Immune System Part I: The Evolution of the Immune System

1. Immune System Part I: The Evolution of the Immune System

2. Immune System and Innate Immunity • The human body has over 100 trillion bacteria living onit or withinit. • An immune system protects an organism from pathogens and other foreign material. • The innate immune system provides the first line of defense by • activating a small variety of immune cells to produce molecules that stop the invading pathogens and its resulting disease • providing physical barriers to stop a pathogen

3. Adaptive Immune System • The innate immune system is immediate and utilized by many multicellular organisms. • In contrast, an adaptive immune system produces antibodies specific to a pathogen or foreign particle after the pathogen activates B- and T-lymphocytes. • The adaptive immune response is slower than the innate immune response and it may take days to become effective. • Present only in jawed vertebrates

4. Homeostasis and the Immune System • Pathogens invade organisms because they are seeking: • a source of food or water • protection • a place for reproduction • Defense mechanisms evolved to rid the organism of pathogens and return the organism back to its original state.

5. Evolution of the Immune System • Ancestral amoebas performed phagocytosis to obtain food. • It would be advantageous for these ancestral amoeba to be able to distinguish between self and non-self when ingesting other cells. • The interaction between receptors and signature molecules could provide this distinction mechanism.

6. General Cell Communication Propose a cell communication mechanism that ancestral amoeba may have used to distinguish between foreign cells and other amoeba cells.

7. General Cell Communication

8. Cell Communication and Immune System • Example of receptors and various signature molecules or PAMPs. • Explain how this part of the immune system is an example of cell communication. • List all the observations you can make about this diagram.

9. Evolution and Immunity Toll-like receptor (TLR) pathways comparisonfor plants, invertebrates and vertebrates List any similarities that you observe among the 3 pathways. If this pathway was once in an ancestral cell, explain why the differences exist between the three organisms.

10. Plant Defenses • Plants, like animals, must defend against pathogens and herbivores with: • physical barriers • secondary metabolites • immune responses

11. Plants’ Physical Defenses • Pathogens can invade plants. • Plants’physical defenses include: • hairs that insects cannot penetrate • thorns or spines that large herbivores avoid • waxy cuticles that bacteria and fungi cannot penetrate

12. Plant Defenses Against Herbivory • Herbivores harm plants by eating them. • Defenses against herbivory include production of secondary metabolites.

13. Defense and Secondary Metabolites

14. Plant Defenses Against Herbivory

15. Plant Defenses Against Herbivory

16. Coevolution of Herbivores and Plants • Certain herbivores and plants have coevolved with one another. • This butterfly can breakdown the secondary metabolite produced by the passion vine and use a nitrogen by-product in protein metabolism.

17. Induced Defense Response • Certain pathogens will produce molecules that produce the hypersensitive response (HR). • This results in localized death of plant cells very quickly.

18. Systemic Acquired Resistance • Methyl salicylate from the HR is spread to rest of the plant. • Once converted to salicylic acid, a transduction pathway is activated causing systemic acquired resistance (SAR) for the entire plant that lasts for several days.

19. Immunity and Invertebrates -- Physical Barriers • Examples of innate immunity in Drosophila: • First line of defense is the exoskeleton made of chitin. • Chitin also lines the digestive tract. • The enzyme lysozyme found in the gut breaks down the cell walls of bacteria.

20. Innate Immunity • If the pathogen escapes the digestive tract, it will be in a fluid called hemolymph. • Moving throughout the hemolymph are hemocytes. • Some hemocytes can destroy pathogens by phagocytosis.

21. Innate Immunity • Some hemocytes have Toll receptors that produce antimicrobial peptides which inactivate or kill fungal or bacteria by disrupting plasma membranes. • Each Toll receptor identifies certain signature molecules as a pathogen or foreign material.

22. Toll Receptor • The Toll receptor recognizes signature molecules or PAMPs. • This activates signal transduction pathways, often producing transcription factors. • These transcription factors activate genes needed to synthesize anti-microbial peptides for destruction or deactivation of pathogens.

23. Evidence These flies were engineered so that the immune cells expressed a green fluorescent protein when the innate immune system was activated. The top fly was inoculated with bacteria and the one below was “stabbed” with a sterile needle (no injection of bacteria). The top fly’s immune system was activated while the bottom fly’s was not.

24. Created by: Carol Leibl Science Content Director National Math and Science