Question 1

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

Studies of inherited immunodeficiency diseases reveal which essential immune mechanism is required for resistance to each category of pathogen. This information is important for understanding the pathogenesis of the disease and developing appropriate therapeutic strategies.

Question 2

The spleen is a secondary lymphoid organ that performs several functions. In addition to its role as a site for initiating adaptive immune responses, the spleen is important in removing dead or damaged red blood cells from the circulation. Its immune function is important because blood-borne pathogens will not be transported to draining lymph nodes via the lymph fluid.

Accepted Answer

The spleen is a secondary lymphoid organ that plays an important role in initiating immune responses and removing damaged red blood cells from circulation. Its immune function is crucial in preventing blood-borne pathogens from reaching lymph nodes via lymph fluid.

Question 3

T_H1, T_H2, T_H17, and T follicular helper (T_FH) cells represent four different subsets of CD4 effector cells. Each of these subsets produces a distinct set of cytokines when stimulated, that in turn, act to mobilize distinct immune effector mechanisms. While T_H1, T_H2, and T_H17 cells recruit and activate innate immune cells, T_FH cells act to amplify the adaptive immune response.

Accepted Answer

Each of the subsets produces a distinct set of cytokines that mobilize distinct immune effector mechanisms. T_H1, T_H2, and T_H17 cells recruit and activate innate immune cells, while T_FH cells amplify the adaptive immune response.

Question 4

One surprising aspect of the immune system is that individuals make responses to human tissues from a different individual, causing serious problems for organ and tissue transplantation. The basis for this immune response is:

Accepted Answer

The major component of the graft rejection response is due to recognition of the 'foreign' MHC proteins on the graft by the recipient's T lymphocytes. This occurs because of the extensive polymorphism of MHC genes in the human population. As a result, two different individuals nearly always express different MHC molecules from each other. Since MHC molecules are efficiently recognized by T cells, the T cells in the recipient will respond to the donor's tissue and destroy it, just as if it were a pathogen.

Question 5

Individuals with defects in T cell development have a severe immunodeficiency disease called SCID (severe combined immunodeficiency disease). In these individuals, the absence of all T cells causes defects in both cell-mediated (T cell-based) and humoral (antibody-based) immune responses. The defect in antibody responses in SCID patients is due to:

Accepted Answer

T follicular helper cells, a subset of T cells, play a crucial role in helping B cells produce high-affinity antibodies and undergo class switching, which are essential for generating effective and long-lasting antibody responses. In SCID patients, the absence of T cells, including T follicular helper cells, leads to compromised antibody responses.

Question 6

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 7

The effector activities important in eliminating infectious organisms from our bodies can be categorized into four different groups: cytotoxicity, intracellular immunity, mucosal and barrier immunity, and extracellular immunity. Briefly describe why the immune system requires four different effector modules for maximum protection.

Accepted Answer

The answer of The effector activities important in eliminating infectious...

Question 8

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

Secondary lymphoid organs concentrate antigens in centralized locations, allowing rare lymphocytes to encounter and respond to them efficiently. This is essential for the initiation of adaptive immune responses. Additionally, B, C, D, and E are incorrect because they do not adequately explain the efficiency of secondary lymphoid organs in initiating adaptive immune responses.

Question 9

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

Recirculating lymphocytes enter the lymph node from the blood by crossing the high endothelial venules.

Question 10

The pattern recognition receptors on cells of the innate immune system are genetically encoded, meaning that their sequences and specificities are determined prior to the development of the individual. In contrast, the antigen receptors of B and T lymphocytes arise from a random rearrangement process that occurs differently in each lymphocyte as it develops. One potential problem entailed by the random process that generates lymphocyte antigen receptors is the possibility that:

Accepted Answer

The answer of The pattern recognition receptors on cells of...

Question 11

When complement proteins are covalently deposited onto the surface of a bacterium, this can sometimes lead to direct lysis of the bacterium. However, more commonly, the deposition of complement proteins onto the bacterial surface does not directly harm the bacterium. Instead, these complement proteins aid in bacterial elimination by:

Accepted Answer

When complement proteins are deposited onto the bacterial surface, they can act as opsonins, meaning they can help to "tag" the bacterium for phagocytosis by cells like macrophages and neutrophils. These cells have complement receptors on their surface, allowing them to bind to and engulf the bacterium. Therefore, choice E is the best answer.

Question 12

The best evidence supporting the concept of immunological memory is:

Accepted Answer

The increased rapidity and magnitude of the secondary response to the same antigen is the best evidence supporting the concept of immunological memory. This is because it shows that the immune system has "remembered" the antigen from previous exposure and is able to mount a quicker and more effective response upon re-exposure. This is a hallmark of immunological memory.

Question 13

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

Antibodies bind to the virus or toxin and neutralize it, preventing it from attaching to and entering our cells.

Question 14

The mucosal tissues of the body have their own unique set of immune structures that function as sites for initiating adaptive immune responses. The necessity for mucosa-associated lymphoid tissues to have unique cell types (M cells) and structures is because:

Accepted Answer

Mucosal sites are exposed to a vast number of diverse microbes, necessitating specialized immune structures and cells like M cells to efficiently sample and respond to antigens.

Question 15

T cells expressing the co-receptor CD8 are generally cytotoxic cells, with an important function in eliminating virus infections that can occur in many different cell types and tissues. In contrast, CD4 T cells directly interact with a very restricted set of cells, such as dendritic cells, macrophages, and B cells. Describe one important mechanism that accounts for this division of labor between CD8 and CD4 T cells.

Accepted Answer

The answer of T cells expressing the co-receptor CD8 are...

Question 16

Several subsets of innate lymphoid cells (ILCs) have been identified that share their patterns of cytokine production with the known subsets of T cells. The combined activity of related ILC and T cell subsets is effective in eradicating pathogenic infections because:

Accepted Answer

ILCs provide an early response to infections at the site of infection and produce cytokines that activate and recruit T cells. T cells provide the later, more robust response to the pathogen by killing infected cells and producing their own cytokines to support other immune cells. Together, the two cell types effectively eradicate the pathogen. Other choices are not accurate descriptions of ILC and T cell activities.

Question 17

Naive B and T lymphocytes are small, quiescent cells with little cytoplasm and low metabolic activity. Yet within hours after being activated following encounter with their antigen, these cells enlarge and up-regulate many biosynthetic and metabolic pathways. Approximately one day later, the cells begin dividing, and for several days they are the most rapidly dividing cells in the body, undergoing 2-4 rounds of cell division every day. In order to maintain this phenomenal rate of cell division, lymphoblasts must:

Accepted Answer

The lymphoblasts up-regulate many biosynthetic and metabolic pathways including those involved in glucose transport and glycolysis. This suggests that they rely on glucose as a primary source of energy. Therefore, we can eliminate choices A, B, D, and E. Choice C is the best answer as it accurately describes the up-regulation of glucose transporters and glycolysis enzymes to meet the high metabolic demand of rapidly dividing lymphoblasts.

Question 18

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

The statement is correct. Memory cells are long-lived lymphocytes that are generated during the primary immune response and play a critical role in mediating the secondary response. They are responsible for the enhanced speed, magnitude, and quality of the secondary immune response by quickly recognizing and responding to the same antigen.

Question 19

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 20

An infant with recurrent bacterial and fungal infections is suspected to have an immunodeficiency disease. Within two days after exposure to a pathogen, the organisms have proliferated to dangerous levels requiring immediate systemic antibiotic treatment. It is unlikely that this infant has a defect in B or T lymphocyte responses to the infection because:

Accepted Answer

The question states that within two days after exposure to a pathogen, the organisms have proliferated to dangerous levels. This suggests a rapid response by the pathogen in the absence of an effective immune response. B and T lymphocytes are important components of the adaptive immune response, but it takes time for them to recognize and respond to a new pathogen. Therefore, it is unlikely that a defect in B or T lymphocyte responses to the infection is responsible for the recurrent infections seen in this infant.

Quiz 1: Basic Concepts in Immunology