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SPECIFIC IMMUNE
SYSTEM
T - 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
• IDENTIFY THE VARIETY OF T LYMPHOCYTES.
• EXAMINE THE ACTION/FUNCTION FOR EACH T
CELL POPULATION
THIRD LINE OF DEFENCE
• SPECIFIC (ONLY ACTS ON PARTICULAR
PATHOGEN)
• INVOLVES LYMPHOCYTES
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
LYMPHOCYTES
• LYMPHOCYTES ARE A TYPE OF WHITE BLOOD CELL. THERE ARE A
NUMBER OF DIFFERENT TYPES OF LYMPHOCYTE;
• TWO OF THE MOST IMPORTANT ARE B LYMPHOCYTES AND T
LYMPHOCYTES.
• T LYMPHOCYTES ARE ALSO CALLED T CELLS. THEY ARE FORMED
IN THE THYMUS GLAND – HENCE THEIR NAME.
• T LYMPHOCYTES PLAY AN IMPORTANT ROLE IN THE IMMUNE
SYSTEM AND THEY ACCOUNT FOR MORE THAN 4/5 FOURFIFTHS OF CIRCULATING LYMPHOCYTES.
• THERE ARE TWO MAIN GROUPS OF T LYMPHOCYTES:
• CYTOTOXIC T CELLS
• HELPER T CELLS.
HELPER T CELLS (TH CELLS)
• HELPER T CELLS (TH CELLS) ; SECRETE CYTOKINES THAT
ACTIVATE PHAGOCYTES, T CELLS AND B CELLS.
Helper T cells are not able to destroy infected cells.
Instead they produce
cytokines – a chemical
signal that activate B
lymphocytes and
phagocytes, which can
then act to destroy the
infected cell.
CYTOTOXIC T CELLS (TC CELLS)
• CYTOTOXIC T CELLS (TC CELLS) ; DESTROY INFECTED
CELLS BY SEVERAL METHODS INCLUDING THE
INDUCTION OF APOPTOSIS
• THE CYTOTOXIC T CELLS ARE ALSO CALLED KILLER T
CELLS. THEY RECOGNISE ANTIGENS ON INFECTED
CELLS, BIND TO THE ANTIGEN AND CAN DESTROY THE
CELLS BY APOPTOSIS.
• APOPTOSIS IS A FORM OF PROGRAMMED CELL
DEATH – THE CELL IS INSTRUCTED TO DESTROY ITSELF.
Killer T-cells:
Can attach themselves to cells with foreign
antigens on their surface and destroy them
1. Virus attaches
to and
enters
host cell
2. Viral DNA causes host cell to express viral
anitgens on its surface
3. Killer T-cell attaches
to viral
antigen on
infected cell
4. Killer T-cell induces
death of
infected cell
Killer T-cells and cancer:
1. As cell becomes cancerous
mutations take place
2. Mutations cause cancerous cell to
express abnormal antigens
3. Killer T-cell binds to
abnormal antigens
4. Killer T-cell induces
death of
cancerous cell
(Usually)
MEMORY CELLS
• ONCE CYTOTOXIC T CELLS HAVE COMPLETED
THEIR JOB, THE MAJORITY OF CELLS UNDERGO
APOPTOSIS.
• HOWEVER, A FEW CELLS
BECOME ‘MEMORY CELLS’,
WHICH WILL REMAIN ON
HAND TO RESPOND SHOULD
THE ANTIGEN REAPPEAR AT
SOME POINT IN THE FUTURE.
* 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
SUMMARY SLIDE
SPECIFIC DEFENCES
T LYMPHOCYTES
• ONE GROUP OF T LYMPHOCYTES DESTROY INFECTED CELLS
BY INDUCING APOPTOSIS.
• ANOTHER GROUP OF T LYMPHOCYTES SECRETE CYTOKINES
THAT ACTIVATE B LYMPHOCYTES AND PHAGOCYTES.
• WHEN PATHOGENS INFECT TISSUE, SOME PHAGOCYTES
CAPTURE THE PATHOGEN AND DISPLAY FRAGMENTS OF ITS
ANTIGENS ON THEIR SURFACE.
• THESE ANTIGEN PRESENTING CELLS ACTIVATE THE
PRODUCTION OF A CLONE OF T LYMPHOCYTES THAT MOVE
TO THE SITE OF INFECTION UNDER THE DIRECTION OF
CYTOKINES.
SUMMARY SLIDE
SPECIFIC DEFENCES
T LYMPHOCYTES
• T LYMPHOCYTES HAVE SPECIFIC SURFACE PROTEINS THAT ALLOW
THEM TO DISTINGUISH BETWEEN THE SURFACE MOLECULES OF THE
BODY’S OWN CELLS AND CELLS WITH FOREIGN MOLECULES ON THEIR
SURFACE.
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.
•
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
CYTOTOXIC T CELLS (TC CELLS)
• CYTOTOXIC T CELLS (TC CELLS) ; DESTROY INFECTED CELLS BY SEVERAL METHODS INCLUDING THE
INDUCTION OF APOPTOSIS
• THE CYTOTOXIC T CELLS ARE ALSO CALLED KILLER T CELLS. THEY RECOGNISE ANTIGENS ON
INFECTED CELLS, BIND TO THE ANTIGEN AND CAN DESTROY THE CELLS BY APOPTOSIS.
• APOPTOSIS IS A FORM OF PROGRAMMED CELL DEATH – THE CELL IS INSTRUCTED TO DESTROY
ITSELF.
• ONCE CYTOTOXIC T CELLS HAVE COMPLETED THEIR JOB, THE MAJORITY OF CELLS UNDERGO
APOPTOSIS.
• HOWEVER, A FEW CELLS BECOME ‘MEMORY CELLS’, WHICH WILL REMAIN ON HAND TO RESPOND
SHOULD THE ANTIGEN REAPPEAR AT SOME POINT IN THE FUTURE.
•