Download The Immune System

The Immune System
Introduction
Immune system
The body’s defenses against pathogens that produce
disease
2 types of immunity
1. Nonspecific defenses (Innate defense)
• Provide general protection against invasion by a wide
range of pathogens
• Present at birth–innate
2. Specific Defenses
• Specific lymphocytes combat particular pathogens
Overview of the body’s defense
Three lines of defense protect us from pathogens
Nonspecific Defenses
A set of physical barriers and chemicals
that prevent foreign invaders from
getting inside our bodies
1st Line of Defense
External Barriers
1. PHYSICAL BARRIERS:
An outer layer of skin
Hair in the nostrils
Mucous membranes of the digestive and
respiratory tracts
Cilia lining the upper
respiratory tract
propel trapped
particles up and out
Goblet cells secrete mucus, which coats the epithelial cells.
Mucus contains lysozyme, that breaks down bacterial cell
walls.
Bacteria and other debris become trapped in the thick mucus.
Cilia sweep it up and out of the respiratory tract,
where it is expelled from the body by coughing, sneezing,
or even swallowing!
The Skin
I. Epidermis - outer layer of skin that provides a
barrier against infection. Any microbes attached
to outer layer of dead cells will be shed with
those cells.
II. Dermis contains :
a. sweat glands
– they produce salty perspiration to flush microbes and
other contaminants out of the pores.
– Sweat also contains a special enzyme called
lysozyme,.
.
b. sebaceous glands that coat the skin with
sebum, which is an oily substance that
contains fatty acids that lower the pH of the
skin surface to inhibit microbial growth
2. Chemical defenses (barriers)
Sweat, saliva, and tears contain enzymes that
kill bacteria.
Glands produce oils and acids
The acid pH of the stomach kills many bacteria
3. Resident Bioflora
Beneficial microbes living on our skin and in
our bodies that help block infection by
disease-causing microbes
Where does all the dead skin go?
• Dead skin cells can be found on our sheets,
pillows, clothes, and even in the dust particles
that form in our homes.
• Dead skin cells are broken down by dust
mites, which are microscopic parasites that
live on our skin, hair, and eyelashes.
2nd Line of Defense
• Acts when an invader
penetrates the body’s
external barriers
• Nonspecific – combats
all invading microbes
• Depend on white blood
cells and defensive
proteins.
White Blood Cells
(cells that fight infection)
2nd Line of Defense
Leukocytes – “Warriors of the immune system”
AKA white blood cells
Produced in the bone marrow
Include:
basophils, eosinophils, mast cells,
neutrophils, monocytes, macrophages
Lymphocytes (specific immunity)
2nd Line of Defense
2nd Line of Defense
• When the external barriers fail, a set of
nonspecific internal defenses stands ready – the
second line of protection
• Antimicrobial proteins
Interferon
Complement
• WBCs: phagocytic cells and natural killer cells
• Inflammation
• Fever
Antimicrobial proteins–
Interferons (IFNs)
• Protect body against
viral infection
• Cells infected by viruses
produce interferon
• IFNs stimulate healthy
cells to produce
proteins that inhibit
viral reproduction
Antimicrobial proteins–
the complement system
complement
• A group of ~20 proteins in
blood plasma and cell
Membranes
• “Complement” proteins
cause invading cells to
lyse
– Form a “membrane attack
complex” that makes holes
in some microbes
– Causes the microbe to lyse
proteins
membrane
attack complex
fluids
fluids
The 2nd line of defense: WBCs
• Phagocytes
• Engulf microbes or other
particles (by phagocytosis)
• Phagocytes migrate to
infected area by chemotaxis
(attracted to chemicals
released by invading
microbes and host cells)
A Macrophage in action
• White blood cells have specialized receptors
on their surface that enable them to
determine what is "self" and "non-self”
• When "non-self" proteins are encountered, an
immune response is mounted to destroy the
foreign (non-self) substance.
Cell Type
Location in Body
Function
Neutrophils
Circulate in body, few in tissue
except during inflammation
Phagocytize and digest
engulfed materials
Eosinophils
Mainly in blood except during
inflammation and allergies
Participate in inflammatory
reaction and immunity to
some parasites
Basophils
Mast Cells
Basophils in circulation, mast cells
present in most tissues
Release histamine and
other inflammation causing
chemicals
In circulation. Differentiate into
macrophages or dendritic cells
when they migrate into tissue
Phagocytize and digest
englulfed material
Macrophages
Present in virtually all tissues
Phagocytize and digest
englulfed material
Dendritic Cells
Initially in tissues but migrate to
lymph nodes and other secondary
organs
Gather antigen from tissues
and present it to
lymphocytes
Lymphocytes
In lymphoid organs and circulation
Participate in
Mononuclear
Phagocytes
(Monocytes)
Natural Killer (NK) cells
• Destroy infected body
cells and cancerous cells
• NK cells bind to infected
cells
• Release perforins that
penetrate the plasma
membrane of infected
cells causing them to
lyse (similar effect as
complement)
Chemical Messengers
Cytokines – Include:
•
•
•
•
•
Interleukin I and II
Histamine
Prostaglandins
Complement
Interferons
The 2nd line of defense:
Inflammation
• Occurs when tissue is damaged
• Inflammation
• an attempt to dispose of microbes
• prevent their spread to other tissues
• prepare the site for tissue repair
• 4 hallmark symptoms of the inflammatory response:
• Redness
• Pain
• Swelling
• Heat (warm to the touch)
What happens when you cut
your finger?
Phagocytes engulf
bacteria
Tissue heals
Steps in the Inflammatory Response
1. Tissue damage
2. Mast cells release Histamine
 Histamine increases blood flow (by
vasodilation) to damaged area (redness).
 Causes capillaries to become leaky
(swelling).
3. Damaged cells in area produce other
chemicals that attract phagocytic cells to site.
Inflammatory Response
4. Prostaglandins produced – induces pain, and
important in production of fever.
5. Chemicals released attract neutrophils which
“stick” to capillary walls (margination),
eventually “squeezing” through the leaky
capillaries (extravasation).
6. Neutrophils and other phagocytes attracted
to damaged site via cytokines.
7. Ingest and destroy bacteria.
8. Platelets and clotting factors help to heal
wound and confine infectious agents at
wound site.
(McGraw Hill video)