Medical Laboratory Science Review Harr. - 3 Immunology 1

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

A 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

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

A 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.

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

A 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.

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

A 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

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

A 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

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

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

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

A. IgG A 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.

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

B 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.

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

B 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.

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

B 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.

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

B 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.

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

B 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

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

B 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.

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

B 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.

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

B. CD2 B 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)

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

B. Contains V and C regions on each of its chains B 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.

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

B. Thymus and bone marrow B 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.

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

C 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.

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

C 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.

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

C 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.

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

C 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.

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

C 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.

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

C 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.

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

C. T cytotoxic C 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.

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

D 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.

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

D 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.

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

D 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.

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

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

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

D 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

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

D 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.

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

D. Immunoglobulin D 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.