Download The Immune System

Lecture PowerPoint to accompany
Foundations in
Microbiology
Sixth Edition
Talaro
Chapter 14
Nonspecific Host
Defenses
1st Line of Defense
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The Immune System
Part 1
Nonspecific Host Defenses
1st Line of Defense
Our Immune System
• Ability to differentiate between self and
non-self
• Antigen – anything that triggers an
immune response
• Pathogen – disease causing organism
Size does matter
Pathogen Offense
• Most bacteria are harmless
• Some are pathogens
• Bacterial pathogens have characteristic
“weapons” or “armor” that enhance their
ability to enter the body, multiply, and exit
the body.
• These “weapons” are called virulence
factors
Virulence Factors
• Flagella – help bacterial pathogens swim
through the mucous membranes
• Pili – mediates the attachment of bacteria
to the surface of the mucous membranes
• Biofilms – groups of bacteria bonded
together on surfaces that function as a unit
– Plaque on teeth
Virulence Factors
• Invasive virulence factors – help bacterial
pathogens invade across the mucous
membranes into the tissue space below.
• Capsule – armor-like coating made of
polysaccharides or proteins that protect bacterial
pathogens from being engulfed and digested by
the body’s phagocytic white blood cells,
neutrophils, and macrophages.
Virulence Factors
• Toxins – released by pathogenic bacteria,
also kill incoming phagocytic white blood
cells.
– Allows pathogen to escape phagocytosis and
multiply in body tissues
Defense Mechanisms of the
Host
• To protect the body against pathogens, the
immune system relies on a multilevel network
of physical barriers, immunologically active
cells, and a variety of chemicals.
– first line of defense – any barrier that blocks
invasion at the portal of entry – nonspecific
– second line of defense – protective cells and
fluids; inflammation and phagocytosis –
nonspecific
– third line of defense – acquired with exposure to
foreign substance; produces protective antibodies
and creates memory cells – specific
Physical or Anatomical Barriers:
First Line of Defense
Skin and mucous membranes of respiratory,
urogenital, eyes and digestive tracts
– outermost layer of skin is composed of epithelial cells
compacted, cemented together and impregnated with
keratin; few pathogens can penetrate if intact
– flushing effect of sweat glands
– damaged cells are rapidly replaced
– mucous coat impedes attachment and entry of
bacteria
– blinking and tear production
– stomach acid
– nasal hair traps larger particles
Nonspecific Chemical
Defenses
• Sebaceous secretions
• Lysozyme, an enzyme that hydrolyzes the cell
wall of bacteria, in tears
• High lactic acid and electrolyte concentration in
sweat
• Skin’s acidic pH
• Hydrochloric acid in stomach
• Digestive juices and bile of intestines
• Semen contains antimicrobial chemical.
• Vagina has acidic pH.
Genetic Defenses
• Some hosts are genetically immune to
the diseases of other hosts.
• Some pathogens have great specificity.
• Some genetic differences exist in
susceptibility.