Quiz 4 Flashcards
(18 cards)
Your patient is a 13-month-old female with a history of infections and failure to thrive. She has been diagnosed with the rare inherited immunodeficiency disease called “Bare Lymphocyte Syndrome,” whose biochemical basis is the failure of cells to express Class II MHC molecules. This failure is MOST LIKELY to DIRECTLY interfere with
A.killing of bacteria living in macrophage phagolysosomes.
B.killing of virus-infected cells by CTL.
C.phagocytosis of antigen by macrophages.
D.production of cell surface IgM by B cells.
E.secretion of cytokines by monocytes.
Answer Key: A
Feedback:
A: CORRECT – failure to express in class II molecules will prevent the thymic development of CD4+ T cells, a primary function of which is to provide T cell help for the killing of phagocytosed bacteria by macrophages.
B: Incorrect – CTLs are derived from CD8+ T cells, which do not require class II MHC for their development.
C: Incorrect – while the failure to express class II MHC results in a loss of T cell help for the killing of phagocytosed bacteria, the ability of macrophages to phagocytose antigens is not affected.
D: Incorrect - while the failure to express class II MHC results in a loss of T cell help, B cells can produce IgM in the absence of T cell help.
E: Incorrect – secretion of cytokines by monocytes does not require class II MHC molecules.
During a viral infection, which ONE of the following anti-viral soluble mediators is produced first?
A.C3
B.IFN-α/β
C.IL-1 β
D.IL-4
E.MCP-1
Answer Key: B
The combined action of numerous soluble and cell-bound molecules participate in the pathway by which a B cell becomes activated by a foreign protein antigen. The signals generated by these mediators contribute to the secretion of high-affinity antibody of non-IgM isotypes. Of the following molecules, all contribute to B cell activation responses that lead to production of non-IgM isotypes EXCEPT
A.C3d.
B.CD40.
C.Granzyme B.
D.IL-4.
E.MHC class II.
A: Incorrect; C3d is part of the B cell recptor which increases the capcity to bind antigen more avidly
B: Incorrect; CD40 is a co-stimulatory signal for B cells ; promotes growth and isotype swtiching
C:CORRECT; Granzyme B is one of the serine proteases located in the granules of CTLs and NK cells
D: Incorrect; cytokine produced by T cells that plays a role in isotype switiching of B cells to IgE
E: Incorrect; plays critical role in the activation of CD4+ helper T cells which produce the cytokines that regulate isotype class switching.
If an immunoglobulin molecule is found to have one kappa light chain, what can be said about the other light chain?
A.It could be any light chain.
B.It must be a mu chain.
C.It must be a kappa chain
D.It must be a lambda chain.
E.Not enough information is given to make a decision.
Answer Key: C
Feedback:
A: Incorrect – both light chains in an immunoglobulin molecule are the product of the same light chain allele. If one light chain is a product of a kappa light chain gene, the other light chain must also be a kappa chain produced by the same gene.
B: Incorrect – the term mu chain applies only to immunoglobulin heavy chains and not to light chains.
C: CORRECT - both light chains in an immunoglobulin molecule are the product of the same light chain allele. If one light chain is a product of a kappa light chain gene, the other light chain must also be a kappa light chain produced by the same gene.
D: Incorrect - both light chains in an immunoglobulin molecule are the product of the same light chain allele. If one light chain is a product of a kappa light chain gene, the other light chain cannot be a lambda chain.
E: Incorrect – since we know one light chain in the molecule is a kappa chain, we can deduce that the other light chain must also be a kappa light chain.
A 10 y.o. male is brought to the clinic because he has developed a cough, sore throat and a fever of 101 F. He has been well and has reached all his developmental milestones until onset of the symptoms 2 days ago. As part of your physical examination, you depress his tongue and shine a light into his throat. The structure that you are most likely to examine first is which of the following?
A.pharyngeal tonsil.
B.cervical lymph node.
C.Peyer’s patch.
D.palatine tonsil.
E.high endothelial venule.
Answer Key: D
Feedback:
Correct ans. D.
Explanation -the pharyngeal tonsil is located above and behind the soft palate in the nasal passages and would not be immediately visible; cervical lymph nodes are deeper structures and are not visible on the surface of the oral cavity. Peyer’s patch is an intestinal lymphoid structure; high endothelial venules are microscopic vascular structures found in secondary lymphoid parafollicular regions that are not visible to the naked eye. Palantine tonsils are paired lymphoid structures that are situated on the oropharynx lateral wall. They increase in size until puberty when they start to involute and decrease in size. At their maximum size they are about 2 cm long and 1 cm wide and should be visible upon examination.
An 8-year-old male presents with symptoms consistent with a diagnosis of chicken pox. The characteristic blisters of chicken pox are caused by viral infection of skin cells. All of the following molecules or cellular components are expressed by virus-infected skin cells and participate in T cell recognition and elimination of virally-infected skin cells EXCEPT
A.β2-microglobulin.
B.the endoplasmic reticulum.
C.the invariant chain.
D.the proteasome.
E.the TAP-1/TAP-2 complex.
A: Incorrect; β2-microglobulin is a component of the class I MHC molecule and is therefore required for CD8+ T cell recognition and killing of virus-infected cells
B: Incorrect; the endoplasmic reticulum is the cellular compartment where class I MHC molecules are assembled and associate with antigenic peptide. This compartment is thus required for CD8+ T cell recognition and killing of virus-infected cells
C: CORRECT; the invariant chain is a partner of the MHC class II molecule required for assembly in the endoplasmic reticulum. MHC class II is expressed only by professional antigen presenting cells, and not by skin cells. Also, MHC class II is relevant for activation of CD4+ T cells, and not for activation of CD8+ T cells.
D: Incorrect; the proteasome is responsible for processing cytoplasmic proteins into the peptides that are loaded into class I MHC molecules. It is therefore required for CD8+ T cell recognition and killing of virus-infected cells
E: Incorrect; the TAP-1/TAP-2 complex is responsible for pumping antigenic peptides from the cytoplasm to the endoplasmic reticulum, where they are loaded into MHC class I molecules, and is therefore required for CD8+ T cell recognition and killing of virus-infected cells
A 4-year-old child who has had repeated infections with staphylococci and streptococci (both bacteria that colonize extracellular spaces), has normal phagocytic function and delayed-type hypersensitivity (DTH) responses. A lymph node biopsy would MOST LIKELY reveal an absence of
A.CD8+ T cells.
B.germinal centers.
C.macrophages.
D.paracortical areas.
E.postcapillary venules.
A: Incorrect; since the DTH responses are normal, there is no evidence of a T- cell defect
B: CORRECT; germinal centers are the location of B celles and antibody production and staph and strep are extracellular pathogens (which favors a humoral response)
C: Incorrect; phagocytic function in the child is normal and macrophages are a major phagocytic cell
D: Incorrect; the paracortex is the area within the secondary lymphoid organs where T cells reside and since the DTH responses are normal, there is no evidence of a T- cell defect.
E: Incorrect; venules located in lymphoid tissue; these are the site of recirculation of lymphocytes from the blood to the lymphoid tissue; not associated with absence or presence of cells
When the sequences of different MHC class I molecules are compared, the variation between molecules is concentrated within which ONE of the following?
A.Areas of the molecule that bind CD4 and CD8
B.Areas of the molecule that bind to the TCR and the antigenic peptide
C.β2-microglobulin
D.Cytoplasmic domains of the molecule
E.Transmembrane domains of the molecule
Answer Key: B
Feedback:
A: Incorrect; MHC class I molecules don’t bind CD4. The α3 domain of MHC class I molecule binds CD8 which is invariant among MHC molecules
B: CORRECT; these areas vary among different Class I alleles and allow expression of different peptides within the groove of the Class I molecule
C: Incorrect; β-2 microglobulin is not associated with the binding site on Class I molecules and is encoded on a different chromosome
D: Incorrect; variability among Class I molecules is associated with expression of the α 1 and α2 domains of the α chain of the Class I molecule on the cell surface of the antigen presenting cell
E: Incorrect; variability among Class I molecules is associated with expression of the α 1 and α2 domains of the α chain of the Class I molecule on the cell surface of the antigen presenting cell
Cytolytic T lymphocytes kill their target cells by secretion of
A.antibodies and complement.
B.complement and acute-phase proteins.
C.Fas and Fas ligand.
D.pore-forming proteins and proteases.
E.soluble T cell receptors.
A: Incorrect – cytolytic T cells do not secrete antibodies or complement.
B: Incorrect – cytolytic T cells do not secrete complement or acute phase proteins.
C: Incorrect – Fas ligand is expressed on the surface of cytolytic T cells but is not secreted.
D: CORRECT – pore-forming proteins such as perforins are secreted by the cytolytic T cell and create pores in the membranes of target cells. Proteases such as granzymes are secreted by cytolytic T cells and enter target cells via the perforin-induced pores, causing target cell death.
E: Incorrect – T cell receptors are retained in membrane-bound form on the cell surface and are not secreted.
An individual with a defect in CTLA-4 will be MOST LIKELY to have which ONE of the following?
A.Defective B cell activation
B.Defective neutrophil rolling and extravasation
C.Generalized immunodeficiency
D.Lymphoproliferative disease
E.Recurrent infections
Answer Key: D
Feedback:
A: Incorrect – CTLA-4 is not required for B cell activation.
B: Incorrect – CTLA-4 is not required for neutrophil rolling and extravasation.
C: Incorrect – There are many immune mechanisms that function independently of CTLA-4.
D: CORRECT – CTLA-4 is an important (down) regulator of T cell responses. A deficiency in CTLA-4 is therefore likely to lead to excessive lymphocyte proliferation.
E: Incorrect – Immune responses to many pathogens are not dependent on CTLA-4.
In the diagram above, the region within the square, one is most likely to find which of the following?
A.B cells interacting with Langerhans cells
B.developing T cells interacting cortical epithelioreticular cells.
C.developing T cells interacting with M cells of the lymphoepithelium.
D.mature plasma cells
E.High endothelial venules.
B. this is the cortex of the thymus where T Cells develop.
In an antibody-producing B cell, one heavy chain Ig allele has undergone recombination, while the other has a germline configuration. This is evidence that
A.a similar pattern will occur in light chain genes.
B.during development the initial rearrangement was productive.
C.during development the pre-B receptor was not expressed.
D.more than one allele may be expressed.
E.the B cell may make a different antibody later.
nswer Key: B
Feedback:
A: Incorrect; light chain genes re-arrange after a productive re-arrangement of a heavy chain allele ; re-arrangement of one of the light chains may or may not be productive
B: CORRECT; if the first heavy chain re-arrangement had not been productive then re-arrangement would have been initiated in the second heavy chain allele and neither of the Ig alleles would be in germline configuration
C: Incorrect; expression of the pre-B receptor occurs before re-arrangement of the heavy chain alleles during development
D: Incorrect; re-arrangement occurs in a tightly regulated stepwise manner; if re-arrangement on the first heavy chain was not productive, only then is re-arrangement on the second allele initiated
E: Incorrect: ; antibody specificity is encoded in the VJ and VDJ segments of the Ig genes and specificity is determined before heavy chain re-arrangement begins
The T cell and B cell antigen-specific receptors are similar in that they both
A.are bivalent, with two antigen combining sites.
B.are secreted and reach high circulating levels.
C.have constant region genes that undergo class switching.
D.have V regions resulting from VDJ gene arrangements.
E.recognize soluble native antigen.
Answer Key: D
Feedback:
A: Incorrect – the T cell antigen receptor is monovalent.
B: Incorrect – the T cell receptor is not secreted.
C: Incorrect – class switching is only a property of the B cell receptor/immunoglobulin heavy chain genes.
D: CORRECT – both T and B cell receptors have variable regions that are formed by rearrangement of V, D and J gene segments.
E: Incorrect – T cell receptors do not recognize soluble native antigens.
C3b and IgG cooperatively facilitate which of the following?
A.antibody-dependent cell-mediated cytotoxicity.
B.antigen-specific recognition.
C.chemotaxis.
D.cytokine secretion.
E.phagocytosis.
Answer Key: E
Feedback:
A: incorrect; ADCC is mediated by IgG (not complement)
B: incorrect; antigen-specific recognition is mediated by IgG (not complement)
C: incorrect; chemotaxis is mediated by chemokines (not IgG or complement)
D: incorrect; cytokine secretion is mediated by leukocytes (not IgG or complement)
E: correct; C3b and IgG together are opsonins, mediating phagocytosis of antigens
Patient X is a 7-year-old female with a history of recurrent infections. In the course of your extensive evaluation of Patient X, you perform a fluorescence-activated cell sorting (FACS) analysis on peripheral blood from this patient and a normal control, using two antibodies: FITC- anti-T cell receptor (TCR) and PE-anti-CD4. Note that FITC and PE are two distinct fluorescent molecules that can be discriminated by FACS analysis.
Based on your conclusions about what is wrong with this patient, she will be MOST vulnerable to which agent or class of pathogen?
A.Encapsulated bacterium (extracellular)
B.Non-encapsulated bacterium (extracellular)
C.Parasitic worm
D.Superantigen
E.Virus
Answer Key: E
Feedback:
A: Incorrect; the FACS data shows that the patient lacks T cells that do not express CD4 (i.e., CD8+ T cells). Patients without CD8+ T cells are most vulnerable to viral infections
B: Incorrect; the FACS data shows that the patient lacks T cells that do not express CD4 (i.e., CD8+ T cells). Patients without CD8+ T cells are most vulnerable to viral infections
C: Incorrect; the FACS data shows that the patient lacks T cells that do not express CD4 (i.e., CD8+ T cells). Patients without CD8+ T cells are most vulnerable to viral infections
D: Incorrect; the FACS data shows that the patient lacks T cells that do not express CD4 (i.e., CD8+ T cells). Patients without CD8+ T cells are most vulnerable to viral infections
E: CORRECT; the FACS data shows that the patient lacks T cells that do not express CD4 (i.e., CD8+ T cells). Patients without CD8+ T cells are most vulnerable to viral infections
An investigator injects an experimental animal with a newly discovered bacterial strain to evaluate T lymphocyte activation. Macrophages engulf these organisms and bacterial-derived peptides are presented to CD4+ T lymphocytes. Which ONE of the following cell-surface molecules on the macrophage is MOST DIRECTLY involved in the presentation of the processed peptides?
A.CD28
B.Class II MHC
C.Fc receptor
D.Interleukin-2 (IL-2) receptor
E.Membrane immunoglobulin
Answer Key: B
Feedback:
A: Incorrect – CD28 is expressed by T cells.
B: CORRECT – bacterium-derived peptides are presented to T cells by their insertion into the peptide-binding grooves of class II MHC molecules, which are then expressed on the surface of the macrophage.
C: Incorrect – Fc receptors participate in the binding of immunoglobulin molecules.
D: Incorrect – IL-2 receptor is not expressed by macrophages.
E: Incorrect – macrophages do not express membrane immunoglobulin.
A formula-fed, 1-month-old boy is exposed to his sister who has chickenpox, which is caused by the varicella zoster virus (VZV). He does not develop any clinical signs of VZV infection. His mother had the infection 15 years ago. The boy has MOST LIKELY been protected from developing chickenpox by
A.CD8+ T cells.
B.IgG.
C.IgM.
D.Neutrophils.
E.TNF-α.
Answer Key: B
Feedback:
A: Incorrect; CD8+ T cells cannot cross the placenta from mother to fetus; the infant would not have VZV-specific memory CD8+ T cells at the time of infection.
B:CORRECT; IgG crosses the placenta from mother to fetus and is stable in the circulation for several months after birth. If the mother previously had chickenpox (or the vaccine), some of her IgG would be specific for VZV, neutralizing the virus in the infant.
C: Incorrect; IgM cannot cross the placenta from mother to fetus, and the infant would have VZV-specific IgM-secreting B cells at the time of infection.
D: Incorrect; neutrophils do not play a major role in anti-viral immunity
E: Incorrect; TNFa does not provide sterilizing anti-viral immunity
In a secondary immune response, the affinity of the antibody is higher than in the primary response, which preceded it. Which process makes the largest contribution to this increased affinity?
A.Differentiation of B cells into plasma cells
B.Loss of IgD production
C.Replacement of IgM by IgG
D.Repression of RAG-1 and RAG-2 activity
E.Somatic mutation of immunoglobulin variable region DNA
Answer Key: E
Feedback:
A: Incorrect – plasma cell differentiation is not unique to secondary immune responses.
B: Incorrect – loss of IgD expression occurs as B cells undergo isotype switching, but this does not affect the antigen-binding specificity of the antibody produced.
C: Incorrect – the isotype of the antibody produced does not directly affect the antigen specificity of the antibody.
D: Incorrect –V(D)J recombinase activity does not affect the antigen specificity of antibodies made in secondary immune responses.
E: CORRECT – somatic hypermutation of immunoglobulin variable region DNA during primary responses allows for the refinement of antibody affinity, so that higher affinity antibodies are produced quickly upon induction of a secondary immune response.
