Exam 2: Practice Set 1 Flashcards
Epitope-specific receptors of T lymphocytes are found
A. as either cytosolic or membrane-bound proteins.
B. in blood plasma, lymph, and other secretory fluids.
C. on the surface of plasma cells.
D. as transmembrane polypeptides.
E. in the nuclear lipid bilayer.
The answer is D.
The epitope specific TCRs are displayed as membrane-bound molecules on their cell surfaces. TCRs are not found as soluble molecules. Epitope-specific molecules produced by plasma cells are genetically distinct from T cell receptor molecules.
Antibodies (immunoglobulins)
A. are synthesized and secreted by both B and T cells.
B. bind to several different epitopes simultaneously.
C. contain four different light chain polypeptides.
D. recognize specific epitopes together with self-molecules.
E. tag antigens for destruction and removal.
The answer is E.
Antibodies bind to epitopes on antigens to identify them or tag them for destruction by other elements of the immune system. They are synthesized only by B cells and plasma cells. An antibody molecule contains two (lgD, lgG, lgE, and serum lgA), four (secretory lgA), or ten (secreted lgM) identical epitope-binding sites. An antibody monomer contains two identical light chains and two identical heavy chains. Self-recognition is not required for antibody molecules.
The constant regions of the five major types of heavy chains of immunoglobulin molecules dictate the molecule's A. epitope. B. Fab fragment. C. isotype. D. tyrosine activation motif. E. variable domain.
The answer is C.
The heavy chain constant regions determine immunoglobulin isotypes: mu (, lgM), delta (, lgD), gamma (, lgG), epsilon (, lgE), and alpha (, lgA). ab fragments are enzymatic cleavage products of immunoglobulin monomers. Immuno-receptor tyrosine activation motifs are not present on immunoglobulin molecules. Variable domains show extensive amino acid sequence variability among immunoglobulins, even within the same isotype.
When an immunoglobulin molecule is subjected to cleavage by pepsin, the product(s)
A. are individual heavy and light chains.
B. can no longer bind to antigen.
C. consist of two separated antigen-binding fragments.
D. crystallize during storage in the cold.
E. is a dimeric antigen-binding molecule.
The answer is E.
Enzymatic cleavage of the immunoglobulin monomer by pepsin occurs distal to the variable domain and distal to heavy-heavy chain disulfide bonds, which remain intact resulting in a molecule with two epitope-binding sites. lnterchain disulfide bonds are unaffected by pep- sin cleavage. The epitope-binding site remains intact on pepsin cleavage of the heavy chain. Papain cleavage of the immunoglobulin monomer occurs distal to the variable domain but proximal to the heavy-heavy chain disulfide bond, resulting in two separate epitope-binding ab fragments. Pepsin enzymatically degrades the CH2 portion of the immunoglobulin molecule resulting in fragments that rarely, if ever, form crystals.
In humans, MHC class II molecules are expressed by
A. all nucleated cells.
B. B cells, dendritic cells, and macrophages.
C. erythrocytes.
D. mast cells.
E. naïve T cells.
The answer is B. B cells, dendritic cells, monocytes, and macrophages constitutively express MHC class II molecules. Only professional APCs expresses MHC class II molecules and it does not include mast cells or naive T cells. Erythrocytes do not express MHC class II molecules.
The basic structure of a T cell receptor consists of
A. a membrane-bound α/β or γ/δ heterodimer.
B. a complex of disulfide-linked heavy and light chains.
C. covalently linked CD3 and CD247 molecules.
D. peptide-MHC complexes.
E. soluble antigen-binding homodimers.
The answer is A.
The T-cell receptor (TCR) is a heterodimer composed of α/β or γ/δ polypeptide chains. Neither the α/β or γ/δ heterodimers nor their associated molecules (CD3 and CD247) are linked by disulfide bonds. TCR recognize peptide-MHC complexes on APCs. TCRs are found only on the surfaces of T cells and are not soluble.
Migration of a B lymphocyte to specific sites (such as a lymph node) is dependent in part on the use of A. antibodies. B. CD8. C. CD3. D. complement. E. selectins.
The correct answer is E.
Selectins are adhesion molecules that participate in the recognition that occurs between different types of cells and tissues. Antibodies do not serve as guides for such homing. CD8 and CD3 are expressed on T cells, not on B cells, and are responsible for lymphocyte homing. Complement fragments may be chemoattractants for leukocytes, but they attract those cells to the site of immune responses rather than to specific organs.
Which of the following molecules is expressed by a mature T cell that functions as a helper T cell? A. CD4 B. CD8 C. GlyCAM-1 D. lgA E. lgG
The correct answer is A.
CD4+ T cells are also called T-helper cells. CD8+ T cells have cytotoxic or suppressive functions. GlyCAM-1 is an adhesion molecule found on certain vascular epithelial cells within lymph nodes. lgA and lgG are not expressed on T cells.
Following cytokine binding to a specific cell-surface receptor, a lymphocyte is stimulated to undergo signaling via the JAK-STAT pathway. In this pathway, which of the following will be induced to translocate to the cell's nucleus to regulate transcription? A. JAK B. Ras C. SH2-containing adapter proteins D. STAT dimers E. tyrosine kinase
The correct answer is D.
STAT dimers translocate into the nucleus. JAKs are cytosolic tyrosine kinases that bind to the intracellular domain of the tyrosine-phosphorylated receptor and never enter the nucleus. Ras is a membrane-bound GTP binding protein that is bound by cytosolic proteins with SH2 domains that also bind to phosphotyrosine residues within the intracellular portion of the receptor. Catalytic receptors signal by stimulating tyrosine kinase, either of the receptor itself (intrinsic activity) or by associating with nonreceptor tyrosine kinases (e.g., JAK), neither of which enters the nucleus.
B lymphocytes synthesize and express immunoglobulin
A. containing multiple epitope specificities.
B. in cytoplasmic phagosomes.
C. in membrane complexes also containing CD3.
D. on their cell membrane surface.
E. only after leaving the bone marrow.
The correct answer is D.
B cells synthesize and express immunoglobulin on their cell surfaces. Immunoglobulins within an individual B cell contain specificity for one epitope, not several. Cytoplasmic phagosomes are involved in degradation of unwanted materials. Membrane complexes also containing CD3 are T-cell receptors (TCR) on the surfaces of T cells. B cells express surface lgM/IgD before leaving the bone marrow.
Which of the following molecules is expressed on the surface of mature CD4+ T cells? A. BCRs B. CD1d C. CD3 D. CD8 E. CD19
The correct answer is C. Mature T cells (both CD4+ and CD8+) express CD3, a molecular complex associated with the TCR. CD4+ cells are T cells with T helper function and do not express B-cell receptors. CD1d is a specialized, non-classical MHC class I molecule on NKT cells. CD8 is a molecule expressed by T cytotoxic and suppressor cells. CD19 is expressed on B cells.
Positive selection refers to
A. the ability of single positive cells to bind both MHC class I and II.
B. cortical thymocytes’ acquisition of TCR.
C. migration of stem cells to the thymus to become T cells.
D. programmed cell death of single positive T cells.
E. recognition of MHC by CD4+CD8+ thymocytes.
The correct answer is E. Positive selection refers to recognition of MHC class I (by CD8) or MHC class II (by CD4) by double-positive (CD4+CD8+) thymocytes. Single positive thymocytes (and T cells) are either CD4+ or CD8+ and recognize either MHC class II (CD4) or MHC class I (CD8), but not both. Cortical thymocytes acquire a nascent TCR as well as CD4 and CD8 surface molecules, resulting in formation of double-positive (CD4+CD8+) thymocytes. Precursor T cells migrate or traffic from the bone marrow to the thymus before acquiring CD4 and CD8, which they will do as cortical thymocytes. Cells that fail to complete positive selection undergo programmed cell death (apoptosis).
The white pulp of the spleen is enriched in
A. erythrocytes carrying hemoglobin.
B. CD4+CD8+ T cells binding to MHC.
C. NK cells recognizing targets.
D. plasma cells secreting immunoglobulin.
E. precursor cells developing into mature B cells.
The correct answer is D.
The white pulp of the spleen is enriched in plasma cells secreting immunoglobulin, in addition to B and T lymphocytes. Erythrocytes are found within the red pulp of the spleen. CD4+CD8+ T cells are found in the thymus. Natural killer cells function within peripheral blood. Precursors of B cells are located in the bone marrow.
A 2-year-old child exposed to an antigen for the first time already possesses a B cell with immunoglobulin specific for that antigen. This finding is best explained by
A. antigen-independent immunoglobulin gene rearrangements.
B. antigen stimulation of T cell cytokine production.
C. maternally derived antibodies to that antigen.
D. memory B cells that recognize the antigen.
E. somatic hypermutation of immunoglobulins.
The answer is A.
Determination of antibody specificity occurs prior to and independent from an individual’s first encounter with antigen. This process begins developmentally during prenatal and neonatal life. This process is independent of soluble factors (cytokines) produced by T cells and occurs independently of maternal immune function. By definition, memory B cells have previously encountered antigen. Somatic hypermutation occurs only after previous exposure to antigen.
Serum immunoglobulins containing both maternally and paternally derived Vκ light chains are found within an individual. A given B cell, however, expresses only maternally derived or paternally derived Vκ chains but never both. This finding is the result of A. allelic exclusion. B. antibody diversity. C. isotype switching. D. junctional diversity. E. random VD and VDJ joining.
The answer is A.
A given B cell or plasma cell expresses a single maternal or paternal allele of a chromosome pair. This process, known as allelic exclusion, applies to both heavy and light chain genes. An additional exclusion allows for the expression of only a κ (chromosome 2) or λ (chromosome 22) gene, never both within the same cell. Allelic exclusion has only a slight impact on genetic variation. lsotype switching, junctional diversity, and random V(D)J joining occur after allelic exclusion.
