Download Level 2 ZOOL 21014 Immunity

Immunity
 Specific immunity (Antigens & antibodies)
 Formation of T cells & B cells
 Cellular immunity
 Antibody mediated immunity
 Primary & secondary responses to antigen
exposure
At the end of the lecture you should be able
to,
• Discuss the cellular and antibody
mediated immune responses in the human
body
• Explain primary & secondary responses to
antigen exposure
Specific Immunity
• Involves production of a specific
lymphocyte or antibody against a
specific antigen
• Mediated by T lymphocytes (T cells) &
B lymphocytes (B cells)
Antigens
• Any chemical substance that when
introduced to body cause the body to
produce specific antibodies that react
with the antigen
e.g. microbes, microbial
structures, pollen,
incompatible blood cells,
transplants
Antibodies
• Globular proteins produced by the
body in response to the presence of
antigen
• 5 classes of antibodies in the human
Ig G, Ig A, Ig M, Ig D,
Ig E
Formation of T cells & B cells
Lymphatic stem cells in embryonic bone marrow
Thymus gland
T cells
Bone marrow,
fetal liver , spleen,
gut associated tissue
B cells
Lymphoid tissue
(lymph nodes, spleen, GI tract, bone marrow)
Cell mediated immunity
• Formation of specially sensitized T cells
that have the capacity to attach to the
foreign agent & destroy it
• Effective against fungi, parasites,
intracellular viral infections, cancer cells,
foreign tissue transplants
1. When antigen enters the body,
macrophage phagocytose the antigen &
present it to the lymphoid tissue ( many
different types of T cells in lymphoid tissue capable of
responding to different antigens)
2. Particular T cell specifically programmed
to react with antigen become activated
(sensitized)
3. Sensitized T cell enlarges & divides &
produce 3 subpopulations of cells
– Killer cells
– Helper cells
– Memory cells
T cells in lymphoid tissue
Macrophage
present the antigen
to T cells
Memory T cells
Helper T cells
Sensitized T cell
enlarges & divides
Killer T cells
Killer cells
Leave the lymphoid tissue & migrate to the
site of invasion & destroy the antigen
– directly by producing cytotoxic substances
– Indirectly by attracting more macrophages &
increasing phagocytic activity of macrophages
Helper T cells
• Cooperate with B cells to help increase
antibody production from B cells
Memory T cells
• Recognize original invading antigen. When
pathogen invades the body later stage, the
memory cells start a faster reaction than
during the first invasion
• Pathogen is destroyed, before any sign of
the disease occur
Antibody mediated immunity
• Production of circulating antibodies by B
cells, these antibodies are capable of
attacking an invading agent & destroy it
• Particularly effective against bacterial &
viral diseases
Macrophage
present the antigen
to B cells
Plasma cells
B cells in lymphoid tissue
Sensitized B
cell enlarges
& divides
Memory B cells
blood
Antigen-antibody
complex
Memory B cells
• Recognize the original invading antigen
when same antigen appear again
Plasma cells
• Secrete specific antibodies to circulation,
these antibodies circulate in the blood &
lymph & reach the site of invasion.
• Once the antigen-antibody complex is
formed, antibody activates complement
enzymes for attack
Memory
cells
1
2
What would happen to
the antibody levels if
antigen is injected in
the second time ?
Reason for secondary response
• Some of the specific lymphocytes formed
during primary response remain as
memory cells.
• Add to the pool of cells that can respond
to the antigen
• Their response is more intense
Basis for immunization against certain diseases
Summary
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Antigens & antibodies
Formation of T cells & B cells
Cellular immunity
Antibody mediated immunity
Primary & secondary responses to
antigen exposure