1. Adaptive Immune System
Julie Lowe
BIO422
2014

2. “Jobs” of the Immune System

3. “Jobs” of the Immune System
Recognize that invaders are present
Recognize that these are different than self
Recruit more cells/factors to fight invaders
Kill the invaders
Block any toxins produced by the invaders
Learn from past encounters to increase future effectiveness

4. Overview of Host Response to Pathogens

5. Time Course of an Immune Response

6. Levels of the Immune Response
PAMP (Pathogen Associated Molecular Pattern)
Receptor
Signaling Cascade
Transcription factors
Cytokines/chemokines

7. PAMP + Receptor
Complex Signaling Cascade
Cytokine/
chemokine
release
Transcription factor activation

8. Levels of the Immune Response

9. Levels of the Immune Response

10. Adaptive Responses Are Specific to Individual “Epitopes”
Antigen: the molecule recognized by the response
The epitope is the specific part of the antigen recognized
Each adaptive immune cell can only recognize one epitope

11. Epitopes are small parts of antigens
Figure 24.2

12. Concept Questions Can an antigen have more than one epitope?
Yes, almost always
Can an epitope have more than one antigen? No
You found two adaptive immune cells that respond to pilin. Are these cells specific for the same epitope?
Not necessarily: they could respond to two different epitopes on the same antigen

13. Two Branches of Adaptive Response
Cellular Immunity
Humoral Immunity
Main cells are T cells
Useful against intracellular pathogens
B cells and antibodies
Useful against extracellular microbes and toxins

14. Cellular Immune Response
T cell Mediated Immunity

15. Roles of T cells in Host Defense
CD8+
CD4+

16. How do T cells recognize antigen?
T cell receptor
Recognizes small parts of proteins “presented” on MHC molecules
MHC is present on antigen presenting cells

17. Two types of MHC: MHCI and MHCII
MHCI is present on all nucleated cells
CD8+ cytotoxic T cells recognize MHCI
MHCII is present on professional antigen presenting cells  pAPCs
CD4+ helper T cells recognize MHCII
Figure 24.20

18. Intracellular antigens are processed and displayed on MHCI for CD8+ cytotoxic T cells
Figure 24.21

19. Extracellular antigens are processed and displayed on MHCII for CD4+ helper T cells
Figure 24.21

20. Initial recognition by pAPCs
Professional antigen presenting cells
Dendritic cells, macrophages, and B cell
Offer activating signals to T cells—primes for activity, causes proliferation

21. Types of T cells Cytotoxic T cells: CD8+ T cells
Recognize antigens on MHCI
Releases granules to kills target cells
Helper T cells: CD4+ T cells
Recognize antigens on MHCII
Secrete cytokines to activate other cells
Two major types: Th1 and Th2

22. CD8+ Cytotoxic T cells
Death of cells infected with virus or cytoplasmic bacteria, cancer cell, etc.

23. CD4+ Helper T cells (Th) Th1 cells: activate phagocytes
Th2 cells: activate B cells

24. Concept Question What do cytotoxic T cells recognize?
Exogenous peptides on MHCI
Endogenous peptides on MHCI
Exogenous peptides on MHCII
Carbohydrates on bacteria cells
Endogenous peptides on MHCII
Change

25. Concept Question
T helper 1 cells (Th1) are important for defense from…
Extracellular pathogens
Fungi only
Viruses only
Cytoplasmic pathogens
Phagocytosed/Endosomal pathogens
Change

26. T cell summary Cell Type Cytotoxic T cell Th1 Helper T cell
Type of MHC
MHCI
MHCII
Location of MHC
All nucleated cells
Professional antigen presenting cells
Location of antigen
Endogenous—within the cytoplasm of the cell
Exogenous—present in the phagosome
Type of epitope
Small linear peptide
Response to initial recognition
Proliferate and activate to effector
Activated cell recognizing epitope releases
Granules—perforins, granzymes
Cytokines
Which…
Kill the target cell
Activate phagocytes (WBC) to kill phagocytosed microbes
Activate B cells to proliferate, produce antibodies, and develop memory

27. Humoral Immune Response
B cell Mediated Immunity

28. B cells Produce Antibodies
Defense from extracellular pathogens and toxins
Recognize antigen in native form

29. Activation of B cells B cell receptor (BCR) recognizes antigen
Membrane bound antibody
Th2 cells help activation and are required for memory
B cell differentiates to plasma cell, which produces antibodies

30. Antibody Structure Immunoglobulins (Ig) “Y” shaped proteins
4 polypeptides linked by disulfide bonds
Two identical heavy chains
Two identical light chains
Has variable and constant regions
Variable regions are responsible for recognizing the epitope

31. Antibody Structure
Figure 24.7

32. Structure of Different Antibody Types

33. Functions of Antibodies

34. Concept Question B cells recognize _____ with membrane bound_____.
Peptides only MHCs
Whole antigens MHCs
Peptides only Antibodies
Carbohydrates only TLRs
Whole antigens Antibodies
change

35. Immunological Memory
Secondary responses to infection

36. Timing of Adaptive Response

37. Immunological Memory

38. Secondary Immune Response

39. Memory Responses
Small populations of B and T cells retained from first exposure
Survive for a long time
Begin faster than first response
Stronger than first response
Vaccinations take advantage of memory responses

40. Concept Question
When you’re exposed to a pathogen for the second time, your innate and adaptive immune responses will be
Innate and adaptive both faster and stronger
Adaptive faster and stronger but innate only faster
Innate and adaptive both faster only
Innate the same, adaptive both faster and stronger
Innate the same, adaptive faster only

41. Immune System Summary

42. Adaptive Immune System

43. What types of adaptive responses would be best at fighting the listeria at A, B, and C?