MCAT Biology : Types of Immune System Cells

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #371 : Biology

Which of the following is a granulocyte?

Possible Answers:

B-cell

Megakaryocyte

Neutrophil

Macrophage

Correct answer:

Neutrophil

Explanation:

The granulocytes that participate in innate immunity have vesicles filled with chemicals and proteins, such as perforin and trypsin, that are released to kill foreign bacteria, fungi, and parasites. The granulocytes include neutrophils, eosinophils, basophils, and mast cells.

Neutrophils are involved in bacterial infections and eosinophils in parasitic infections. Basophils and mast cells are involved in allergic reactions and inflammation.

Example Question #372 : Biology

Which of the following immune cells is responsible for engulfing foreign bacteria, viruses, and parasites and presenting antigens to lymphocytes to initiate an immune reaction?

Possible Answers:

Megakaryocyte

T-cell

Macrophage

B-cell

Correct answer:

Macrophage

Explanation:

Macrophages are responsible for ingesting and degrading bacteria and viruses, and presenting their antigens on major histocompatibility complexes (MHCs) to B- and T-cells. Macrophages are thus responsible for mediating the initiation of an immune reaction.

Megakaryocytes produce platelets, and B- and T-cells are the lymphocytes to which macrophages present ingested antigens.

Example Question #361 : Systems Biology And Tissue Types

Which of the following cells is responsible for producing platelets?

Possible Answers:

Megakaryocytes

B-cells

T-cells

Macrophages

Correct answer:

Megakaryocytes

Explanation:

Megakaryocytes are responsible for producing platelets, the remnants of cells that help form clots.

B-cells and T-cells are responsible for humoral and cell-mediated immunity. Macrophages ingest bacteria and viruses and present them to B- and T-cells to initiate an immune reaction.

Example Question #362 : Systems Biology And Tissue Types

Which of the following cells secretes antibodies after being stimulated by helper T-cells?

Possible Answers:

Plasma cell

Memory B-cell

Natural killer cell

Macrophage

Correct answer:

Plasma cell

Explanation:

Plasma cells are differentiated B-cells that serve to secrete antibodies after being stimulated by a helper T-cell.

Natural killer cells are also stimulated by helper T-cells and secrete perforin to kill invading pathogens. Memory B-cells are differentiated B-cells that are specialized to detect a re-infection by the same pathogen, allowing for a quick immune response. Macrophages ingest infecting agents.

Example Question #363 : Systems Biology And Tissue Types

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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One of the functions of antibodies is to facilitate the phagocytosis of pathogens by macrophages or other professional phagocytes. Which of the following organelles is likely to be found in abundance in professional phagocytes, relative to most other cell types?

Possible Answers:

Golgi apparatus

Endosomes

Smooth endoplasmic reticulum

Ribosomes

Rough endoplasmic reticulum

Correct answer:

Endosomes

Explanation:

Endosomes function to shuttle phagocytosed material to the lysosome, where cellular digestion can take place. This means that professional phagocytes, such as macrophages, can be expected to have a larger number of endosomes than other cells that are less specialized for this process.

Example Question #364 : Systems Biology And Tissue Types

Which type of infection would a plasma cell be most effective in clearing from the human body?

Possible Answers:

An extracellular bacterial infection

Dormant HIV

An infection by a newly-evolved bacterial strain

A Mycobacterium tuberculosis that has been endocytosed by a macrophage 

Correct answer:

An extracellular bacterial infection

Explanation:

The role of a plasma cell in the immune system is to produce antibodies. These antibodies are effective in binding to extracellular pathogens. Antibodies produced by plasma cells would not be effective in binding to intracellular pathogens, such as M. tuberculosis and intracellular HIV. Only one answer choice specifies an extracellular pathogen.

Plasma cells are developed from B-lymphocyte precursors in response to the presence of a specific antigen, and are part of the adaptive immune response. As such, they would be relatively ineffective at fighting a newly-evolved microbe to which the body has never been exposed before.

Example Question #365 : Systems Biology And Tissue Types

Where in the body do B-lymphocytes mature?

Possible Answers:

Thymus

Lymph nodes

Red bone marrow

Yellow bone marrow

Correct answer:

Red bone marrow

Explanation:

Both B-lymphocytes and T-lymphocytes are derived from lymphoid progenitor cells, a division of hematopoietic stem cells. These progenitors are housed in red bone marrow. B-lymphocytes remain in the red bone marrow to mature, but T-lymphocytes transition to the thymus for positive selection.

The lymph nodes and spleen are secondary immune tissues, responsible for housing mature B- and T-lymphocytes in order to carry out the immune response. The lymph nodes and spleen are not responsible for immune cell development. Yellow bone marrow is primarily used for fat storage and is not involved in the lymphatic system or immune response.

Example Question #366 : Systems Biology And Tissue Types

Where in the body do T-lymphocytes mature?

Possible Answers:

Bone marrow

Lymph nodes

Thyroid

Thymus

Correct answer:

Thymus

Explanation:

T-lymphocytes and B-lymphocytes both arise in the bone marrow from the lymphoid progenitor lineage of stem cells. B-lymphocytes remain in the bone marrow for maturation, while T-lymphocytes migrate to the thymus. In the thymus, T-lymphocytes are exposed to antigens from the body's own cells. If the T-cell reacts to the antigen, it is destroyed to prevent autoimmune disorders. This process is known as positive selection.

The thyroid is an endocrine gland, and is not a site for immune cell development. The lymph nodes are secondary immune tissues and are responsible for conducting the immune response and housing mature lymphocytes, not for immune cell development. 

Example Question #367 : Systems Biology And Tissue Types

Which type of T-lymphocyte directly destroys infected cells?

Possible Answers:

Helper T-lymphocytes

Regulatory T-lymphocytes

Cytotoxic T-lymphocytes

Follicular helper T-lymphocytes

Correct answer:

Cytotoxic T-lymphocytes

Explanation:

Cytotoxic T-lymphocytes, also known as kill T-cells, directly destroy infected cells by releasing their cytotoxic granules into the cells and causing them to lyse.

Helper T-lymphocytes produce cytokines, which are involved in cell signaling and propagating the immune response. Follicular helper T-lymphocytes control B-cells in lymph nodes. Regulatory T-lymphocytes inhibit the immune response. 

Example Question #368 : Systems Biology And Tissue Types

Plasma cells and memory cells are categorized under which division of the immune system?

Possible Answers:

Non-specific defense mechanisms

Innate immunity

Humoral immunity

Cell-mediated immunity

Correct answer:

Humoral immunity

Explanation:

The immune system can be broken down into two main categories: innate and adaptive. Innate immunity includes nonspecific defense mechanisms, and the adaptive side is broken down into two primary sections, humoral and cell-mediated immunity. The key players in cell-mediated immunity are T-cells (including helper, suppressor, memory and cytotoxic T-cells). The humoral response occurs through B-cells, which are the precursors for plasma cells and memory cells. Once a B-cell is exposed to a matching antigen, it will begin to produce two types of daughter cells: plasma cells and memory cells. Plasma cells produce large amounts of antibodies in order to fight the infection at hand, where memory cells will remain in the lymph nodes for the rest of the organism's life. Memory cells are key in an organism's quick secondary response to a microbe that was previously encountered.

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