MCAT Biology : Types of Immune System Cells

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #11 : Types Of Immune System Cells

Which of the following are NOT involved in cell-mediated immunity?

Possible Answers:

Cytotoxic T-cells

B-cells

Neutrophils

Macrophages

Helper T-cells

Correct answer:

B-cells

Explanation:

Cell-mediated immunity involves the response of specific cells toward an invading pathogen or organism. This is in contrast to humoral, or antibody-mediated immunity. Both of these are types of adaptive immunity, however, cell-mediated immunity involves the initial identificaiton of an unknown pathogen, while humoral immunity requires prior exposure to the antigen.

B-cells secrete antibodies and are the main actor in humoral immunity; they do not participate directly in cell-mediated immunity. Cytotoxic T-cells are activated by helper T-cells to recognize and destroy infected cells in the body. The process also involves cytokines which recruit neutrophils to digest the infected cell or microbes.

Example Question #11 : Types Of Immune System Cells

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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Macrophages, similar to neutrophils, are another professional phagocyte, and a type of antigen-presenting cell. Antigen-presenting cells digest invaders, and then present their foreign proteins to B-cells and T-cells for further immune response. Which of the following is true of antigen-presenting cells?

I.  They present their antigens on major histocompatibility complex molecules.

II.  They migrate to lymph nodes to present their antigens to B-cells and T-cells.

III.  Antigen-presenting cells form a link between the innate and adaptive immune systems.

Possible Answers:

I, II, and III

I, only

I and II

I and III

II and III

Correct answer:

I, II, and III

Explanation:

Antigen-presenting cells do all of these functions, thus working to stimulate an adaptive response in regional lymph nodes.

Histocompatibility complex molecules, or MHCs, are keys for carrying antigens and developing antibodies. Once antigen-presenting cells encounter an antigen, they will bind it and carry it to the lymph nodes to activate the adaptive immune response, or to establish cellular memory of a new foreign antigen.

Example Question #361 : Biology

Where in the human body do T-Cells mature?

Possible Answers:

Thymus

Blood

Lymph

Bone marrow

Correct answer:

Thymus

Explanation:

T-cells and B-cells are derived from stem cells that originate in the bone marrow. B-cells continue to mature in the bone marrow; however, T-cells mature in the thymus. Once they are mature, they travel through the blood and reside in the lymph.

Example Question #361 : Biology

Cell-mediated immunity involves the action of which of the following cells?

Possible Answers:

Plasma cells

Cytotoxic T-cells

B-lymphocytes

Neutrophils

Correct answer:

Cytotoxic T-cells

Explanation:

Cell-mediated immunity involves all of the differentiated forms of T-lymphocytes. Cytotoxic T-cells (also called killer T-cells) are antigen-specific, and responsible for the destruction of infected cells bearing the given antigen.

Plasma cells and B-cells are part of humoral (antibody) immunity, while neutrophils play an important role in the innate immune response.

Example Question #13 : Types Of Immune System Cells

Which answer choice correctly matches the cell type with its progenitor cell?

Possible Answers:

Plasma cells are derived from B-cells

Erythrocytes are derived from lymphocytes

Dendritic cells are derived from T-cells

Mast cells are derived from monocytes

Lymphocytes are derived from erythrocytes
Correct answer:

Plasma cells are derived from B-cells

Explanation:

When an antigen is presented to a B-cell, it can develop the ability to produce antibodies against that specific antigen. Once the B-cell gains this ability, it is a plasma cell.

T-cells, B-cells, and dendritic cells are derived from lymphoid progenitor stem cells. Together, the group of cells derived from this cell type is known as the lymphocytes. Mast cells, erythrocytes, and monocytes are derived from myeloid progenitor stem cells. Macrophages are derived from monocytes.

Example Question #11 : Types Of Immune System Cells

Which of the following cells is NOT a lymphocyte?

Possible Answers:

Plasma cell

Helper T-cell

Neutrophil

Cytotoxic T-cell

Natural killer cell

Correct answer:

Neutrophil

Explanation:

Blood cells can be broken into two main categories based on their originating stem cells. Myeloid progenitor cells are the source of erythrocytes and most granulocytes. Lymphoid progenitor cells give rise to lymphocytes.

Lymphocytes are mostly involved in the adaptive immune response, and include dendritic cells, T-cells, B-cells, and the derivatives of these cells, such as plasma cells and memory cells. Natural killer cells, however, are granulocytes that are involved in the innate immune response, but are still derived from lymphoid progenitor cells. Natural killer cells are thus lymphocytes as well.

Neutrophils are granulocytes involved in the innate immune response, and are generated from myeloid progenitor cells; neutrophils are not lymphocytes.

Example Question #11 : Types Of Immune System Cells

The thymus is responsible for producing which of the following immune cells?

Possible Answers:

Granulocytes

Macrophages

B-cells

T-cells

Correct answer:

T-cells

Explanation:

The thymus is responsible for the maturation of T-cells. The thymus, a gland centered in the chest, allows T-cells to be tested against a "self-antigen." If the T-cell does not react against the self-antigen, it is allowed to leave the thymus and enter into circulation to detect foreign antigens. If the T-cell does react to the self-antigen, it is generally destroyed. Failure to destroy these T-cells can result in autoimmune attacks. Upon detection of foreign antigens, mature T-cells differentiate into a variety of other T-cell types and stimulate B-cells to produce antibodies.

Example Question #362 : Biology

Which of the following immune cells primarily mediates reactions to parasitic infections?

Possible Answers:

Megakaryocytes

Basophils

Eosinophils

Neutrophils

Correct answer:

Eosinophils

Explanation:

Eosinophils primarily mediate reactions to parasitic infections, including worms. Neutrophils respond to bacterial infections, and basophils to allergies (IgE). Megakaryocytes are responsible for making platelets.

Example Question #11 : Immune System

Which of the following immune cells is involved in responding to allergies and drug reactions?

Possible Answers:

Eosinophil

Megakaryocyte

Neutrophil

Basophil

Correct answer:

Basophil

Explanation:

Basophils and mast cells are responsible for secreting factors like histamine in response to allergens and drugs. Release of the histamine can cause throat constriction, hives, and inflammation. Eosinophils mediate reactions to parasitic infections and neutrophils to bacterial infections. Megakaryocytes produce platelets.

Example Question #42 : Immune And Lymphatic Systems

Which of the following innate immune cells primarily protects against bacterial infections?

Possible Answers:

Eosinophil

Megakaryocyte

Basophil

Neutrophil

Correct answer:

Neutrophil

Explanation:

Neutrophils contain antimicrobial products in vesicles, which are secreted when they come into contact with foreign cells. Neutrophils primarily mediate reaction to bacterial infections and are the primary component of the white pus found in bacterial inflammation. Eosinophils respond to parasitic infections and basophils to allergies (IgE). Megakaryocytes produce platelets.

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