Innate immune system
- Nonspecific and starts with barriers
- Operate continuously in healthy individuals and are physical, microbial, and chemical
- Protect host by carrying out opsonization, inflammation and cell communication
Innate immune system barriers - microbial
- Commensal organisms
- Purpose: Compete for resources
- Time: 0-1 hour
Innate immune system barriers - Physical
- Epithelium and mucus membrane
- Purpose: Blocks entry
- Time: 0-1 hour
Innate immune system barriers - chemical
- Antimicrobial peptides and cytokines
- Purpose: Neutralize invasion
- Time: 0-6 hours
Innate immune system - Cells
- Dendrites, macrophage, neutrophil, and natural killer
- Purpose: Initiate phagocytosis or apoptosis
- Time: 6-12 hours
Innate immune system - Processes
- Phagocytosis, opsonization, inflammation, cell communication
- Purpose: Recruit, combine, integrate responses to start to combat infection
- Time: 6-72 hours
Innate immune cells capable of phagocytosis
- Macrophages
- Neutrophils
- Dendritic cells
Phagocytosis step 1
Pseudopodia surround microbes
Phagocytosis step 2
Microbes are engulfed into the cell
Phagocytosis step 3
Vacuoles containing microbes form
Phagocytosis step 4
Vacuoles and lysosomes fuse
Phagocytosis step 5
Toxic compounds and lysosomal enzymes destroy microbes
Phagocytosis step 6
Microbial debris is released by exocytosis
What is opsonization?
When phagocytosis is improved by coating a bacterium with opsonins like antibodies or complement proteins in blood plasma
How do antibodies act as opsonins?
Antibodies bound to a bacterium are recognized by the Fc receptor on a phagocytic cell
How does the complement system help in opsonization?
C3b coats the pathogen and binds to C3b receptors on phagocytes, helping them attach and engulf the microbe
What happens once a bacterium is coated with opsonins?
The bacterium is bound, engulfed, and destroyed by the phagocyte, improving pathogen clearance
What are complement proteins and how are they activated?
- Complement proteins (>30) circulate in the blood in inactive form
- They become active when C3 is cleaved into C3a and C3b in the presence of pathogens
What are the three complement activation pathways?
- Classical: antibodies bind pathogen
- Lectin: host protein binds mannose on pathogen
- Alternative: C3 interacts with bacterial motifs, forming C3b
What does C3 activation lead to?
- increases immune cell recruitment (inflammation)
- enhances phagocytosis
- can form a membrane attack complex (MAC) that makes pores in pathogen membranes causing lysis
What type of pathogen is the MAC most effective against?
- Gram-negative pathogens because it passes through the outer membrane
- Gram-positive cells resist due to their thick peptidoglycan layer
What do Natural Killer (NK) cells do?
- NK cells work in both innate and adaptive immunity to detect and destroy infected, stressed, or tumor cells
- They are nonphagocytic and kill by releasing proteins that cause apoptosis
How do NK cells target cells?
- They target using antibodies to microbial antigens (adaptive immunity)
- They activate cell receptors that trigger cell death (innate immunity)
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Module 1: Section 124
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Module 1: Section 236
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Module 2: Section 1A26
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Module 2: Section 1B54
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Module 2: Section 1C8
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Module 2: Section 1D7
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Module 2: Section 2A16
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Module 2: Section 2B6
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Module 2: Section 2C5
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Module 2: Section 2D12
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Module 3: Section 1A15
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Module 3: Section 1B19
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Module 3: Section 1C16
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Module 3: Section 2A18
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Module 3: Section 2B22
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Module 3: Section 2C31
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Module 3: Section 2D23
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Module 3: Section 2E14
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Module 4: Section 1A24
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Module 4: Section 1B24
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Module 4: Section 2A15
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Module 4: Section 2B14
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Module 4: Section 3A34
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Module 4: Section 3B31
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Module 4: Section 3C21
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Module 5: Section 1A15
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Module 5: Section 1B9
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Module 5: Section 1C14
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Module 5: Section 2A30
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Module 5: Section 2B13
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Module 5: Section 2C32
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Module 6: Section 1A15
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Module 6: Section 1B24
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Module 6: Section 1C14
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Module 6: Section 2A14
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Module 6: Section 2B32
