Q.1 What is an antigen?
A protein that triggers an immune response
A type of antibody
A virus that infects immune cells
A chemical that suppresses immunity
Explanation - Antigens are molecules that elicit an immune response by being recognized as foreign by the immune system.
Correct answer is: A protein that triggers an immune response
Q.2 Which part of an antibody binds to an antigen?
Fc region
Variable region
Heavy chain
Light chain
Explanation - The variable region of an antibody contains the antigen-binding sites.
Correct answer is: Variable region
Q.3 What is the main role of B cells in antibody production?
To destroy pathogens directly
To present antigens to T cells
To differentiate into plasma cells that secrete antibodies
To release cytokines that suppress immunity
Explanation - B cells mature into plasma cells, which produce and release antibodies specific to antigens.
Correct answer is: To differentiate into plasma cells that secrete antibodies
Q.4 Which of the following best describes IgG antibodies?
The most common antibody in blood and extracellular fluid
Only found in mucosal secretions
Can cross the placenta
Has the largest molecular weight of all antibodies
Explanation - IgG is the predominant antibody in circulation, providing long-term protection.
Correct answer is: The most common antibody in blood and extracellular fluid
Q.5 Which technique is commonly used to detect antigens in a sample?
Western blotting
ELISA (Enzyme-Linked Immunosorbent Assay)
PCR (Polymerase Chain Reaction)
Flow cytometry
Explanation - ELISA uses antigen-antibody interactions to detect and quantify specific antigens.
Correct answer is: ELISA (Enzyme-Linked Immunosorbent Assay)
Q.6 What is the primary difference between IgA and IgM antibodies?
IgA is secreted in mucosal areas, IgM is not
IgM forms pentamers, IgA is monomeric
IgA is larger in size than IgM
IgM has a higher affinity for antigens than IgA
Explanation - IgM typically forms pentameric structures for efficient complement activation, while IgA is usually monomeric or dimeric.
Correct answer is: IgM forms pentamers, IgA is monomeric
Q.7 Which of the following is NOT a class of immunoglobulins?
IgD
IgE
IgF
IgA
Explanation - The five classes of human immunoglobulins are IgG, IgA, IgM, IgD, and IgE.
Correct answer is: IgF
Q.8 In ELISA, what role does the enzyme conjugated to the secondary antibody play?
Binds directly to the antigen
Catalyzes a color change that indicates binding
Inhibits non-specific binding
Provides structural support to the assay plate
Explanation - The enzyme linked to the secondary antibody reacts with a substrate to produce a measurable signal.
Correct answer is: Catalyzes a color change that indicates binding
Q.9 Which of the following is a characteristic of a monoclonal antibody?
Produced by multiple B cell clones
Has heterogeneous antigen-binding sites
Derived from a single B cell clone
Contains only light chains
Explanation - Monoclonal antibodies come from one clone, ensuring identical specificity.
Correct answer is: Derived from a single B cell clone
Q.10 Which cytokine is essential for the class-switch recombination of B cells?
Interleukin-2
Interleukin-4
Tumor necrosis factor-alpha
Interferon-gamma
Explanation - IL-4 drives B cells to switch from IgM to IgE or IgG subclasses.
Correct answer is: Interleukin-4
Q.11 What is the primary function of IgE antibodies?
Neutralize bacterial toxins
Activate complement pathway
Facilitate allergic reactions by binding to mast cells
Transport antibodies across the placenta
Explanation - IgE binds to Fc receptors on mast cells, triggering histamine release during allergies.
Correct answer is: Facilitate allergic reactions by binding to mast cells
Q.12 Which assay would you use to quantify the concentration of a specific antigen in a serum sample?
Northern blot
Southern blot
Western blot
Sandwich ELISA
Explanation - Sandwich ELISA captures the antigen between two antibodies, allowing precise quantification.
Correct answer is: Sandwich ELISA
Q.13 Which of the following best describes the term ‘epitope’?
A region of a T cell receptor
The binding site on an antibody
A specific part of an antigen recognized by an antibody
The constant region of an antibody
Explanation - An epitope is the specific antigenic determinant that antibodies bind to.
Correct answer is: A specific part of an antigen recognized by an antibody
Q.14 In the immune response, what is the role of helper T cells?
Directly kill infected cells
Activate B cells and cytotoxic T cells
Produce antibodies
Serve as antigen-presenting cells
Explanation - Helper T cells release cytokines that help B cells produce antibodies and activate cytotoxic T cells.
Correct answer is: Activate B cells and cytotoxic T cells
Q.15 Which immunoglobulin is primarily found in breast milk?
IgG
IgA
IgM
IgE
Explanation - Secretory IgA provides passive immunity to infants via breast milk.
Correct answer is: IgA
Q.16 What is the main advantage of using polyclonal antibodies in diagnostics?
They are specific to a single epitope
They are inexpensive to produce
They recognize multiple epitopes on the same antigen
They have a longer shelf life
Explanation - Polyclonal antibodies are generated from many B cell clones, increasing detection sensitivity.
Correct answer is: They recognize multiple epitopes on the same antigen
Q.17 Which of the following is NOT a mechanism by which antibodies neutralize pathogens?
Blocking receptor binding
Opsonization for phagocytosis
Directly lysing viral particles
Activating complement cascade
Explanation - Antibodies cannot directly lyse viruses; they prevent attachment or mark them for other immune mechanisms.
Correct answer is: Directly lysing viral particles
Q.18 Which method is used to isolate a single B cell clone that produces a desired antibody?
Flow cytometry sorting
Cloning by hybridoma technique
Western blot analysis
PCR amplification
Explanation - The hybridoma method fuses a single B cell with myeloma cells, creating a monoclonal antibody source.
Correct answer is: Cloning by hybridoma technique
Q.19 What does the ‘Fc’ region of an antibody refer to?
The fragment crystallizable region
The fragment variable region
The constant region that binds antigens
The fragment that binds Fc receptors
Explanation - Fc is the constant tail region of an antibody that interacts with cell receptors and complement.
Correct answer is: The fragment crystallizable region
Q.20 Which antibody subclass is most abundant in the serum?
IgG1
IgG2
IgG3
IgG4
Explanation - IgG1 constitutes roughly 60–70% of total IgG in human serum.
Correct answer is: IgG1
Q.21 A patient shows high levels of IgM but normal IgG after infection. What does this indicate?
Acute phase of the infection
Late chronic infection
Vaccine failure
Autoimmune disorder
Explanation - IgM rises early in infection; IgG appears later; high IgM suggests a recent or active infection.
Correct answer is: Acute phase of the infection
Q.22 What is a key difference between passive and active immunity?
Passive immunity involves antibody production by the host; active does not
Passive immunity is transferred from another individual; active is self-generated
Passive immunity provides long-term protection; active is short-lived
Active immunity is temporary; passive provides lifelong immunity
Explanation - Passive immunity comes from external antibodies (e.g., maternal IgG), while active immunity is produced by the individual's immune system.
Correct answer is: Passive immunity is transferred from another individual; active is self-generated
Q.23 Which assay is best suited for detecting antigens in a complex mixture with high sensitivity?
Rapid test strip
Western blot
Flow cytometry
ELISA with signal amplification
Explanation - Enhanced ELISA techniques (e.g., chemiluminescence) can detect very low antigen levels.
Correct answer is: ELISA with signal amplification
Q.24 What is the main function of complement component C3b when bound to an antigen?
Neutralizes toxins directly
Opsonizes the antigen for phagocytosis
Induces B cell proliferation
Promotes T cell activation
Explanation - C3b tags the antigen, facilitating recognition by phagocytes through complement receptors.
Correct answer is: Opsonizes the antigen for phagocytosis
Q.25 In a competitive ELISA, what is being measured?
Amount of antibody in a sample
Amount of antigen in a sample
Amount of enzyme conjugate
Amount of substrate converted
Explanation - Competitive ELISA measures antigen concentration by competition between sample antigen and a labeled antigen for limited antibody.
Correct answer is: Amount of antigen in a sample
Q.26 Which type of antibody is commonly used in monoclonal antibody production due to its ability to bind to the same epitope?
Polyclonal antibodies
Monoclonal antibodies
Natural antibodies
Idiotypic antibodies
Explanation - Monoclonal antibodies are derived from a single clone and bind identically to a specific epitope.
Correct answer is: Monoclonal antibodies
Q.27 What role does the hinge region of an antibody play?
Determines antibody subclass
Provides flexibility between Fab and Fc regions
Binds antigens
Anchors antibody to cell membrane
Explanation - The hinge region allows the antibody arms to move relative to the tail for optimal antigen binding.
Correct answer is: Provides flexibility between Fab and Fc regions
Q.28 Which of the following is an example of a T cell-dependent antigen?
Bacterial polysaccharide
Protein vaccine
Lipopolysaccharide
Polysaccharide capsule
Explanation - Protein antigens require T cell help for B cell activation, whereas polysaccharides often trigger T cell-independent responses.
Correct answer is: Protein vaccine
Q.29 What does the term 'immunofluorescence' refer to?
Using fluorescent antibodies to detect antigens
Measuring antibody concentration with fluorescence
Staining antigens directly with fluorescent dyes
Using antibodies to neutralize fluorescent pathogens
Explanation - Immunofluorescence employs labeled antibodies to visualize antigen distribution in cells or tissues.
Correct answer is: Using fluorescent antibodies to detect antigens
Q.30 Which component is not part of a typical antibody molecule?
Light chain
Heavy chain
Glycan moiety
DNA strand
Explanation - Antibody proteins consist of heavy and light chains; DNA is not part of the antibody structure.
Correct answer is: DNA strand
Q.31 Which of the following best describes an immune complex?
A single antibody bound to an antigen
A cluster of antigens forming a ring
A mixture of antigens and antibodies that precipitate
A protein that binds to complement
Explanation - Immune complexes are formed when antibodies bind multiple antigens, potentially leading to precipitation.
Correct answer is: A mixture of antigens and antibodies that precipitate
Q.32 Which antibody is known for having the highest affinity for antigens?
IgM
IgG
IgA
IgE
Explanation - IgG antibodies generally have higher affinity due to affinity maturation during immune responses.
Correct answer is: IgG
Q.33 Which of the following is a direct method for measuring antibody levels in serum?
Hemagglutination inhibition assay
Western blot
PCR amplification of antibody genes
Flow cytometry for B cell surface markers
Explanation - This assay quantitatively measures antibodies that can inhibit hemagglutination by viruses like influenza.
Correct answer is: Hemagglutination inhibition assay
Q.34 Which of these antibodies is best suited for mucosal immunity?
IgM
IgA
IgG
IgE
Explanation - Secretory IgA is the main antibody class found in mucosal secretions like saliva and tears.
Correct answer is: IgA
Q.35 What is the primary purpose of the Fc receptor on phagocytic cells?
Bind antigens directly
Bind antibody-antigen complexes for phagocytosis
Secrete antibodies
Activate T cells
Explanation - Fc receptors recognize the Fc region of antibodies, directing phagocytosis of opsonized targets.
Correct answer is: Bind antibody-antigen complexes for phagocytosis
Q.36 Which technique is used to determine the 3D structure of an antibody?
Mass spectrometry
X-ray crystallography
ELISA
Northern blot
Explanation - X-ray crystallography can reveal detailed structural information about antibody molecules.
Correct answer is: X-ray crystallography
Q.37 In vaccine development, why are conjugate vaccines often used for polysaccharide antigens?
To increase antigen size for easier detection
To allow T cell help and improve immunogenicity
To reduce side effects
To avoid antibody production
Explanation - Conjugation to a protein carrier enables T cell-dependent responses, enhancing antibody production.
Correct answer is: To allow T cell help and improve immunogenicity
Q.38 Which antibody subclass is most effective at activating complement?
IgG1
IgG2
IgG3
IgG4
Explanation - IgG3 has the longest hinge region and is the most potent complement activator among IgG subclasses.
Correct answer is: IgG3
Q.39 Which of the following is a hallmark of a Th1 immune response?
High IL-4 production
Activation of macrophages
Induction of IgE production
Promotion of B cell proliferation
Explanation - Th1 cells secrete IFN-γ, which activates macrophages for cell-mediated immunity.
Correct answer is: Activation of macrophages
Q.40 Which assay is commonly used to detect autoantibodies in autoimmune diseases?
Hemolytic assay
Antinuclear antibody (ANA) test
Serum creatinine measurement
Complete blood count (CBC)
Explanation - ANA tests detect antibodies targeting nuclear components, characteristic of many autoimmune disorders.
Correct answer is: Antinuclear antibody (ANA) test
Q.41 What is the purpose of the hinge region in IgG antibodies?
Determines antigen specificity
Provides flexibility between Fab and Fc domains
Increases the antibody's charge
Stabilizes the antibody in serum
Explanation - The hinge region allows the two Fab arms to move independently for optimal antigen binding.
Correct answer is: Provides flexibility between Fab and Fc domains
Q.42 Which of the following is NOT a type of immunoglobulin class found in humans?
IgA
IgB
IgC
IgE
Explanation - Human immunoglobulins include IgG, IgA, IgM, IgD, and IgE; IgC is not a recognized class.
Correct answer is: IgC
Q.43 Which of these is a direct method to detect antigenic proteins in tissue samples?
Immunohistochemistry
PCR
Gram staining
Lactate dehydrogenase assay
Explanation - Immunohistochemistry uses antibody staining to visualize antigens in tissue sections.
Correct answer is: Immunohistochemistry
Q.44 Which type of antibody is typically the first to appear in a primary immune response?
IgA
IgM
IgG
IgE
Explanation - IgM is the initial antibody produced during a primary response before class switching.
Correct answer is: IgM
Q.45 Which of the following is a major function of IgG antibodies?
Transport antibodies across placenta
Neutralize toxins
Activate the complement system
All of the above
Explanation - IgG antibodies can cross the placenta, neutralize toxins, and activate complement.
Correct answer is: All of the above
Q.46 In a competitive ELISA, why is the signal inversely proportional to antigen concentration?
High antigen levels outcompete labeled antigen, reducing binding
The enzyme activity decreases with higher antigen
The plate becomes saturated at high antigen levels
The secondary antibody only binds to low antigen amounts
Explanation - More antigen in the sample competes with the labeled antigen for antibody binding, lowering the detectable signal.
Correct answer is: High antigen levels outcompete labeled antigen, reducing binding
Q.47 Which of the following best describes a paratope?
A part of the antibody that binds to Fc receptors
The antigen-binding region of an antibody
A site on the antigen for antibody binding
The constant region of the light chain
Explanation - The paratope is the variable part of the antibody that recognizes an epitope.
Correct answer is: The antigen-binding region of an antibody
Q.48 Which of these is a feature of IgM antibodies that makes them effective as first responders?
Monomeric structure
Pentameric structure providing high avidity
High affinity for antigen
Ability to cross the placenta
Explanation - IgM's pentameric form allows strong binding through avidity, enabling rapid pathogen neutralization.
Correct answer is: Pentameric structure providing high avidity
Q.49 What is the role of the CDR (Complementarity-Determining Region) in antibodies?
Determines the isotype of the antibody
Provides the constant region of the antibody
Defines the antigen-binding specificity
Anchors the antibody to the cell membrane
Explanation - CDRs are hypervariable loops in the variable domain that directly contact the antigen.
Correct answer is: Defines the antigen-binding specificity
Q.50 Which of the following assays is suitable for detecting IgE levels in allergic patients?
Skin prick test
Specific IgE ELISA
Hemolytic plaque assay
Northern blot
Explanation - Specific IgE ELISA quantifies IgE antibodies in serum, aiding allergy diagnosis.
Correct answer is: Specific IgE ELISA
Q.51 Why do secretory IgA antibodies have a secretory component?
To increase their size
To protect them from proteases in mucosal surfaces
To allow them to bind to Fc receptors
To enable them to cross the placenta
Explanation - The secretory component shields IgA from degradation in harsh mucosal environments.
Correct answer is: To protect them from proteases in mucosal surfaces
Q.52 Which antibody subclass is most effective in antibody-dependent cellular cytotoxicity (ADCC)?
IgA
IgG1
IgG2
IgM
Explanation - IgG1 binds well to Fcγ receptors on NK cells, mediating ADCC.
Correct answer is: IgG1
Q.53 Which of the following is NOT a function of the constant region of an antibody?
Determines the antibody isotype
Interacts with Fc receptors
Binds antigens
Activates complement
Explanation - Antigen binding is performed by the variable (antigen-binding) region, not the constant region.
Correct answer is: Binds antigens
Q.54 In the context of immunotherapy, what does the term 'checkpoint inhibitor' refer to?
A drug that enhances antibody production
An antibody that blocks inhibitory receptors on T cells to boost immune response
A vaccine component that induces T cell checkpoints
A small molecule that blocks antigen presentation
Explanation - Checkpoint inhibitors release the brakes on T cells, promoting anti-tumor activity.
Correct answer is: An antibody that blocks inhibitory receptors on T cells to boost immune response
Q.55 Which of the following best describes an idiotype?
A unique antigenic determinant on the variable region of an antibody
A type of complement protein
The constant region of IgM
A receptor on B cells for antigen binding
Explanation - Idiotype refers to the unique antigenic structure present on an antibody's variable region.
Correct answer is: A unique antigenic determinant on the variable region of an antibody
Q.56 Which of the following is a primary feature of IgD antibodies?
They are abundant in serum
They function as B cell co-receptors
They are the first antibodies produced in response to infection
They are secreted into mucosal surfaces
Explanation - IgD serves as a co-receptor on naive B cells, helping initiate antibody production.
Correct answer is: They function as B cell co-receptors
Q.57 Which of the following is an advantage of using monoclonal antibodies in diagnostics?
They bind multiple epitopes on an antigen
They have high specificity to a single epitope
They are cheaper to produce
They are produced by natural immune responses
Explanation - Monoclonals offer precise targeting, reducing background in diagnostic assays.
Correct answer is: They have high specificity to a single epitope
Q.58 What does the term 'affinity maturation' refer to in the context of B cells?
Increasing the number of B cells during an immune response
Increasing the strength of antibody-antigen binding through somatic hypermutation
Reducing antibody production over time
The process by which antibodies gain the ability to cross the placenta
Explanation - Affinity maturation fine-tunes antibodies to bind antigens more tightly.
Correct answer is: Increasing the strength of antibody-antigen binding through somatic hypermutation
Q.59 Which of the following is a hallmark of a T cell-independent antigen?
Requires helper T cell activation
Induces a strong memory response
Elicits IgM production without T cell help
Stimulates IgE class switching
Explanation - Polysaccharide antigens often trigger IgM responses independently of T cells.
Correct answer is: Elicits IgM production without T cell help
Q.60 Which antibody is most involved in neutralizing viral infections in the bloodstream?
IgM
IgA
IgG
IgE
Explanation - IgG circulates in blood and neutralizes viruses effectively.
Correct answer is: IgG
Q.61 Which of the following is a function of complement component C5a?
Activates macrophages directly
Acts as a chemoattractant for neutrophils
Binds antigens directly
Inhibits B cell activation
Explanation - C5a is a potent chemotactic factor that recruits neutrophils to infection sites.
Correct answer is: Acts as a chemoattractant for neutrophils
Q.62 Which of the following is NOT a type of B cell receptor?
Immunoglobulin M
Immunoglobulin D
Immunoglobulin G
Immunoglobulin Kappa
Explanation - Kappa refers to a light chain type; it is part of the Ig molecule but not a separate receptor.
Correct answer is: Immunoglobulin Kappa
Q.63 Which of these processes is essential for generating antibody diversity?
V(D)J recombination
Glycosylation
Translation
DNA replication
Explanation - V(D)J recombination assembles variable gene segments to create diverse antibody repertoires.
Correct answer is: V(D)J recombination
Q.64 What is the main function of the complement system?
To produce antibodies
To mediate direct cell killing and opsonization
To activate B cell proliferation
To transport antigens to lymph nodes
Explanation - Complement proteins facilitate pathogen lysis and enhance phagocytosis.
Correct answer is: To mediate direct cell killing and opsonization
Q.65 Which antibody subclass is the least effective at activating complement?
IgG1
IgG2
IgG3
IgG4
Explanation - IgG4 is poor at complement activation compared to other IgG subclasses.
Correct answer is: IgG4
Q.66 Which of the following best explains why IgA is often found in tears?
It provides systemic immunity
It protects mucosal surfaces from pathogens
It neutralizes blood toxins
It promotes T cell activation
Explanation - IgA in tears helps guard the ocular surface against infections.
Correct answer is: It protects mucosal surfaces from pathogens
Q.67 What is a key characteristic of a humoral immune response?
Involves antibody-mediated pathogen neutralization
Primarily mediated by cytotoxic T cells
Requires direct cell-to-cell contact
Depends on interferon-gamma only
Explanation - Humoral immunity centers on antibody production to fight extracellular pathogens.
Correct answer is: Involves antibody-mediated pathogen neutralization
Q.68 Which of the following best describes a subunit vaccine?
A vaccine that uses whole attenuated pathogen
A vaccine that contains only specific antigenic subunits
A vaccine that delivers DNA encoding antigens
A vaccine that uses live virus particles
Explanation - Subunit vaccines include purified pieces of the pathogen, such as proteins or polysaccharides.
Correct answer is: A vaccine that contains only specific antigenic subunits
Q.69 Which antibody is primarily responsible for the clearance of old or damaged red blood cells?
IgG
IgM
IgA
IgE
Explanation - IgG opsonizes senescent erythrocytes for phagocytic removal.
Correct answer is: IgG
Q.70 Which of the following is a direct function of the Fc fragment of IgG?
Binding to the antigen
Binding to Fcγ receptors on effector cells
Binding to antigenic epitopes
Binding to MHC molecules
Explanation - Fc region interacts with Fcγ receptors to mediate antibody-dependent cellular functions.
Correct answer is: Binding to Fcγ receptors on effector cells
Q.71 What does the term 'cross-reactivity' refer to in immunology?
Antibody binding to multiple epitopes on the same antigen
Antibody binding to a structurally unrelated antigen
Antibody binding to self-antigens only
Antibody binding to both IgM and IgG simultaneously
Explanation - Cross-reactivity occurs when an antibody recognizes similar epitopes on different antigens.
Correct answer is: Antibody binding to a structurally unrelated antigen
Q.72 Which of these best explains why IgG antibodies can cross the placenta?
Their small size allows them to pass through the placenta
They are actively transported by FcRn receptors in the placenta
They are produced by fetal liver cells
They are not subject to degradation in the placenta
Explanation - The neonatal Fc receptor (FcRn) mediates transcytosis of IgG into fetal circulation.
Correct answer is: They are actively transported by FcRn receptors in the placenta
Q.73 Which of the following is a typical method to assess the presence of antigen-specific B cells?
Flow cytometry using fluorescently labeled antigen probes
ELISA for antigen
Northern blot for B cell mRNA
PCR for antibody genes
Explanation - Flow cytometry with labeled antigens can detect antigen-specific B cells in a sample.
Correct answer is: Flow cytometry using fluorescently labeled antigen probes
Q.74 What is the main difference between IgG and IgM in terms of structure?
IgG is pentameric, IgM is monomeric
IgG has a longer hinge region than IgM
IgM is pentameric, IgG is monomeric
IgG contains light chains while IgM does not
Explanation - IgM forms pentamers, giving high avidity, whereas IgG is a simple monomeric antibody.
Correct answer is: IgM is pentameric, IgG is monomeric
Q.75 Which of the following is an example of a therapeutic antibody?
Rituximab
Hemagglutinin
DNA polymerase
Actin
Explanation - Rituximab is a monoclonal antibody used clinically to target CD20 on B cells.
Correct answer is: Rituximab
Q.76 What role does the J chain play in IgM and IgA antibodies?
It is required for dimerization of IgA and polymerization of IgM
It acts as the antigen-binding domain
It mediates complement activation
It anchors the antibody to the cell membrane
Explanation - The J chain assists in the assembly of IgM pentamers and IgA dimers.
Correct answer is: It is required for dimerization of IgA and polymerization of IgM
Q.77 Which of the following best describes a 'neutralizing' antibody?
An antibody that binds to and destroys pathogens directly
An antibody that blocks a pathogen's ability to infect cells
An antibody that triggers the complement cascade
An antibody that promotes phagocytosis
Explanation - Neutralizing antibodies prevent pathogens from entering host cells by blocking key interactions.
Correct answer is: An antibody that blocks a pathogen's ability to infect cells
Q.78 Which of the following is a primary feature of IgA in saliva?
It has no Fc region
It is found in monomeric form only
It provides first-line defense in the oral cavity
It is the most abundant antibody in blood
Explanation - IgA in saliva protects the oral mucosa from microbial invasion.
Correct answer is: It provides first-line defense in the oral cavity
Q.79 In a sandwich ELISA, the detection antibody binds to which part of the antigen?
The same epitope as the capture antibody
A different epitope on the same antigen
The Fc region of the capture antibody
The light chain of the capture antibody
Explanation - Detection antibodies bind a separate epitope, allowing sandwich formation.
Correct answer is: A different epitope on the same antigen
Q.80 Which type of antibody is primarily responsible for the allergic response in IgE-mediated reactions?
IgG
IgA
IgE
IgM
Explanation - IgE binds to mast cell receptors, triggering histamine release during allergies.
Correct answer is: IgE
Q.81 Which of the following best describes the function of the hinge region in IgG antibodies?
Determines the antibody's isotype
Provides flexibility for antigen binding
Increases the antibody's charge
Stabilizes the antibody in the bloodstream
Explanation - The hinge allows Fab arms to move, enhancing antigen interaction.
Correct answer is: Provides flexibility for antigen binding
Q.82 What is a key advantage of using synthetic peptide antigens in ELISA assays?
They are cheaper than full-length proteins
They guarantee higher sensitivity
They require no purification
They can be used to detect antibodies against any antigen
Explanation - Synthetic peptides are inexpensive and can mimic specific epitopes.
Correct answer is: They are cheaper than full-length proteins
Q.83 Which of the following best describes a 'polyclonal' antibody preparation?
Antibodies from a single B cell clone
Antibodies from multiple B cell clones recognizing various epitopes
Antibodies with identical isotype
Antibodies with no affinity for antigens
Explanation - Polyclonal antibodies are produced by multiple B cell populations.
Correct answer is: Antibodies from multiple B cell clones recognizing various epitopes
Q.84 Which of the following is NOT a method to detect complement activation?
CH50 assay
ELISA for C3a
PCR for complement genes
C5b-9 membrane attack complex detection
Explanation - PCR detects gene sequences; complement activation is measured by functional assays.
Correct answer is: PCR for complement genes
Q.85 Which type of antibody is most abundant in the intestinal lumen?
IgG
IgM
IgA
IgE
Explanation - Secretory IgA dominates mucosal secretions such as intestinal fluids.
Correct answer is: IgA
Q.86 Which of the following is an example of a 'checkpoint molecule' used in cancer immunotherapy?
PD-1
IgG1
HLA-DR
CD19
Explanation - PD-1 is a checkpoint protein targeted by immune checkpoint inhibitors.
Correct answer is: PD-1
Q.87 What is the primary function of a 'capture antibody' in an ELISA plate?
Bind to the antigen in the sample
Detect bound antigen with a secondary antibody
Catalyze substrate conversion
Inhibit non-specific binding
Explanation - The capture antibody immobilizes the antigen on the plate surface.
Correct answer is: Bind to the antigen in the sample
Q.88 Which of the following best describes an 'antibody-dependent cellular cytotoxicity (ADCC)' mechanism?
Complement-mediated lysis of target cells
Direct phagocytosis of antibodies by macrophages
NK cell-mediated killing of antibody-coated target cells
T cell-mediated cytokine production
Explanation - ADCC involves NK cells recognizing Fc regions on antibody-coated cells.
Correct answer is: NK cell-mediated killing of antibody-coated target cells
Q.89 Which of the following best explains why IgM is a poor activator of the classical complement pathway?
Its pentameric structure interferes with C1q binding
It lacks an Fc region
It has a low affinity for antigen
It cannot bind to Fcγ receptors
Explanation - IgM’s pentameric arrangement reduces its ability to effectively activate complement.
Correct answer is: Its pentameric structure interferes with C1q binding
Q.90 Which of the following is NOT a component of an antibody?
Heavy chain
Light chain
Peptide nucleic acid
Glycan moiety
Explanation - Antibodies consist of heavy and light chains, often with glycosylation; they do not contain peptide nucleic acids.
Correct answer is: Peptide nucleic acid
Q.91 Which of the following is a common use for monoclonal antibodies in research?
As a vaccine antigen
As a standard in immunoassays
To induce autoimmunity
To act as a pathogen
Explanation - Monoclonal antibodies serve as precise, reproducible standards in assays.
Correct answer is: As a standard in immunoassays
Q.92 Which of the following best describes the role of a 'secondary antibody' in an ELISA?
Captures the antigen from the sample
Binds to the captured antigen and carries the detection enzyme
Inhibits the reaction
Directly binds to the plate
Explanation - The secondary antibody binds the primary antibody and contains the enzyme for signal generation.
Correct answer is: Binds to the captured antigen and carries the detection enzyme
Q.93 What is a 'heterophilic' antibody?
An antibody that cross-reacts with antigens from different species
An antibody that binds to itself
An antibody produced by a single B cell clone
An antibody that recognizes both IgG and IgM
Explanation - Heterophilic antibodies bind to animal proteins used in assays, potentially causing interference.
Correct answer is: An antibody that cross-reacts with antigens from different species
Q.94 Which of the following best describes the 'FcRn' receptor?
The receptor responsible for B cell activation
The receptor that transports IgG across the placenta
The receptor that initiates complement activation
The receptor that binds to IgE on mast cells
Explanation - FcRn mediates IgG transport between maternal and fetal blood.
Correct answer is: The receptor that transports IgG across the placenta
Q.95 Which of the following best explains why IgA is found in the tear film?
It provides systemic immunity
It protects against ocular infections by neutralizing pathogens
It activates complement in the tear film
It binds to T cell receptors
Explanation - Secretory IgA in tears helps block pathogens from colonizing the eye.
Correct answer is: It protects against ocular infections by neutralizing pathogens
Q.96 Which of the following best describes the 'antibody response to a booster vaccination'?
A decrease in antibody levels due to tolerance
An increased speed and magnitude of antibody production
No change in antibody levels
Production of only IgM antibodies
Explanation - Boosters elicit a faster, stronger response due to memory B cells.
Correct answer is: An increased speed and magnitude of antibody production
Q.97 What is the main difference between an 'intracellular' and an 'extracellular' antigen?
Intracellular antigens are only proteins; extracellular can be any molecule
Intracellular antigens are presented on MHC class I; extracellular on MHC class II
Intracellular antigens are larger than extracellular ones
Extracellular antigens are not recognized by antibodies
Explanation - Antigen processing routes differ based on location within the cell.
Correct answer is: Intracellular antigens are presented on MHC class I; extracellular on MHC class II
Q.98 Which of the following is an example of a 'direct-acting' therapeutic antibody?
An antibody that blocks a cytokine receptor
An antibody that enhances T cell activation
An antibody that directly binds to a viral envelope protein to neutralize infection
An antibody that functions only by engaging complement
Explanation - Direct-acting antibodies neutralize pathogens by binding to them.
Correct answer is: An antibody that directly binds to a viral envelope protein to neutralize infection
Q.99 Which of the following is NOT a step in the ELISA detection process?
Coating the plate with capture antibody
Adding the sample containing the target antigen
Incubating with a detection antibody conjugated to an enzyme
Sequencing the DNA of the captured antigen
Explanation - ELISA is an immunoassay, not a DNA sequencing technique.
Correct answer is: Sequencing the DNA of the captured antigen
Q.100 Which type of antibody is most commonly used to detect intracellular antigens in immunofluorescence microscopy?
IgA
IgM
IgG
IgE
Explanation - IgG antibodies are typically used for intracellular staining due to their size and specificity.
Correct answer is: IgG
Q.101 Which of the following best explains why IgG can neutralize toxins?
IgG binds to the toxin's active site, preventing its interaction with host cells
IgG forms large aggregates that trap toxins
IgG blocks the secretion of toxins by pathogens
IgG does not neutralize toxins; only IgM does
Explanation - By binding the toxin, IgG physically blocks its harmful effects.
Correct answer is: IgG binds to the toxin's active site, preventing its interaction with host cells
Q.102 Which of the following best describes a 'neutralizing antibody'?
An antibody that directly kills pathogens
An antibody that blocks the interaction between a pathogen and host cells
An antibody that binds to complement proteins
An antibody that causes autoimmunity
Explanation - Neutralizing antibodies prevent infection by blocking pathogen entry.
Correct answer is: An antibody that blocks the interaction between a pathogen and host cells
Q.103 What is the major function of complement component C3b in immune complexes?
Binds to pathogens for direct lysis
Opsonizes pathogens for phagocytosis
Activates T cells
Inhibits B cell proliferation
Explanation - C3b tags pathogens, enhancing uptake by phagocytes.
Correct answer is: Opsonizes pathogens for phagocytosis
Q.104 Which of the following best explains the concept of 'antibody affinity maturation'?
The process of increasing antibody production over time
The refinement of antibody binding strength through somatic hypermutation and selection
The switch from IgM to IgG isotype
The reduction in antibody diversity
Explanation - Affinity maturation improves the strength of antigen-antibody interactions.
Correct answer is: The refinement of antibody binding strength through somatic hypermutation and selection
Q.105 Which of the following best describes a 'polyvalent' antibody?
An antibody with multiple antigen-binding sites
An antibody that binds multiple different antigens
An antibody produced from a single B cell clone
An antibody lacking specificity
Explanation - Polymers like IgM have multiple binding sites, enhancing avidity.
Correct answer is: An antibody with multiple antigen-binding sites
Q.106 What is the primary function of the J chain in IgA and IgM antibodies?
It provides a binding site for antigens
It facilitates polymerization of these antibodies
It binds to Fc receptors on immune cells
It anchors the antibody to the cell membrane
Explanation - The J chain helps form IgM pentamers and IgA dimers.
Correct answer is: It facilitates polymerization of these antibodies