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

The Correct Answer is: 2 Fab fragments and 1 Fc fragment

Explanation:

Papain, a proteolytic enzyme, digests an IgG antibody molecule by cleaving it above the hinge region. This digestion separates the antibody into three distinct fragments:

1. Two Fab (Fragment Antigen Binding) fragments:

   • These fragments each contain a light chain and part of the heavy chain, forming the antigen-binding sites.
   • Fab fragments are responsible for antigen recognition and binding.

2. One Fc (Fragment Crystallizable) fragment:

   • The Fc fragment is derived from the constant region of the two heavy chains.
   • This region mediates effector functions such as binding to Fc receptors and activating complement.

Source: https://www.researchgate.net/publication/285954753/figure/fig2/AS:602001532538885@1520539758144/Different-fragments-of-IgG-obtained-by-pepsin-and-papain-digestion.png

Process of Papain Digestion:

• Papain cleaves at a specific site in the hinge region of the IgG molecule.
• This separates the antigen-binding domains (Fab) from the effector domain (Fc).

Why Other Options Are Incorrect:

• Option 2: IgG digestion does not produce 2 Fc fragments; only 1 Fc fragment is generated.
• Option 3: This is incorrect as digestion produces only 2 Fab fragments and not 4.
• Option 4: Papain digestion generates 2 Fab fragments, not 1.

The correct answer is ​A, B, and C

Explanation:

A. Natural killer (NK) cells can directly kill virus-infected cells by recognizing stressed cells in the absence of antibodies and MHC.

• This statement is correct. Natural killer (NK) cells play a crucial role in the innate immune response. They can induce apoptosis in virus-infected cells or cancerous cells by recognizing certain stress-induced molecules on these cells in the absence of antibodies and MHC.

B. Dendritic cells act as messengers between the innate and the adaptive immune systems, primarily by presenting antigens to T cells.

• This statement is correct. Dendritic cells are a critical component of the immune system. They capture antigens from pathogens and present them on their surface to T cells, thus serving as a bridge between the innate and adaptive immune responses.

C. Regulatory T cells (Tregs) suppress immune responses and help maintain tolerance to self-antigens, preventing autoimmune diseases.

• This statement is correct. Regulatory T cells (Tregs) are a subset of T cells that function to maintain immune tolerance by suppressing excessive immune responses and thereby preventing autoimmune diseases.

D. Helper T cells (Th cells) are involved in activating and directing other immune cells, but they destroy infected cells directly.

• This statement is incorrect. Helper T cells (Th cells) do not directly destroy infected cells. Instead, they play a pivotal role in activating and regulating the activity of other immune cells such as B cells, cytotoxic T cells, and macrophages through the secretion of cytokines.

E. Cytotoxic T cells kill infected cells by recognizing and binding to antigens presented by Class II MHC molecules.

• This statement is incorrect. Cytotoxic T cells recognize antigens presented by Class I MHC molecules, not Class II. It is the helper T cells that recognize antigens presented by Class II MHC molecules.

The correct option is: 2

Explanation:

• Phagocytosis
  Phagocytosis is primarily the function of macrophages and neutrophils. While B cells can bind to antigens using their B-cell receptors, their role in phagocytosis is minimal and not their primary function.

• Antibody production
  B cells play a critical role in adaptive immunity by differentiating into plasma cells, which produce antibodies. These antibodies recognize and neutralize specific antigens, aiding in the clearance of pathogens. This is the primary and defining function of B cells in the immune system.

• Killing infected cells directly
  This is the function of cytotoxic T cells (CD8+ T cells). They recognize infected cells via antigen presentation on MHC class I molecules and directly kill them. B cells are not involved in direct cell killing.

• Producing histamine
  Histamine production is associated with mast cells and basophils, which release histamine during allergic and inflammatory responses. B cells do not produce histamine.

• B-cell Activation:

  • B cells are activated upon encountering their specific antigen and receiving help from T-helper cells (CD4+ T cells).
  • Once activated, they proliferate and differentiate into plasma cells (for antibody production) and memory B cells (for long-term immunity).

The correct option is: 3

Explanation:

• Option (A): Activation of mast cells
  This function is primarily associated with IgE, which binds to Fcε receptors on mast cells and triggers their activation during allergic reactions. IgA does not activate mast cells.

• Option (B): Binding to Fc receptors on phagocytes
  Although IgA binds to Fc receptors, specifically FcαRI on phagocytes, this interaction does not involve the J-chain. The J-chain is crucial in the polymeric structure and function of IgA, not in its interaction with Fc receptors.

• Option (C): Transcytosis across epithelial cells
  The J-chain is an integral component of multimeric (dimeric) IgA. It facilitates the binding of IgA to the polymeric immunoglobulin receptor (pIgR) on epithelial cells. This binding is essential for the transcytosis process, allowing IgA to be transported across epithelial cells and secreted into mucosal surfaces, such as the respiratory, gastrointestinal, and urogenital tracts, where it provides immune protection.

• Option (D): Neutralization of antigens
  Neutralization is a general function of IgA but does not specifically involve the J-chain. The J-chain plays no direct role in the antigen-binding or neutralizing activity of IgA.

 Additional Information

• IgA and the J-Chain:

  • IgA exists in two main forms: monomeric (in blood) and multimeric (in secretions).
  • The J-chain (joining chain) is a small polypeptide that links two monomers of IgA, forming the dimeric structure crucial for its secretory functions.
  • In the multimeric form, the J-chain allows IgA to bind to pIgR, which facilitates its transport across epithelial cells and secretion as secretory IgA (sIgA).

• Secretory IgA (sIgA):

  • Plays a pivotal role in mucosal immunity by preventing pathogens from adhering to epithelial surfaces and neutralizing toxins.
  • It is resistant to proteolytic enzymes, making it well-suited for mucosal defense.

The correct option is: 2

Explanation:

• Class I MHC molecules present intracellular antigens.
  This is correct. Class I MHC molecules present peptides derived from intracellular proteins, such as viral or self-antigens, to cytotoxic T-cells (CD8+ T-cells). They are expressed on all nucleated cells.

• Class II MHC molecules are expressed on all nucleated cells.
  This is false. Class II MHC molecules are expressed only on antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells. They are not expressed on all nucleated cells, which is a key distinction from Class I MHC molecules.

• Class II MHC molecules are involved in activating helper T-cells.
  This is correct. Class II MHC molecules present extracellular antigens to helper T-cells (CD4+ T-cells), playing a crucial role in the activation of these cells and initiating an immune response.

• Dendritic cells express both Class I and Class II MHC molecules.
  This is correct. Dendritic cells are professional antigen-presenting cells that express both Class I and Class II MHC molecules, allowing them to present antigens to both cytotoxic T-cells (via Class I) and helper T-cells (via Class II).

 Additional Information

• MHC Class I: Found on all nucleated cells; presents endogenous peptides; interacts with CD8+ T-cells.
• MHC Class II: Found on APCs; presents exogenous peptides; interacts with CD4+ T-cells.
• Role of APCs: APCs, including dendritic cells, macrophages, and B cells, are specialized to activate adaptive immune responses by presenting antigens via MHC molecules.

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.