Unlike NK cells of the innate immune system, B cells (B lymphocytes) are a type of white blood cell that gives rise to antibodies, whereas T cells (T lymphocytes) are a type of white blood cell that plays an important role in the immune response. T cells are a key component in the cell-mediated response—the specific immune response that utilizes T cells to neutralize cells that have been infected with viruses and certain bacteria.
There are three types of T cells: cytotoxic, helper, and suppressor T cells. Cytotoxic T cells destroy virus-infected cells in the cell-mediated immune response, and helper T cells play a part in activating both the antibody and the cell-mediated immune responses. Suppressor T cells deactivate T cells and B cells when needed, and thus prevent the immune response from becoming too intense.
An antigen is a foreign or “non-self” macromolecule that reacts with cells of the immune system. Not all antigens will provoke a response. For instance, individuals produce innumerable “self” antigens and are constantly exposed to harmless foreign antigens, such as food proteins, pollen, or dust components. The suppression of immune responses to harmless macromolecules is highly regulated and typically prevents processes that could be damaging to the host, known as tolerance.
Terms and Answers to Learn
Antigens processing and presentation?
is a way for a cell to give information about its activities
Why would a body cell that is not a phagocyte need to present antigens?
Non-phagocytic body cells can become infected with a virus
How do phagocytes communicate to other cells what they have captured?
They present antigens from engulfed foreign cells
Which structure do antigens presenting cells utilize to directly help them present bacterial antigens?
Phagolysosome
Which of the following are likely to be found on a MHC-I protein?
Damaged mitochondrial fragment
What would a virally infected skin epithelial cell have on its cell surface?
Class I MHC with skin cell antigens
Which of the following would you likely see on the surface of a human dendritic cell following phagocytosis of a bacterium?
Class I MHC with dendritic cell antigens and Class I MHC with engulfed bacteria
Tom has a genetic disorder in which he does not synthesize class I MHC proteins for functional NK cells. Which of the following statements would be true for Tom:
Tom would not be able to destroy virally-infected cells
Which part of the adaptive immune response involves B cells?
Humoral
Antibodies are a part of which type of immunity
Humoral
If a patient has been exposed to an antigen for the first time, which class of immunoglobulin appears first?
IgM
Which type of cell directly attacks infected cells?
Cytotoxic T cells
Immune cells that secrete cytokines and activate other immune cells are?
Helper T cells
HIV directly infects T cells. Why is this problematic for cell-mediated immunity?
Cytotoxic T cells begin to attack the virally infected T cells, reducing the number of T cells in the body
How do helper T cells and cytotoxic T cells work together?
Helper T cells produce cytokines to activate other cells of the immune system
Which type of T cell is involved in activating macrophages and stimulating development of cytotoxic T cells?
TH1 cells
Match the key terms and the concepts of the immune system with their descriptions:
a. Includes cilia, mucous membranes, dendritic cells
b. Immunological response brought about by antibody production
c. Immunological response that kills infected host cells
d. Use(s) BCRs to recognize epitope. First step in clonal selection
e. Phagocytes that engulf anything foreign. Eventually display epitope to helper T cells using MHC I or II
f. Lymphocytes that activate B cells and CTLs
g. Differentiated B cells that are stored in lymph nodes to provide protection against future infections by the same pathogen
h. Produce and secrete antibodies
i. Kills infected host cells
a. Includes cilia, mucous membranes, dendritic cells
b. Immunological response brought about by antibody production
c. Immunological response that kills infected host cells
d. Use(s) BCRs to recognize epitope. First step in clonal selection
e. Phagocytes that engulf anything foreign. Eventually display epitope to helper T cells using MHC I or II
f. Lymphocytes that activate B cells and CTLs
g. Differentiated B cells that are stored in lymph nodes to provide protection against future infections by the same pathogen
h. Produce and secrete antibodies
i. Kills infected host cells
a. Innate Immunity
b. Humoral Immunity
c. Cellular Immunity
d. Immature B cells
e. Dendritic cells
f. Th cells
g. Memory cells
h. Plasma cells
i. Cytotoxic T cells
b. Humoral Immunity
c. Cellular Immunity
d. Immature B cells
e. Dendritic cells
f. Th cells
g. Memory cells
h. Plasma cells
i. Cytotoxic T cells
An individual may be exposed to a pathogen and become infected without actually getting sick. This is known as a subclinical infection. Even in subclinical infections, the individual’s adaptive immune system can generate memory for the pathogen. What type of adaptive immunity is this?
naturally acquired active immunity
Consider a helminthic infection in which an individual is colonized by a parasitic worm. The worm is too big to be engulfed by a phagocytic cell. How does the immune system respond?
The worm gets coated with antibodies, which activate other cells in the immune system to secrete chemicals that kill it.
The primary immune response involves
an immediate increase in the concentration of antibodies, followed by an immediate and sharp decline.
a slow rise in the concentration of antibodies, followed by a gradual decline.
a slow rise in the concentration of antibodies, followed by a rapid decline.
an immediate increase in the concentration of antibodies, followed by a slow decline.
a slow rise in the concentration of antibodies, followed by a gradual decline.
According to the animation, for approximately how many days is IgG present in the serum?
Ten days
According to the animation, on what day does IgM first appear?
Day five
What makes agglutination by antibodies possible?
Each antibody has at least two antigen-binding sites.
What is the role of plasma cells in humoral immunity?
Plasma cells produce antibodies.
Which of the following most accurately describes how a pathogenic bacterium might be affected by antibodies?
The antibodies may block proteins necessary for binding the pathogen to the host, may opsonize the bacterium, or may agglutinate bacteria.
Where are MHC molecules located on a cell?
On the surface of the cell
What is a feature of the small fragments presented by MHC-I proteins?
They are small peptides, roughly 8-10 amino acids long.
Which organelle assists directly with the presentation of MHC-I antigens?
The endoplasmic reticulum
When does MHC-II loading occur?
During the fusion of vesicles containing MHC-II proteins with vesicles containing digested pathogens
Which of the cells listed below can present antigens on Class II MHC proteins?
Macrophages
What is apoptosis?
The process of programmed cell death.
What is the function of the CD8 receptor?
Bind to MHC molecules
The primary function of the humoral, or antibody-mediated, immune response is to control freely circulating pathogens
Indicate the correct order of events for the mechanism of antibody-mediated immunity
Antibodies
B-cell
Extracellular antigen
Plasma cell
Indicate the correct order of events for the mechanism of antibody-mediated immunity
Antibodies
B-cell
Extracellular antigen
Plasma cell
Correct order:
1. Extracellular antigen
2. B cell
3 Plasma cell
4 Antibodies
1. Extracellular antigen
2. B cell
3 Plasma cell
4 Antibodies
The dual nature of the adaptive immune response allows for controlling freely circulating pathogens (humoral) via antibody-mediated mechanisms and controlling intracellular pathogens (cellular) via cell-mediated mechanisms.
Please sort each of the following descriptions of essential humoral and cellular immune factors to its corresponding item from A to E.
1. This molecule is made up of protein chains that form a complex with antigens. This complex serves to tag foreign cells and molecules for destruction by phagocytes and complement.
2. This cell is responsible for the enhanced secondary response to an antigen and is produced via clonal selection and differentiation of B cells
3. This cell is an effector cell that has the ability to recognize and kill target cells that are considered nonself cells
4. The helping function of this cell is activated by two signals; one signal occurs with the binding of the T cell receptor (TCR) to a processed antigen, and the second signal is a costimulatory cytokine.
5. This cell becomes activated when its immunoglobulins binds to its specific epitope, and in order to be activated, it may require assistance via helper cells.
A. T helper cell
B. Memory cell
C. B-cell
D. Antibodies
E. Cytotoxic T lymphocyte
Please sort each of the following descriptions of essential humoral and cellular immune factors to its corresponding item from A to E.
1. This molecule is made up of protein chains that form a complex with antigens. This complex serves to tag foreign cells and molecules for destruction by phagocytes and complement.
2. This cell is responsible for the enhanced secondary response to an antigen and is produced via clonal selection and differentiation of B cells
3. This cell is an effector cell that has the ability to recognize and kill target cells that are considered nonself cells
4. The helping function of this cell is activated by two signals; one signal occurs with the binding of the T cell receptor (TCR) to a processed antigen, and the second signal is a costimulatory cytokine.
5. This cell becomes activated when its immunoglobulins binds to its specific epitope, and in order to be activated, it may require assistance via helper cells.
A. T helper cell
B. Memory cell
C. B-cell
D. Antibodies
E. Cytotoxic T lymphocyte
1) Antibodies (D)
2) Memory Cell (B)
3) Cytotoxic T lymphocyte (E)
4) T helper cells (A)
5) B cell (C)
2) Memory Cell (B)
3) Cytotoxic T lymphocyte (E)
4) T helper cells (A)
5) B cell (C)
For pathogen below, choose the type of cell that would be used in the adaptive immune response.
Helminth
Helminth
Th2 cell
Hint: The cell type will be a helper cell that produces cytokines to signal other cells (specifically the eosinophils) to help with the removal of this large extracellular parasite.
For pathogen below, choose the type of cell that would be used in the adaptive immune response.
Intracellular bacteria and protozoa
Intracellular bacteria and protozoa
Th1 cells
Hint: The cell type will be a helper cell that produces cytokines (specifically IFN-y) that stimulate the macrophages and allows for phagocytosis
Hint: The cell type will be a helper cell that produces cytokines (specifically IFN-y) that stimulate the macrophages and allows for phagocytosis
For pathogen below, choose the type of cell that would be used in the adaptive immune response
FungiExtracellular bacteria
FungiExtracellular bacteria
Th17 cells
Hint: The cell type is a helper cell that produces large quantities of a specific cytokine, IL-17, which recruits the neutrophils to induce phagocytic activity and clear extracellular pathogens.
Hint: The cell type is a helper cell that produces large quantities of a specific cytokine, IL-17, which recruits the neutrophils to induce phagocytic activity and clear extracellular pathogens.
Which type of adaptive immunity does the following statement describe?
This time of immunity is acquired via injection of antibodies from an individual or host that has immunological memory to the specific pathogen or antigen.
This time of immunity is acquired via injection of antibodies from an individual or host that has immunological memory to the specific pathogen or antigen.
artificially acquired passive immunity
Hint: What makes this time of immunity unique is that antibodies are introduced from another host. Does this sound like an active or passive process? And would you consider this to be naturally or artificially acquired?
Hint: What makes this time of immunity unique is that antibodies are introduced from another host. Does this sound like an active or passive process? And would you consider this to be naturally or artificially acquired?
Which type of adaptive immunity does the following statement describe?
This type of immunity is acquired via the passing of antibodies from a mother to a child to give immunity during the development of the child’s immune system.
This type of immunity is acquired via the passing of antibodies from a mother to a child to give immunity during the development of the child’s immune system.
naturally acquired passive immunity
Hint: What makes this type of immunity unique is that antibodies are passed to the child through the placenta or the mother’s milk. In this case, does the child acquire the antibodies actively or passively? And would you consider this to be naturally or artificially acquired?
Hint: What makes this type of immunity unique is that antibodies are passed to the child through the placenta or the mother’s milk. In this case, does the child acquire the antibodies actively or passively? And would you consider this to be naturally or artificially acquired?
Which type of adaptive immunity does the following statement describe?
This type of immunity is acquired when a person is vaccinated for a specific type of infection via the introduction of antigens. These antigens normally have undergone some type of modification and may not confer the same type of long-lasting memory that would occur with unmodified antigens.
This type of immunity is acquired when a person is vaccinated for a specific type of infection via the introduction of antigens. These antigens normally have undergone some type of modification and may not confer the same type of long-lasting memory that would occur with unmodified antigens.
artificially acquired active immunity
Hint: What makes this type of immunity unique is that modified antigens are used to elicit an immune response. Does this sound like an active or passive process? And would you consider this to be naturally or artificially acquired?
Hint: What makes this type of immunity unique is that modified antigens are used to elicit an immune response. Does this sound like an active or passive process? And would you consider this to be naturally or artificially acquired?
What type of adaptive immunity does the following statement describe?
This type of immunity is acquired when antigens enter the body and an infection occurs. The immune system works to fight the infection via the innate and adaptive immune responses and creates an immunological memory of that particular antigen.
This type of immunity is acquired when antigens enter the body and an infection occurs. The immune system works to fight the infection via the innate and adaptive immune responses and creates an immunological memory of that particular antigen.
naturally acquired active immunity
Hint: This type of immunity is not very unique in that it is acquired through daily exposure to antigens that are introduced via many different mechanisms, including everyday activities such as eating and breathing. These antigens may or may not produce a serious infections, but they do serve to create immunological memory. When they cause infection, they elicit a primary and secondary immune response. Does this sound like an active or passive process? And would you consider this to be naturally or artificially acquired?
Hint: This type of immunity is not very unique in that it is acquired through daily exposure to antigens that are introduced via many different mechanisms, including everyday activities such as eating and breathing. These antigens may or may not produce a serious infections, but they do serve to create immunological memory. When they cause infection, they elicit a primary and secondary immune response. Does this sound like an active or passive process? And would you consider this to be naturally or artificially acquired?
What is the term for a foreign molecule that triggers an immune response?
antigen
Which cell type is responsible for cellular immunity
T cells
What is the term for the communication molecules used by T cells to coordinate and regulate immune responses?
cytokines
Which cell type forms plasma cells
B cells
On an antibody molecule, what is the term for the stem region of the antibody molecule?
The Fc region
What part of an antibody molecule binds an antigenic determinant?
the variable regions
Which class of antibody is found in body secretions and on mucous membranes
IgA
Which type of T cell is also called CD4 T cell?
a helper T cell
What is the term used for coating of a target cell with antibody to enhance phagocytosis?
opsonization
True or False
Humoral immunity involves B cells and the production of antibodies
Humoral immunity involves B cells and the production of antibodies
True
True or False
Antigens are usually proteins or large polysaccharides
Antigens are usually proteins or large polysaccharides
True
What type of immunity occurs following a vaccination? Is it A) naturally acquired immunity or B) artificially acquired active immunity?
B) artificially acquired active immunity
Which of these is an antigen-presenting cell
A) A plasma cell
B) a macrophage
A) A plasma cell
B) a macrophage
B) macrophage
Which class of antibodies is involved in allergic reactions?
IgE
What is the term for the clumping of antigens with antibodies?
agglutination
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