MCAT Biology : Adaptive and Innate Immunity

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #45 : Immune System

Which of the following cells is a part of the adaptive immune response?

Possible Answers:

Cytotoxic T-cells

Natural killer (NK) cells

Neutrophils

Mast cells

Correct answer:

Cytotoxic T-cells

Explanation:

An adaptive immune response only occurs once a specific antigen has been presented to a T-cell by an antigen-presenting cell, which activates a highly specific immune system response. The cells most directly involved in the adaptive immune response (for the purposes of the MCAT) are helper T-cells, cytotoxic T-cells, and B-cells.

On the other hand, our immune system also evades pathogens by non-specific, innate responses which encompass a wide range of cells and biological systems. While the other three answer choices are recognzied as "immune cells", they are not involved an adaptive immune response, making them incorrect answers.

Example Question #46 : Immune System

One component of the immune system is the neutrophil, a professional phagocyte that consumes invading cells. The neutrophil is ferried to the site of infection via the blood as pre-neutrophils, or monocytes, ready to differentiate as needed to defend their host.

In order to leave the blood and migrate to the tissues, where infection is active, the monocyte undergoes a process called diapedesis. Diapedesis is a process of extravasation, where the monocyte leaves the circulation by moving in between endothelial cells, enters the tissue, and matures into a neutrophil.

Diapedesis is mediated by a class of proteins called selectins, present on the monocyte membrane and the endothelium. These selectins interact, attract the monocyte to the endothelium, and allow the monocytes to roll along the endothelium until they are able to complete diapedesis by leaving the vasculature and entering the tissues.

The image below shows monocytes moving in the blood vessel, "rolling" along the vessel wall, and eventually leaving the vessel to migrate to the site of infection.

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A scientist is investigating what attracts monocytes to the site of infection, thus prompting diapedesis. He finds that a class of soluble mediators are given off by infected cells. This soluble mediator is most likely __________.

Possible Answers:

a fibroblast growth factor (FGF) protein

an sonic hedgehog (SHH) protein

a JAK-STAT protein

a Wnt protein

a chemokine protein

Correct answer:

a chemokine protein

Explanation:

Chemokines and cytokines are the main inflammatory mediators that drive a cellular response to inflammation or infection.

The JAK-STAT pathways are most linked to cell growth and division, while the hedgehog pathway (including SHH) is linked to early development. Wnt proteins are also linked to early development, but have been linked to carcinogenesis as well. Finally, fibroblast growth factor is linked with wound healing, but not with the initial immune response or recruitment.

Example Question #47 : Immune System

Which of the following is not involved in innate immunity?

Possible Answers:

Mucous

Skin

Macrophages

Plasma cells

Neutrophils

Correct answer:

Plasma cells

Explanation:

Plasma cells are mature B-cells, and are not part of the innate immune response. B-cell and T-cells are part of the adaptive immune response.

The innate immune response is mainly comprised of physical barriers and phagocytes. Skin and mucous are examples of such physical barriers, while macrophages and neutrophils are examples of non-specific phagocytes.

Example Question #48 : Immune System

Which of the following is not part of the innate immune response of the body?

Possible Answers:

Neutrophils

Macrophages

Digestive enzymes

Plasma cells

Correct answer:

Plasma cells

Explanation:

Innate immunity can be considered the general immune response that attacks any oncoming pathogens. The skin, digestive enzymes, and phagocytic cells are all part of the innate immune response. Plasma cells are modified B-cells, and are part of the acquired immune response. They are responsible for synthesizing free antibodies in response to a specific identified pathogen.

Example Question #49 : Immune System

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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The T-cells and B-cells described in the passage are both examples of lymphocytes. Lymphocytes are involved in adaptive immunity. Which of the following are characteristics of the adaptive immune system?

I. It shows a stronger reaction to a pathogen upon a second exposure, relative to the first

II. It is the first line of defense against a pathogen in the environment

III. It involves the use of macrophages and other professional phagocytes

Possible Answers:

II, only

I and II

I, II, and III

I and III

I, only

Correct answer:

I, only

Explanation:

The cells of the adaptive immune system are adaptive because they change upon exposure to a pathogen, such as a virus, and mount a stronger response upon a second exposure. Initial exposure allows for the formation of memory B-cells, which will be able to react quickly to a second exposure to the antigen.

The innate immune system, comprised of non-specific cells like macrophages, is the first line of defense against environmental pathogens and does not differ between a first and second encounter with an antigen.

Example Question #50 : Immune System

In the event of re-infection with the same pathogen, which immune cell allows for a quick response?

Possible Answers:

Natural killer cell

Helper T-cell

Plasma cell

Memory B-cell

Correct answer:

Memory B-cell

Explanation:

Memory B-cells are differentiated B-cells that specifically allow for a quick response to re-infection with the same antigen. The memory B-cells proliferate after coming into contact with an antigen that they recognize, spawning plasma cells that can secrete antibodies into circulation. Helper T-cells activate immature B-cells, while natural killer cells release perforin to kill invading bacteria.

Example Question #11 : Adaptive And Innate Immunity

Which of the following is not part of the adaptive immune response?

Possible Answers:

B-cells

Monocytes

Eosinophils

T-cells

Correct answer:

Monocytes

Explanation:

The adaptive immune system responds specifically to antigens on the bacteria, virus, or parasite surface. The adaptive immune response includes B- and T-cells, eosinophils, and basophils.

Monocytes differentiate into macrophages in response to infection or injury; they do not respond to specific antigens, and are not involved in the adaptive immune response.

Macrophages phagocytose viruses and bacteria and present their antigens to helper T-cells. Helper T-cells identify the presented antigen and activate B-cells to produce antibodies against the specific antigens. Eosinophils, basophils, additional macrophages, and killer T-cells can then respond to the antibodies to help defend against invading bacteria, viruses, and parasites.

Example Question #52 : Immune System

Which of the following correctly matches the type of immunity to the way it was recieved?

Possible Answers:

Active immunity—administering antibodies to a patient

Passive immunity—intentionally exposing yourself to infected individuals

Active immunity—antibody exchange during pregnancy

Passive immunity—having the illness itself

Active immunity—vaccination

Correct answer:

Active immunity—vaccination

Explanation:

Active immunity is when you are exposed to a pathogen, either through vaccination, another person with the disease, or any other means, and your body responds by producing specific antibodies with B-cells to destroy the pathogen. Passive immunity is acquired from antibody transfer, so the body does not produce its own antibodies.

Example Question #53 : Immune System

In the crusade to create a vaccine for Poliomyelitis, Jonas Salk and Albert Sabin created two separate vaccines that proved to be successful in preventing Polio onset.

The Salk vaccine, which is given by standard injection, contained virus particles inactivated by an organic solvent. This method has the advantage of inactivating each of the three Polio strains with no bias.

Albert Sabin's vaccine, given by oral inoculation via sugar water, contained live virus particles that had been genetically attenuated. With this method, each of the three Polio strains acquired separate mutations that made them unable to infect the human host cells. Strain 2 in particular contained one single nucleotide polymorphism in the internal ribosomal entry site (IRES) that prevented successful viral replication.

What type of immune response does inoculation with either vaccine stimulate? 

Possible Answers:

The adaptive immune response

The innate immune response 

Humoral immunity 

The lymphatic immune response

Correct answer:

The adaptive immune response

Explanation:

The adaptive immune response is responsible for encountering antigens and creating lasting immunity against it. The humoral immune response plays a role in adaptive immunity, but is more active during the secondary exposure to an antigen.

Example Question #54 : Immune System

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.

What is the best characterization of the immune response described in the passage?

Possible Answers:

Initially adaptive immunity, then innate immunity

Auto-immunity; neither innate nor adaptive immunity describe an autoimmune reaction

Initially innate immunity, then adaptive immunity

Innate immunity

Adaptive immunity

Correct answer:

Initially innate immunity, then adaptive immunity

Explanation:

The initial response is an effort to repair physical damage, while the chronic response involves the recognition of antigens. Innate immunity refers to the body's natural untargeted defenses, such as the cells that would work to repair damage. Adaptive immunity is targeted to specific pathogens via antigen presentation. Thus, the pattern described in the passage is initially innate immunity, then adaptive immunity.

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