Skip to main content
Biology LibreTexts

17.E: The Immune System and Desease (Exercises)

17.1: Viruses

Viruses are acellular, parasitic entities that are not classified within any domain because they are not considered alive. They have no plasma membrane, internal organelles, or metabolic processes, and they do not divide. Instead, they infect a host cell and use the host’s replication processes to produce progeny virus particles. Viruses infect all forms of organisms including bacteria, archaea, fungi, plants, and animals.

Review Questions

Which statement is true?

A. A virion contains DNA and RNA.
B. Viruses are acellular.
C. Viruses replicate outside of the cell.
D. Most viruses are easily visualized with a light microscope.


The viral ________ plays a role in attaching a virion to the host cell.

A. core
B. capsid
C. envelope
D. both b and c


Which statement is true of viral replication?

A. In the process of apoptosis, the cell survives.
B. During attachment, the virus attaches at specific sites on the cell surface.
C. The viral capsid helps the host cell produce more copies of the viral genome.
D. mRNA works outside of the host cell to produce enzymes and proteins.


Free Response

Why can’t dogs catch the measles?

The virus cannot attach to dog cells because dog cells do not express the receptors for the virus or there is no cell within the dog that is permissive for viral replication.

Why is immunization after being bitten by a rabid animal so effective?

Rabies vaccine works after a bite because it takes two weeks for the virus to travel from the site of the bite to the central nervous system, where the most severe symptoms of the disease occur. The vaccine is able to cause an immune response in the body during this time that clears the infection before it reaches the nervous system.


17.2: Innate Immunity

Innate immunity is not caused by an infection or vaccination and depends initially on physical and chemical barriers that work on all pathogens, sometimes called the first line of defense. The second line of defense of the innate system includes chemical signals that produce inflammation and fever responses as well as mobilizing protective cells and other chemical defenses.

Review Questions

Which of the following is a barrier against pathogens provided by the skin?

A. low pH
B. mucus
C. tears
D. cilia


Although interferons have several effects, they are particularly useful against infections with which type of pathogen?

A. bacteria
B. viruses
C. fungi
D. helminths


Which innate immune system component uses MHC class I molecules directly in its defense strategy?

A. macrophages
B. neutrophils
C. NK cells
D. interferon


Free Response

Different MHC class I molecules between donor and recipient cells can lead to rejection of a transplanted organ or tissue. Suggest a reason for this.

If the MHC class I molecules expressed on donor cells differ from the MHC class I molecules expressed on recipient cells, NK cells may identify the donor cells as not normal and produce enzymes to induce the donor cells to undergo apoptosis, which would destroy the transplanted organ.

If a series of genetic mutations prevented some, but not all, of the complement proteins from binding antibodies or pathogens, would the entire complement system be compromised?

The entire complement system would probably be affected even when only a few members were mutated such that they could no longer bind. Because the complement involves the binding of activated proteins in a specific sequence, when one or more proteins in the sequence is absent, the subsequent proteins would be incapable of binding to elicit the complement’s pathogen-destructive effects.

17.3: Adaptive Immunity

The adaptive immune response is a slower-acting, longer-lasting, and more specific response than the innate response. However, the adaptive response requires information from the innate immune system to function. APCs display antigens on MHC molecules to naïve T cells. T cells with cell-surface receptors that bind a specific antigen will bind to that APC. In response, the T cells differentiate and proliferate.

Review Questions

The humoral immune response depends on which cells?

A. TC cells
B. B cells
C. B and TH cells
D. TC and TH cells


The fact that the body does not normally mount an immune response to the molecules in food is an example of _______.

A. secondary immune response
B. immunological memory
C. immune tolerance
D. passive immunity


Foreign particles circulating in the blood are filtered by the ____________.

A. spleen
B. lymph nodes
D. lymph


Free Response

How do B and T cells differ with respect to antigens that they bind?

T cells bind antigens that have been digested and embedded in MHC molecules by APCs. In contrast, B cells function as APCs to bind intact, unprocessed antigens.

Why is the immune response after reinfection much faster than the adaptive immune response after the initial infection?

Upon reinfection, the memory cells will immediately differentiate into plasma cells and CTLs without input from APCs or TH cells. In contrast, the adaptive immune response to the initial infection requires time for naïve B and T cells with the appropriate antigen specificities to be identified and activated.

17.4: Disruptions in the Immune System

A functioning immune system is essential for survival, but even the sophisticated cellular and molecular defenses of the mammalian immune response can be defeated by pathogens at virtually every step. In the competition between immune protection and pathogen evasion, pathogens have the advantage of more rapid evolution because of their shorter generation time, large population sizes and often higher mutation rates. Thus pathogens have evolved a diverse array of immune escape mechanisms.

Review Questions

Allergy to pollen is classified as ________.

A. an autoimmune reaction
B. immunodeficiency
C. delayed hypersensitivity
D. immediate hypersensitivity


A potential cause of acquired autoimmunity is ________.

A. tissue hypersensitivity
B. molecular mimicry
C. histamine release
D. radiation exposure


Autoantibodies are probably involved in ________.

A. reactions to poison ivy
B. pollen allergies
C. systemic lupus erythematosus


Free Response

Some photographers develop a sensitivity to certain film developing chemicals leading to severe rashes on their hands such that they are unable to work with them. Explain what is probably happening.

This is probably a delayed sensitivity reaction to one or more chemicals in the developer. An initial exposure would have sensitized the individual to the chemical and then subsequent exposures will induce a delayed inflammation reaction a day or two after exposure.