1. Chapter 35
Innate Immunity

2. You Must Know The elements of the innate immune response
How cells in the immune system communicate with each other

3. Pathogens (such as bacteria, fungi, and viruses)
INNATE IMMUNITY
(all animals)
Barrier defenses:
Skin
Mucous membranes
• Rapid response
Secretions
Internal defenses:
Phagocytic cells
Natural killer cells
Antimicrobial proteins
Inflammatory response
Pathogens, agents that cause disease, infect a wide range of animals, including humans. The immune system enables an animal to avoid or limit many infections. All animals have innate immunity, a defense that is active immediately upon infection. Vertebrates also have adaptive immunity. Innate immunity is present before any exposure to pathogens and is effective from the time of birth. It involves nonspecific responses to pathogens. Innate immunity consists of external barriers plus internal cellular and chemical defenses. Adaptive immunity, or acquired immunity, develops after exposure to agents such as microbes, toxins, or other foreign substances. It involves a very specific response to pathogens.
ADAPTIVE IMMUNITY
(vertebrates only)
Video: Crash Course 3

4. Innate Immunity: Barrier Defenses
Born with it
Innate immunity is found in all animals and plants. Innate immunity is present before any exposure to pathogens and is effective from the time of birth. Barrier defenses include the skin and mucous membranes of the respiratory, urinary, and reproductive tracts. Mucus traps and allows for the removal of microbes. Many body fluids including saliva, mucus, and tears are hostile to many microbes. The low pH of skin and the digestive system prevents growth of many bacteria.

5. Innate Immunity: Internal Defenses
Phagocytic cells
cells that protect the body by phagocytosing (eating) other cells.

6. Phagocytosis PHAGOCYTIC CELL Pathogen 1 Pseudopodia
surround pathogens.
engulfed by endocytosis.
Pathogens 2
Vacuole forms. 3
Phagocytosis
Lysosome containing enzymes
Vacuole and
lysosome fuse. 4
Phagocytosis, the ingestion and breakdown of foreign substances including bacteria.
Pathogens
destroyed. 5
Debris from
pathogens released. 6

7. How do your phagocytic cells “know who the bad guys are”?7

8. In innate immunity, recognition and response rely on traits common to groups of pathogens
EXTRACELLULAR FLUID
Lipopolysaccharide
Helper protein
Flagellin
TLR4
PHAGOCYTIC CELL
Lipopolysaccharide
TLR5
Flagellin
TLR9
CpG DNA
Pathogens entering the mammalian body are subject to phagocytosis. Phagocytic cells recognize groups of pathogens by Toll-like receptors (TLRs). Each mammalian TLR binds to fragments of molecules characteristic to a set of pathogens.
Phagocytic cells recognize groups of pathogens by Toll-like receptors (TLRs).
VESICLE
Innate immune responses
TLR3
dsRNA 8

9. There are two main types of phagocytic cells in mammals:
Neutrophils circulate in the blood and are attracted by signals from infected tissues
Macrophages are found throughout the body
cytokine
TLR
Macrophages

10. Infection

11. Inflammatory Response
Movement of fluid 2
Antimicrobial peptides enter tissue. Neutrophils are recruited.
Phagocytosis 3
Neutrophils digest pathogens and cell debris. Tissue heals.
Pathogen
Splinter
Macro- phage
Signaling molecules
Mast cell
cytokine
histamine
Capillary
Red blood cells
The inflammatory response, such as pain and swelling, is brought about by molecules released upon injury of infection. Mast cells release histamine, which triggers blood vessels to dilate and become more permeable. Activated macrophages and neutrophils release cytokines, signaling molecules that modulate the immune response and promote blood flow to the site of injury or infection. Enhanced blood flow to the site helps deliver antimicrobial peptides. This results in an accumulation of pus, a fluid rich in white blood cells, dead pathogens, and cell debris from damaged tissues.
Neutrophil 1
Histamines and cytokines released. Capillaries dilate. 11

12. Innate Immunity: Natural killer cells
When good cells go bad
Cancerous or
viral infected cell
natural killer cell
Cellular innate defenses in vertebrates also involve natural killer cells.
These circulate through the body and detect abnormal cells. They release chemicals leading to cell death, inhibiting the spread of virally infected or cancerous cells.