MCAT Biology : Adaptive and Innate Immunity

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1 : Adaptive And Innate Immunity

Which of these choices is not a function of T-cells?

Possible Answers:

Inhibit the activity of both B- and T-cells

Secrete cytokines

Directly produce antibodies after the first response to an antigen

Locate and kill cells that contain antigens bound to MHC-I proteins

Increase the activity of immune cells (such as B-cells and macrophages) through the release of chemical messengers

Correct answer:

Directly produce antibodies after the first response to an antigen

Explanation:

The only choice that is not a function of any type of T-cell is the direct production of antibodies (which is performed by B-cells). Cytotoxic T-cells kill other cells that are bound to antigen/MHC-I complexes. Suppressor T-cells tone down the response of both B- and T-cells, and helper T-cells secrete cytokines, which increase the activity of many other immune cell types.

Example Question #2 : Adaptive And Innate Immunity

Sexually transmitted diseases are a common problem among young people in the United States. One of the more common diseases is caused by the bacterium Neisseria gonorrhoeae, which leads to inflammation and purulent discharge in the male and female reproductive tracts.

The bacterium has a number of systems to evade host defenses. Upon infection, it uses pili to adhere to host epithelium. The bacterium also uses an enzyme, gonococcal sialyltransferase, to transfer a sialyic acid residue to a gonococcal surface lipooligosaccharide (LOS). A depiction of this can be seen in Figure 1. The sialyic acid residue mimics the protective capsule found on other bacterial species.

Once infection is established, Neisseria preferentially infects columnar epithelial cells in the female reproductive tract, and leads to a loss of cilia on these cells. Damage to the reproductive tract can result in pelvic inflammatory disease, which can complicate pregnancies later in the life of the woman.

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The first line of defense by a human host against a potential Neisseria infection is which of the following?

Possible Answers:

Genetic immunity

Innate immune defense

Cytotoxic defense

Lymphocyte-mediated defense

Antibody defense

Correct answer:

Innate immune defense

Explanation:

Innate defenses, such as the skin or macrophages, are the first line of defense against infection. Other responses only become effective if a pathogen cannot be repelled by innate mechanisms.

Example Question #3 : Adaptive And Innate Immunity

Which of the following is not an example of innate immunity?

Possible Answers:

Antibody production by B-cells

Removal of bacterial organisms by cilia

Histamine release by mast cells

Degradation of bacterial cell walls by saliva

Correct answer:

Antibody production by B-cells

Explanation:

All of the following are examples of non-specific defense mechanisms of the immune system, except for antibody production by B-cells. B-cells respond to specific antigens within the body via immunoglobulins located on the plasma membrane of B-cells. This type of response is known as adaptive immunity, and develops only after a particular pathogen has invaded the immune system.

Example Question #4 : Adaptive And Innate Immunity

Which of the following is not a component of innate immunity?

Possible Answers:

Stomach acid

Macrophages

Mast cells

Plasma cells

Correct answer:

Plasma cells

Explanation:

The innate immune system defends against pathogens, even without identifying what the pathogens are. Innate immunity includes physical and chemical barriers, such as the skin and stomach acid, which can kill some bacteria or prevent their entry into the body. Macrophages are responsible for phagocytosis of foreign pathogens without antibody mediation. Mast cells release histamine in response to infection or injury. Plasma cells, however, are mature B-cells that secrete antibodies in response to initiation of the adaptive immune response.

Example Question #5 : Adaptive And Innate Immunity

Hypersensitivity reactions occur when body tissues are affected by an abnormal immune reaction. The result is damage to normal tissues and clinical illness. A peanut allergy is an example of a hypersensitivity reaction, but there are three additional broad classes.

One class involves the abnormal production or deposition of antibodies. Antibodies are B-cell derived molecules that normally adhere to pathogens, rendering them unable to continue an infection. When antibodies are produced against normal tissues, however, disease can result. Figure 1 depicts a schematic structure of an antibody.

Antibodies can be divided into two peptide chains: heavy and light. Heavy chains form the backbone of the antibody, and are attached to light chains via covalent bonding. Each heavy and light chain is then further divided into constant and variable regions. Variable regions exhibit molecular variety, generating a unique chemical identity for each antibody. These unique patterns help guarantee that the body can produce antibodies to recognize many possible molecular patterns on invading pathogens.

 

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An antibody response is similar to an inflammatory response in that:

I. They are both innate immune responses

II. They are both most effective immediately following the first infection with a pathogen

III. They are both dependent on chemical mediators, such as cytokines, for function

Possible Answers:

II only

III only

I and II

I and III

I, II, and III

Correct answer:

III only

Explanation:

Cytokines are important immune mediators, and are components of both adaptive and innate immunity. B- and T-lymphocytes are mediators of adaptive immunity, while inflammation is a non-specific innate immune response to a pathogen. While innate immunity, such as the inflammatory response, is active immediately following an infection, adaptive immunity requires a previous exposure to the pathogen to become most effective. The body must already recognize the invading antigen in order to activate the antibody response.

Statement I is false, statement II is false, and statement III is true.

Example Question #6 : Adaptive And Innate Immunity

Duchenne Muscular Dystrophy is an X-linked recessive genetic disorder, resulting in the loss of the dystrophin protein. In healthy muscle, dystrophin localizes to the sarcolemma and helps anchor the muscle fiber to the basal lamina. The loss of this protein results in progressive muscle weakness, and eventually death.

In the muscle fibers, the effects of the disease can be exacerbated by auto-immune interference. Weakness of the sarcolemma leads to damage and tears in the membrane. The body’s immune system recognizes the damage and attempts to repair it. However, since the damage exists as a chronic condition, leukocytes begin to present the damaged protein fragments as antigens, stimulating a targeted attack on the damaged parts of the muscle fiber. The attack causes inflammation, fibrosis, and necrosis, further weakening the muscle.

Studies have shown that despite the severe pathology of the muscle fibers, the innervation of the muscle is unaffected.

Which compound is most likely responsible for initiating the inflammation response that results from the autoimmune attack?

Possible Answers:

Histamine

Fibrinogen

Fibrin

Dopamine

Fibrogen

Correct answer:

Histamine

Explanation:

Fibrin and fibrinogen are involved in wound healing and scab formation. Dopamine is a neurotransmitter in the brain. Fibrogen is not a real protein at all.

Histamine is the primary inflammatory molecule in the body and is released from mast cells during an immune response or trauma.

Example Question #5 : Adaptive And Innate Immunity

Type 1 diabetes is a well-understood autoimmune disease. Autoimmune diseases result from an immune system-mediated attack on one’s own body tissues. In normal development, an organ called the thymus introduces immune cells to the body’s normal proteins. This process is called negative selection, as those immune cells that recognize normal proteins are deleted. If cells evade this process, those that recognize normal proteins enter into circulation, where they can attack body tissues. The thymus is also important for activating T-cells that recognize foreign proteins.

As the figure below shows, immune cells typically originate in the bone marrow. Some immune cells, called T-cells, then go to the thymus for negative selection. Those that survive negative selection, enter into general circulation to fight infection. Other cells, called B-cells, directly enter general circulation from the bone marrow. It is a breakdown in this carefully orchestrated process that leads to autoimmune disease, such as type 1 diabetes.

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Which of the following constitutes a loss of innate immunity in an immunocompromised patient?

Possible Answers:

The loss of a memory immune response in a patient who did not receive follow up vaccinations

The down-regulation of an antibody response in a patient receiving immunosuppressive drugs

The loss of intact skin in a burn patient

The loss of pre-lymphocytes in a patient undergoing a bone marrow transplant

The loss of a thymus in a patient with Di George syndrome

Correct answer:

The loss of intact skin in a burn patient

Explanation:

The immune system comprises more than what you might initially expect. Intact skin is an important part of innate immunity, while all the other choices listed are more precisely components of the adaptive immune system. T-cells and B-cells are not involved in innate immunity.

Example Question #6 : Adaptive And Innate Immunity

Cryptosporidium is a genus of gastrointestinal parasite that infects the intestinal epithelium of mammals. Cryptosporidium is water-borne, and is an apicomplexan parasite. This phylum also includes Plasmodium, Babesia, and Toxoplasma. 

Apicomplexans are unique due to their apicoplast, an apical organelle that helps penetrate mammalian epithelium. In the case of cryptosporidium, there is an interaction between the surface proteins of mammalian epithelial tissue and those of the apical portion of the cryptosporidium infective stage, or oocyst. A scientist is conducting an experiment to test the hypothesis that the oocyst secretes a peptide compound that neutralizes intestinal defense cells. These defense cells are resident in the intestinal epithelium, and defend the tissue by phagocytizing the oocysts. 

She sets up the following experiment:

As the neutralizing compound was believed to be secreted by the oocyst, the scientist collected oocysts onto growth media. The oocysts were grown among intestinal epithelial cells, and then the media was collected. The media was then added to another plate where Toxoplasma gondii was growing with intestinal epithelial cells. A second plate of Toxoplasma gondii was grown with the same type of intestinal epithelium, but no oocyst-sourced media was added.

A patient is hiking through Nepal and comes down with a case of diarrhea caused by cryptosporidium. You determine that his body was fighting this infection mainly by mounting an antibody response. Where do the cells most directly responsible for this response develop?

Possible Answers:

Liver

Bone marrow

Spleen

Thymus

Adrenal glands

Correct answer:

Bone marrow

Explanation:

Antibodies are produced by B-cells, which develop in the bone marrow. T-cells develop in the thymus.

You can remember B for bone marrow, T for thymus.

Example Question #9 : Adaptive And Innate Immunity

Cryptosporidium is a genus of gastrointestinal parasite that infects the intestinal epithelium of mammals. Cryptosporidium is water-borne, and is an apicomplexan parasite. This phylum also includes Plasmodium, Babesia, and Toxoplasma. 

Apicomplexans are unique due to their apicoplast, an apical organelle that helps penetrate mammalian epithelium. In the case of cryptosporidium, there is an interaction between the surface proteins of mammalian epithelial tissue and those of the apical portion of the cryptosporidium infective stage, or oocyst. A scientist is conducting an experiment to test the hypothesis that the oocyst secretes a peptide compound that neutralizes intestinal defense cells. These defense cells are resident in the intestinal epithelium, and defend the tissue by phagocytizing the oocysts. 

She sets up the following experiment:

As the neutralizing compound was believed to be secreted by the oocyst, the scientist collected oocysts onto growth media. The oocysts were grown among intestinal epithelial cells, and then the media was collected. The media was then added to another plate where Toxoplasma gondii was growing with intestinal epithelial cells. A second plate of Toxoplasma gondii was grown with the same type of intestinal epithelium, but no oocyst-sourced media was added.

In the initial stages of a cryptosporidium infection, you can observe macrophages migrating to the area of infection. This process is called chemotaxis. What is likely to be the chemical mediator responsible for chemotaxis?

Possible Answers:

Cytokines and chemokines

Growth hormone

Neurotransmitters

cAMP

Androgens

Correct answer:

Cytokines and chemokines

Explanation:

Cytokines and chemokines are general classes of inflammatory mediators secreted by inflammatory cells like macrophages. They not only govern inflammation, but can also recruit surrounding cells via chemotaxis.

Example Question #7 : Adaptive And Innate Immunity

Identify the cells that correspond to the adaptive immune system and to the innate immune system.

Possible Answers:

Adaptive immune system—T-cells and macrophages

Innate immune system—monocytes, neutrophils, and B-cells

Adaptive immune system—B-cells and T-cells

Innate immune system—monocytes, neutrophils, and macrophages

Adaptive immune system—monocytes, neutrophils, and B-cells

Innate immune system—T-cells and macrophages

Adaptive immune system—monocytes, neutrophils, and macrophages

Innate immune system—B-cells and T-cells

Correct answer:

Adaptive immune system—B-cells and T-cells

Innate immune system—monocytes, neutrophils, and macrophages

Explanation:

B-cells and T-cells are part of the adaptive immune system, while monocytes, neutrophils, and macrophages are part of the innate immune system. Activation of the adaptive immune response requires prior exposure to a pathogen and the involvement of antibodies, while the innate immune response will occur whether a pathogen has been exposed before or not.

This list only contains a few examples of immune cells for each response, and is not exhaustive.

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