Types of Immune System Cells
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MCAT Biological and Biochemical Foundations of Living Systems › Types of Immune System Cells
Which type of infection would a plasma cell be most effective in clearing from the human body?
An extracellular bacterial infection
Dormant HIV
A Mycobacterium tuberculosis that has been endocytosed by a macrophage
An infection by a newly-evolved bacterial strain
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.
Which of the following are NOT involved in cell-mediated immunity?
B-cells
Macrophages
Cytotoxic T-cells
Helper T-cells
Neutrophils
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.
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?
Macrophage
Megakaryocyte
B-cell
T-cell
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.
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.
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?
Endosomes
Ribosomes
Smooth endoplasmic reticulum
Rough endoplasmic reticulum
Golgi apparatus
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.
Plasma cells and memory cells are categorized under which division of the immune system?
Humoral immunity
Cell-mediated immunity
Innate immunity
Non-specific defense mechanisms
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.
Which of the following cells is responsible for producing platelets?
Megakaryocytes
B-cells
T-cells
Macrophages
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.
Which of the following molecules is not associated with the function of cytotoxic T-cells?
MHC II
MHC I
CD8
Cytokines
Explanation
In terms of MHC restriction, students should be familiar with the fact that cytotoxic T-cells are CD8+ and MHC I restricted. The alternative T subset, the helperT-ell, is CD4+ and MHC II restricted. Both cells rely on cytokines for growth, survival, and their effector functions.
Which of the following is NOT an antigen presenting cell?
T-Cells
B-Cells
Dendritic cells
Macrophages
Explanation
This question asks which of the following is NOT an antigen presenting cell, therefore, any option that is an antigen presenting cell in the immune system is an INCORRECT answer.
During an immune response, the cells involved in antigen presentation are dendritic cells, macrophages, and B-cells. T-cells, then, must be the answer choice that is NOT an antigen presenting cell, and thus is the correct answer.
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.
A key immune response to Neisseria in humans is the activity of macrophages. What is true of how macrophages combat infection?
Macrophages use reactive oxygen species after ingesting pathogens
Macrophages undergo apoptosis and release toxic compounds
Macrophages produce antibodies to target pathogens
Macrophages only recruit other cells that are then able to kill pathogens
Macrophages use isolation as their main defense, and wall off pathogens
Explanation
Macrophages are professional phagocytic cells. They ingest pathogens, and often use reactive oxygen species to kill pathogens via a burst of radical activity in specialized cellular compartments.
The thymus is responsible for producing which of the following immune cells?
T-cells
B-cells
Macrophages
Granulocytes
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.