Immune System MCQ Quiz - Objective Question with Answer for Immune System - Download Free PDF

The correct answer is B, C, and D

Explanation:

• T cell precursors exit the bone marrow and migrate to the thymus where they undergo positive and negative selection processes. These processes are crucial for the development of functional and non-self-reactive T cells.
• The thymus provides a specialized microenvironment where thymocytes interact with stromal cells to ensure proper selection.
• Positive selection ensures that T cells can recognize self-MHC molecules, while negative selection eliminates auto-reactive T cells that could cause autoimmune diseases.
  • Statement B: The selection process relies on the transcription factor 'Aire'.
    • Aire (Autoimmune Regulator) is crucial for the expression of a wide range of tissue-specific antigens in medullary thymic epithelial cells.
    • This enables the negative selection of thymocytes that could potentially react to self-antigens, preventing autoimmunity.
    • Thus, this statement is correct as Aire plays a pivotal role in the selection process by ensuring tolerance to self-antigens.
  • Statement C: The selection process can lead to the generation of CD4 cells that can interact with dendritic cells (DCs) as well as B cells.
    • CD4+ T cells, also known as helper T cells, are critical for coordinating immune responses. They interact with antigen-presenting cells (like dendritic cells) and B cells to initiate and regulate adaptive immunity.
    • Positive selection ensures that these T cells can recognize self-MHC class II molecules, which is essential for their role in interacting with DCs and B cells.
    • Therefore, this statement is correct as it highlights the functional diversity of CD4+ T cells in immune responses.
  • Statement D: The selection process can lead to the generation of regulatory CD4 T cells.
    • Regulatory CD4 T cells (Tregs) are specialized T cells that play a key role in maintaining immune tolerance and preventing autoimmune diseases.
    • During the selection process in the thymus, some self-reactive T cells are not eliminated but instead differentiate into Tregs under the influence of signals such as TGF-β.
    • This ensures that the immune system remains balanced and self-reactivity is kept in check. Thus, this statement is correct.

Other Options:

• Statement A: The selection process involves negative selection of auto-reactive cells in the cortex followed by their migration to the medulla.
  • This statement is incorrect because negative selection primarily occurs in the medulla, not the cortex.
  • Positive selection occurs in the cortex where thymocytes are screened for their ability to bind self-MHC molecules.

The correct answer is B and D

Explanation:

• The complement system is a part of the innate immune response and consists of a group of proteins that work together to combat pathogens. It can be activated via three pathways: the classical pathway, the lectin pathway, and the alternative pathway.
• The alternative pathway is unique because it does not require antibody binding for activation. Instead, it is triggered by different mechanisms, including spontaneous hydrolysis and other factors like properdin.

Statement A: "The pathway is initiated when antibodies bind to the pathogen."

• This statement is incorrect. The alternative pathway is distinct from the classical pathway, which is initiated by antibodies (IgG or IgM) binding to antigens on the pathogen. The alternative pathway does not require antibodies for activation.

Statement B: "The pathway is initiated by spontaneous hydrolysis of serum complement."

• This statement is correct. The alternative pathway is primarily initiated by the spontaneous hydrolysis of complement protein C3 into C3(H₂O), which can then bind to factor B. This process leads to the formation of the C3 convertase and subsequent activation of the pathway.

Statement C: "The pathway uses the same C3- and C5-convertases as the lectin pathway."

• This statement is incorrect. While the alternative pathway and the lectin pathway both involve C3 and C5 convertases, the structures of these enzyme complexes differ. In the alternative pathway, the C3 convertase is C3bBb, while in the lectin pathway, it is C4b2a.

Statement D: "The pathway can be initiated by properdin and thrombin."

• This statement is correct. Properdin, a positive regulator of the complement system, can stabilize the C3 convertase in the alternative pathway, thereby amplifying the response. Additionally, thrombin, a coagulation protein, can also interact with complement components, providing a link between coagulation and complement activation..

The correct answer is A, B, and C

Concept:

Enzyme-Linked Immunosorbent Assay (ELISA) is a widely used method in immunology to detect the presence of antibodies or antigens in a sample. The procedure involves multiple steps, including coating wells with antigen, blocking unoccupied sites, adding primary antibodies, detecting with enzyme-conjugated secondary antibodies, and using a substrate to produce a measurable color change. Proper execution of each step ensures the assay's sensitivity and specificity.

• Blocking: Blocking with a protein like BSA (Bovine Serum Albumin) prevents non-specific binding of antibodies or other proteins to the well surface, which could interfere with the assay's specificity.
• Washing Steps: Washing the plates between key steps is crucial for removing unbound proteins or antibodies that could otherwise lead to false positives or negatives, affecting both specificity and sensitivity.
• Substrate and Enzyme Reaction: OPD (o-Phenylenediamine dihydrochloride) serves as the substrate for horseradish peroxidase (HRP), resulting in a color change when the reaction occurs. H₂SO₄ stops the enzymatic reaction and stabilizes the developed color, allowing for measurement.

Explanation:

Statement A: If the plates are not blocked with BSA, the specificity of the assay decreases.

• Blocking with BSA prevents non-specific binding of proteins to the plate surface. Without blocking, other proteins or antibodies may adhere to the wells, leading to background noise and reduced specificity. Therefore, statement A is correct.

Statement B: If the plates are not washed between addition of serum sample and addition of anti-mouse IgG-HRP, the sensitivity of the assay decreases.

• Washing removes any unbound serum antibodies, ensuring that only specific binding occurs. Failure to wash can result in interference or noise, decreasing the assay's sensitivity. Thus, statement B is correct.

Statement C: If the plates are not washed between addition of anti-mouse IgG-HRP and addition of H₂O₂ + OPD, the specificity of the assay decreases.

• Washing after adding anti-mouse IgG-HRP removes unbound or excess enzyme-conjugated antibodies that could contribute to non-specific color development. This ensures a clear and specific signal, making statement C correct.

Incorrect Statements:

Statement D: OPD is the substrate for the enzyme.

• This statement is correct. OPD serves as the substrate for HRP, producing a color change upon reaction. 

Statement E: Without H₂SO₄, no color is developed.

• This statement is incorrect. H₂SO₄ does not initiate color development; it only halts the enzymatic reaction and stabilizes the developed color for measurement. Color development occurs due to the reaction between HRP and OPD.

The correct answer is VDJ recombination

Explanation:

• Isotype switching, also known as class switch recombination (CSR), is a biological process that allows a B cell to change the class of antibody it produces while retaining the specificity for the antigen. This process enables the immune system to tailor its response to different pathogens.
• During isotype switching, a B cell changes its production of IgM antibodies to another type, such as IgE, IgG, or IgA, depending on the signals it receives. This involves complex molecular mechanisms.
• VDJ recombination is a process that occurs during the early stages of B cell development in the bone marrow, where variable (V), diversity (D), and joining (J) gene segments are rearranged to create a unique antigen-binding site for the immunoglobulin molecule. This process is essential for generating the initial diversity of antibodies but is not involved in isotype switching.
  • ​Isotype switching only alters the constant region of the antibody (which determines the antibody class) and not the variable region (which determines antigen specificity). Therefore, VDJ recombination is NOT required for isotype switching.
• Double-stranded break repair: Isotype switching involves double-stranded DNA breaks in the switch regions of immunoglobulin genes. These breaks are repaired through DNA repair mechanisms, which are essential for the recombination process that facilitates the switch from one antibody class to another. This step is required for isotype switching.
• Cell division: Isotype switching occurs in activated B cells, which undergo cell division as part of their activation and proliferation. This step is important for producing sufficient numbers of B cells capable of secreting antibodies of the desired isotype. 
• T cell cytokines: T helper cells play a crucial role in providing cytokine signals (e.g., IL-4 for IgE switching) that guide B cells in determining which antibody class to switch to. 

The correct answer is A and B

Explanation:

C. elegans, a model organism, is frequently used in aging research due to its short life span and well-characterized genetics. Aging in C. elegans is regulated by specific genetic pathways, including the insulin/IGF-1 signaling pathway (DAF-2 and DAF-16), p53, and mTOR signaling. These pathways are evolutionarily conserved and provide insights into longevity mechanisms.

• Statement A: This statement is correct. p53 is a transcription factor that is typically bound to a repressor protein in most cells to keep it inactive. Under oxidative stress or DNA damage, p53 is separated from its repressor, becoming active. Once activated, p53 can induce repair mechanisms or apoptosis, contributing to cellular health and longevity regulation.
• Statement B: This statement is correct. DAF-2, an insulin-like growth factor receptor in C. elegans, negatively regulates the Forkhead transcription factor DAF-16. When DAF-2 signaling is reduced, DAF-16 becomes active, leading to the expression of genes associated with stress resistance and longevity, effectively increasing the life span.

• Statement C: This statement is incorrect. When DAF-2 is inactive, DAF-16 is activated, which promotes the production of DNA repair enzymes and stress resistance proteins, enhancing longevity. The statement incorrectly suggests that cells reduce DNA repair enzymes when DAF-2 is inactive.
• Statement D: This statement is incorrect. Dietary restriction is known to decrease mTORC1 activity, not increase it. Reduced mTORC1 activity enhances autophagy and stem cell function, which contributes to increased longevity. The statement incorrectly claims that dietary restriction increases mTORC1 activity.

The correct answer is Option 3 i.e.Differential RNA processing.

Concept:

Differential RNA Processing- 

• Differential RNA processing plays a crucial role in determining whether the Ig(immunoglobulin) will be expressed as a membrane bound receptor or a secreted antibody.
• The determination of whether the Ig will be receptor bound or secreted is primarily controlled by the process of alternative RNA splicing during m-RNA maturation.
• This process involves several steps, including transcription, splicing and translation.
• The splicing process involves the removal of certain exon and the joining of others, resulting in different protein products. 
• For membrane-bound immunoglobulins, exons encoding a hydrophobic transmembrane domain are retained, anchoring the immunoglobulin to the B-cell membrane.
• In contrast, for secretory Ig, these transmembrane domain-encoding exons are spliced out, leading to the transmembrane domain, allowing the Ig to be secreted and circulate in body fluids.
• This differential RNA processing enables B-cells to produce both membrane bound and secretory forms of immunoglobulins, allowing them to function effectively in different immune responses, such as on the cell surface for antigen recognition or as soluble antibodies to combat pathogen in body fluids.

Additional Information

Allelic exclusion -​

• The function of allelic exclusion mechanism is to assure that each antibody forming cell will produce antibodies of only a single specificity.

Class switch recombination-

• The function of class switch recombination is to replaces the Immunoglobulin constant region for the isotype which can protect again the pathogen.

Codominant expression-

• In genetic inheritance when two alleles of the same gene are expressed separately to yield different traits in an individual, is known as codominant expression.

Conclusion:-Hence, Option 3 is correct.

The correct answer is Option 4 i.e. For HAT selection of hybridoma, the antibody producing B‐cells are pre‐treated with 8‐azaguanine to block salvage pathway of DNA synthesis.

Concept:

• Monoclonal antibodies (mAb) are crucial tools used in biomedical research, disease detection, and cancer and other types of disease treatment.
• These antibodies are created by cell lines or clones derived from animals that have received vaccinations against the research chemical.
• B cells from the immunized animal are fused with myeloma cells to create the cell lines.
• The cells must be cultivated in one of two methods in order to create the necessary mAb.
• in vitro tissue culture or injection into the peritoneal cavity of an appropriately prepped mouse (the in vivo, or mouse ascites, approach). 
• To get mAb with the desired purity and concentration, additional processing of the tissue-culture supernatant and mouse ascitic fluid may be necessary.

Explanation:

Option A:- CORRECT

• Monoclonal antibodies are made from B cell clones that each produce a single antibody with a well-defined specificity.
• Without an antibody, B cells won't typically divide.

Option B:- CORRECT

• When mammalian cells that make a particular antibody combine with tumor cells that can multiply indefinitely, the outcome is a fusion known as a hybridoma that continuously produces antibodies. Because they originate from a single type of cell, the hybridoma cell, those antibodies are referred to as monoclonal.

Option C:- CORRECT

• Aminopterin, a medication that inhibits dihydrofolate reductase to act as a potent inhibitor of folate metabolism, is combined with hypoxanthine, a purine derivative, and thymidine, a deoxynucleoside, which are intermediates in DNA synthesis, to create HAT Medium, a selection medium for mammalian cell culture.

Option D:- INCORRECT

• The ability of mammalian cells to manufacture nucleotides using either the salvage pathway or the de novo pathway is what makes HAT selection possible. Aminopterin, a folic acid analog, blocks the de novo process by which a methyl or formyl group is transferred from an active form of tetrahydrofolate.

The correct answer is Innate immunity has only a narrow range of specificity.

Explanation:

• Innate immunity is the body's first line of defense against pathogens and is present from birth. It is non-specific, meaning it responds to a wide range of pathogens using general mechanisms rather than highly specific responses like the adaptive immune system. It provides an immediate, response to a wide variety of pathogens, including bacteria, viruses, fungi, and parasites. Unlike adaptive immunity, which is highly specific to particular pathogens and involves memory, innate immunity is generic but broad in its target range.

• Pattern recognition receptors (PRRs) are indeed a key component of innate immunity. They recognize pathogen-associated molecular patterns (PAMPs) found on a broad range of pathogens, which triggers an immune response. These receptors can detect many types of invaders, making innate immunity broad in its action.

• Serum complement proteins are part of innate immunity. These proteins help identify and clear pathogens by marking them for destruction and aiding in their removal through processes like phagocytosis.

• The outcome of innate immunity is rapid recognition and destruction of pathogens. This involves processes like phagocytosis, where immune cells engulf and destroy invaders, and inflammatory responses to contain and eliminate threats.

Thus, the statement about "narrow specificity" is incorrect because innate immunity is actually broad and non-specific in its recognition of pathogens.

The correct answer is A and D

Explanation:

Class Switching in B cells: B cells can undergo class switch recombination (CSR) to change the antibody isotype they produce without altering the antigen specificity. This switch is typically unidirectional due to the loss of intervening DNA sequences in the constant region of the immunoglobulin gene.

Possible Isotype Switching Pathways:

• IgM → IgG1
• IgG1 → IgA (Class switching from IgG1 to IgA is possible)
• IgM → IgA
   

Statement Analysis:

• Statement A: Cells that have switched to IgG1 may undergo further switching to IgA.
  • True: IgG1 B cells can switch to IgA because class switching can continue to downstream isotypes.
• Statement B: Cells that have switched to IgA may undergo further switching to IgG1.
  • False: Once a B cell switches to IgA, it cannot revert back to IgG1 because the DNA segment for IgG1 has been deleted.
• Statement C: A single cell can simultaneously secrete IgG1 and IgA.
  • False: A single B cell secretes only one class of antibody at a time. The presence of both IgG1 and IgA in wells indicates independent events from different cells.
• Statement D: The progeny of proliferating cells may undergo independent switching events.
  • True: This is consistent with the observed data where proliferating B cells can switch individually to different isotypes. Thus, progeny can independently switch to IgG1 or IgA from IgM.

Key Points

• Class switching in B cells is a unidirectional process.
• IgG1 can switch to IgA, but IgA cannot revert to IgG1.
• A single B cell cannot simultaneously secrete two isotypes.
• Independent progeny cells from the proliferation can undergo separate class switching events.
   

Conclusion:

• Statement A is correct because IgG1 B cells can switch to IgA.
• Statement D is correct because progeny cells from proliferating B cells can independently switch to different isotypes.

The correct answer is A - iii, B - i, C - ii, D - iv.

Explanation:

The correct answer is "A" will be protected against both the ancestral strain and the Delta variant.

Explanation:  

Two different types of immune components are transferred to two unrelated recipients:

Recipient "A" receives pooled serum from successfully vaccinated individuals. Serum contains neutralizing antibodies that were generated in response to the ancestral (Wuhan) strain of Covid-19.

• These antibodies likely also offer some protection against related strains like the Delta variant, which shares many spike protein features with the ancestral strain.
• However, the Omicron variant has significant mutations in the spike protein, which make it more resistant to neutralization by antibodies induced by the ancestral strain vaccine.
• Thus, Recipient "A" will have protection against both the ancestral strain and the Delta variant due to the neutralizing antibodies but will not be protected against the Omicron variant.

Recipient "B" receives pooled T cells from vaccinated individuals. These T cells, especially cytotoxic T lymphocytes (CTLs), are specific to the ancestral strain and are less dependent on spike protein variations compared to neutralizing antibodies. However, T cells may not offer the same breadth of protection across variants because of differences in the antigen presentation.

Other Options:

• B" will be protected against ancestral strain but not against the Delta variant: While T cells could protect against the ancestral strain, they may still offer some cross-reactivity to other strains like Delta, as T cell responses tend to recognize more conserved viral elements. So, this option is unlikely.
• "A" will be protected against infection with the Omicron variant: Omicron has extensive mutations in the spike protein, so it is less likely that serum containing antibodies generated against the ancestral strain will protect against Omicron.
• "A" will make antibodies against interferon gamma present in the donor serum: This is not a common or expected response. The transferred serum contains neutralizing antibodies, not interferon gamma, and such immune responses against interferon gamma are not typically seen.

The correct answer is Option 4 i.e. TAP1, TAP2 proteins and proteosome‐like subunits LMP2, LMP7

Concept:-

Processing and presentation of endogenous antigens: Cytosolic pathway

• Endogenous antigens are synthesized inside a cell; typically they are derived from pathogens (e.g. viruses, bacteria, and parasites) that have infected the cell.
• MHC I proteins present peptide antigens derived from endogenous protein antigens.
• Processing of endogenous antigens occurs in the cytoplasm rather than in the acid vesicles.
• The major mechanism for generating peptide fragments in the cytoplasm is via a giant protein complex known as the proteasome.
• This cleaves proteins into peptides about 15 amino acids in length. Cytosolic enzymes (amino peptidases) remove even more amino acids from the peptides.
• Peptide antigens are transported via an energy-dependent reaction into the endoplasmic reticulum (ER) through a pore formed by proteins, called the transporters associated with antigen processing (TAP).
• Once the peptides have entered the ER, they are bound by the MHC I protein, held in place near the TAP site by a group of chaperone proteins such as calnexin, calreticulin, tapasin, and ERp57.
• The MHC 1-peptide complex is then released from the chaperone and moves to the cell surface where it integrates into the membrane and can be recognized by T cells.
• The part of a processed antigen that binds to the MHC molecule is termed an agretope.

Explanation:-

Option 1:- TAP1 and TAP2 proteins only

• This option is correct but incomplete and does not fully satisfy the answer.
• Hence, option 1 is incorrect.

Option 2:- Invariant chain (Ii)

• Invariant chain ii belongs to MHC II, not MHC 1.
• The conserved Ii chain and polymorphic MHC class II molecules are selectively coexpressed in a tissue-specific fashion in conventional antigen-presenting cells such as B cells, macrophages, and dendritic cells known to be responsible for initiating CD4+ T cell responses. 
• Hence, option 2 is incorrect.

Option 3:- Proteosome‐like subunits LMP2 and LMP7 only

• This option is correct but incomplete and does not fully satisfy the answer.
• Hence, option 3 is incorrect.

Option 4:- TAP1, TAP2 proteins and proteosome‐like subunits LMP2, LMP7

• The MHC genes that code for LMP2 and LMP7 are closely related to the genes that code for TAP, a transporter that carries peptides from the cytosol to the endoplasmic reticulum where they are assembled with MHC class I molecules.
• The proteasome is a huge molecular assembly with many proteolytic activities that are thought to break down undesired and damaged cellular proteins. LMP2 and LMP7 are subunits of a subset of proteasomes.
• After cells are exposed to IFN-gamma, LMP gene expression is increased, just like TAP and class I molecules themselves.
• These results suggest that LMP2 and LMP7 are involved in the cytosolic synthesis of antigenic peptides.
• Hence, option 4 is correct.

The correct answer is Option 2

Concept:

• NF-κB (Nuclear Factor kappa-light-chain-enhancer of activated B cells) is a transcription factor that regulates the expression of genes involved in immune and inflammatory responses.
• IκBα (Inhibitor of kappa B alpha) is an inhibitory protein that binds to NF-κB, sequestering it in the cytoplasm and preventing it from entering the nucleus.
• TNF (Tumor Necrosis Factor) triggers a signal that leads to the degradation of IκBα, freeing NF-κB to enter the nucleus, where it activates the transcription of target genes, including the gene encoding IκBα itself.

Negative Feedback Loop:

• TNF exposure causes degradation of IκBα, leading to NF-κB activation.
• NF-κB enters the nucleus and promotes the transcription of various genes, including the IκBα gene.
• Newly synthesized IκBα binds NF-κB and brings it back to the cytoplasm, thus inhibiting its activity again.
• This forms a negative feedback loop, where IκBα suppresses NF-κB after it has been activated.

Explanation:​

Pulse TNF exposure (a):

• A brief, transient exposure to TNF leads to a quick degradation of IκBα and a corresponding spike in NF-κB activity.
• After the pulse, IκBα re-synthesis occurs, inhibiting NF-κB and returning it to its inactive state.
• Hence, the graph should show a single peak of NF-κB activation followed by a decline back to baseline.

Continuous TNF exposure (b):

• Continuous TNF exposure sustains the degradation of IκBα, allowing NF-κB to repeatedly enter the nucleus.
• Due to the negative feedback loop (IκBα re-synthesis), NF-κB activity does not stay high indefinitely. Instead, it shows oscillations, where NF-κB is periodically activated and inhibited in cycles.

Analyzing the Graphs:

• For Pulse (a): A single sharp peak in NF-κB activity due to the brief TNF exposure, followed by a return to baseline after IκBα re-synthesis.
• For Continuous (b): Oscillations in NF-κB activity, as repeated cycles of NF-κB activation and IκBα-mediated inhibition occur during sustained TNF exposure.

Row 2 is correct because:

• The pulse condition shows a single sharp peak of NF-κB activity, representing transient activation followed by a decline.
• The continuous condition shows oscillations in NF-κB activity, which is characteristic of the feedback loop involving IκBα when TNF is continuously present.

The correct answer is Option 3 i.e.A,C,D

Key Points

Scatchard Plot:

• This is a graphical method used to analyze equilibrium ligand binding data.
• It helps determine various characteristics of binding interactions, such as the number of ligand-binding sites, whether there are cooperative interactions, and the affinities of each site.

Antibody Affinity:

• Antibody affinity refers to the strength of the binding interaction between an antibody and its target antigen.
• Higher affinity indicates a stronger binding, while lower affinity indicates a weaker binding.
• In the context of Scatchard plots, if all antibodies have the same affinity, the plot will yield a straight lin e.
• If antibodies with a range of affinities are pooled, the plot will yield a curved line, with a constantly changing slope.

Explanation:

• Here n (X intercept) for R is 2 means it is having 2 binding sites , which can be IgG, while Q has 4 binding sites means its valency 4 so it can be IgA, hence statement D is correct and E is incorrect.
• If all antibodies have the same affinity, then a Scatchard plot yields a straight line.
• If the antibodies are pooled and have a range of affinities, a Scatchard plot yields a curved line, whose slope is constantly changing hence A is correct.

Hence the correct answer is Option 3

Explanation:

• A chronic disease develops slowly and the body's reactions may be less severe but, the disease is likely to be continual or recurrent for long period.
• Infectious mononucleosis, syphilis, tuberculosis and leprosy falls into this category.
• IgG antibodies account for about 80% of all antibodies in serum.
• These protect against, circulating bacteria and viruses, neutralize bacterial toxins, trigger the complement system and when bound to antigens enhance the effectiveness of phagocytic cells.