SPECIFIC IMMUNE
SYSTEM
B-LYMPHOCYTES
Immune system
diseases
Non specific
immunity
Disease survival
mechanisms
Physical &
chemical barriers
Infectious
Disease
Inflammatory
Non-specific
Cellular response
Specific
immunity
Transmission
Epidemiology
Vaccination
Public Health
Immunological
surveillance
T cells
B cells
Clonal Selection
theory
BIG PICTURE
LEARNING OUTCOMES
• EXPLAIN THE ROLE OF LYMPHOCYTES, B CELLS
IN THE IMMUNE SYSTEM
• IDENTIFY THE NEED FOR IMMUNOLOGICAL
MEMORY
• APPLY THE IMPORTANCE OF PRIMARY AND
SECONDARY RESPONSES
THIRD LINE OF DEFENCE
• SPECIFIC (ONLY ACTS ON PARTICULAR PATHOGEN)
• FIRST IMMUNOLOGICAL SURVEILLANCE OCCURS TO
FIND/ DISCOVER PATHOGEN
• THEN CLONAL SELECTION NEEDS TO OCCUR TO
FIND THE CORRESPONDING LYMPHOCYTE TO
COMBAT THE PATHOGEN
Line of
Specific (s) or
defence non-specific (ns)
Mechanism employed
Function
3rd
S
Antibodies production from B
cells from bone marrow
Make antibodies (humoral
response)and are found in the
lymphoid organs (except the
thymus)
3rd
S
Response by T cells from thymus
gland
Cellular immunity but also with the
regulation of the humoral response
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)
SPECIFIC IMMUNITY
ANTIBODY-ANTIGEN INTERACTION
• ANTIGEN - ANY AGENT
CAPABLE OF ELICITING AN
IMMUNE RESPONSE
• ISOLATED MOLECULES
• MOLECULES ON
SURFACE OF CELL OR
VIRUS *
• A SPECIFIC ANTIBODY
MOLECULE WILL BE ABLE
TO RECOGNIZE A SPECIFIC
(EPITOPE ) ANTIGEN
• ANTIBODY BINDS TO
ANTIGEN
B CELL ACTIVATION
B CELLS PLAY THREE IMPORTANT
ROLES IN THE IMMUNE
RESPONSE:
• THEY PRODUCE ANTIBODIES IN
RESPONSE TO SPECIFIC
ANTIGENS
• THEY PERFORM THE ROLE OF
ANTIGEN-PRESENTING CELLS
• THEY DEVELOP INTO MEMORY B
CELLS.
B CELL ANTIBODIES
EACH B CELL CAN A PRODUCE A SPECIFIC ANTIBODY THAT CAN
RECOGNISE A SPECIFIC ANTIGEN FROM A PATHOGEN OR
TOXIN. THE ANTIBODY WILL BIND TO THE ANTIGEN, FORMING
AN ANTIGEN–ANTIBODY COMPLEX.
THE ANTIGEN–ANTIBODY COMPLEX HAS TWO MODES OF
ACTION:
• IT MAY INACTIVATE THE PATHOGEN/TOXIN (NEUTRALISATION),
RENDERING IT SUSCEPTIBLE TO PHAGOCYTOSIS.
• IT MAY STIMULATE A RESPONSE, RESULTING IN CELL LYSIS.
Agglutination
 Antibodies can cause
microbes to stick
together
 This makes it
easier for
phagocytes to
engulf them
Inactivate
 Antibodies can bind to pathogen
 Causing them to become
inactive / rendering them harmless
Neutralisation
 Some pathogens make us ill by producing toxins
 Some antibodies work by
neutralising these
toxins
Stimulate cell lysis
 The binding of an antibody to the surface of a pathogen can
set of a chain reaction with blood proteins, which...
 ... causes the pathogen to swell up an burst.
NEED A LITTLE HELP FROM MY FRIENDS ....
• B CELLS CAN IDENTIFY SPECIFIC ANTIGENS AND
PRESENT THEM TO T CELLS.
• T CELLS CAN THEN DESTROY THE PATHOGEN.
* T HELPER CELLS
Signal 2 - T cell help
B
Y
Signal 1
antigen & antigen
receptor
Th
Th
1. T cell antigen receptor
2. Co-receptor (CD4)
3.CD40 Ligand
More About T-Lymphocytes
Helper T-cells:
B-cell
Help the humoral response by
involvement in the maturation of B cells
and by triggering the production of
antibodies by B-cells
Antigen
SIGNAL
Helper T-cell
CLONAL SELECTION THEORY
• THE BODY HAS A LARGE NUMBER
OF LYMPHOCYTES EACH WITH A
SINGLE TYPE OF MEMBRANE
RECEPTOR SPECIFIC FOR ONE
ANTIGEN.
Cell division
• WHEN A RECEPTOR IS ACTIVATED
BY THE BINDING OF AN ANTIGEN,
THE LYMPHOCYTE REPEATEDLY
DIVIDES RESULTING IN A CLONAL
POPULATION OF LYMPHOCYTES.
SUMMARY SLIDE
SPECIFIC DEFENCES
IMMUNE SURVEILLANCE
• A RANGE OF WHITE BLOOD CELLS CONSTANTLY CIRCULATE
MONITORING THE TISSUES.
• IF TISSUES BECOME DAMAGED OR INVADED, CELLS RELEASE
CYTOKINES WHICH INCREASE BLOOD FLOW RESULTING IN SPECIFIC
WHITE BLOOD CELLS ACCUMULATING AT THE SITE OF INFECTION OR
TISSUE DAMAGE.
• RECOGNITION OF SELF AND NON SELF THROUGH SPECIFIC SURFACE
PROTEINS (ANTIGENS)
• LYMPHOCYTES RESPOND SPECIFICALLY TO ANTIGENS ON FOREIGN
CELLS, CELLS INFECTED BY PATHOGENS AND TOXINS RELEASED BY
PATHOGENS.
SUMMARY SLIDE
SPECIFIC DEFENCES
B LYMPHOCYTES
• EACH B LYMPHOCYTE CLONE PRODUCES A SPECIFIC ANTIBODY
MOLECULE THAT WILL RECOGNISE A SPECIFIC ANTIGEN SURFACE
MOLECULE ON A PATHOGEN OR A TOXIN.
• ANTIGEN-ANTIBODY COMPLEXES MAY INACTIVATE A PATHOGEN
OR TOXIN OR RENDER IT MORE SUSCEPTIBLE TO PHAGOCYTOSIS.
• IN OTHER CASES THE ANTIGEN-ANTIBODY COMPLEX STIMULATES A
RESPONSE WHICH RESULTS IN CELL LYSIS.
• B LYMPHOCYTES ACTIVATED BY ANTIGEN PRESENTING CELLS AND T
LYMPHOCYTES PRODUCE A CLONE OF B LYMPHOCYTES THAT
SECRETE ANTIBODIES INTO THE LYMPH AND BLOOD WHERE THEY
MAKE THEIR WAY TO THE INFECTED AREA.
SUMMARY SLIDE
SPECIFIC DEFENCES
IMMUNOLOGICAL 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.
•