Innate(natural) immune defenses: 14.6: Innate (Nonspecific) Defenses
Species Resistance:
• A species is resistant to diseases that affect other species
• Based on the following factors:
• Different chemical environments
• A body temperature that does not provide the conditions required by the pathogens
Innate Defenses: Mechanical Barriers
Mechanical barriers:
• Prevent the entry of certain pathogens by providing a physical separation of pathogens and internal tissues • Examples: unbroken skin and mucous membranes of the body
• Includes hair, mucus, and sweat
• Mechanical barriers represent the body’s first line of defense
• The rest of the innate defenses are part of the second line of
defense
Innate Defenses: Inflammation
Inflammation:
• A tissue response to injury or infection
• Function of inflammation is to stop the spread of pathogens
and infection
• Characterized by redness, swelling, heat, and pain
• Major events of the inflammatory response include:
• Dilation of blood vessels, to increase of blood volume (causes redness)
• Increased capillary permeability, which leads to edema and heat
• Attraction of white blood cells into the affected area, for phagocytosis
• Blood clotting & fibrin thread formation
• Fibroblasts secrete chemicals that produce a sac around the area to wall
off infection; inhibits spread of infection
Innate Defenses: Chemical Barriers
Chemical barriers:
• Chemicals that kill many pathogens
• Acidic environment provided by HCl in gastric juice is lethal to some pathogens
• Enzymes, such as pepsin in the stomach and lysozyme in tears,
destroy many pathogens
• Interferons, hormone-like peptides secreted by lymphocytes
and fibroblasts when viruses or tumor cells are present, block
viral replication and slow tumor growth
Innate Defenses: Natural Killer (NK) Cells
Natural killer (NK) cells:
• Small group of lymphocytes, other than T cells and B cells
• Defend the body against viruses and cancer cells by secreting cytolytic substances called perforins, which lyse (break apart)
cell membranes of pathogens
• NK cells also secrete substances that enhance inflammation
Innate Defenses: Phagocytosis
Phagocytosis:
• Engulfment and digestion of pathogens, foreign particles, and
debris
• Most active phagocytes are neutrophils and monocytes, which
leave bloodstream in areas of injury
• Phagocytes are attracted to the injured area by chemotaxis, in
which they are attracted by chemicals from injured cells
• Neutrophils engulf smaller particles; monocytes attack larger ones
• Monocytes give rise to macrophages outside the blood, which are
either free or become fixed in various tissues