16-7 Summary

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The immune system has three key abilities. First is the ability to detect entities that might do us harm. Innate to this system is the ability to recognize antigens at the molecular level, and antibodies and T cell receptors are the key proteins. Each antibody or T cell receptor recognizes a unique shape and this variability is achieved through the random mixing of genes during the differentiation of T and B cells. Second, the immune system is tolerant. Since antibody and T cell receptor differentiation is a random process, immature B cells and T cells are created that react with our own macromolecules. These potentially lethal cells are identified and nullified by a number of mechanisms. This last part is the key step that allows the immune system to only attack antigens that are non-self. Third, the immune system is adaptive. After an initial challenge by an antigen, the immune system has a memory in the form of the aptly named memory cells. A second challenge by a similar antigen elicits a more rapid and stronger immune response and, in the case of a pathogen, prevents it from causing disease. One great advance in treating disease has been the activation of the immune system against a pathogen by presenting its antigens, but in a form that does not cause disease. We are, of course, referring to vaccination and its use has been one of the major methods of preventing infectious diseases, as we will describe in Chapter 17.

Our bodies are constantly bombarded with trillions of viruses and billions of microorganisms. To withstand this onslaught, multicellular organisms evolved various abilities to defend themselves against these invaders. While these pathogens are resourceful and persistent, the multi-faceted nature of the immune system and its adaptability successfully fends off these attacks. The immune system is critical to our survival and the constantly increasing knowledge that we have of its function will likely lead to many revolutionary treatments in the future.

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1. IgG

A. is the major type of antibody in serum
B. is a multivalent antibody
C. can activate the complement cascade
D. can cross the placenta

2. B cells that react with an antigen

A. proliferate at an equal rate so that there are many different antibodies for the antigen
B. compete with each other to make the most antibodies
C. have different strengths of reaction, with the strongest biding antibody being made at the highest levels
D. all make the same antibody

3. How can an antibody function when there is so much change (deletion, splicing, mutation) in its amino acid sequence?


4. MHC II molecules

A. are found on many cells of the body
B. are found on antigen presenting cells
C. bind antibodies
D. are found on T cells, B cells and macrophages

5. What is the difference between a chemokine and a cytokine?


6. Which of the following is not a cytokine


7. Compare and contrast the function of dendritic cells to that of macrophages.


8. The body has a number of mechanisms to prevent self-reacting T and B cells from maturing to active immune cells. Why is this so important?


9. The delay in Type IV hypersensitivity is caused by

A. the time required for T cells that respond to an allergen to reach the site of exposure
B. the time it takes to make antibodies
C. the time to for B cells to proliferate
D. the time required for B cells that respond to an allergen to reach the site of exposure

10. What do allergies and autoimmune diseases have in common?

A. reaction to a foreign antigen
B. Both are inappropriate reactions of the immune system to antigens that pose no threat to the body.
C. weakening of the immune system
D. their incidence increases with age.

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