Exam 2 Flashcards
Microbial protein antigens are mainly captured by __1__ cells and concentrated in __2__, where immune responses are initiated.
- Dendritic
- Lymph nodes
__1__ are membrane proteins on Antigen Presenting Cells that display peptide antigens for recognition by CD8+ 1/1 T lymphocytes.
MHC Class I Molecules
A helper T cell response to a protein antigen requires the participation of antigen-presenting cells that express which of the following types of molecules?
Class II MHC and costimulators
A young adult is exposed to a virus that infects and replicates in mucosal epithelial cells of the upper respiratory tract. Cytotoxic T lymphocytes (CTLs) are mobilized to combat this infection because:
Mucosal epithelial cells express class I MHC molecules and are able to process cytoplasmic viral proteins and display complexes of class I MHC and bound viral peptides on their cell surfaces.
Name a type of antigen recognized by antibodies that is not recognized by T cell receptors.__1__
bacterial polysaccharide
Name a type of antigen recognized by T cell receptors?__1__
Peptide fragments (ex: viral peptide fragment)
What mechanism contributes the most to the diversity of antibody molecules?
Addition and deletion of nucleotides during joining of V, D, and J gene segments
Reading left to right, what is the order of events during T lymphocyte maturation leading to development of a mature CD4+ T cell?
double-negative T cell, pre-TCR expression, double-positive T cell, complete TCR expression, weak recognition of class II MHC plus bound peptide
Which of the following best describes a condition that leads to negative selection during T-cell development in the thymus?
cell strongly recognizes a peptide bound to a MHC molecule
After 2 years of hard work, a graduate student finally succeeds in creating a gene knockout mouse lacking CD4. The student is particularly careful to keep this mouse line in a microbe-free animal facility because these mice are
expected to show:
Impaired ability to produce antibodies and activate macrophages
What is the most important costimulator for naïve T cell activation?
B7 ligand
What signal would stimulate a dendritic cell to produce B7 molecules?
> B: peptidoglycan binding TLR
What cytokine is the principal growth factor for T cells? __1__
IL-2
What additional mechanism is required for a CD4+ effector T cell bound to an MHC class II molecule plus antigen on a macrophage to activate the macrophage killing functions?
> D: CD40 ligand on T cell binding to CD40 on macrophage
16 What is NOT a property of memory T lymphocytes elicited in response to a particular microbe?
> C: Restricted to residing in lymphoid organs
What mechanism draws naive T cells out of lymph nodes if they do not recognize an antigen in the lymph node?
> D: Increased expression of S1P receptor by naïve T cells in the lymph node
What is a key property of the Th2 subset of CD4 + effector T cells?
> D: main defense role is fighting helminths
What types of pathogens are the main target of the Th-17 subset of CD4 + effector T cells?
> D: extracellular bacteria and fungi
Granzyme B and Perforin delivery to target cells across an immune synapse is the effector mechanism of what specific immune system cell type?
> A: CD8+ CTL
21 What pathogens evade cell-mediated immunity by inhibiting phagosomal-lysosomal fusion? __1__ 0/1
Mycobacteria
22 Which one of the following statements about humoral immune responses is true? 1/1
Naive B cells are required for initiation of primary responses and memory B cells are required for initiation of secondary responses.
23 Which of the following statements about induction or maintenance of T cell tolerance is NOT true? 1/1
Peripheral T cell tolerance to an antigen may be induced by persistent and repeated stimulation of lymphocytes by that antigen in tissues.
Which type of hypersensitivity disease is caused by deposition of antigen-antibody complexes in blood vessel walls?
Type III
Failure of self-tolerance is the cause of which one of the following types of diseases?
Autoimmunity
Immunologic tolerance is defined as:
> C: Unresponsiveness of the immune system to self antigens
Which of the following anatomic regions is normally protected from pathogens only by humoral immune responses and not by cell-mediated immune responses?
> B: Intestinal lumen
Treatment of antibodies with the enzyme papain under conditions of limited proteolysis results in hinge-region 1/1 cleavage, yielding monovalent antigen-binding Fab fragments that lack a constant region. Which effector function
of antibodies would Fab fragments be able to perform?
> E: Microbe neutralization
Which of the following events does NOT occur within germinal centers?
> E: Ig gene V(D)J recombination
Which of the following statements about Ig isotype switching is NOT true?
> D: Isotype switching only occurs in activated T cells.
Which one of the following statements about primary and secondary antibody responses is NOT true?
> E: Primary responses are characterized by IgG antibodies, whereas secondary responses are dominated by IgM antibodies.
32 __1__ is the enhancement of phagocytosis by binding of IgG-coated microbes to Fc receptors on phagocytes. 1/1
Opsonization
Which of the following is best associated with the viridans Streptococci?
> C: dental caries
Name a population group we discussed in class that is particularly susceptible to meningitis and pneumonia due to infections by Streptococcus agalactiae.__1__
Infantss
Name a property of Streptococcus pyogenes M protein.__1__
Binds to keratinocytes
Over 90% of Staphylococcus aureus strains are resistant to what antibiotic?__1__
Penicillin
What bacterial virulence factor reduces phagocyte killing by converting hydrogen peroxide to water and oxygen?
Catalase
What organism causes food poisoning due to superantigen toxins?
staphylococcus
Give 2 examples of adhesins from Gram positive bacteria that promote attachment to other cells. __1____2__
Answer 1: fibronectin binding protein (assists with bacterial attachment to host cells) Answer 2: Srap protein (assits with bacterial aggregation in endocarditis)
Give an example of a bacterial exotoxin that acts outside a host cell to help microbes spread through tissue. __1__
Collagenase
What is NOT true about the ADP ribosylation function of some A-B toxins?
> D: ADP ribosylation inactivates a target protein of the bacterial pathogen
Which of the following is a function of lipopolysaccharide (LPS) on bacterial cells?
> C: blocks access of the membrane attack complex to the bacterial plasma membrane
Which of the following is not a mechanism used by bacteria to survive inside phagocytes?
> E: increasing cAMP levels in the extracellular environment
Which one of the following statements about dendritic cells is true?
> A: Immature dendritic cells are ubiquitously present in skin and mucosal tissues.
Which of the following is the main criterion that determines whether a protein is processed and presented via the class I MHC pathway in an antigen-presenting cell (APC)?
> C: Present in the cytosol of the APC
Which one of the following statements about T cell tolerance to self proteins is accurate?
Self peptide/self MHC complexes are formed and displayed by antigen-presenting cells in both class I and class II MHC pathways, but T cells that recognize these complexes usually are not present or are functionally inactive.
Most T lymphocytes have a dual specificity for which one of the following pairs of molecules (i.e. the T lymphocytes recognize both molecules of the pair)?
> A: A particular allelic form of a major histocompatibility complex (MHC) molecule and a peptide bound to the MHC molecule
A healthy 45-year-old child-care worker becomes infected with a virus and develops a sore throat, cough, and fever. Infected cells in the bronchial mucosa of this patient process virus-encoded proteins through an intracellular pathway and display peptides derived from the protein on the cell surface bound to class I MHC molecules. CD8 T cells migrate to the mucosa and recognize these peptide-MHC complexes. Which of the following components of the TCR actually bind to the viral peptide-MHC complex?
> B: Complementarity-determining regions: 3 in the alpha chain, 3 in the beta chain
The T cell receptor (TCR) complex differs from an immunoglobulin molecule in which one of the following ways?
> A: On average, a TCR binds antigen with much lower affinity than does an Ig molecule.
Both CD28 and CTLA-4 are receptors on T cells that are critical for regulating T cell activation. In which one of the following ways does CD28 differ from CTLA-4?
> C: CD28 is constitutively expressed on naive T cells, whereas CTLA-4 is expressed on activated T cells.
All of the following protein-protein interactions are involved in activation of naive helper T cells by antigen- presenting cells (APCs) EXCEPT:
> D: Binding of CD40L on the T cell with CD40 on the APC
Which one of the following descriptions of cytokine interleukin-2 (IL-2) is NOT true?
> D: It is only involved in the proliferation of helper T cells and not CTLs.
What type of molecule on antigen-presenting cells (APCs) binds to CD28 on naive T cells in a co-stimulatory role for T cell activation?
B7
Increased expression of what cell surface molecule on naive T cells contributes to migration of the cells to lymph no
CCR-7
Activated macrophages perform all of the following functions EXCEPT:
> A: Reduce expression of MHC molecules
Which pair of molecules is a component of cytolytic T lymphocyte (CTL) granules and is important in the mechanism of CTL killing of target cells?
> E: Perforin and granzyme B
Which subset of CD4+ helper T lymphocytes activate eosinophils?
Th2
Which subset of CD4+ helper T lymphocytes activate macrophages to kill phagocytosed microbes?
Th1
Which one of the following statements about primary and secondary antibody responses is NOT true?
> A: Antibodies in primary responses generally have higher affinity for antigen than those produced in secondary responses.
Which one of the following statements about humoral immune responses is true?
Naive B cells are required for initiation of primary responses and memory B cells are required for initiation of secondary responses.
Which of the following events does NOT occur within germinal centers?
> E: Ig gene V(D)J recombination
Which of the following statements about Ig isotype switching is true?
> D: Isotype switching only occurs in activated B cells.
In 1890, Emil von Behring and Shibasaburo Kitasato demonstrated the efficacy of serum transfer at conferring infection resistance a process now known as passive immunity. The researchers isolated serum from animals that had recovered from infection with the diphtheria bacilli and subsequently injected the serum into other healthy animals. This procedure conferred specific resistance against the pathologic effects of diphtheria infection in the recipient animals. Which of the following immune phenomena were primarily responsible for these effects?
> C: Diphtheria-specific antibodies in the transferred serum neutralized bacillus toxins and promoted bacterial elimination by innate effector cells.
Most effective vaccines that are currently in widespread use are specific for pathogenic viruses, and the immunity induced by the vaccines is mediated largely by antibodies. Which of the following statements accurately describes the major mechanism by which these vaccine-dependent antibody responses function?
> A: The antibodies bind extracellular viral particles and prevent them from infecting cells.
Which of the following binds to and is readily phagocytosed by mononuclear phagocytes and neutrophils?
> B: Complement protein C3b bound to a bacterium
The classical pathway of the complement system starts with recognition of antigen-engaged antibodies by
> D: complement C1 protein
Unresponsiveness of the immune system to an antigen, which is induced by previous exposure to that antigen is called:
> A: Immunologic tolerance
Central T lymphocyte tolerance
> A: is induced when immature developing T cells in bone marrow or thymus encounter self antigens.
A mechanism of central B lymphocyte tolerance is
> B: receptor editing by expression of a new Ig V light chain
Which of the following is a function of lipopolysaccharide (LPS) on bacterial cells?
> C: blocks access of the membrane attack complex to the bacterial plasma membrane
What virulence factor is expressed on the surface of bacterial cells (EPEC E. coli for example) and mediates bacterial entry into host cells by interacting with a receptor that has been translocated into the host cell?
> B: intimin
Gram-negative bacteria often bind to host cells by
> A: bacterial fimbriae proteins interacting with host cell glycolipids
Gram-positive bacteria often bind to host cells by
> B: binding to host fibronectin
LPS
> C: causes fever in the host organism
Which of the following is NOT an example of a means by which pathogenic bacteria can cause death of human host cells either directly or indirectly?
> D: LPS activiation of the complement system
What is true about the ADP ribosylation function of some A-B toxins?
> E: ADP ribosylation inactivates a target protein of host cells
What is NOT true about the ADP ribosylation function of some A-B toxins?
> D: ADP ribosylation inactivates a target protein of the bacterial pathogen
Reading left to right, what is the order of events during T lymphocyte maturation leading to development of a mature CD4+ T cell?
Double-negative T cell, pre-TCR expression, double-positive T cell, complete TCR expression, weak recognition of class II MHC plus bound peptide
What types of pathogens are the main target of the Th-17 subset of CD4 + effector T cells?
> D: extracellular bacteria and fungi
What is NOT a property of memory T lymphocytes elicited in response to a particular microbe?
> C: Restricted to residing in lymphoid organs
Antigen-presenting cells (APCs) perform which of the following functions in adaptive immune responses?
> C: Display MHC-associated peptides on their cell surfaces for surveillance by T lymphocytes
Which of the following is the main criterion that determines whether a protein is processed and presented via the class I MHC pathway in an antigen-presenting cell (APC)?
> C: Present in the cytosol of the APC
Which one of the following statements about T cell tolerance to self proteins is accurate?
Self peptide/self MHC complexes are formed and displayed by antigen-presenting cells in both class I and class II MHC pathways, but T cells that recognize these complexes usually are not present or are functionally inactive.
Most T lymphocytes have a dual specificity for which one of the following pairs of molecules (i.e. the T lymphocytes recognize both molecules of the pair)?
> A: A particular allelic form of a major histocompatibility complex (MHC) molecule and a peptide bound to the MHC molecule
Both CD28 and CTLA-4 are receptors on T cells that are critical for regulating T cell activation. In which one of the following ways does CD28 differ from CTLA-4?
> C: CD28 is constitutively expressed on naive T cells, whereas CTLA-4 is expressed on activated T cells.
All of the following protein-protein interactions are involved in activation of naive helper T cells by antigen- presenting cells (APCs) EXCEPT:
> D: Binding of CD40L on the T cell with CD40 on the APC
Which one of the following statements about primary and secondary antibody responses is NOT true?
> A: Antibodies in primary responses generally have higher affinity for antigen than those produced in secondary responses.
Which one of the following statements about humoral immune responses is true?
> A: Naive B cells are required for initiation of primary responses and memory B cells are required for initiation of secondary responses.
Which of the following events does NOT occur within germinal centers?
> E: Ig gene V(D)J recombination
Which of the following statements about Ig isotype switching is true?
> D: Isotype switching only occurs in activated B cells.
In 1890, Emil von Behring and Shibasaburo Kitasato demonstrated the efficacy of serum transfer at conferring infection resistance—a process now known as “passive immunity.” The researchers isolated serum from animals that had recovered from infection with the diphtheria bacilli and subsequently injected the serum into other healthy animals. This procedure conferred specific resistance against the pathologic effects of diphtheria infection in the recipient animals. Which of the following immune phenomena were primarily responsible for these effects?
Diphtheria-specific antibodies in the transferred serum neutralized bacillus toxins and promoted bacterial elimination by innate effector cells.
Most effective vaccines that are currently in widespread use are specific for pathogenic viruses, and the immunity induced by the vaccines is mediated largely by antibodies. Which of the following statements accurately describes the major mechanism by which these vaccine-dependent antibody responses function?
> A: The antibodies bind extracellular viral particles and prevent them from infecting cells.
The classical pathway of the complement system starts with recognition of antigen-engaged antibodies by
> D: complement C1 protein
Which of the following best describes a condition that leads to negative selection during T-cell development in the thymus?
> E: cell strongly recognizes a peptide bound to a MHC molecule
17 What is the most important costimulator for naïve T cell activation? 1/1
B7
18 What cytokine is the principal growth factor for T cells? __1__ 1/1
IL-2
19 What additional mechanism is required for a CD4+ effector T cell bound to an MHC class II molecule plus antigen 1/1
> D: CD40 ligand on T cell binding to CD40 on macrophage
What is a key property of the Th2 subset of CD4 + effector T cells?
> D: main defense role is fighting helminths
Granzyme B and Perforin delivery to target cells across an immune synapse is the effector mechanism of what specific immune system cell type?
> A: CD8+ CTL
What pathogens evade cell-mediated immunity by inhibiting phagosomal-lysosomal fusion? __1__
Mycobacterium
23 __1__ is the enhancement of phagocytosis by binding of IgG-coated microbes to Fc receptors on phagocytes. 1/1
Opsonization
24 Immunologic tolerance is defined as: 1/1
> C: Unresponsiveness of the immune system to self antigens
Failure of self-tolerance is the cause of which one of the following types of diseases?
Autoimmunity
Which of the following statements about induction or maintenance of T cell tolerance is NOT true?
> C: Peripheral T cell tolerance results when T cells recognize antigen in the setting of an innate immune response to the antigen.
What role does catalase have for those pathogenic bacteria that express it?
> C: Removes hydrogen peroxide produced by phagocytes
What role does protein A play for Staphylococcus aureus?
> C: competes with neutrophils for binding of Fc part of IgGs
What is false about Staphylococcus aureus ?
> D: is coagulase negative
What bacterial virulence factor has an activity that results in creation of a fibrin coat around bacteria?
coagulase
Scarlet fever is a caused by what organism?
> A: Streptococcus pyogenes
Which of the following lists one or more virulence factors for Streptococcus pneumoniae?
> C: Pneumolysin O and a polysaccharide capsule
What is true about Streptococcus pneumoniae?
> A: is an alpha-hemolytic, encapsulated bacterium
What Streptococcus pyogenes virulence factor binds to keratinocytes, binds to fibrinogen, and also binds to complement factor H?
> C: M protein
Which of the following is associated with Neisseria gonorrhoeae?
> E: infections are frequently asymptomatic
What is true about antigenic variation involving the pilin protein of Neisseria gonorrhoeae?
> C: involves recombination between silent and expressed copies of the pilin gene
37 Which of the following is true about infections by Neisseria meningitidis? 1/1
> E: preventable by vaccination against capsular polysaccharides for some meningiococcal strains
38 What factor is the most important in allowing intravascular survival of Neisseria meningitidis? 1/1
> A: bacterial capsule
39 Bacteroides fragilis is a strict anaerobe but is oxygen resistant because among its other properties it possesses 1/1
> A: superoxide dismutase
40 Which of the following is a feature of infections caused by a breach in the gut wall? 0/1
> E: host production of a thick fibrin capsule at the infection site decreases blood flow into the area
Which of the following is not a mechanism that pathogenic bacteria use to evade host immune system defenses?
> D: stable attachment to the surface of host cells
Which of the following is a function of lipopolysaccharide (LPS) on bacterial cells?
> C: blocks access of the membrane attack complex to the bacterial plasma membrane
What virulence factor is expressed on the surface of bacterial cells (EPEC E. coli for example) and mediates bacterial entry into host cells by interacting with a receptor that has been translocated into the host cell?
Intimin
Gram-negative bacteria often bind to host cells by
> A: bacterial fimbriae proteins interacting with host cell glycolipids
LPS
> C: activates the complement cascade in the host organism
46 Which of the following is NOT an example of a means by which pathogenic bacteria can cause death of human host cells either directly or indirectly?
> D: binding Fc portion of IgG by bacterial surface proteins
What is true about the ADP ribosylation function of some A-B toxins?
> E: ADP ribosylation inactivates a target protein of host cells
Give an example of a bacterial exotoxin that acts outside a host cell to help microbes spread through tissue. __1__
Collagenase
Which one of the following statements about dendritic cells is true?
> A: Immature dendritic cells are ubiquitously present in skin and mucosal tissues.
Which of the following events does NOT occur within germinal centers?
> E: Ig gene V(D)J recombination
Which of the following binds to and is readily phagocytosed by mononuclear phagocytes and neutrophils?
> B: Complement protein C3b bound to a bacterium
What cells do not display MHC-associated peptides on their cell surfaces for surveillance by and activation of a class of T cells?
> C: Bacterial cells
Which of the following statements about the antigen-presenting function of macrophages is correct?
> B: Macrophages become activated by the helper T cells to which they present microbial peptides, and as a result of this activation they become efficient at killing the microbes.
hich of the following is the main criterion that determines whether a protein is processed and presented via the class I MHC pathway in an antigen-presenting cell (APC)?
> C: Present in the cytosol of the APC
Name a type of antigen recognized by antibodies that is also recognized by T cell receptors.__1__
Peptide
A T cell receptor (TCR) differs from a B cell receptor in which one of the following ways?
> A: On average, a B cell receptor binds antigen with much higher affinity than does a TCR.
What mechanism within the germinal center contributes the most to creation of antibody molecules with higher and higher affinity for an antigen?
> B: Addition and deletion of nucleotides during joining of V, D, and J gene segments
Which of the following best describes a condition that leads to positive selection during T-cell development in the thymus?
> B: cell weakly recognizes a peptide bound to a MHC molecule in the thymus
The cytokine IL-2 is the principal growth factor for what type of cells? __1__
T-cells
Which subset of CD4+ helper T lymphocytes activate eosinophils to kill helminths?
Th2
What mechanism do mycobacteria employ to survive within phagocytic cells? __1__
Answer 1: inhibit fusion of phagosomal - lysosomal complex
Which one of the following statements about primary and secondary antibody responses is true?
> B: Secondary responses reach peak levels more quickly than primary responses.
Which one of the following statements about humoral immune responses is true?
> B: Antibody responses to bacterial polymeric antigens (DNA, for example) do not involve CD4+ helper T cells.
Which of the following statements about Ig isotype switching is true?
> B: Isotype switching involves recombination of a V(D)J complex with downstream C region DNA and the deletion of intervening C region DNA.
In 1890, Emil von Behring and Shibasaburo Kitasato demonstrated the efficacy of serum transfer at conferring infection resistance. The researchers isolated serum from animals that had recovered from infection with the diphtheria bacilli and subsequently injected the serum into other healthy animals. This procedure conferred specific resistance against the pathologic effects of diphtheria infection in the recipient animals. What immune phenomenon was primarily responsible for these effects?
Passive immunity
The current SARS-CoV-2 vaccines induce immunity by causing the production of antibodies. Which of the following statements accurately describes the major mechanism by which these vaccine-dependent antibody responses function?
> A: The antibodies bind extracellular viral particles and prevent them from infecting cells.
The classical pathway of the complement system starts with recognition of antigen-engaged antibodies by which complement protein? __1__
Answer 1: C1 complement protein
Failure of self-tolerance is the cause of what type of disease? __1__
Autoimmune diseases
Which of the following statements about induction or maintenance of T cell tolerance is true?
> C: Peripheral T cell tolerance results when T cells recognize antigen without B7-1 or B7-2 mediated costimulation.
What is the most important costimulator for naïve T cell activation?
> B: B7 ligand
What is NOT a property of memory T lymphocytes elicited in response to a particular microbe?
> C: Restricted to residing in lymphoid organs
What mechanism draws naive T cells out of lymph nodes if they do not recognize an antigen in the lymph node?
> D: Increased expression of S1P receptor by naïve T cells in the lymph node
What types of pathogens are the main target of the Th-17 subset of CD4 + effector T cells?
> D: extracellular bacteria and fungi
Immunologic tolerance is defined as:
> C: Unresponsiveness of the immune system to self antigens
Which of the following is not a mechanism used by bacteria to survive inside phagocytes?
> E: increasing cAMP levels in the extracellular environment
Gram-negative bacteria often bind to host cells by
> A: bacterial fimbriae proteins interacting with host cell glycolipids
Which of the following is a mechanism that pathogenic bacteria use to evade host immune system defenses?
> C: addition of sialic acid to LPS
The translocated intimin receptor (TIR) mediates attachment to host cells for which bacterium?
> B: enteropathogenic E. coli (EPEC)
LPS
> C: causes fever in the host organism
Which of the following is NOT an example of a means by which pathogenic bacteria can cause death of human host cells either directly or indirectly?
> D: binding Fc portion of IgG by bacterial surface proteins
What is the effect of collagenases when they are toxins encoded by pathogenic bacteria? __1__
Answer 1: they degrade collagen and allow bacteria to enter host cell or penetrate host tissues
What role does protein A play for Staphylococcus aureus?
> C: competes with neutrophils for binding of Fc part of IgGs
What bacterial virulence factor has an activity that results in creation of a fibrin coat around bacteria?
Coagulase
What is a role that staphylokinase plays for Staphylococcus aureus?
> E: cleaves C3b and IgG
What organism causes scalded skin syndrome?
> B: Staphylococcus aureus
What gram-positive coccus is one of the main causes of hospital acquired infections of the elderly and displays resistance to multiple antibiotics?
> A: Enterococcus faecalis
What is true about rheumatic fever?
> E: causes myocarditis in susceptible individuals
What is true about Streptococcus pneumoniae?
> A: is an alpha-hemolytic, encapsulated bacterium
Which of the following is NOT true regarding Streptococcus pyogenes M protein?
> A: anti-M protein antibodies are not produced during an infection by Streptococcus pyogenes
Neisseria meningitidis
> C: is transmitted by aerosol
Which of the following is true about infections by Neisseria meningitidis?
> E: preventable by vaccination against capsular polysaccharides for some meningiococcal strains
What factor is the most important in allowing intravascular survival of Neisseria meningitidis?
> A: bacterial capsule
Which of the following is a feature of infections caused by a breach in the gut wall?
> C: abscess formation initiates with a mixed population of bacteria spilled into the abdomen
Bacteroides fragilis is a strict anaerobe but is oxygen resistant because among its other properties it possesses
> A: catalase
Antigen-presenting cells (APCs) perform which of the following functions in adaptive immune responses?
> C: Display MHC-associated peptides on their cell surfaces for surveillance by T lymphocytes
Which one of the following statements about dendritic cells is true?
> A: Immature dendritic cells are ubiquitously present in skin and mucosal tissues.
Which one of the following statements about T cell tolerance to self proteins is accurate?
> D: Self peptide/self MHC complexes are formed and displayed by antigen-presenting cells in both class I and class II MHC pathways, but T cells that recognize these complexes usually are not present or are functionally inactive.
Which of the following is the main criterion that determines whether a protein is processed and presented via the class II MHC pathway in an antigen-presenting cell (APC)?
> B: Only present within vesicular compartments of the APC during processing
A young adult is exposed to a virus that infects and replicates in mucosal epithelial cells of the upper respiratory tract. Cytotoxic T lymphocytes (CTLs) are mobilized to combat this infection because:
> B: Mucosal epithelial cells express class I MHC molecules and are able to process cytoplasmic viral proteins and display complexes of class I MHC and bound viral peptides on their cell surfaces.
The T cell receptor (TCR) complex differs from an immunoglobulin molecule in which one of the following ways?
> A: On average, a TCR binds antigen with much lower affinity than does an Ig molecule.
Both CD28 and CTLA-4 are receptors on T cells that are critical for regulating T cell activation. In which one of the following ways does CD28 differ from CTLA-4?
> C: CD28 is constitutively expressed on naive T cells, whereas CTLA-4 is expressed on activated T cells.
Name a type of antigen recognized by antibodies that is also recognized by T cell receptors.__1__
Peptide
Which of the following best describes a condition that leads to negative selection during T-cell development in the thymus?
> E: cell strongly recognizes a peptide bound to a MHC molecule
The cytokine IL-2 is the principal growth factor for what type of cells? __1__
T cells
What signal would stimulate a dendritic cell to produce B7 molecules?
> B: peptidoglycan binding TLR
What additional mechanism is required for a CD4+ effector T cell bound to an MHC class II molecule plus antigen on a macrophage to activate the macrophage killing functions?
> D: CD40 ligand on T cell binding to CD40 on macrophage
What is NOT a property of memory T lymphocytes elicited in response to a particular microbe?
> C: Restricted to residing in lymphoid organs
Activated macrophages perform all of the following functions EXCEPT:
> A: Reduce expression of MHC molecules
Which pair of molecules is a component of cytolytic T lymphocyte (CTL) granules and is important in the mechanism of CTL killing of target cells?
> E: Perforin and granzyme B
Which subset of CD4+ helper T lymphocytes activate macrophages to kill phagocytosed microbes?
> A: Th1
What types of pathogens are the main target of the Th-17 subset of CD4 + effector T cells?
> D: extracellular bacteria and fungi
What pathogens evade cell-mediated immunity by inhibiting phagosomal-lysosomal fusion? __1__
Answer 1: mycobacterium
Which of the following events does NOT occur within germinal centers?
> E: Ig gene V(D)J recombination
Which of the following statements about Ig isotype switching is true?
> D: Isotype switching only occurs in activated B cells.
Which one of the following statements about humoral immune responses is true?
> A: Naive B cells are required for initiation of primary responses and memory B cells are required for initiation of secondary responses.
Which one of the following statements about primary and secondary antibody responses is NOT true?
> E: Primary responses are characterized by IgG antibodies, whereas secondary responses are dominated by IgM antibodies.
Which of the following binds to and is readily phagocytosed by mononuclear phagocytes and neutrophils?
> B: Complement protein C3b bound to a bacterium
The classical pathway of the complement system starts with recognition of antigen-engaged antibodies by
> D: complement C1 protein
__1__ is the enhancement of phagocytosis by binding of IgG-coated microbes to Fc receptors on phagocytes.
Opsonization
Which of the following anatomic regions is normally protected from pathogens only by humoral immune responses and not by cell-mediated immune responses?
> B: Intestinal lumen
Central T lymphocyte tolerance
> A: is induced when immature developing T cells in bone marrow or thymus encounter self antigens.
A mechanism of central B lymphocyte tolerance is
> B: receptor editing by expression of a new Ig V light chain
Immunologic tolerance is defined as:
> C: Unresponsiveness of the immune system to self antigens
Which of the following is not a mechanism that pathogenic bacteria use to evade host immune system defenses?
> D: stable attachment to the surface of host cells
Which of the following is a function of lipopolysaccharide (LPS) on bacterial cells?
> C: blocks access of the membrane attack complex to the bacterial plasma membrane
Give a specific example of a molecule on a human cell that is recognized and bound by SRRPs (serine rich repeat proteins) present on bacterial cell surfaces .
Sialic acid
Fibronectin is a host protein that helps mediate indirect attachment of which bacterium to host cells?
> E: Staphylococcus aureus
Which of the following is NOT an example of a means by which pathogenic bacteria can cause death of human host cells either directly or indirectly?
> D: LPS activiation of the complement system
What is true about the ADP ribosylation function of some A-B toxins?
> E: ADP ribosylation inactivates a target protein of host cells
What is the direct action of lipases, which sometimes are found as toxins encoded by pathogenic bacteria?
Answer 1: to degrade/break down lipids
Which hypersensitivity is caused by immune complexes, composed of circulating antigens and IgM or IgG antibodies, that are deposited in vascular basement membranes?
> C: Type III
Over 90% of Staphylococcus aureus strains are resistant to what antibiotic?__1__
Penicillin
What role does catalase have for those pathogenic bacteria that express it?
> C: Removes hydrogen peroxide produced by phagocytes
What bacterial virulence factor has an activity that results in creation of a fibrin coat around bacteria?
> B: coagulase
What is a role that staphylokinase plays for Staphylococcus aureus?
> E: cleaves C3b and IgG
What genus of gram-positive coccus contains one of the main causes of hospital acquired infections of the elderly and displays resistance to multiple antibiotics?
Answer 1: enterococcus fracilis
Which of the following lists one or more virulence factors for Streptococcus pneumoniae?
> C: Pneumolysin O and a polysaccharide capsule
What is true about Streptococcus pneumoniae?
> A: is an alpha-hemolytic, encapsulated bacterium
What Streptococcus pyogenes virulence factor binds to keratinocytes, binds to fibrinogen, and also binds to complement control proteins?
> C: M protein
Which of the following is associated with Neisseria gonorrhoeae?
> E: infections are frequently asymptomatic
Which of the following is true about infections by Neisseria meningitidis?
> E: preventable by vaccination against capsular polysaccharides for some meningiococcal strains
The bacterial capsule is an important factor for what specific aspect Neisseria meningitidis infections?
> A: intravascular survival
Which of the following is a feature of infections caused by a breach in the gut wall?
> E: host production of a thick fibrin capsule at the infection site decreases blood flow into the area
Bacteroides fragilis is the most frequently isolated bacterium from abscesses caused by intestinal bacteria. This is partly because
> D: its ability to resist phagocytosis
