Download Non-specific Defenses

Immunology
Non-specific Host Defenses
Non-specific means that the defenses that are used
to protect the body act the same no matter what
the infection is. Specific defenses are specific to
the disease, such as antibodies made for each
individual disease.
Nonspecific Host Defenses
• Skin and mucous membranes: provide a
mechanical barrier to keep organisms from
entering the body. They work only if there are no
cracks or tears, etc.
– Additional aids to contribute to the defense provided by
the skin and mucous membranes are:
• Lacrimal secretions (tears): wash dirt and germs from the eyes
• Saliva: washes food and germs off of the teeth
• Mucous in RT and GIT: traps dirt and germs so they can’t
colonize the membrane surface
• Ciliated cells: move mucous, dirt and germs out of
the body
• Urine: washes dirt and germs out of the urethra
• Vaginal secretions: helps maintain normal pH,
washes out dirt and germs
• Chemical factors that aid in defense
– Sebum: oil made by glands of the skin, trap
dirt and germs
– Perspiration: flush org. off skin and produce
lysozyme (break down cell wall of G+)
– Gastric juice: destroys most bacteria and toxins
due to pH and acids
– Normal Microbiota:
• Aid in preventing disease by
– competing for attachment sites.
– competing for nutrients.
– making and excreting antimicrobials.
– Genetics:
• Some host are genetcially resistant to infection by
some organisms. For example, many diseases are
specific to humans and do not infect animals, or vice
versa.
– Monkeypox infects monkeys but does not cause disease in
humans
Nonspecific Defenses in the Blood
• Phagocytes (White Blood Cells): 2nd line of
defense.
– Neutrophils: first responder to the scene of the
accident. Neutrophils begin cleaning up
invading microorganisms by phagocytosis.
– As the infection progresses, macrophages
dominate the clean up process.
• They begin as monocytes. Monocytes are not active
phagocytes while in the blood. Once they move out
of the blood vessels and into the infected tissue, they
mature into macrophages, active phagocytes.
The process of phagocytosis
• See Fig. 14.19
– Recognition: Pathogen recognized as foreign by
phagocyte due to foreign proteins on the surface of the
organism.
• Proteins on the surface of cells are used as markers to identify
the “good guys” and the “bad guys”. The body’s cells have
markers that tell the immune system that they belong there and
not to attack while the bad guys have foreign markers that are
not recognized and signal the immune system that it doesn’t
belong there.
– Adherence: phagocyte binds to pathogen.
– Ingestion: pseudopods are extended around the
pathogen and the pathogen is engulfed into a sac inside
the cell. This is called a phagosome.
– Digestion: lysosomes within the cell migrate to
the phagosome and merge with it, creating a
phagolysosome. Chemicals that are toxic to the
pathogen are released inside the phagolysosome
leading to its digestion.
– Release of Debris: Once the pathogen has
been digested into small particles, the cell
releases the undigestible debris into the
surrounding environment.
Inflammation
• Triggered by damage to body’s tissues.
• 5 signs and symptoms:
–
–
–
–
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Redness
Pain
Heat
Swelling
Sometimes loss of function
• Purpose of Inflammation:
– Destroy injurious agent and remove it if
possible.
– Limit effects on body by walling off injurious
agent and its by-products away from the rest of
the body.
– Repair tissue damaged by the injurious agent or
its by-products.
• 3 stages of Inflammation
– Vasodilation and increased permeability of
blood vessels
• Increase in blood flow to help get the immune cells
to the injured site more quickly and dilute toxic
substances.
• Allows defensive substances, such as phagocytes, to
pass through the walls and enter the injured area.
– Phagocyte Migration and Phagocytosis
• Blood flow decreases, phagocytes begin to squeeze
between endothelial cells to reach damaged area.
• Phagocytes begin destroying invading
microorganisms.
– Tissue repair
• Begins during inflammation but cannot be
completed until all harmful substances have been
removed or neutralized.
– Fever
• The benefits of fever as still being debated and
proved.
• It was thought as recently as 5-10 years ago that the
increased body temperature killed invading
microorganisms by providing an atmosphere that
was too hot for them to survive.
• That has since been shown to be mostly false. Most
microorganisms require a much higher temperature
change to be affected than that caused by a fever.
• However, your textbook does mention a few
organisms that seem to be sensitive to the small
temperature change, such as the Polio virus and the
Chickenpox virus.
• There is some evidence that fever impedes the
nutrition of bacteria by reducing the available iron.
• And it increases metabolism and immune responses.
• In general, whether or not slight to moderate fevers
should be treated is still being debated.
Other Antimicrobial Substances
In Blood
• Complement and Interferon
• Complement: Has several different functions.
– 20 different proteins found in normal serum.
– Punch holes in membranes of pathogens, releasing
cellular contents. Called the Membrane Attack
Complex or MAC.
– Contribute to development of inflammation.
– Coat outside surface of pathogen which enhances
phagocytosis.
• Interferon: chemical made and released by cells
infected by viruses.
– When the interferon is released it binds to receptors on
the outside of neighboring cells.
– It actually works to block the virus from being able to
bind to neighboring cells. That means that the virus
can’t infect neighboring cells because the attachment
sites are taken by interferon.
– It also signals the cell to make antiviral proteins that
inhibit viral replication.
– It sounds like a great treatment for viral infections but
generally it isn’t very effective. It is thought that the
reason is because the amount of interferon needed to
actually coat the cells and keep them continually
protected is too great to maintain.
– See Fig. 14.20
– No HW.