The
non-specific defenses or
innate defenses are designed to protect the body against different types of
pathogens, but not specific
pathogens. The
non-specific defenses make up the first and second lines of defense in the body.
The
non-specific internal defenses are designed to protect the body against types of invaders that have passed the first line of defense and entered the
blood and surrounding
tissues.
The
non-specific internal defenses consist of:
Phagocytosis
Neutrophils and
monocytes are both types of
macrophages. They patrol body
tissues following
chemical trails left by microbial invaders in a process called
chemotaxis. Once they have found an invader they engulf and destroy it.
NK (natural killer) cells
NK cells patrol the
blood and
lymph looking for
virus-infected
cells and cancer
cells. Infected or cancerous
cells lack surface markers or display surface markers that the NK cell does not recognize. The NK cell then releases
perforin, a
chemical that causes the target
cell to
lyse.
Complement system
Complement proteins are created by the
liver and circulate in the
plasma in an inactive form. Once they have been exposed to foreign microorganisms or activated by the presence of
antibodies, five
complement proteins come together to form a
membrane attack complex (MAC). The MAC is a cylindrical
structure that pierces the
membrane of a target
cell, causing it to
lyse in a process called a
MAC attack.
Interferons
Interferons are
chemical signals that can temporarily protect healthy
cells from
viral infection. They are produced by a
virus-infected
cell and bind to
membrane receptors of healthy
cells. The healthy
cell then produces
virus-blocking
enzymes on its surface and cytoplasmic
enzymes that can break down
viral mRNA. The response by the healthy
cell only lasts a short amount of time, after which the
enzymes are broken down and recycled. If the
virus has a dormant period before it spreads, then
interferons are not effective. However, if the
virus spreads quickly, then the
interferons serve an important role in helping give the immune system enough time to react to a
viral attack.
Inflammatory response
The
inflammatory response is a non-specific response to an injury or a localized
infection. When
cells are damaged they release
chemical signals into the surrounding
tissues.
Mast cells in the
connective tissue release
histamine, a
chemical that increases capillary permeability and vasodilation in the immediate area.
Alarm
chemicals released by the damaged
cells attract
neutrophils,
monocytes and lymphocytes to the area to destroy any invading
microbes. When
neutrophils are attracted to an injury site by
chemotaxis from alarm
chemicals, they travel in the
blood system towards the injury site. They then
marginate, clinging to the capillary wall close to the injury site. They then cross from the blood to the interstitial space by
diapedesis, a process in which the
neutrophil squeezes through the capillary wall between the epithelial
cells.
Click here to see a tutorial about the inflammatory response
Fever
Once an
infection has been
detected in the body,
pyrogens are released into the
blood. The
pyrogens cause a rise in body temperature, making the body less hospitable to invading
microbes.
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1 - Anatomy and Physiology Basics