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Bellwork

Discuss with your group what you think is
happening in the following processes.
◦ Why does your body undergo an allergic
reaction?
◦ Why do some people’s bodies attack
themselves (autoimmune diseases)?
◦ How does AIDS escape the human immune
systems?
◦ Why do we have an inflammatory response
when we are injured?
Innate immunity



Present before any exposure to pathogens
and is effective from the time of birth
Involves nonspecific responses to pathogens
Innate immunity consists of external barriers
plus internal cellular and chemical defenses
Acquired immunity,
AKA adaptive immunity, develops after
exposure to agents such as microbes,
toxins, or other foreign substances
 It involves a very specific response to
pathogens

Major parts of Innate Immunity
Barrier defenses
 Phagocytosis
 Antimicrobial peptides
 Inflammatory response
 Natural killer cells

Innate Immunity - Phagocytosis
Groups of pathogens
are recognized by
TLR, Toll-like
receptors
 Once recognized,
cells engulf the
pathogen

Innate Immunity - Phagocytosis

There are different
types of phagocytic
cells:
◦ Neutrophils engulf and
destroy microbes
◦ Macrophages (big
eaters) are part of the
lymphatic system and are
found throughout the body
◦ Eosinophils discharge
destructive enzymes to kill
multicellular parasites
◦ Dendritic cells stimulate
development of acquired
immunity
Innate Immunity – antimicrobial
peptides (AKA proteins)
Interferons – induce
nearby viral infected cells
to secrete substances that
inhibit viral reproduction
 Complement systemProteins in the blood
plasma that fight infection.
Can react to form a
complex that leads to
lysing of invading cells

Innate Immunity – Inflammatory
response

Changes brought about by chemical signal
◦ At the site, mast cells in the connective tissue
release histamine
◦ Histamine triggers nearby blood vessels to
dilate and become more permeable
◦ This helps deliver antimicrobial proteins,
neutrophils and macrophages
◦ Pus, a fluid rich in white blood cells, dead
microbes, and cell debris, accumulates at the
site of inflammation
Fig. 43-8-3
Pathogen
Mast cell
Splinter
Chemical Macrophage
signals
Capillary
Red blood cells
Phagocytic cell
Fluid
Phagocytosis
Check for Understanding

On a sheet of paper, write an essay to
describe the inflammatory response
Innate Immunity - Natural Killer
Cells

Help recognize and eliminate certain
diseased cells
Define
Antigen
 Antibody
 lymphocytes

Acquired Immunity
White blood cells recognize and respond
to antigens (foreign molecules) and then
create immunological memory
 Lymphocytes that mature in the thymus
are called T cells, and those that mature
in bone marrow are called B cells

Acquired Immunity
B cells and T cells have receptor proteins
that can bind to foreign molecules
 Each individual lymphocyte is specialized
to recognize a specific type of molecule

Acquired Immunity – With all the
variation in receptors, why does it
not attack itself?
As lymphocytes mature in bone marrow
or the thymus, they are tested for selfreactivity
 Lymphocytes with receptors specific for
the body’s own molecules are destroyed
by apoptosis, or rendered nonfunctional

Acquired Immunity
B cells can make receptors that detach
from the cell membrane (antibody)
 Epitope – a foreign molecule that a
specific antibody or lymphocyte binds to

But Before we talk about that… lets
see how it all begins
A cell engulfs the pathogen (either a
regular cell, dendritic cells, macrophages,
and B cells)
 Molecules within the cells attach to the
antigen and present it to T cells

Fig. 43-12
Infected cell
Microbe
1 Antigen
associates
with MHC
molecule
Antigen
fragment
Class I MHC
molecule
Antigen
fragment
1
1
2
2
T cell
receptor
(a)
Antigenpresenting
cell
T cell
receptor
2 T cell
recognizes
combination
Cytotoxic T cell
Class I MHC is found in all body cells
and can only present it to cytotoxic T
cells
Class II MHC
molecule
(b)
Helper T cell
Class II MHC is found in specialized
phagocytic cells, such as dendritic cells,
macrophages and B cells. These present
the antigen to either cytotoxic T cells or
Helper T cells
Once they recognize the antigen
they call for help!
Acquired immunity has two branches: the
humoral immune response and the cellmediated immune response
 Humoral immune response involves
activation and clonal selection of B cells,
resulting in production of secreted
antibodies
 Cell-mediated immune response
involves activation and clonal selection of
cytotoxic T cells
*Helper T cells can stimulate either response

A focus on cell mediated response

Activated helper T cells secrete cytokines
that stimulate other lymphocytes
◦ Includes cytotoxic T cells which kill the
infected cells
A focus on cell mediated response
The binding of a mature lymphocyte to an
antigen induces the lymphocyte to divide
rapidly
 This proliferation of lymphocytes is called
clonal selection
 Two types of clones are produced: shortlived activated effector cells and longlived memory cells
 Lets see it again!

Now, the humoral response
A focus on the humoral response
The helper T cell sends signals to recruit
B cells
 The B cells proliferate into memory cells
and plasma cells
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A focus on the humoral response
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The B cells send out antibodies
The Role of Antibodies in Immunity
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Neutralization occurs when a pathogen can no
longer infect a host because it is bound to an
antibody
Opsonization occurs when antibodies bound to
antigens increase phagocytosis
Antibodies together with proteins of the
complement system generate a membrane attack
complex and cell lysis
There are different types of
antibodies
Why is our body better at fighting a
pathogen off the second time?
The first exposure to a specific antigen
represents the primary immune
response
 During this time, effector B cells called
plasma cells are generated, and T cells
are activated to their effector forms
 In the secondary immune response,
memory cells facilitate a faster, more
efficient response

Summarize

Compare and contrast B and T cells
So now… what are vaccinations and
how does this help our immune
system?

We introduce the epitope to our bodies
so our body makes memmory cells, then
when our immune system is faced with
the actual pathogen, it can quickly destroy
it
What are allergies?
Allergies are exaggerated (hypersensitive)
responses to antigens called allergens
 In localized allergies such as hay fever, IgE
antibodies produced after first exposure
to an allergen attach to receptors on
mast cells

Allergies
Autoimmune disorders
What do you think has gone wrong?
 The mechanisms for detecting receptors
that attack its own cells are not working
properly

Bellwork

Discuss with your group why your
immune system does not have a
secondary response to AIDS like most
other viruses. How does it escape the
immune system?
AIDS
Human immunodeficiency virus (HIV)
infects helper T cells
 The loss of helper T cells impairs both the
humoral and cell-mediated immune
responses and leads to AIDS
 HIV eludes the immune system because
of antigenic variation and an ability to
remain latent while integrated into host
DNA
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