Basic Principles of Immunology HARR

Question 1

From the following, identify a specific component of the adaptive immune system that is formed in response to antigenic stimulation:
A. Lysozyme
B. Complement
C. Commensal organisms
D. Immunoglobulin

Answer 1

Immunoglobulin

Immunoglobulin is a specific part of the adaptive immune system and is formed only in response to a specific antigenic stimulation. Complement, lysozyme, and commensal organisms all act nonspecifically as a part of the adaptive immune system. These three components do not require any type of specific antigenic stimulation.

Question 2

Which two organs are considered the primary
lymphoid organs in which immunocompetent
cells originate and mature?
A. Thyroid and Peyer’s patches
B. Thymus and bone marrow
C. Spleen and mucosal-associated lymphoid tissue (MALT)
D. Lymph nodes and thoracic duct

Answer 2

Thymus and bone marrow

The bone marrow and thymus are considered primary lymphoid organs because immunocompetent cells either originate or mature in them. Some immunocompetent cells mature or reside in the bone marrow (the source of all hematopoietic cells) until transported to the thymus, spleen, or Peyer’s
patches, where they process antigen or manufacture antibody. T lymphocytes, after originating in the bone marrow, travel to the thymus to mature and differentiate.

Question 3

What type of B cells are formed after antigen
stimulation?
A. Plasma cells and memory B cells
B. Mature B cells
C. Antigen-dependent B cells
D. Receptor-activated B cells

Answer 3

Plasma cells and memory B cells

Mature B cells exhibit surface immunoglobulin
that may cross link a foreign antigen, thus forming the activated B cell and leading to capping and internalization of antigen. The activated B cell gives rise to plasma cells that produce and secrete immunoglobulins and memory cells that reside in lymphoid organs.

Question 4

T cells travel from the bone marrow to the thymus for maturation. What is the correct order of the maturation sequence for T cells in the thymus?
A. Bone marrow to the cortex; after thymic
education, released back to peripheral circulation
B. Maturation and selection occur in the cortex; migration to the medulla; release of mature T cells to secondary lymphoid organs
C. Storage in either the cortex or medulla; release of T cells into the peripheral circulation
D. Activation and selection occur in the medulla; mature T cells are stored in the cortex until activated by antigen

Answer 4

Maturation and selection occur in the cortex; migration to the medulla; release of mature T cells to secondary lymphoid organs

Immature T cells travel from the bone marrow to the thymus to mature into functional T cells. Once in the thymus, T cells undergo a selection and maturation sequence that begins in the cortex and moves to the medulla of the thymus. Thymic factors such as thymosin and thymopoietin and cells within the thymus such as macrophages and dendritic cells assist in this sequence. After completion of the maturation cycle, T cells are released to secondary lymphoid organs to await antigen recognition and activation.

Question 5

Which cluster of differentiation (CD) marker
appears during the first stage of T-cell
development and remains present as an
identifying marker for T cells?
A. CD1
B. CD2
C. CD3
D. CD4 or CD8

Answer 5

CD2

The CD2 marker appears during the first stage of T-cell development and can be used to differentiate T cells from other lymphocytes. This T-lymphocyte receptor binds sheep red blood cells (RBCs). This peculiar characteristic was the basis for the classic E rosette test once used to enumerate T cells in peripheral blood. CD2 is not specific for T cells, however, and is also found on large granular lymphocytes (LGL or natural killer [NK] cells).

Question 6

Which markers are found on mature, peripheral helper T cells?
A. CD1, CD2, CD4
B. CD2, CD3, CD8
C. CD1, CD3, CD4
D. CD2, CD3, CD4

Answer 6

CD2, CD3, CD4

Mature, peripheral helper T cells have the CD2
(E rosette), CD3 (mature T cell), and CD4 (helper) markers.

Question 7

Which T cell expresses the CD8 marker and acts specifically to kill tumors or virally infected cells?
A. Helper T
B. T suppressor
C. T cytotoxic
D. T inducer/suppressor

Answer 7

T cytotoxic

T cytotoxic cells recognize antigen in association with major histocompatibility complex (MHC) class I complexes and act against target cells that express foreign antigens. These include viral antigens and the
human leukocyte antigens (HLA) that are the target of graft rejection.

Question 8

How are cytotoxic T cells (TC cells) and natural
killer (NK) cells similar?
A. Require antibody to be present
B. Effective against virally infected cells
C. Recognize antigen in association with HLA class II markers
D. Do not bind to infected cells

Answer 8

Effective against virally infected cells

Both TC and NK cells are effective against virally infected cells, and neither requires antibody to be present to bind to infected cells. NK cells do not exhibit MHC class restriction, whereas activation of TC cells requires the presence of MHC class I molecules in association with the viral antigen.

Question 9

What is the name of the process by which
phagocytic cells are attracted to a substance
such as a bacterial peptide?
A. Diapedesis
B. Degranulation
C. Chemotaxis
D. Phagotaxis

Answer 9

Chemotaxis

Chemotaxis is the process by which phagocytic cells are attracted toward an area where they detect a disturbance in the normal functions of body tissues. Products from bacteria and viruses, complement components, coagulation proteins, and cytokines from other immune cells may all act as chemotactic factors

Question 10

All of the following are immunologic functions
of complement except:
A. Induction of an antiviral state
B. Opsonization
C. Chemotaxis
D. Anaphylatoxin formation

Answer 10

Induction of an antiviral state

Complement components are serum proteins
that function in opsonization, chemotaxis, and
anaphylatoxin formation but do not induce an
antiviral state in target cells. This function is
performed by interferons

Question 11

Which complement component is found in both the classic and alternative pathways?
A. C1
B. C4
C. Factor D
D. C3

Answer 11

C3

C3 is found in both the classic and alternative
(alternate) pathways of the complement system. In the classic pathway, C3b forms a complex on the cell with C4b2a that enzymatically cleaves C5. In the alternative pathway, C3b binds to an activator on the cell surface. It forms a complex with factor B called C3bBb which, like C4b2a3b, can split C5.

Question 12

Which immunoglobulin(s) help(s) initiate the
classic complement pathway?
A. IgA and IgD
B. IgM only
C. IgG and IgM
D. IgG only

Answer 12

IgG and IgM

Both IgG and IgM are the immunoglobulins that help to initiate the activation of the classic complement pathway. IgM is a more potent complement activator, however.

Question 13

How is complement activity destroyed in vitro?
A. Heating serum at 56°C for 30 min
B. Keeping serum at room temperature of 22°C for 1 hour
C. Heating serum at 37°C for 45 min
D. Freezing serum at 0°C for 24 hours

Answer 13

Heating serum at 56°C for 30 min

Complement activity in serum in vitro is destroyed by heating the serum at 56°C for 30 min. In test procedures where complement may interfere with the test system, it may be necessary to destroy complement activity in the test sample by heat inactivation.

Question 14

What is the purpose of C3a, C4a, and C5a, the
split products of the complement cascade?
A. To bind with specific membrane receptors of lymphocytes and cause release of cytotoxic
substances
B. To cause increased vascular permeability,
contraction of smooth muscle, and release of
histamine from basophils
C. To bind with membrane receptors of
macrophages to facilitate phagocytosis and the
removal of debris and foreign substances
D. To regulate and degrade membrane cofactor protein after activation by C3 convertase

Answer 14

To cause increased vascular permeability,
contraction of smooth muscle, and release of
histamine from basophils

C3a, C4a, and C5a are split products of the
complement cascade that participate in various biological functions such as vasodilation and smooth muscle contraction. These small peptides act as anaphylatoxins, e.g., effector molecules that participate in the inflammatory response to assist in the destruction and clearance of foreign antigens

Question 15

Which region of the immunoglobulin molecule
can bind antigen?
A. Fab
B. Fc
C. CL
D. CH

Answer 15

Fab

The Fab (fragment antigen binding) is the region of the immunoglobulin molecule that can bind antigen. Two Fab fragments are formed from hydrolysis of the immunoglobulin molecule by papain. Each consists of a light chain and the VH and CH1 regions of the heavy chain. The variable regions of the light and heavy chains interact, forming a specific
antigen-combining site.

Question 16

Which region determines whether an
immunoglobulin molecule can fix
complement?
A. VH
B. CH
C. VL
D. CL

Answer 16

CH

The composition and structure of the constant
region of the heavy chain determine whether that immunoglobulin will fix complement. The Fc fragment (fragment crystallizable) is formed by partial immunoglobulin digestion with papain and includes the CH2 and CH3 domains of both heavy chains. The complement component C1q molecule will bind to the CH2 region of an IgG or IgM molecule

Question 17

Which immunoglobulin class(es) has (have) a
J chain?
A. IgM
B. IgE and IgD
C. IgM and sIgA
D. IgG3 and IgA

Answer 17

IgM and sIgA

Both IgM and secretory IgA have a J chain joining individual molecules together; the J chain in IgM joins five molecules and the J chain in sIgA joins two molecules.

Question 18

Which immunoglobulin appears first in the
primary immune response?
A. IgG
B. IgM
C. IgA
D. IgE

Answer 18

IgM

The first antibody to appear in the primary immune response to an antigen is IgM. The titer of antiviral IgM (e.g., IgM antibody to cytomegalovirus [anti-CMV]) is more specific for acute or active viral infection than IgG and may be measured to help differentiate active from prior infection.

Question 19

Which immunoglobulin appears in highest titer in the secondary response?
A. IgG
B. IgM
C. IgA
D. IgE

Answer 19

IgG

A high titer of IgG characterizes the secondary
immune response. Consequently, IgG antibodies comprise about 80% of the total immunoglobulin concentration in normal serum.

Question 20

Which immunoglobulin can cross the placenta?
A. IgG
B. IgM
C. IgA
D. IgE

Answer 20

IgG

IgG is the only immunoglobulin class that can cross the placenta. All subclasses of IgG can cross the placenta, but IgG2 crosses more slowly. This process requires recognition of the Fc region of the IgG by placental cells. These cells take up the IgG from the maternal blood and secrete it into the fetal blood, providing humoral immunity to the neonate for the
first few months after delivery.

Question 21

Which immunoglobulin cross links mast cells to release histamine?
A. IgG
B. IgM
C. IgA
D. IgE

Answer 21

IgE

IgE is the immunoglobulin that cross links with
basophils and mast cells. IgE causes the release of such immune response modifiers as histamine and mediates an allergic immune response.

Question 22

All of the following are functions of
immunoglobulins except:
A. Neutralizing toxic substances
B. Facilitating phagocytosis through opsonization
C. Interacting with TC cells to lyse viruses
D. Combining with complement to destroy cellular antigens

Answer 22

Interacting with TC cells to lyse viruses

Cytotoxic T cells lyse virally infected cells directly, without requirement for specific antibody. The TC cell is activated by viral antigen that is associated with MHC class I molecules on the surface of the infected
cell. The activated TC cell secretes several toxins, such as tumor necrosis factor, which destroy the infected cell and virions.

Question 23

Which of the following cell surface molecules is
classified as an MHC class II antigen?
A. HLA-A
B. HLA-B
C. HLA-C
D. HLA-DR

Answer 23

HLA-DR

The MHC region is located on the short arm of
chromosome 6 and codes for antigens expressed on the surface of leukocytes and tissues. The MHC region genes control immune recognition; their products include the antigens that determine transplantation rejection. HLA-DR antigens are expressed on B cells. HLA-DR2, DR3, DR4, and DR5 antigens show linkage with a wide range of autoimmune diseases.

Question 24

Which MHC class of molecule is necessary for
antigen recognition by CD4-positive T cells?
A. Class I
B. Class II
C. Class III
D. No MHC molecule is necessary for antigen
recognition

Answer 24

Class II

Helper T lymphocytes (CD4-positive T cells)
recognize antigens only in the context of a class II molecule. Because class II antigens are expressed on macrophages, monocytes, and B cells, the helper T-cell response is mediated by interaction with processed antigen on the surface of these cells.

Question 25

Which of the following are products of HLA
class III genes?
A. T-cell immune receptors
B. HLA-D antigens on immune cells
C. Complement proteins C2, C4, and Factor B
D. Immunoglobulin VL regions

Answer 25

Complement proteins C2, C4, and Factor B

Complement components C2 and C4 of the classic pathway and Factor B of the alternative pathway are class III molecules. HLA-A, HLA-B, and HLA-C antigens are classified as class I antigens, and HLA-D, HLA-DR, HLA-DQ, and HLA-DP antigens as class II antigens.

Question 26

What molecule on the surface of most T cells
recognizes antigen?
A. IgT, a four-chain molecule that includes the tau heavy chain
B. MHC protein, a two-chain molecule encoded by the HLA region
C. CD3, consisting of six different chains
D. TcR, consisting of two chains, alpha and beta

Answer 26

TcR, consisting of two chains, alpha and beta

T cells have a membrane bound receptor (T-cell receptor or TcR) that is antigen specific. This two-chain molecule consists of a single α-chain, similar to an immunoglobulin light chain, and a single β-chain, similar to an immunoglobulin heavy chain. Some T cells may express a γ-δ receptor instead of the α-β molecule. There is no τ heavy chain. MHC and
CD3 molecules are present on T cells, but they are not the molecules that give antigen specificity to the cell.

Question 27

The T-cell antigen receptor is similar to
immunoglobulin molecules in that it:
A. Remains bound to the cell surface and is never secreted
B. Contains V and C regions on each of its chains
C. Binds complement
D. Can cross the placenta and provide protection to a fetus

Answer 27

Contains V and C regions on each of its chains

The antigen binding regions of both the α- and
β-chains of the T-cell receptor are encoded by
V genes that undergo rearrangement similar to that observed in immunoglobulin genes. The α-chain gene consists of V and J segments, similar to an immunoglobulin light chain. The β-chain consists of V, D, and J segments, similar to an immunoglobulin heavy chain. The α- and β-chains each have a single C-region gene encoding the constant region of the molecule. While answer A is true for T-cell receptors,
it is not true for immunoglobulins that can be cell bound or secreted. Answers C and D are true for certain immunoglobulin heavy-chain isotypes but are not true for the T-cell receptor

Question 28

Toll-like receptors are found on which cells?
A. T cells
B. Dendritic cells
C. B cells
D. Large granular lymphocytes

Answer 28

Dendritic cells

Toll-like receptors (TLR) are the primary antigen recognition protein of the innate immune system. They are found on antigen-presenting cells such as dendritic cells and macrophages. Eleven TLRs have been described. TLRs recognize certain structural
motifs common to infecting organisms. TLR 4, for example, recognizes bacterial lipopolysaccharide (LPS). The name comes from their similarity to the Toll protein in Drosophila.

Question 29

Macrophages produce which of the following
proteins during antigen processing?
A. IL-1 and IL-6
B. γ-Interferon
C. IL-4, IL-5, and IL-10
D. Complement components C1 and C3

Answer 29

IL-1 and IL-6

Interleukin-1 (IL-1) and IL-6 are proinflammatory macrophage-produced cytokines. In addition to their inflammatory properties, they activate T-helper cells during antigen presentation. γ-Interferon, IL-4, 5, and 10 are all produced by T cells. Complement
components are produced by a variety of cells but are not part of the macrophage antigen presentation process.

Question 30

A superantigen, such as toxic shock syndrome
toxin-1 (TSST-1), bypasses the normal antigen
processing stage by binding to and cross linking:
A. A portion of an immunoglobulin molecule and complement component C1
B. Toll-like receptors and an MHC class 1 molecule
C. A portion of an immunoglobulin and a portion of a T-cell receptor
D. A portion of a T-cell receptor and an MHC
class II molecule

Answer 30

A portion of a T-cell receptor and an MHC
class II molecule

A superantigen binds to the V β portion of the T-cell receptor and an MHC class II molecule. This binding can activate T cells without the involvement of an antigen-presenting cell. In some individuals, a single V β protein that recognizes TSST-1 is expressed on up to 10%–20% of T cells. The simultaneous activation of this amount of T cells causes a heavy cytokine release, resulting in the vascular collapse and pathology of toxic shock syndrome.

Question 31

T regulator cells, responsible for controlling
autoimmune antibody production, express which of the following phenotypes?
A. CD3, CD4, CD8
B. CD3, CD8, CD25
C. CD3, CD4, CD25
D. CD8, CD25, CD56

Answer 31

CD3, CD4, CD25

T regulator cells are believed to be the primary
immune suppressor cells and express CD3, CD4, and CD25. CD25 is the interleukin 2 receptor. CD25 may be expressed by activated T cells, but is constitutively expressed by the T-regulator cells. CD25 expression on T-regulator cells occurs in the thymus and is regulated by the FOXP3 protein