1. Recognize invading foreign organisms
2. Prevent them from spreading
3. Clear them from the body

1. Bacteria (single cell)
2. Viruses (single cell)
3. Fungi (single or multicellular)
4. Parasites (single or multicellular)

• Number of species they can infect
• The ability to survive outside the host
• How much of an initial dose of the organism is needed to overwhelm the immune system
• The mechanism by which the organism hurts host cells

• Endotoxins - toxins found on the surface of the cell to damage host cells
• Exotoxins - toxins released outside the organism to damage host cells
• Cytopathic Effect - Killing a host cell directly

Replicates outside the cell

Habitually cause disease

(influenza, gonorrhea, etc.)

• Don't usually cause disease
• Commensals - Microbes that normally perform tasks for the host but can cause issues if they end up in areas outside of their niche
• Environmentals

1. A complex molecule of high molecular weight that the immune system recognizes as foreign
2. A substance that causes a specific immune response and react with the products of that response

• Foreign or non-self
• High chemical complexity 
• Large in size
• contain many Epitopes
• [image]

• non-specific immunity 
• 1st line of defense
• Kill anything foreign by recognizing and activating effector functions
• external defense
• cells
• proteins (complement)
• Inflammation (containment) 

• Specific Immunity
• recognize and kill specific targets
• develops memory
• B cells, T cells, plasma cells, antibodies
• takes time to develop (days to weeks)

• Intact Skin
• Mucosal Surfaces
• Inflammation

1. Redness
2. Swelling
3. Heat
4. Pain
5. Loss of Function