Which of the following statements concerning antigen-presenting cells is true?

They are involved in activating T cells.

What is the correct sequence of events for activation of a B cell by a T-dependent antigen?

(1) Immunoglobulin receptors on the B cell recognize and bind the antigen. (2) An antigen fragment in complex with MHC class 2 is displayed on the B cell's surface. (3) The MHC-antigen complex binds a receptor on a TH cell. (4) The TH cell secretes cytokines that activate the B cell.

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 of the following statements concerning cellular immunity is FALSE?

Cellular immunity involves cells that recognize antigens and make specific antibodies against them.

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

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

What is the fate of activated cytotoxic T-cells?

They proliferate into a clone of cells specific to the same antigen; some of these cells then differentiate into long-lived memory T-cells, while others mature to attack infected cells.

Which molecule triggers apoptosis?

Granzyme

Which event happens first during cytotoxic T-cell activation?

CD8 binds to MHC molecules of infected cells

Which receptor on the helper T-cell recognizes the specific antigen from an antigen-presenting cell?

TCR

TH2 cells produce cytokines that activate

B cells.

Which proteins on the antigen-presenting cell are recognized by the helper T-cell?

MHC proteins

When do helper T-cells develop into TH1 or TH2 cells?

After proliferation into a clonal population

Natural killer cells are activated by

TH1 cells.

What type of immunity results from vaccination?

artificially acquired active immunity

Newborns' immunity due to the transfer of antibodies across the placenta is an example of

naturally acquired passive immunity.

Which of the following statements is NOT a possible outcome of antigen-antibody reaction?

clonal deletion

When an antibody binds to a toxin, the resulting action is referred to as

neutralization.

The specificity of an antibody is due to

the variable portions of the H and L chains.

Which of the following is NOT a characteristic of B cells?

They recognize antigens associated with MHC I.

Plasma cells are activated by a(n)

antigen

The antibodies found in mucus, saliva, and tears are

IgA.

The antibodies found on the surface of B cells, and which always exist as monomers, are

IgD.

In addition to IgG, the antibodies that can fix complement are

IgM.

The most abundant class of antibodies in serum is

IgG.

Memory cells do not require B cell receptors.

False

Plasma cells will eventually differentiate into memory cells.

False

The variable region of the antibody is solely responsible the significant diversity of antigen targets.

False

Only dendritic cells produce interleukins.

False

Cytokines are protein-based chemical messengers that allow for communication between cells of the immune system.

True

IL-2, produced by TH cells,

Stimulates TH cell mutation

Which of the following statements about natural killer cells is FALSE?

They are stimulated by an antigen.

The following events occur in cellular immunity. What is the third step?

TH cells proliferate.

Which of the following destroys virus-infected cells?

CTL

Which of the following bacterial components would most likely result in B cell stimulation by T-independent antigens?

capsule

In the figure, what can attach to a host cell?

e

Which of the following statements is FALSE?

The constant region of a heavy chain is the same for all antibodies.

In the figure, the arrow at time (c) indicates

the secondary response.

Which of the following is the best definition of antigen?

a chemical that elicits an antibody response and can combine with these antibodies

The following events elicit an antibody response. What is the third step?

TH cell recognizes antigen-digest and MHC II.

In the figure, which areas are similar for all IgG antibodies?

c and d