Innate and Adaptive Immunity
Recognition and response rely on traits common to groups of pathogens.
• Pathogens are agents that cause disease such as bacteria, viruses, fungi, or others
• Dedicated cells of the immune system enable animals to avoid or limit many infections
• First lines of defence help prevent pathogens from gaining entry to the body.
- Integumentary system
- Mucosa
• Within the body, 2 types of molecular recognition allow detection of non-self (foreign)
molecules, particles, and cells
- Innate recognition
- Adaptive recognition
Innate Immunity
A defence mechanism which is active immediately upon infection.
Many cellular innate defences involve the lymphatic system.
Innate immunity includes the following mechanism:
1. Barrier defences
- Skin + mucous membranes (respiratory, urinary, and reproductive tracts)
- Mucus traps and allows removal of microbes
- Body fluids (saliva, mucus, and tears) are hostile to many microbes
- Low pH of skin and digestive system prevents growth of many bacteria (not H.
pylori – bacteria that live in digestive tract)
1
, 2. Phagocytosis (cellular defences)
- Innate immune cells detect, devour, and destroy invading pathogens
- Recognise groups of pathogens using TLR (toll-like receptors)
TLRs recognise fragments of molecules characteristic of a set of pathogens
- 2 main types of phagocytic cells:
Neutrophils → circulate in blood, first responders, alert cells in immune system
Macrophages → migrate through the body or reside permanently in organs and
tissues, are abundant in lysosomes, function in digestion
- 2 additional types of phagocytic cells:
Dendritic cells → stimulate development of adaptive immunity, migrate to
lymph nodes after interacting with pathogens
Eosinophils → discharge destructive enzymes against parasites
3. Antimicrobial peptides
- Involved in inflammatory response
4. Natural killer cells
- These cells circulate through the body and detect abnormal cells
- Release chemical leading to cell death → inhibit the spread of virally infected /
cancerous cells
5. Interferons
- Group of signalling proteins made and released by host cells in response to the
presence of several viruses
- Causes nearby cells to heighten their ant-viral defences
6. Local inflammatory response
- Includes heat and swelling → brought by molecules released upon injury and
infection
- Mast cells (immune cells found in loose CT) discharge cytokines, signalling
molecules that recruit neutrophils to the site
- Mast cells release histamine → triggers blood vessels to dilate → becoming more
permeable
- Cycles of signalling and response continue inflammation
- Enhanced blood flow → antimicrobial peptides delivered
Result in accumulation of pus
Pus = fluid rich in WBC, dead pathogens, debris from damaged tissues
- At the end of local inflammatory response → pus + excess fluid taken up as lymph
Fluid transported in lymphatic system
Lymph nodes → throughout body, contain macrophages → engulf pathogens
that enter lymph
2
Recognition and response rely on traits common to groups of pathogens.
• Pathogens are agents that cause disease such as bacteria, viruses, fungi, or others
• Dedicated cells of the immune system enable animals to avoid or limit many infections
• First lines of defence help prevent pathogens from gaining entry to the body.
- Integumentary system
- Mucosa
• Within the body, 2 types of molecular recognition allow detection of non-self (foreign)
molecules, particles, and cells
- Innate recognition
- Adaptive recognition
Innate Immunity
A defence mechanism which is active immediately upon infection.
Many cellular innate defences involve the lymphatic system.
Innate immunity includes the following mechanism:
1. Barrier defences
- Skin + mucous membranes (respiratory, urinary, and reproductive tracts)
- Mucus traps and allows removal of microbes
- Body fluids (saliva, mucus, and tears) are hostile to many microbes
- Low pH of skin and digestive system prevents growth of many bacteria (not H.
pylori – bacteria that live in digestive tract)
1
, 2. Phagocytosis (cellular defences)
- Innate immune cells detect, devour, and destroy invading pathogens
- Recognise groups of pathogens using TLR (toll-like receptors)
TLRs recognise fragments of molecules characteristic of a set of pathogens
- 2 main types of phagocytic cells:
Neutrophils → circulate in blood, first responders, alert cells in immune system
Macrophages → migrate through the body or reside permanently in organs and
tissues, are abundant in lysosomes, function in digestion
- 2 additional types of phagocytic cells:
Dendritic cells → stimulate development of adaptive immunity, migrate to
lymph nodes after interacting with pathogens
Eosinophils → discharge destructive enzymes against parasites
3. Antimicrobial peptides
- Involved in inflammatory response
4. Natural killer cells
- These cells circulate through the body and detect abnormal cells
- Release chemical leading to cell death → inhibit the spread of virally infected /
cancerous cells
5. Interferons
- Group of signalling proteins made and released by host cells in response to the
presence of several viruses
- Causes nearby cells to heighten their ant-viral defences
6. Local inflammatory response
- Includes heat and swelling → brought by molecules released upon injury and
infection
- Mast cells (immune cells found in loose CT) discharge cytokines, signalling
molecules that recruit neutrophils to the site
- Mast cells release histamine → triggers blood vessels to dilate → becoming more
permeable
- Cycles of signalling and response continue inflammation
- Enhanced blood flow → antimicrobial peptides delivered
Result in accumulation of pus
Pus = fluid rich in WBC, dead pathogens, debris from damaged tissues
- At the end of local inflammatory response → pus + excess fluid taken up as lymph
Fluid transported in lymphatic system
Lymph nodes → throughout body, contain macrophages → engulf pathogens
that enter lymph
2
