Question 1

A common mechanism by which sensor cells in the host detect micro-organisms relies on the production of unique microbial components not found in the host. Propose a strategy by which a clever microbe could evade this type of response.

Accepted Answer

The answer of A common mechanism by which sensor cells...

Question 2

Innate lymphoid cells and NK cells are effector cells that respond rapidly after encountering a pathogen. Several different subsets of innate lymphoid cells exist, and each is specialized to respond to a category of pathogen (e.g., viruses, extracellular bacteria, helminthic parasites, etc). Innate lymphoid cells reside primarily in tissues such as the lungs, the lining of the gastrointestinal tract, and the skin, because these sites represent the major routes of entry of pathogens into the body.

Accepted Answer

A) True 
 B)False

Question 3

One factor that contributes to the enhanced secondary response to an antigen is the increased number of antigen-specific lymphocytes present after the primary response; these are known as memory cells.

Accepted Answer

A) True 
 B)False

Question 4

The majority of vaccines work by eliciting pathogen-specific antibodies that circulate in our bodies and protect us in the event that we are later exposed to that specific pathogen. For most viruses and bacterial toxins that we are vaccinated against, these pre-existing antibodies are protective because:

Accepted Answer

A)  They neutralize the virus or toxin, preventing it from attaching to and entering our cells. 
B)  They bind to the virus or toxin and carry it to the liver where it can be degraded. 
C)  They bind to the virus or toxin and directly induce lysis. 
D)  They induce mucus production that helps flush the toxin or virus out of the body. 
E)  They bind to epithelial cells and induce the production of antimicrobial peptides.

Question 5

Adaptive immune responses are slow to develop, taking days to weeks after exposure to reach their peak. However, these responses are more specific than innate responses, and also generate immunological memory. These latter features, which provide enhanced protection upon re-infection with the same pathogen, are the basis of:

Accepted Answer

A)  Vaccines 
B)  Antibiotics 
C)  Systemic shock 
D)  Complement activation 
E)  Phagocytosis

Question 6

Some Pattern Recognition Receptors (PRRs) recognize nucleic acids, like RNA or DNA. Since our own cells contain human RNA and DNA, the activation of innate immune pathways by these PRRs must rely on additional criteria to discriminate self from nonself. Additional criteria include everything EXCEPT:

Accepted Answer

A)  The subcellular location of the RNA 
B)  The presence of adenosine residues in viral RNA 
C)  The methylation state of the DNA 
D)  Unique structures found on viral RNA 
E)  The subcellular location of the DNA

Question 7

The immune system evolved to protect us against infections from pathogenic microorganisms. However, immune responses can also cause, rather than prevent disease. Give two examples of situations in which an immune response causes a disease, whereas the absence of a response has no consequences.

Accepted Answer

The answer of The immune system evolved to protect us...

Question 8

When macrophages in a tissue encounter bacteria, they release cytokines that induce an inflammatory response. These cytokines act on other immune cells, to recruit them to the site of infection and to enhance their activities. In addition, these cytokines act on the endothelial cells of the blood vessel wall to:

Accepted Answer

A)  Increase their permeability, allowing fluid and proteins to leak into the tissue 
B)  Solidify the tight junctions to prevent the bacteria from entering the blood 
C)  Proliferate, allowing the blood vessel to enlarge 
D)  Up-regulate microbicidal mechanisms, so they can kill bacteria 
E)  Secrete anti-microbial peptides

Question 9

Inherited immunodeficiency diseases result from a single gene defect in one component of the immune system. By identifying the class of microbial pathogens a given immunodeficient individual becomes susceptible to, studies of these diseases indicate:

Accepted Answer

A)  Which type of antibiotics each patient should be given 
B)  The essential immune mechanism required for resistance to each category of pathogen 
C)  Whether the disease is a genetically inherited or an acquired form of immunodeficiency 
D)  Whether the immunodeficiency disease is likely to be transmitted to another individual 
E)  Whether the disease is likely to be life-threatening or not

Question 10

Dendritic cells are phagocytic, but also capable of ingesting large amounts of extracellular fluid and its contents, a process known as macropinocytosis. What specialized function do dendritic cells have in immunity that might account for their need to perform macropinocytosis?

Accepted Answer

The answer of Dendritic cells are phagocytic, but also capable...

Question 11

Dendritic cells, also called 'antigen-presenting-cells' are considered the bridge between the innate and the adaptive immune responses. Describe two key features of dendritic cells that are essential for them to provide this bridging function.

Accepted Answer

The answer of Dendritic cells, also called 'antigen-presenting-cells' are considered...

Question 12

The antibody protein is often depicted as an uppercase letter Y, with the two variable regions (antigen-binding domains) pointing up, and the stem consisting of the Fc region (constant domain). An analogy has been made between an antibody protein and a guided missile, with one type of antibody domain functioning as the guidance system, and the other type of domain as the 'payload.' Which antibody domain serves as the guidance system, and which as the payload? Explain your answer.

Accepted Answer

The answer of The antibody protein is often depicted as...

Question 13

Given the enormous heterogeneity of antigen receptors expressed on the populations of naive B and T lymphocytes, the adaptive immune response relies on a process whereby the rare lymphocyte that binds to the antigen is first induced to proliferate, before it can perform its effector function. For B cells, there is a clever mechanism that ensures that the specificity of the antibody secreted by the plasma cell will recognize the same pathogen that initially stimulated the B cell antigen receptor and induced B cell proliferation. This mechanism is:

Accepted Answer

A)  The naive B cell expresses an array of different B cell antigen receptors, and randomly chooses which specificity of antibody to secrete as a plasma cell. 
B)  The naive B cell expresses a single specificity of B cell antigen receptor, and then up-regulates the expression of this receptor so it can bind tightly to the pathogen. 
C)  The plasma cell proliferates after it has finished secreting antibody to generate more plasma cells with specificity for the pathogen. 
D)  The plasma cell traps secreted antibody molecules in its extracellular matrix and uses these antibodies to bind to the pathogen. 
E)  The naive B cell expresses a membrane-bound form of the antibody as a receptor, and secretes that same antibody when it differentiates into a plasma cell.

Question 14

Lymph nodes function as meeting points between antigen-bearing dendritic cells arriving from the tissue and recirculating B and T lymphocytes. Whereas the dendritic cells coming from the tissue enter the lymph node via the afferent lymphatic vessels, the recirculating lymphocytes enter the lymph node:

Accepted Answer

A)  Also from the lymph fluid draining the tissue 
B)  Directly from their primary lymphoid organ where they develop 
C)  From the blood by crossing the high endothelial venules 
D)  By being trapped in the lymphoid follicle by resident macrophages 
E)  By being carried there by dendritic cells

Question 15

Unlike B lymphocytes, T lymphocytes do not generate a secreted form of their antigen receptor after they are activated and proliferate. This is because the effector functions of T cells are restricted to:

Accepted Answer

A)  Responses important in protozoan infections, but not other types of infections 
B)  Interactions with large helminthic parasites, which cannot be phagocytosed 
C)  Interactions with other cells, such as virus-infected cells or other immune cells 
D)  Responses important in mucosal surfaces (e.g., the lung), where antibodies cannot go 
E)  Stimulating B cells and not any other types of cells

Question 16

Vaccination against many infectious diseases has provided enormous benefit in developed countries, leading to the virtual eradication of diseases such as polio, measles, smallpox, and others. However, efforts to create long-lasting vaccines against some viral infections, like Influenza and HIV, have not been successful to date because:

Accepted Answer

A)  Viruses like HIV and Influenza undergo antigenic variation to evade previous immune responses. 
B)  Viruses like HIV and Influenza spread too rapidly in the population for a vaccine to be effective. 
C)  Viruses like HIV and Influenza have RNA, rather than DNA genomes, and are resistant to current vaccine strategies. 
D)  Viruses like HIV and Influenza infect via mucosal surfaces, a route that is not well protected by current vaccine strategies. 
E)  Viruses like HIV and Influenza are transmitted vertically (from mother to child) during fetal development, so babies are infected before they can be vaccinated.

Question 17

Secondary (or peripheral) lymphoid organs are sites for initiation of adaptive immune responses. Given the rarity of lymphocytes specific for any given antigen and the vast amount of body tissue that must be protected, the system of secondary lymphoid tissues is efficient because:

Accepted Answer

A)  It concentrates antigens in centralized locations for rare lymphocytes to encounter 
B)  It provides the optimal environment for the rapid proliferation of lymphocytes 
C)  It traps the pathogens and antigens in a contained environment so they cannot spread to other tissues in the body 
D)  It helps the innate immune cells eliminate the infection by using lymphatic fluid to drain pathogens from the infected tissue 
E)  It filters the lymph fluid and removes pathogenic organisms before they can enter the bloodstream

Question 18

Most B and T lymphocytes in the circulation appear as small, inactive cells, with little cytoplasm, few cytoplasmic organelles, and nuclei containing condensed inactive chromatin. Yet these cells comprise the adaptive immune response, without which individuals die in infancy. What is the explanation for this apparent dichotomy?

Accepted Answer

The answer of Most B and T lymphocytes in the...

Question 19

In patients with lymphomas, the cancer cells invade the bone marrow and destroy the environment required for normal hematopoiesis. This leads to bone marrow failure, which disrupts the production of hematopoietic cell lineages. All of the following cell types would be affected by this EXCEPT:

Accepted Answer

A)  Red blood cells 
B)  Macrophages 
C)  Lymphocytes 
D)  Endothelial cells 
E)  Granulocytes

Question 20

The best evidence supporting the concept of immunological memory is:

Accepted Answer

A)  The increased numbers of antigen receptors expressed by lymphocytes after primary exposure to an antigen 
B)  The increased levels of cytokines made by lymphocytes after primary exposure to an antigen 
C)  The increased rapidity and magnitude of the secondary response to the same antigen 
D)  The increased swelling of lymph nodes during the secondary response to the same antigen 
E)  The long lifespan of vertebrates, which would be impossible without immunological memory

Exam 1: Basic Concepts in Immunology