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Chapter 15
Innate and Adaptive Immunity
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Innate Immunity
• Always present
• Attacks non-self microbes
• Does not distinguish between different microbes
• Mechanisms include:
– Epithelial barriers
– Phagocytic cells
– Plasma proteins
– Cell messenger molecules
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Adaptive Immunity
• Attacks specific microbes (antigens)
• Develops after exposure to the specific antigen
• Mechanisms include:
– Humoral immunity (antibody proteins in the
blood that attack the specific antigen)
– Cell-mediated immunity (phagocytic cells
that attack the specific antigen)
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Question
Tell whether the following statement is true or false:
A vaccination is an example of adaptive immunity.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Answer
True
In adaptive/acquired immunity, specific antigens are
attacked, and immunity develops after exposure to the
specific antigen. When you get a vaccine, you are
getting a live, weakened, or dead microbe (a specific
antigen). Your body develops antibodies to attack that
antigen after you are exposed.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Immune Cells
• Regulatory cells control the immune response
– T helper cells
– T suppressor cells
– Antigen presenting cells
• Effector cells then carry out the attack on the
antigen
– T cytotoxic (or T killer) cells
– B cells (produce antibodies)
– Leukocytes
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Antigen-Presenting Cells Tell the Immune
System What to Attack
• Eat the invading antigen
• Break it down into pieces called epitopes
• Put epitopes on the cell surface, attached to MHC II
proteins
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Antigens Attached to MHC Proteins
Can Be “Seen” by Immune Cells
• The immune cells have
receptors that attach to
MHC proteins and “see”
the antigen
• They also have antigen
receptors
• Only those T cells
whose antigen
receptors “fit” the
antigen being displayed
will respond to it
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Question
AIDS is an example of a disease in which patients are
immunocompromised. Which immune cells are affected
in AIDS?
a. T lymphocytes
b. B lymphocytes
c. Antigen presenting cells
d. Leukocytes
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Answer
a. T lymphocytes
As you can see in slide 08, the virus is attaching itself to
CD4 receptor sites, located on T cells (T lymphocytes).
Only helper T cells have this receptor.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
MHC I and MHC II Proteins Both Display
Antigens
• MHC II proteins display antigens eaten by a
phagocytic cell
• MHC I proteins display antigens made inside an
infected cell
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MHC I and MHC II Proteins Both Display
Antigens (cont.)
• MHC II proteins tell T helper cells to start an
immune response against the antigen
• MHC I proteins tell T cytotoxic cells to kill the
infected cell before it can infect other cells
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Where Do Lymphocytes
Come From?
• Stem cells in the bone marrow or fetal liver
• B cells mature in the bone marrow
• T cells mature in the thymus
• Then they move to the lymph nodes to wait for
an antigen-presenting cell to activate them
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T Lymphocytes Differentiate in the
Thymus
• T helper cells
(CD4+)
• T cytotoxic
cells (CD8+)
– CD4
receptors
attach to
MHC II
proteins
– CD8
receptors
attach to
MHC I
proteins
– Start an
immune
response
– Kill infected
cells
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Question
All but which of the following is true about CD8
receptors?
a. They can be found on cytotoxic T cells.
b. They attach to MHC I proteins.
c. They signal the start of the immune response.
d. They differentiate in the thymus.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Answer
c. They signal the start of the immune response.
CD8 receptors do all of those things, but they don’t kick off
the immune response (the helper T cell does that). CD8
receptors are found on cytotoxic T cells; as the name
implies, they kill the infected cell.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Two Kinds of T Helper Cells
• TH1 cells
– Stimulate the T cytotoxic cells and other
phagocytic cells to attack the antigen
• TH2 cells
– Stimulate the B cells to create antibodies
against the antigen
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TH Cells Release Cytokines
• Cytokines are chemicals that control the immune
response
– Inflammatory mediators: cause fever; attract
WBCs to the infection
– Growth factors: cause WBCs to divide and
mature
– Cell communication molecules: used to
control activity of other WBCs
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
B Lymphocytes
• Like T cells, B cells
have antigen
receptors
• They can only be
activated to attack
the antigen if a T
helper cell shows it
to them
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Activated B Cells Divide into
Two Kinds Of Cells:
• Memory B cells remain in the body
– In the future, they will fight off the antigen
without a
T helper cell telling them to do so
• Plasma cells create antibodies, special proteins
designed to attach to that antigen and destroy it
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Question
Which immune cell creates antibodies in response to
antigens?
a. Cytotoxic T lymphocytes
b. Helper T lymphocytes
c. Cytokines
d. B lymphocytes
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Answer
d. B Lymphocytes
Remember that antibodies are created in response to
antigens. B lymphocytes have antigen receptors and
are activated to attack a specific antigen if a T helper
cell directs them to do so.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Discussion:
Which would cause the most severe immune deficiency?
• A lack of B cells
• A lack of Tc cells
• A lack of TH1 cells
• A lack of TH2 cells
• A lack of macrophages
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Antibodies or Immunoglobulins
• IgG: circulates in body fluids, attacking antigens
• IgM: circulates in body fluids; has five units to pull
antigens together into clumps
• IgA: found in secretions on mucus membranes;
prevents antigens from entering the body
• IgD: found on the surface of B cells; acts as an
antigen receptor
• IgE: found on mast cells in tissues; starts an
inflammation
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Complement Proteins
• Highly toxic proteins
• Circulate in the blood in an inactive form
• When an antibody attaches to an antigen, the
resulting immune complex can activate
complement
• Complement then destroys the antigen
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Discussion:
A woman has type a blood…
• What antigens does she have on the surface of her
red blood cells?
• What antibodies against RBC antigens has her body
produced?
• What will happen if she is given type B blood?
• What will happen if her blood is given to a person
with type B blood?
• What will happen if she is given type O blood?
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Primary Immune
Response
• The macrophage must eat the antigen, then present
it to TH cells
• TH cells must activate B cells
• B cells produce antibodies
• Then plasma antibody levels rise
• This can take 2–3 weeks
• Vaccination produces a primary immune response
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Secondary Immune
Response
• B memory cells respond to the antigen immediately
• Plasma antibody levels rise within days
• Booster shots cause a secondary immune response
so antibody levels will be high before the disease is
encountered
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Active Immunity vs. Passive Immunity
Scenario:
• A woman was bitten by a rattlesnake last summer;
she received antiserum against the snake venom,
and she survived.
• This summer she will be vacationing in the same
area
Question:
• Should she get a booster shot against snakebite
before her vacation?
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Active Immunity vs. Passive Immunity
(cont.)
Scenario:
• A woman's baby is HIV-positive
Question:
• Does this mean the baby has HIV?
• Does it mean the father has HIV?
• Does it mean the mother has HIV?
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Active Immunity vs. Passive Immunity
(cont.)
Discussion:
• The woman says that since her immunity went to
her baby, the baby will not need any vaccinations.
Is this correct?
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Question
Tell whether the following statement is true or false:
Active immunity is achieved much quicker than passive
immunity.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Answer
False
In active immunity, an individual is exposed to an antigen,
the immune response begins, and antibodies are formed
in 7–10 days. In passive immunity, antibodies are
created outside the host and injected, giving the
individual immunity immediately.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins