Copyright 2010. PEER.tamu.edu
Immunity –
The War Against Infection
 Immunity: ability of an
organism to resist disease.
 Antigen: any substance
that elicits an immune
response.
 Antibodies: made in
response to specific
antigens; can inactivate the
antigen that triggered the
antibody formation.
The Body Fights Back: 2 Ways
 Surface Barriers Keep
Intruders Out
• Prevents entry of antigens inside
our body
• Skin, Mucosa
 Two immune mechanisms:
• Cell Mediated Immunity: Cell
activates itself to defend against the
attack
• Humoral Immunity: Cell produces
antibodies carried in blood to
combat the intrusion
The Invaders
 The Antigen
The Enemy Invader
• Usually a bacteria or
virus
The Warriors
Three Defense Systems:
1. Macrophage cells
2. T cells
3. B cells
The Warriors
 The Macrophage
Body's Radar
 Type of cell normally
present in the blood
 Detects the enemy
and engulfs (eats) it
The Warriors
 The T-Helper Cell
Communication Link
 Communication Link
Between the body's
macrophages and Bcells
Inactivated in HIV infections
Macrophage Presents Antigen
to T Cells
Virus
Virus
Virus
The Warriors
 The B-Cell
The War Factory
 Produces antibodies
custom tailored for
the type of enemy
antigen
B-Cells in Action
Virus
Virus
Virus
Virus
Antibodies Need Help
 Antibodies
Antigen Busters
 Designed to seek and
destroy the specific
enemy antigen
 Complement
Support Troops
 Assists the antibodies
to neutralize the
enemy antigen
Antibody Protein & Humoral Immunity
Since antibodies circulate through the body fluids(humours),
the protection afforded by B cells is called humoral immunity.
Structure of
antibodies
(Y-shaped
proteins)
So what does an
antibody do?
1. Binds to molecules
(antigens) on the surface
of invading organism.
2. Inactivates or renders the
microorganism susceptible
to destruction by the
immune system.
Review 1
 What is the enemy called that invades the
cell?
 What keeps intruders out?
 What are the two kinds of immunity?
Surface Barriers or Mucosal
Immunity
Skin
Cilia
Tears, Saliva, Urine.
Sticky mucus
Stomach:
Hydrochloric Acid
Analogy
 Suppose the classroom is a body.
 All students are cells.
 Rats are Antigens.
 Doors and Windows prevent them from entering
- Surface Barriers.
 Some of you Tough ones (T-cells) will capture
the rodents - Cell-mediated Immunity.
 Some of you Brainiacs (B-cells) will call pest
control (Antibodies) to capture the rodents –
Humoral Immunity.
The Cells in Blood
Source: National Library of Medicine
*Lymphocyte not shown. Looks like
a monocyte, except nucleus mostly
fills the cell and does not have a
notch in it.
The Role of Neutrophils
When a wound occurs,
neutrophils migrate out of
blood to rush to the wound
and phagocytize (“eat”) the
bacteria. This is what pus is
made of.
“old” neutrophil surrounded by red
blood cells
The Role of
Monocytes
Eosinophils
Turn into Macrophages
Attack Internal Parasites
Note the notch in the nucleus.
Otherwise, it looks like a
lymphocyte.
Note the red granules
in the cytoplasm.
The Role of Macrophages
Engulf and then digest cellular debris and
microbes in the body tissues.
Note the irregular cell
membrane. These are
monocytes in the
bloodstream and once they
migrate into the tissues
they become
macrophages.
The Role of Platelets
Blood Clotting
They can clump together
to form clots. No role in
immunity.
Leukocytosis
 Leukocytosis: white blood cell count increased
above the normal range.
 It is not a disorder or a disease, but a sign of
illness.
 It occurs in response to a wide variety of
conditions, including
 viral, bacterial, fungal, or parasitic infection
 cancer
 Hemorrhage (internal bleeding)
 exposure to certain medications or chemicals
including steroids.
Leukopenia
 Leukopenia: a decrease in the number of
circulating white blood cells in the blood.
 As white blood cells get “used up” during
infection, leukopenia can place patients at
higher risk for infection.
 Causes:
 Influenza, typhus, malaria, HIV, tuberculosis, dengue, Rickettsial
infections, enlargement of the spleen and folate deficiencies.
 chemotherapy, radiation therapy, leukemia , myelofibrosis and
anemia.
 many common medications like minocyclen.
HIV (Human Immunodeficiency Virus)
 HIV infection causes AIDS (Acquired
ImmunoDeficiency Syndrome).
 AIDS causes the immune system to fail, leading to life-
threatening opportunistic infections.
 Infection with HIV occurs by the transfer of blood,
semen, vaginal fluid, pre-ejaculate, or breast milk.
 The four major routes of transmission are




unprotected sexual intercourse,
contaminated needles
breast milk
transmission from an infected mother to her baby at birth.
AIDS (Acquired ImmunoDeficiency Syndrome)
 Virus infects vital cells such as helper T
cells and macrophages.
 When T cell numbers decline below a
critical level, cell-mediated immunity is
lost, and infections with a variety of
opportunistic microbes appear.
Cell-mediated immunity
 It is an immune response that does not involve
antibodies, but rather the cells act as the killers
themselves.
 It protects the body by:
 Activating antigen-specific T-cells that destroy
infected cells.
 Activating macrophages that destroy
intracellular pathogens.
 Activating NK (Natural Killer) cells that release
a protein that kills the target cells
Review 3
 What is Leukopenia and what does it
cause?
 What immune response does not involve
antibodies?
Immune System Research
How do they test for antibodies?
ELISA TEST
Remove blood cells and use the fluid
(serum) to test for presence of
antibody.
A. Place target sample on a support
B. Add serum that has antibody against
antigen being tested for. Antibody, if
present, binds the antigen.
C. Add a second antibody (that was
separately developed to react with the
antibody/antigen complex in step B)
binds it to the complex. Second
antibody was also prepared with an
enzyme attached to it.
D. This new complex is made visible by
reacting it with an enzyme that
converts it to a colored compound
that you can see.