1. Our ability to recognize and respond to pathogens or foreign cells
Immunity
Our ability to recognize and respond to pathogens or foreign cells

2. Parts of the Immune System

3. Innate Immunity
All animals have a type of defense that is activated no matter the pathogen
Includes coverings (shells, skin, exoskeletons)
Chemical secretions guard openings to body fluids
Dependent on receptor molecules to bind to surfaces of invading cell which triggers various responses

4. Innate Immunity: Invertebrates
Chitin exoskeleton (and also found in the intestine where it blocks infection that pathogens that might be ingested in food)
Lysozymes (enzymes specifically targeting the cell wall of bacteria)
Hemocytes travel in the hemolymph and carry out phagocytosis, some will cause the secretion of chemicals that act as antimicrobials
Some immune cells will “tag” foreign cells based on the types of macromolecules found inside (fungi vs. bacteria)

5. Innate Immunity: Vertebrates
Barrier Defenses:
Surface barriers (skin pH slightly acidic as is sweat secretions)
Mucous membranes (also contain lysozyme), ciliated epithelial cells, acidic environment of stomach

6. Innate Immunity: Vertebrates
Cellular Defenses
Toll-like receptors (TLR) bind to molecules characteristic to pathogens helps phagocytic cell recognize and subsequently engulfs and destroys them.
Phagocytic cells destroy foreign invaders by engulfing the cell, trapping it in a vacuole. From there, lysosomes release gases to poison the cell and then release other enzymes that degrade the cell itself.
Neutrophils- circulate in the blood and are triggered by chemical signals
Macrophages usually set up permanent residence in organs most likely to encounter pathogens (spleen, liver etc)
Dendritic cells found in skin help with adaptive immunity (but also phagocytic cell)
Eosinophils found in mucous membranes and work best on multicellular parasites (worms)
Upper left: macrophage with bacteria cell, lower left; neutrophil, upper right- dendritic cell with HIV infected cell, lower right- eosinophils with parasitic worms (dog digestive tract)

7. Innate Immunity- Vertebrates
Cell Defenses Cont’d
Natural killer cells circulate through the body and can detect abnormal surface proteins found in cancer cells and cells infected with a virus. They provide immunity by releasing chemical that will eventually kill the cell
Lymphatic system (lymph nodes and dendritic cell interaction)
Antimicrobial peptides and interferon proteins will act as defense mechanisms by either damaging the cell wall of microbes (bacteria) or secreting chemicals that allow neighboring cells of viral infected cells to be protected (inteferons specifically)
Complement system- group of proteins (up to 30) that are found in the plasma and are only activated by the presence of microbes. Activation leads to cascade of events that will lead to the lysis of foreign cells.

8. Compliment System

9. Inflammatory Response
Involves coordinated action of histamines (released from mast cells), cytokines (released from macrophages and neutrophils) and fever (brought about by macrophages.
Septic shock is inflammation that is overwhelming on the body
Chronic inflammation root of several debilitating diseases and disorders