1. Bellwork
Discuss with your group what you think is happening in the following processes.
Why does your body undergo an allergic reaction?
Why do some people’s bodies attack themselves (autoimmune diseases)?
How does AIDS escape the human immune systems?
Why do we have an inflammatory response when we are injured?

3. Innate immunity
Present before any exposure to pathogens and is effective from the time of birth
Involves nonspecific responses to pathogens
Innate immunity consists of external barriers plus internal cellular and chemical defenses

4. Acquired immunity,
AKA adaptive immunity, develops after exposure to agents such as microbes, toxins, or other foreign substances
It involves a very specific response to pathogens

5. Major parts of Innate Immunity
Barrier defenses
Phagocytosis
Antimicrobial peptides
Inflammatory response
Natural killer cells

6. Innate Immunity - Phagocytosis
Groups of pathogens are recognized by TLR, Toll-like receptors
Once recognized, cells engulf the pathogen

7. Innate Immunity - Phagocytosis
There are different types of phagocytic cells:
Neutrophils engulf and destroy microbes
Macrophages (big eaters) are part of the lymphatic system and are found throughout the body
Eosinophils discharge destructive enzymes to kill multicellular parasites
Dendritic cells stimulate development of acquired immunity

8. Innate Immunity – antimicrobial peptides (AKA proteins)
Interferons – induce nearby viral infected cells to secrete substances that inhibit viral reproduction
Complement system- Proteins in the blood plasma that fight infection. Can react to form a complex that leads to lysing of invading cells

9. Innate Immunity – Inflammatory response
Changes brought about by chemical signal
At the site, mast cells in the connective tissue release histamine
Histamine triggers nearby blood vessels to dilate and become more permeable
This helps deliver antimicrobial proteins, neutrophils and macrophages
Pus, a fluid rich in white blood cells, dead microbes, and cell debris, accumulates at the site of inflammation

10. Pathogen Splinter Chemical signals Macrophage Fluid Mast cell
Fig
Pathogen
Splinter
Chemical
signals
Macrophage
Fluid
Mast cell
Capillary
Phagocytosis
Figure 43.8 Major events in a local inflammatory response
For the Cell Biology Video Chemotaxis of a Neutrophil, go to Animation and Video Files.
Red blood cells
Phagocytic cell

11. Check for Understanding
On a sheet of paper, write an essay to describe the inflammatory response

12. Innate Immunity - Natural Killer Cells
Help recognize and eliminate certain diseased cells

13. Define
Antigen
Antibody
lymphocytes

14. Acquired Immunity
White blood cells recognize and respond to antigens (foreign molecules) and then create immunological memory
Lymphocytes that mature in the thymus are called T cells, and those that mature in bone marrow are called B cells

15. Acquired Immunity
B cells and T cells have receptor proteins that can bind to foreign molecules
Each individual lymphocyte is specialized to recognize a specific type of molecule

16. Acquired Immunity – With all the variation in receptors, why does it not attack itself?
As lymphocytes mature in bone marrow or the thymus, they are tested for self- reactivity
Lymphocytes with receptors specific for the body’s own molecules are destroyed by apoptosis, or rendered nonfunctional

17. Acquired Immunity
B cells can make receptors that detach from the cell membrane (antibody)
Epitope – a foreign molecule that a specific antibody or lymphocyte binds to

18. But Before we talk about that… lets see how it all begins
A cell engulfs the pathogen (either a regular cell, dendritic cells, macrophages, and B cells)
Molecules within the cells attach to the antigen and present it to T cells

19. Infected cell Antigen fragment Class I MHC molecule T cell receptor
Fig
Infected cell
Antigen
fragment
Class I MHC
molecule
T cell
receptor
(a)
associates
with MHC
recognizes
combination
Cytotoxic T cell
(b)
Helper T cell
Class II MHC
Antigen-
presenting
cell
Microbe 1 2 1
Figure The interaction of T cells with antigen-presenting cells
Class II MHC is found in specialized phagocytic cells, such as dendritic cells, macrophages and B cells. These present the antigen to either cytotoxic T cells or Helper T cells
Class I MHC is found in all body cells and can only present it to cytotoxic T cells

20. Once they recognize the antigen they call for help!
Acquired immunity has two branches: the humoral immune response and the cell- mediated immune response
Humoral immune response involves activation and clonal selection of B cells, resulting in production of secreted antibodies
Cell-mediated immune response involves activation and clonal selection of cytotoxic T cells
*Helper T cells can stimulate either response

22. A focus on cell mediated response
Activated helper T cells secrete cytokines that stimulate other lymphocytes
Includes cytotoxic T cells which kill the infected cells

23. A focus on cell mediated response
The binding of a mature lymphocyte to an antigen induces the lymphocyte to divide rapidly
This proliferation of lymphocytes is called clonal selection
Two types of clones are produced: short- lived activated effector cells and long- lived memory cells
Lets see it again!

24. Now, the humoral response

25. A focus on the humoral response
The helper T cell sends signals to recruit B cells
The B cells proliferate into memory cells and plasma cells

27. A focus on the humoral response
The B cells send out antibodies

28. The Role of Antibodies in Immunity
Neutralization occurs when a pathogen can no longer infect a host because it is bound to an antibody
Opsonization occurs when antibodies bound to antigens increase phagocytosis
Antibodies together with proteins of the complement system generate a membrane attack complex and cell lysis

29. There are different types of antibodies

30. Why is our body better at fighting a pathogen off the second time?
The first exposure to a specific antigen represents the primary immune response
During this time, effector B cells called plasma cells are generated, and T cells are activated to their effector forms
In the secondary immune response, memory cells facilitate a faster, more efficient response

31. Summarize
Compare and contrast B and T cells

32. So now… what are vaccinations and how does this help our immune system?
We introduce the epitope to our bodies so our body makes memmory cells, then when our immune system is faced with the actual pathogen, it can quickly destroy it

33. What are allergies?
Allergies are exaggerated (hypersensitive) responses to antigens called allergens
In localized allergies such as hay fever, IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells

34. Allergies

35. Autoimmune disorders What do you think has gone wrong?
The mechanisms for detecting receptors that attack its own cells are not working properly

36. Bellwork
Discuss with your group why your immune system does not have a secondary response to AIDS like most other viruses. How does it escape the immune system?

37. AIDS Human immunodeficiency virus (HIV) infects helper T cells
The loss of helper T cells impairs both the humoral and cell-mediated immune responses and leads to AIDS
HIV eludes the immune system because of antigenic variation and an ability to remain latent while integrated into host DNA