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

The correct answer is P - i; Q - ii; R - iii; S - iv 

Explanation:

Viruses are microscopic infectious agents that require a host cell to replicate. They are classified based on the type of genetic material they possess, which can be DNA or RNA, and whether this genetic material is single-stranded (ss) or double-stranded (ds). The genetic material of viruses determines their replication mechanism and host specificity.

• Bacteriophage Lambda (P):
  • Bacteriophage lambda is a virus that infects bacteria, specifically E. coli. Its genetic material is double-stranded DNA (dsDNA).
• Bacteriophage M13 (Q):
  • Bacteriophage M13 is another bacterial virus, but it has single-stranded DNA (ssDNA) as its genetic material.
• Coronavirus (R):
  • Coronaviruses are a group of RNA viruses that infect animals and humans, causing respiratory illnesses like SARS, MERS, and COVID-19. Their genetic material is single-stranded RNA (ssRNA).
• Reovirus (S):
  • Reoviruses are non-enveloped viruses that infect a variety of organisms, including humans, where they cause gastrointestinal and respiratory symptoms. They are characterized by double-stranded RNA (dsRNA) as their genetic material.

The correct answer is Peak I - IgM; Peak II - IgG

Explanation:

• The adaptive immune system in animals responds to pathogens such as bacteria or viruses through the production of antibodies. These antibodies are specialized proteins that help neutralize or eliminate the invading pathogen.
• The two main classes of antibodies involved in the immune response are Immunoglobulin M (IgM) and Immunoglobulin G (IgG). These antibodies play distinct roles in the primary and secondary immune responses.
• The primary response occurs when the immune system encounters a pathogen for the first time. The secondary response occurs upon subsequent exposures to the same pathogen, which is faster and more robust due to the formation of immunological memory.
• Primary immune response (Peak I):
  • When the mammal is exposed to the pathogen for the first time, the immune system responds by producing IgM antibodies initially. IgM is the first antibody generated in response to an infection.
  • IgM antibodies are short-lived, and their levels peak early during the primary response.
• Secondary immune response (Peak II):
  • Upon a second exposure to the same pathogen, the immune system responds more rapidly and with greater intensity due to the activation of memory B cells.
  • In the secondary response, IgG antibodies dominate. IgG is more specific, longer-lasting, and more efficient at neutralizing the pathogen.
  • The levels of IgG are much higher in the secondary response compared to IgM in the primary response.
• Therefore, the graph showing Peak I (primary response) corresponds to IgM, while Peak II (secondary response) corresponds to IgG.

The correct answer is To grow disease-causing microorganisms.

Explanation:

• Robert Koch, a pioneering microbiologist, is renowned for his groundbreaking work in the field of bacteriology and his contributions to identifying specific pathogens as the cause of specific diseases. One of his significant innovations was the use of nutrient media to cultivate microorganisms in the laboratory, allowing them to grow and be studied in isolation.
• Robert Koch utilized nutrient media to cultivate and isolate microorganisms, such as the bacteria causing tuberculosis (Mycobacterium tuberculosis) and anthrax (Bacillus anthracis) 
• Before Koch, many scientists struggled to grow bacteria outside of the body in a controlled manner.
• Koch's innovation included using nutrient-rich substances like meat extracts (bouillons) and later solidifying them with gelatin and then agar to create a suitable environment for bacterial growth. This allowed him to obtain pure cultures of microorganisms, meaning a population of cells derived from a single cell, free from contamination by other microbial species.
• One of Koch's postulates states: "The microorganism must be isolated from a diseased organism and grown in pure culture." The meat-infused medium provided the necessary nutrients (carbon, nitrogen, vitamins, minerals) for various bacteria, especially pathogenic ones, to thrive in vitro.
•   

The correct answer is P−5 ; Q−4 ; R−2 ; S−1

Explanation:

• The immune system consists of various molecules and proteins that play distinct roles in defending the body against pathogens. These molecules include immunoglobulins (antibodies) such as IgM, IgE, IgA, and others like Major Histocompatibility Complex (MHC).
• Each type of antibody has unique properties and functions, including participating in immune responses, providing protection, and facilitating communication between immune cells.
• MHC proteins are essential for presenting antigens to T cells and initiating adaptive immune responses.
  • IgM - Contains ten heavy and light chains: IgM is the largest antibody and is the first to be produced during an immune response. It forms a pentamer structure, consisting of five antibody units, resulting in ten heavy and light chains. This structural feature enables IgM to efficiently agglutinate antigens.
  • IgE - Associated with allergic reactions: IgE is involved in allergic responses. It binds to allergens and triggers the release of histamine and other chemicals from mast cells and basophils, leading to symptoms such as itching, swelling, and inflammation.
  • IgA - Predominant antibody type in various body secretions: IgA is the primary antibody found in mucosal areas, including saliva, tears, breast milk, and respiratory and intestinal secretions. It plays a vital role in protecting mucosal surfaces by neutralizing pathogens and preventing their adhesion to epithelial cells.
  • MHC - Involved in antigen presentation: Major Histocompatibility Complex (MHC) molecules are critical for the immune system. They present processed antigens to T cells, enabling recognition of foreign substances and initiation of adaptive immune responses.

The correct answer is 𝛼1 and 𝛼2 domains.

Concept:

• The major histocompatibility complex (MHC) is a group of genes that code for proteins found on the surfaces of cells. These proteins play an essential role in the immune system by presenting peptide antigens to T cells.
• MHC molecules are divided into two main classes: MHC class I and MHC class II.
• MHC class I molecules are expressed on almost all nucleated cells and present endogenous antigens (from within the cell) to CD8+ cytotoxic T cells.
• The MHC-I molecule consists of a heavy chain (with three domains: 𝛼1, 𝛼2, and 𝛼3) and a non-covalently associated light chain called β2-microglobulin.
• The peptide-binding cleft of the MHC-I molecule is the region responsible for binding and presenting peptides to T cells. This cleft is highly specific and allows the immune system to recognize and respond to pathogens.
  • The peptide-binding cleft in MHC-I molecules is formed by the 𝛼1 and 𝛼2 domains of the heavy chain.
  • The 𝛼1 and 𝛼2 domains create a groove or cleft that is highly polymorphic, meaning it varies greatly among individuals, allowing for the presentation of a wide variety of peptide antigens.
  • This structure is crucial for the immune system to distinguish between self and non-self antigens.
  • The cleft can accommodate peptides that are typically 8-10 amino acids long, making it suitable for presenting intracellular antigens.​

Fig: Schematic representation of MHC Class I

Fig: Schematic representation of MHC Class II

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 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 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 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.