IS 8

Answer: C

​Rationale:

​A is incorrect: IgG is primarily circulating and lacks a secretory component.

​B is incorrect: IgM contains a J chain in its pentameric form, but not a secretory component.

​C is correct: Secretory IgA contains a secretory component synthesized by epithelial cells, which protects the dimeric IgA molecule from enzymatic digestion in mucosal secretions.

​D is incorrect: IgD is primarily a surface receptor on mature B cells.

​E is incorrect: IgE functions in immediate hypersensitivity and lacks a secretory component.

Which immunoglobulin class possesses a secretory component that protects the molecule from enzymatic cleavage by proteolytic enzymes in mucosal secretions?

​A. IgG

B. IgM

C. IgA

D. IgD

E. IgE

Answer: B

​Rationale:

​A is incorrect: IgG migrates in the slow gamma-globulin region.

​B is correct: IgA (specifically IgA1) exhibits faster electrophoretic mobility towards the anode, migrating in the beta-gamma or fast alpha-2 region.

​C is incorrect: IgM migrates in the slow beta to gamma region.

​D is incorrect: IgD migrates in the fast gamma to beta region.

​E is incorrect: IgE migrates in the slow beta region.

A medical technologist performs serum protein electrophoresis. Which immunoglobulin subclass migrates fastest toward the anode during electrophoresis (fast alpha-2 to beta region)?

​A. IgG1

B. IgA1

C. IgM

D. IgD

E. IgE

Answer: C

​Rationale:

​A is incorrect: IgG1 fixes complement efficiently and crosses the placenta, but IgG3 is the most potent complement fixer.

​B is incorrect: IgG2 has poor complement-fixing ability and poor placental transfer compared to IgG1/IgG3.

​C is correct: IgG3 has the largest hinge region, making it the most efficient at fixing complement, and it crosses the placental barrier readily.

​D is incorrect: IgG4 cannot fix complement via the classical pathway.

​E is incorrect: IgM does not belong to the IgG subclasses and cannot cross the placenta.

Which IgG subclass is most efficient at crossing the placenta and fixing complement via the classical pathway?

​A. IgG1

B. IgG2

C. IgG3

D. IgG4

E. IgM

Answer: D
​Rationale:
​A is incorrect: IgG1 fixes complement strongly.
​B is incorrect: IgG2 fixes complement weakly.
​C is incorrect: IgG3 fixes complement most efficiently.
​D is correct: IgG4 does not fix complement via the classical pathway due to structural alterations in its C_H2 domain.
​E is incorrect: IgG4 fits this description.

Which IgG subclass is completely incapable of activating complement via the classical pathway?

A. IgG1

B. IgG2

C. IgG3

D. IgG4

E. None of the above

Answer: C
​Rationale:
​A is incorrect: The secretory component protects IgA from proteolytic degradation in secretions.
​B is incorrect: C_H4 is an extra constant domain, not a separate joining polypeptide.
​C is correct: The J (Joining) chain is a cysteine-rich polypeptide responsible for linking monomer subunits into dimeric IgA and pentameric IgM.
​D is incorrect: V_L forms the antigen-binding site.
​E is incorrect: The hinge region provides rotational flexibility to Fab arms.

What specialized polypeptide chain holds monomeric units together to form a pentameric IgM or dimeric IgA structure?
​A. Secretory piece
B. Heavy chain constant domain (C_H4)
C. J (Joining) chain
D. Variable light chain (V_L)
E. Hinge peptide

Answer: C
​Rationale:
​A is incorrect: CD8+ T cells recognize Class I MHC molecules.
​B is incorrect: Neutrophils express Fc$\gamma$ receptors for IgG opsonins.
​C is correct: Mast cells and basophils bear high-affinity Fc\epsilonRI receptors that bind the Fc region of IgE. Cross-linking by allergens triggers immediate histamine release.
​D is incorrect: Mature erythrocytes lack Fc receptors.
​E is incorrect: Macrophages express Fc\gamma and Fc\alpha receptors.

Which cell type expresses high-affinity \text{Fc}\epsilon\text{RI} receptors that bind circulating IgE antibodies, triggering degranulation upon antigen cross-linking?
​A. CD8+ T lymphocytes
B. Neutrophils
C. Mast cells and Basophils
D. Red blood cells
E. Macrophages

Answer: C

​Rationale:

​A is incorrect: 2 binding sites describe monomeric IgG, IgD, or IgE.

​B is incorrect: Theoretical valence is 10 because a pentamer has 5 monomers with 2 Fab arms each.

​C is correct: In theory, a pentameric IgM has 10 antigen-binding sites (valence = 10), but due to steric hindrance with large complex antigens, its operational valence is usually 5.

​D is incorrect: Operational valence rarely reaches 10 except for small haptens.

​E is incorrect: Describes dimeric IgA theoretical vs. operational limits.

What is the valence (number of potential antigen-binding sites) of a pentameric IgM molecule in theory vs. its typical operational valence for large antigens?

​A. Theoretical = 2; Operational = 2

B. Theoretical = 5; Operational = 5

C. Theoretical = 10; Operational = 5

D. Theoretical = 10; Operational = 10

E. Theoretical = 4; Operational = 2

Answer: B

​Rationale:

​A is incorrect: Avidity is the sum of all attractive forces between a multivalent antigen and a multivalent antibody (total binding strength).

​B is correct: Affinity is explicitly defined as the initial force of attraction between a single Fab and a single epitope ("tightness of fit").

​C is incorrect: Specificity refers to the ability of an antibody to bind uniquely to its specific antigen.

​D is incorrect: Cross-reactivity occurs when an antibody binds to a similar but non-identical antigen epitope.

​E is incorrect: Zeta potential represents the net negative charge on red blood cell membranes in solution.

What term describes the initial, single force of attraction that exists between a single Fab fragment of an antibody and a single epitope on an antigen?

​A. Avidity

B. Affinity

C. Specificity

D. Cross-reactivity

E. Zeta potential

Answer: E

​Rationale:

​A is incorrect: Omits hydrophobic bonds and Van Der Waals forces.

​B is incorrect: Omits ionic bonds and hydrogen bonds.

​C is incorrect: Omits Van Der Waals forces.

​D is incorrect: Omits ionic bonds.

​E is correct: All four listed forces—Ionic bonds, Hydrogen bonds, Hydrophobic bonds, and Van Der Waals forces—are the specific attractive forces that mediate single Fab-to-epitope binding (affinity).

Which non-covalent intermolecular forces contribute to the initial affinity binding strength between an antibody Fab region and an antigen epitope?

​Ionic bonds

​Hydrogen bonds

​Hydrophobic bonds

​Van Der Waals Forces

​A. 1 and 2 only

B. 3 and 4 only

C. 1, 2, and 3 only

D. 2, 3, and 4 only

E. 1, 2, 3, and 4

Answer: B

​Rationale:

​A is incorrect: Describes single-site affinity, not total avidity.

​B is correct: Avidity is the sum of all attractive forces between antigen and antibody (total binding strength). Increased avidity decreases the tendency of the immune complex to dissociate.

​C is incorrect: Refers to kinetic antibody production rates, not binding forces.

​D is incorrect: Antigen-antibody interactions are non-covalent, not covalent.

​E is incorrect: Describes lag phase duration, which is unrelated to avidity definitions.

How is AVIDITY defined, and how does an increase in avidity affect the immune complex stability?

​A. Initial attraction between a single Fab and epitope; increases dissociation

B. Sum of all attractive forces between an antigen and an antibody; decreases tendency of the complex to dissociate

C. Maximum rate of antibody synthesis during the log phase; increases dissociation

D. Covalent bonding strength between heavy chains; prevents dissociation

E. Time elapsed during the lag phase; decreases overall affinity

Answer: D 
​Rationale:
​A is incorrect: Primary responses feature a longer lag phase and lower titer. 
​B is incorrect: Primary response is dominated by IgM; secondary is dominated by IgG. 
​C is incorrect: Primary responses undergo an abrupt decrease in antibody titer. 
​D is correct: A primary response exhibits a longer lag phase, a lower antibody titer, a predominant IgM class, and an abrupt decrease in titer. 
​E is incorrect: Secondary responses feature a slower decrease in antibody titer.

Which characteristic correctly distinguishes a PRIMARY immune response from a SECONDARY immune response?

A. Shorter lag phase and higher antibody titer in primary response

B. Predominance of IgG in primary response; predominance of IgM in secondary response

C. Slower decrease in antibody levels in primary response

D. Longer lag phase, lower antibody titer, and predominant IgM response in primary response

E. Abrupt decrease in antibody titer during secondary response

Answer: C

​Rationale:

​A is incorrect: IgG represents past exposure or a secondary immune response.

​B is incorrect: IgA is predominant in mucosal surface secretions.

​C is correct: IgM is the primary antibody produced during initial exposure (present/recent infection).

​D is incorrect: IgD serves as a B-cell surface receptor.

​E is incorrect: IgE mediates type I hypersensitivity reactions.

What antibody class is predominantly detected during the early onset of a primary infection, serving as a marker for recent or current exposure?

​A. IgG

B. IgA

C. IgM

D. IgD

E. IgE

Answer: B

​Rationale:

​A is incorrect: Describes polyclonal antibodies.

​B is correct: Monoclonal antibodies are purified antibodies cloned from a single cell, providing uniform specificity against a single antigenic epitope.

​C is incorrect: Monoclonal antibodies are immunoglobulins, not viral antigens.

​D is incorrect: Polyclonal antisera contain products from multiple cell clones.

What are MONOCLONAL ANTIBODIES?

​A. Heterogeneous mixtures of antibodies produced by multiple plasma cell clones

B. Purified antibodies cloned from a single plasma cell line targeting a single epitope

C. Recombinant antigens harvested from viral cultures

D. Polyclonal antisera harvested from immunized rabbits

E. Chemically digested immunoglobulin light chain fragments

Answer: E

​Rationale:

​A is incorrect: Incomplete list.

​B is incorrect: Incomplete list.

​C is incorrect: Omits disease management.

​D is incorrect: Omits surface antigen analysis.

​E is correct: Monoclonal antibodies are used for cell membrane antigen analysis (e.g., flow cytometry CD markers), cancer treatment, and autoimmune disease management.

Monoclonal antibodies are widely used in clinical laboratory medicine and therapeutics for which of the following applications?

​Analysis of cell membrane surface antigens

​Treatment of cancers

​Diagnosis and management of autoimmune diseases

​A. 1 only

B. 2 only

C. 1 and 2 only

D. 2 and 3 only

E. 1, 2 and 3

Answer: B

​Rationale:

​A is incorrect: Aminopterin is a selective metabolic drug added in HAT medium.

​B is correct: Polyethylene glycol (PEG) is the fusing agent used to fuse spleen cells and myeloma cells to form hybridomas.

​C is incorrect: Hypoxanthine provides a substrate for the salvage pathway in HAT medium.

​D is incorrect: Thymidine provides a substrate for the salvage pathway in HAT medium.

In Hybridoma Technology, which chemical agent is added to induce the membrane fusion of antibody-producing spleen cells and immortal myeloma cells?

​A. Aminopterin

B. Polyethylene glycol (PEG)

C. Hypoxanthine

D. Thymidine

E. Mitomycin C

Answer: B

​Rationale:

​A is incorrect: Myeloma cells used in hybridomas are HGPRT-deficient.

​B is correct: Aminopterin is a drug that prevents myeloma cells from making their own purines and pyrimidines via the de novo pathway, forcing cells to use the salvage pathway (requiring hypoxanthine and thymidine supplied by HGPRT+ spleen cell DNA).

​C is incorrect: Unrelated to antibody degradation.

Selective survival of fused hybridoma cells in HAT selective medium relies on the action of AMINOPTERIN. What is the specific biochemical mechanism of aminopterin?

​A. Blocks the HGPRT enzyme in spleen cells

B. Prevents myeloma cells from synthesizing purines and pyrimidines via the de novo pathway

C. Degrades extracellular IgG light chains

D. Stimulates rapid proliferation of unmerged spleen B cells

E. Inhibits cell membrane fusion by blocking PEG

Answer: B

​Rationale:

​A is incorrect: Rat monoclonal antibodies are denoted differently ("-axomab" for rat/mouse bispecifics).

​B is correct: The infix "-omab" designates a 100% Mouse (Murine) monoclonal antibody (which is the most immunogenic in humans).

​C is incorrect: Chimeric antibodies use "-ximab".

​D is incorrect: Fully human antibodies use "-umab".

​E is incorrect: Humanized antibodies use "-zumab".

According to World Health Organization (WHO) nomenclature for monoclonal antibodies, what species origin is indicated by the infix "-omab"?

​A. Rat origin

B. Mouse (Murine) origin

C. Chimeric (Mouse/Human) origin

D. Fully Human origin

E. Humanized origin

Answer: B 
​Rationale:
​A is incorrect: "-omab" indicates 100% mouse origin. 
​B is correct: "-ximab" indicates a chimeric antibody combining mouse variable domains (VH/VL) with human constant domains. 
​C is incorrect: "-zumab" indicates a humanized antibody.
​D is incorrect: "-umab" indicates a fully human antibody.
​E is incorrect: Not an antibody nomenclature infix.

Which monoclonal antibody suffix/infix denotes a CHIMERIC antibody containing mouse variable regions and human constant regions?

A. "-omab"

B. "-ximab"

C. "-zumab"

D. "-umab"

E. "-amab"

Answer: B

​Rationale:

​A is incorrect: Chemokines are a specific subclass of cytokines that enhance white blood cell motility and promote migration.

​B is correct: Cytokines are generic terms for soluble mediators that function as chemical messengers to regulate the immune system.

​C is incorrect: Acute phase reactants are plasma proteins whose levels increase or decrease during inflammation.

​D is incorrect: Immunoglobulins are antibodies produced by plasma cells to bind specific antigens.

​E is incorrect: Opsonins are molecules that coat pathogens to facilitate phagocytosis.

Which term describes chemical messengers/soluble mediators that regulate the immune system, primarily functioning in cell differentiation and activation?

​A. Chemokines

B. Cytokines

C. Acute phase reactants

D. Immunoglobulins

E. Opsonins

Answer: C

​Rationale:

​A is incorrect: Paracrine action occurs when a cytokine binds to receptors on nearby cells.

​B is incorrect: Endocrine action occurs when a cytokine enters blood circulation to act on distant parts of the body.

​C is correct: Autocrine action occurs when a cytokine binds to receptors on the cell that secreted it.

​D is incorrect: Exocrine refers to secretions released through ducts onto an epithelial surface.

​E is incorrect: Juxtacrine requires direct cell-to-cell contact binding.

When a cytokine acts on the exact same cell that secreted it by binding to its own cell surface receptors, this mechanism of action is classified as:

​A. Paracrine

B. Endocrine

C. Autocrine

D. Exocrine

E. Juxtacrine

Answer: B

​Rationale:

​A is incorrect: Primary complications of HBV/HAV relate to hepatocellular injury rather than classical hemorrhagic cytokine storms.

​B is correct: Ebola and Dengue are classic examples associated with hyper-cytokinemia or cytokine storm (overproduction of cytokines causing vascular leakage and shock).

​C is incorrect: Measles and Mumps do not characteristically present with high-mortality systemic cytokine storms.

​D is incorrect: CMV and EBV typically cause lymphoproliferation or mononucleosis-like syndromes.

​E is incorrect: Rabies affects the central nervous system; Poliovirus targets motor neurons.

Uncontrolled overproduction of cytokines ("cytokine storm") is characteristically seen in severe viral manifestations such as:

A. Hepatitis A and Hepatitis B

B. Ebola and Dengue

C. Measles and Mumps

D. Cytomegalovirus and Epstein-Barr Virus

E. Rabies and Poliovirus

Answer: A 
​Rationale:
​A is correct: IL-1 acts as an endogenous pyrogen that causes fever. 
​B is incorrect: IL-2 is T-cell growth factor. 
​C is incorrect: IL-4 regulates Th2 activities and antibody responses. 
​D is incorrect: IL-6 stimulates B cells to become plasma cells. 
​E is incorrect: IL-10 exerts an inhibitory effect on the immune system. 

Which interleukin functions as an endogenous pyrogen that causes fever during an inflammatory response?

​A. IL-1

B. IL-2

C. IL-4

D. IL-6

E. IL-10

Answer: C

​Rationale:

​A is incorrect: IL-2 specifically targets T-cell proliferation and NK activity.

​B is incorrect: IFN-gamma is the primary macrophage activating factor.

​C is correct: IL-2 was formerly known as T-cell growth factor; it promotes growth/differentiation of B and T cells (CD25) and induces lytic activity of NK cells.

​D is incorrect: Lymphotoxin is TNF-beta.

​E is incorrect: Cachectin is TNF-alpha.

What was the former name of Interleukin-2 (IL-2), and what key cell type does it induce lytic activity in?

​A. B-cell growth factor; B cells

B. Macrophage activating factor; Monocytes

C. T-cell growth factor; NK cells

D. Lymphotoxin; Cytotoxic T cells

E. Cachectin; Plasma cells

Answer: B 
​Rationale:
​A is incorrect: IL-6 does not promote Th1 differentiation (IFN-gamma drives Th1).
​B is correct: IL-6 stimulates B cells to differentiate into plasma cells and induces CD4+ cells to produce cytokines. 
​C is incorrect: IL-2 enhances NK cell activity. 
​D is incorrect: Dendritic cells differentiate under GM-CSF and FLT3 ligand influence.
​E is incorrect: IL-3 and IL-9 support mast cell development

Interleukin-6 (IL-6) plays a crucial role in B-cell differentiation by directly stimulating B cells to become:
​A. Helper T cells (Th1)
B. Plasma cells
C. Natural Killer (NK) cells
D. Dendritic cells
E. Mast cells 

Answer: C 
​Rationale:
​A is incorrect: IL-1 mediates pro-inflammatory fever reactions. 
​B is incorrect: IL-2 drives T-cell proliferation. 
​C is correct: IL-4 regulates Th2 immune activities, helps drive the antibody response, and regulates antibody production. 
​D is incorrect: IL-6 drives plasma cell differentiation. 
​E is incorrect: IL-10 suppresses immune functions.

Which interleukin regulates Th2 immune activities, drives antibody production, and controls humoral immunity?
​A. IL-1
B. IL-2
C. IL-4
D. IL-6
E. IL-10

Rationale:

​A, B, C, and D are incorrect: These interleukins are active stimulatory or regulatory factors in immune response pathways.

​E is correct: IL-10 is an anti-inflammatory cytokine that provides an inhibitory effect on the immune system.

Which interleukin exerts an INHIBITORY effect on the immune system, downregulating inflammatory cytokine production?

​A. IL-1

B. IL-2

C. IL-4

D. IL-6

E. IL-10

Answer: B 
​Rationale:
​A is incorrect: Th1 cells produce Type 2 Interferon (IFN-gamma). 
​B is correct: Interferon Alpha (leukocyte interferon) is mainly produced by Null lymphocytes / NK cells (and leukocytes). Interferon Beta is secreted by double-stranded RNA fibroblasts and its major producers are fibroblasts and epithelial cells. 
​C, D, and E are incorrect: Incorrect cell producer combinations based on standard classifications.

Type 1 Interferons (Alpha and Beta) are non-immune products of initial viral responses. What are the major cell producers of Interferon Alpha and Interferon Beta, respectively?
​A. Th1 cells; Macrophages
B. Null lymphocytes/NK cells; Fibroblasts and Epithelial cells
C. Plasma cells; Neutrophils
D. Mast cells; Platelets
E. Endothelial cells; Basophils

Answer: A 
​Rationale:
​A is correct: Interferon Gamma (Type 2) is an immune interferon produced primarily by Th1 cells to mediate cell-mediated immunity. 
​B is incorrect: Th2 cells produce IL-4, IL-5, IL-10, and drive antibody responses. 
​C is incorrect: Fibroblasts produce Interferon Beta. 
​D is incorrect: Platelets release betalysin during coagulation. 
​E is incorrect: B cells differentiate into antibody-secreting plasma cells. 

Type 2 Interferon (Gamma) serves as an immune component of specific immune responses against viral and non-viral pathogens. What cell type is its major producer?
​A. Th1 cells
B. Th2 cells
C. Fibroblasts
D. Platelets
E. B lymphocytes

Answer: A

​Rationale:

​A is correct: TNF-Alpha is produced by macrophages and is also known as cachectin.

​B is incorrect: TNF-Beta is produced by CD4+ and CD8+ cells and is known as lymphotoxin.

​C is incorrect: TGF-Beta induces antiproliferative effects.

​D is incorrect: Betalysin is an antibacterial protein released by platelets.

​E is incorrect: IL-2 is T-cell growth factor.

Which cytokine is produced by MACROPHAGES and is also known as CACHECTIN?

A. Tumor Necrosis Factor-Alpha (TNF-Alpha)

B. Tumor Necrosis Factor-Beta (TNF-Beta)

C. Transforming Growth Factor-Beta (TGF-Beta)

D. Betalysin

E. Interleukin-2

Answer: B 
​Rationale:
​A is incorrect: Cachectin is TNF-alpha. 
​B is correct: TNF-Beta is produced by CD4+ and CD8+ cells and is also known as lymphotoxin (exerts potent activity against Gram-negative organisms). 
​C is incorrect: Monokine is a general term for cytokines released by monocytes/macrophages.
​D is incorrect: Pyrogen describes fever-inducing agents like IL-1. 
​E is incorrect: Histamine is a vasoactive amine released by mast cells/basophils.

What is the alternative name for Tumor Necrosis Factor-Beta (TNF-Beta), which is produced by CD4+ and CD8+ cells?
​A. Cachectin
B. Lymphotoxin
C. Monokine
D. Pyrogen
E. Histamine

Answer: C

​Rationale:

​A is incorrect: Interleukins function primarily in cell differentiation and activation.

​B is incorrect: Interferons provide virus-nonspecific antiviral activity.

​C is correct: Chemokines function to enhance motility and promote migration of white blood cells.

​D is incorrect: Betalysins are heat-stable bactericidal proteins.

Which group of cytokines functions primarily to ENHANCE MOTILITY and promote the directed migration of white blood cells toward sites of inflammation?

​A. Interleukins

B. Interferons

C. Chemokines

D. Betalysins

Answer: B

​Rationale:

​A is incorrect: TNF-beta (lymphotoxin) has cytotoxic activity mentioned against Gram-negative organisms, whereas betalysin acts on Gram-positive organisms.

​B is correct: Betalysin is released by platelets during coagulation and acts specifically against Gram-positive organisms.

​C, D, and E are incorrect: Betalysin target specificity does not primarily encompass acid-fast, intracellular, or wall-less organisms.

Betalysin is a bactericidal substance released by PLATELETS during coagulation. Which group of bacteria is it specifically active against?

​A. Gram-negative bacteria

B. Gram-positive bacteria

C. Acid-fast bacilli

D. Obligate intracellular chlamydiae

E. Mycoplasmas lacking cell walls

Answer: B

​Rationale:

​A is incorrect: Growth factors like IL-2 stimulate proliferation rather than hyper-proliferative pathology.

​B is correct: Transforming Growth Factor-Beta (TGF-Beta) induces an antiproliferative effect to regulate and tone down immune cellular expansion.

​C is incorrect: Lytic activity is enhanced by IL-2 on NK cells.

​D is incorrect: Histamine release is mediated by IgE cross-linking on mast cells.

​E is incorrect: Pyrogenic elevation is caused by IL-1.

What primary regulatory effect does Transforming Growth Factor-Beta (TGF-Beta) induce on cellular proliferation in the immune system?

​A. Hyper-proliferative response

B. Antiproliferative effect

C. Lytic activation

D. Histamine release

E. Pyrogenic elevation