receptors of identical specificity as
the parental cell.
20. â–Ş The specificity of Ab produced by a lymphocyte is
identical to that of its Ag receptor.
â–Ş Those lymphocytes bearing receptors for self
molecules will be deleted at an early stage.
21. Steps of Clonal Selection:
â–Ş In the primary immune response, clonal selection produces
effector cells and memory cells that may confer life-long
immunity.
â–Ş In the secondary immune response, memory cells are
activated by a second exposure to the same antigen, which
initiates a rapid and anamnestic response.
22. â–Ş Random somatic hypermutations during clonal
expansion cause the production of B cells with
increased antibody-binding affinity for their antigens.
â–Ş The clonal selection hypothesis may explain why
secondary immune responses are so effective at
preventing reinfection by the same pathogen.
23.
24. â–Ş It generally takes 4-5 days for a naive Blymphocyte that has
been activated to complete clonal expansion and differentiate
into effector B-lymphocytes.Although Burnet proposed this
theory for B cells and antibody production, but it is equally
applicable to T cells also.
â–Ş Clone: A clone is defined as a group of identical cells derived
from a single cell.
25. Clonal selection: When an antigen encounters the immune
system, its epitopes eventually will react only with B-
lymphocytes with B-cell receptors on their surface that more
or less fit and this activates those B-lymphocytes. This
process is known as clonal selection.
26. Reference
â–Ş Hodgkin, Philip D; Heath, William R; Baxter, Alan G
(2007). "The clonal selection theory: 50 years since the
revolution". Nature Immunology. 8 (10): 1019–
1026PMID 24141853.
â–Ş Burnet, F. M. (1976). "A Modification of Jerne's Theory of
Antibody Production using the Concept of Clonal
Selection". CA: A Cancer Journal for Clinicians. 2
â–Ş Murphy, Kenneth (2012). Janeway's Immunobiology 8th
Edition. New York, NY: Garland
Science. ISBN 9780815342434
27. SKILLS GAINED
â–Ş Communication skill
â–Ş Gain more knowledge
â–Ş Increase confidence level
â–Ş Personal development
â–Ş Time management
â–Ş Personal skills