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The Specific Immune
Response
Objectives:
• Describe the structure and mode of action
of T lymphocytes and B lymphocytes,
including the significance of cell signalling
and the role of memory cells.
The Specific Immune Response
• This refers to the specific
action of lymphocytes T
lymphocytes (cell-mediated
response) and B
lymphocytes
(humoral/antibodymediated response) to
combat infection by
specific pathogens.
• However, overall
coordination of the immune
response also involves the
phagocytes, (in particular
the macrophages in their
role as Antigen Presenting
Cells)
Cell Mediated Response – T cells
• T-killer cells. These T-CELLS attack anything in
the body that is recognised as foreign. They
may kill the invading organism itself, or they
may kill body cells that have been infected with
the organism. The cells literally line up,
membrane to membrane, then the killer cell
punches holes in the other cell’s membrane. It
loses cytoplasm and dies.
• T-helper cells - release cytokines to stimulate
B-cells to divide and to stimulate macrophages
for phagocytosis.
• T-memory cells – remain in the blood ready to
mount the secondary immune response upon reinfection.
Antibody Mediated Response – B cells
• This involves only antibody chemicals,
not the B-cells themselves.
• B-plasma cells – manufacture antibodies.
• B-memory cells – remain in the blood
ready to manufacture the correct
antibody quickly upon secondary
infection.
1.
2.
A pathogen enters your body and multiplies. It has a specific
shaped antigen on its cell surface membrane.
Your lymphocytes with the complementary antibody may come
into contact with this antigen in one of three ways:
- By encountering the pathogen itself
- By your macrophages engulfing the pathogen, then
presenting the antigen on their surface
- By the pathogen infecting your body cells, and your body
cells then displaying the antigens on their surface. The
body cells do this both as a distress signal, and to mark
themselves for destruction by T killer cells.
3. When the correct T and B antibodies bind
with the pathogenic antigens, this is known
as clonal selection.
4. The ‘selected’ lymphocytes will then divide
rapidly by mitosis to make many copies of
themselves. This is known as clonal
expansion or proliferation.
5. The cells now differentiate into particular
types of B or T cells.
6. T-cells differentiate into:
- T Killer Cells (attack infected host cells)
- T Memory Cells (remain in blood)
- T Helper Cells (release cytokines to stimulate B-cells to
divide and to stimulate phagocytosis)
7. B-cells differentiate into:
- Plasma Cells (make antibodies)
- B Memory Cells (remain in blood)
Types of Cytokines
• Cytokines are a group of cell signalling
molecules that are involved in communication
between the white blood cells of the immune
system.
• Macrophages release monokines to attract
neutrophils by chemotaxis, and to stimulate B
cells to differentiate and release antibodies.
• T-cells, B-cells and macrophages release
interleukins to stimulate proliferation and
differentiation of B and T cells.
• Many cells release interferon, which inhibits
virus replication and stimulates the activity of
T Killer cells.