The Immune System

Pus is both a sign of infection and an indicator of immune defenses in action. Explain.

How do the molecules that activate the vertebrate TLR signal transduction pathway differ from the ligands in most other signaling pathways (see Concept 11.2)?

Parasitic wasps inject their eggs into the host larvae of other insects. If the host immune system doesn't kill the wasp egg, the egg hatches, and the wasp larva devours the host larva as food. Why can some insect species initiate an innate immune response to a wasp egg, but others cannot?

DRAW IT Sketch a B cell antigen receptor. Label the V and C regions of the light and heavy chains. Label the antigen-binding sites, disulfide bridges, and transmembrane region. Where are these features located relative to the V and C regions?

Explain two advantages of having memory cells when a pathogen is encountered for a second time.

If both copies of a light chain gene and a heavy-chain gene recombined in each (diploid) B cell, how would this affect B cell development and function?

Assume that on average one out of every 10⁵B cells in the body is specific for antigen A on day 16 and that the number of B cells producing a specific antibody is proportional to the concentration of that antibody. What would you predict is the frequency of B cells specific for antigen A on day 36?

If a child were born without a thymus gland, would the T cells and functions of the immune system be deficient? Explain.

Treatment of antibodies with a particular protease clips the heavy chains in half, releasing the two arms of the Y-shaped molecule. How might the antibodies continue to function?

Suppose that a snake handler bitten by a particularly nasty snake species was treated with antivenin. Why might the same treatment for a second such bite have a harmful side effect?

Plot the data in the above table as a line graph. Which column is the independent variable, and which is the dependent variable? Put the independent variable on the x-axis. (For additional information about graphs, see the Scientific Skills Review in Appendix F.) 

Visually displaying data in a graph can help make patterns in the data more noticeable. Describe any patterns revealed by your graph.

Assume that a drop in parasite abundance reflects an effective immune response by the host. Formulate a hypothesis to explain the pattern you described in question 2.

Note that these data were collected over the same period of infection (days 4–24) as the parasite abundance data you graphed in part A. Therefore, you can incorporate these new data into your first graph, using the same x-axis. However, since the antibody level data are measured in a different way than the parasite abundance data, add a second set of y-axis labels on the right side of your graph. Then, using different colors or sets of symbols, add the data for the two antibody types. Labeling the y-axis two different ways enables you to compare how two dependent variables change relative to a shared independent variable.

Describe any patterns you observe by comparing the two data sets over the same period. Do these patterns support your hypothesis from part A? Do they prove that hypothesis? Explain.

Scientists can now also distinguish the abundance of trypanosomes recognized specifically by antibodies type A and type B. How would incorporating such information change your graph?

People with herpes simplex type 1 viruses often get mouth sores when they have a cold or similar infection. How might this location benefit the virus?

In the muscular disease myasthenia gravis, antibodies bind to and block certain receptors on muscle cells, preventing muscle contraction. Is this disease best classified as an immunodeficiency disease, an autoimmune disease, or an allergic reaction? Explain.

How would a macrophage deficiency likely affect a person’s innate and adaptive defenses?

Which of these is not part of insect immunity? 

(A) enzyme activation of pathogen-killing chemicals 

(B) activation of natural killer cells 

(C) phagocytosis by hemocytes 

(D) production of antimicrobial peptides

Which of the following would not help a virus avoid triggering an adaptive immune response? 

(A) Having frequent mutations in genes for surface proteins 

(B) Infecting cells that produce very few MHC molecules 

(C) Producing proteins very similar to those of other viruses 

(D) Infecting and killing helper T cells

An epitope associates with which part of an antigen receptor or antibody?

(A) the tail

(B) the heavy-chain constant regions only

(C) variable regions of a heavy chain and light chain combined

(D) the light-chain constant regions only

Which statement best describes the difference between responses of effector B cells (plasma cells) and those of cytotoxic T cells? 

(A) B cells confer active immunity; cytotoxic T cells confer passive immunity. 

(B) B cells respond the first time a pathogen is present; cytotoxic T cells respond subsequent times. 

(C) B cells secrete antibodies against a pathogen; cytotoxic T cells kill pathogen-infected host cells. 

(D) B cells carry out the cell-mediated response; cytotoxic T cells carry out the humoral response.

Which of the following statements is not true? 

(A) An antibody has more than one antigen-binding site. 

(B) A lymphocyte has receptors for multiple different antigens. 

(C) An antigen can have different epitopes. 

(D) A liver or muscle cell makes one class of MHC molecule. 

Which of the following should be the same in identical twins?

(A) the set of antibodies produced 

(B) the set of MHC molecules produced 

(C) the set of T cell antigen receptors produced 

(D) the set of immune cells eliminated as self-reactive

Vaccination increases the number of 

(A) different receptors that recognize a pathogen. 

(B) lymphocytes with receptors that can bind to the pathogen. 

(C) epitopes that the immune system can recognize. 

(D) MHC molecules that can present an antigen.

Consider a pencil-shaped protein with two epitopes, Y (the “eraser” end) and Z (the “point” end). They are recognized by antibodies A1 and A2, respectively. Draw and label a picture showing the antibodies linking proteins into a complex that could trigger endocytosis by a macrophage. 

Contrast clonal selection with Lamarck’s idea for the inheritance of acquired characteristics. 

Describe one invertebrate mechanism of defense against pathogens and discuss how it is an evolutionary adaptation retained in vertebrates.

Among all nucleated body cells, only B and T cells lose DNA during their development and maturation. In a short essay (100–150 words), discuss the relationship between this loss and DNA as heritable biological information, focusing on similarities between cellular and organismal generations.

This photo shows a child receiving an oral vaccine against polio, a disease caused by a virus that infects neurons. Given that the body cannot readily replace most neurons, why is it important that a polio vaccine stimulate not only a cell-mediated response but also a humoral response?