Overview of the Immune System

MICR:3164

What is the immune system?

A group of cells and their protein products that are responsible for immunity

What is the role of the immune system?

To protect the body against pathogenic microbes

What is a pathogen?

A microbe that causes disease in its host

Is a pathogen the same as normal flora?

No it is distinct from normal flora

Is there a lot or little of microbes that cause disease?

Only a small fraction of microbes cause disease

What are the characteristics of successful pathogens?

1. Colonize host

2. Find a nutritionally compatible niche in the host

3. Avoid host innate/adaptive immune responses

4. Replicate using host resources

5. Exit and spread to new host

What is an infection?

When a microbe invades the body and multiplies

What is a disease?

Damage that is a result of infection

What is pathogenicity?

The ability of an organism to cause disease

What two things defines the pathogenicity of a microbe?

Both the microbe and the immune response

What are the functions of the immune system?

1. Limit/prevent infection from pathogens

2. Identify and eliminate damaged or abnormal cells

3. Prevent inadvertent damage to the host

4. Prepare for future exposure to previous pathogen

What are the three lines of defense against pathogens?

• Barriers

• Innate Immune Response

• Adaptive Immune Response

What do barriers consist of?

• Physical and mechanical barrier

• Chemical factors

• Normal microbiome

How do physical barriers defend the body?

They block pathogens from entering the body

What are examples of physical barriers?

• Skin

• Mucous membrane

• Epiglottis

• Eyelids

• Tight junctions between epithelial cells

How do mechanical barriers defend the body?

Mechanical actions that remove microbes and debris

What are examples of mechanical barriers?

• Shedding of skin cells

• Cilia movement in lower respiratory track

• Sneezing

• Vomiting

• Tears

• Defecation

How do chemical factors defend the body?

With proteins and other compounds produced by the body that inhibit or kill microbes

What are examples of chemical factors?

• Gastric juices

• Sebum

• Defensins

• Lysozymes

How does normal microbiome defend the body?

Microorganisms that are not pathogenic and are found all over the body, they compete with pathogens

How does the normal microbiome compete with pathogens?

• Compete for nutrients

• Produce toxic substances

• Alter growing conditions

• Take up space

How does the epidermis protect against infection with physical barriers?

• Many layers

• Tight junctions

How does the epidermis protect against infection with mechanical barriers?

• Dead cells shed

• Perspiration

• Keratinocytes continuously divide

How does the epidermis protect against infection with chemical factor?

• Cool, dry, and acidic

• Antimicrobial peptides

  • Defensins

  • Lysozyme

  • Cathelicidin

  • Sebum

How does the epidermis protect against infection with normal flora?

Staphylococcus epidermidis

What is a mucociliary escalator?

How the ciliated cells in lungs that move microbes up the trachea towards the throat to be destroyed by the digestive system