IGNOU BZYET-141 Solved Question Paper PDF Download

IGNOU BZYET-141 Previous Year Solved Question Paper in Hindi

IGNOU BZYET-141 Previous Year Solved Question Paper in English

Q1. (a) Match the terms under Column A with their given under Column B: 5×1=5 Column A Column B (i) Lysozyme (1) Bacterial disease (ii) Allergy (2) Attacks on our own cells (iii) Autoimmunity (3) Clears bacterial cell wall (iv) Pneumonia (4) Interleukin-1 (v) Cytokine (5) Type-I hypersensitivity (b) Define the following terms : 5×1=5 (i) Chemotaxis (ii) Opsonisation (iii) Immunogenicity (iv) Immunoediting (v) Memory T-cells

Ans. (a) The matched pairs are as follows:

• (i) Lysozyme – (3) Clears bacterial cell wall
• (ii) Allergy – (5) Type-I hypersensitivity
• (iii) Autoimmunity – (2) Attacks on our own cells
• (iv) Pneumonia – (1) Bacterial disease
• (v) Cytokine – (4) Interleukin-1 (Interleukin-1 is a prime example of a cytokine)

(b) Definitions of the following terms:

• (i) Chemotaxis: This is the directed movement of a motile cell or organism in response to a chemical stimulus. In immunology, it refers to the migration of immune cells, such as neutrophils and macrophages, towards the site of infection or injury along a concentration gradient of chemical signals called chemokines .
• (ii) Opsonisation: This is the process by which a pathogen is coated with molecules called opsonins (e.g., antibodies like IgG, or complement proteins like C3b). This coating enhances the efficiency of phagocytosis because phagocytes have receptors for these opsonins, making it easier for them to recognize and engulf the pathogen.
• (iii) Immunogenicity: This is the ability of a substance, known as an antigen or immunogen, to provoke an adaptive immune response (both humoral and cell-mediated) within a host. Factors that influence immunogenicity include the substance’s foreignness, molecular size, chemical complexity, and degradability.
• (iv) Immunoediting: Also known as cancer immunoediting, this is a dynamic process describing the dual role of the immune system in both protecting against and shaping the development of tumors. It consists of three phases: Elimination (where the immune system successfully destroys developing tumor cells), Equilibrium (a state where tumor growth is controlled by the immune system), and Escape (where tumor variants evade immune detection and grow uncontrollably).
• (v) Memory T-cells: These are a subset of T lymphocytes that are long-lived and have been previously activated by a specific antigen. Upon re-exposure to the same antigen, these memory cells can mount a faster, stronger, and more effective secondary immune response. They are crucial for long-term immunity following an infection or vaccination.

Q2. (a) Discuss clonal selection theory. 5 (b) Explain the phagocytosis process with schematic flow chart. 5

Ans. (a) Clonal Selection Theory: The clonal selection theory, proposed by Sir Frank Macfarlane Burnet, is the central paradigm of adaptive immunity. It explains how the immune system responds to a specific antigen by activating a specific lymphocyte. The core tenets of the theory are:

• Pre-existence and Specificity: The body contains a vast population of lymphocytes (B and T cells). Each lymphocyte is genetically programmed to express a unique surface receptor that recognizes only one specific antigen (or epitope). This vast diversity of receptors is generated before any encounter with an antigen.
• Selection: When a foreign antigen enters the body, it circulates until it encounters a lymphocyte with a receptor that fits it. This binding “selects” that specific lymphocyte out of the millions of others.
• Proliferation (Clonal Expansion): Upon activation by the antigen, the selected lymphocyte undergoes rapid cell division. This creates a large population of identical cells, or a “clone,” all specific for the same antigen.
• Differentiation: The cells of the clone then differentiate into two main types:
  • Effector Cells: These are short-lived cells that carry out the immediate immune response. Activated B cells differentiate into plasma cells that secrete large quantities of antibodies. Activated T cells differentiate into helper T cells or cytotoxic T cells .
  • Memory Cells: A smaller subset of the clone differentiates into long-lived memory cells . These cells persist after the infection is cleared and provide long-term immunity by enabling a rapid and robust response upon subsequent exposure to the same antigen.

  This theory also explains self-tolerance, as lymphocytes that recognize self-antigens are eliminated during their development in a process called clonal deletion.

  (b) Process of Phagocytosis: Phagocytosis is a fundamental process of the innate immune system where specialized cells called phagocytes (e.g., macrophages, neutrophils, dendritic cells) engulf and digest pathogens, dead cells, and other particulate matter. The process can be broken down into the following steps:

  1. Chemotaxis and Adherence: Phagocytes are attracted to the site of infection by chemical signals (chemotaxis). Once there, the phagocyte must attach to the microbe. This adherence is greatly facilitated by opsonization , where the microbe is coated with opsonins like antibodies or complement proteins.
  2. Ingestion: The phagocyte extends its cell membrane, forming projections called pseudopods that surround the microbe. The pseudopods fuse, enclosing the particle within a membrane-bound vesicle called a phagosome .
  3. Phagolysosome Formation: The phagosome moves into the cytoplasm and fuses with a lysosome . Lysosomes are organelles containing a cocktail of potent digestive enzymes and a low pH environment. The resulting fused vesicle is called a phagolysosome .
  4. Digestion and Killing: Inside the phagolysosome, the microbe is killed and broken down. This is achieved by lysosomal enzymes (e.g., lysozyme, proteases) and by a “respiratory burst,” which generates toxic reactive oxygen species (e.g., superoxide anion, hydrogen peroxide).
  5. Exocytosis/Antigen Presentation: Indigestible debris is expelled from the cell via exocytosis. In the case of antigen-presenting cells like macrophages, some of the digested peptide fragments are loaded onto MHC class II molecules and presented on the cell surface to activate helper T cells, thus linking innate and adaptive immunity.

  
  Schematic Flow Chart:
  

  [Microbe] → [Chemotaxis of Phagocyte] → [Adherence to Microbe] → [Ingestion by Pseudopods] → [Formation of Phagosome] → [Fusion with Lysosome] → [Formation of Phagolysosome] → [Killing and Digestion] → [Formation of Residual Body] → [Discharge/Exocytosis]

  Q3. (a) What is an adaptive immunity ? Enlist its characteristics. 5 (b) Describe the structure and functions of bone marrow with suitable diagram. 5

  Ans. (a) Adaptive Immunity: Adaptive immunity, also known as acquired or specific immunity, is a subsystem of the overall immune system that is composed of highly specialized cells and processes that eliminate pathogens or prevent their growth. Unlike the innate immune system, which is always ready to respond, the adaptive response is developed over a lifetime of encounters with pathogens or through vaccination. It is mediated by lymphocytes (B-cells and T-cells) and is characterized by its high specificity and memory. The key characteristics of adaptive immunity are:

  • Specificity: Adaptive immune responses are precisely targeted against specific antigens. A response to one pathogen or antigen does not confer immunity to another, unrelated one.
  • Diversity: The system is capable of recognizing and responding to a virtually limitless number of different antigens. This is due to the vast repertoire of unique antigen receptors on B and T lymphocytes, generated through genetic recombination.
  • Memory: After an initial encounter with a specific antigen, the adaptive immune system “remembers” it. Subsequent exposures to the same antigen elicit a faster, stronger, and more effective response (the secondary immune response), due to the presence of memory cells.
  • Clonal Expansion: Upon activation by an antigen, specific lymphocytes proliferate rapidly, generating a large clone of cells with the same antigen specificity, sufficient to combat the infection.
  • Self-Tolerance: A crucial feature is the ability to distinguish between foreign antigens (“non-self”) and the body’s own molecules (“self”). This prevents the immune system from attacking the body’s own tissues. Failure of self-tolerance leads to autoimmune diseases.
  • Specialization: The system can mount different types of responses that are optimized for different classes of microbes. For example, humoral immunity is best for extracellular microbes, while cell-mediated immunity is best for intracellular microbes.

  (b)
  
  Structure and Functions of Bone Marrow:
  

  The bone marrow is the spongy tissue found inside the central cavity of bones. It is a primary lymphoid organ and the principal site of hematopoiesis (blood cell formation) in adults.

  
  Structure:
  

  Bone marrow consists of a hematopoietic compartment and a vascular compartment, all supported by a stroma. There are two main types:

  • Red Marrow: This is the hematopoietically active marrow. It is rich in hematopoietic stem cells (HSCs) , which are the progenitors for all blood cells. It also contains a complex network of stromal cells (fibroblasts, endothelial cells, adipocytes), and an extensive network of blood vessels called sinusoids . This intricate microenvironment provides the necessary growth factors and support for the differentiation and maturation of blood cells. Mature cells enter the circulation by passing through the walls of these sinusoids.
  • Yellow Marrow: This marrow is hematopoietically inactive and is composed primarily of fat cells (adipocytes). It serves as an energy reserve. With age, the amount of red marrow decreases and is replaced by yellow marrow. However, under conditions of high demand, such as severe anemia or infection, yellow marrow can revert to red marrow to increase blood cell production.

  
  (A suitable diagram would show a cross-section of a long bone, labeling the outer compact bone, the inner spongy bone filled with red marrow, and the central shaft containing yellow marrow. A magnified view of the red marrow would show HSCs, developing blood cells, adipocytes, and a sinusoid.)
  
  Functions:
  

  1. Hematopoiesis: This is the primary function. The bone marrow produces all cellular components of blood: red blood cells (erythrocytes) for oxygen transport, white blood cells (leukocytes) for immunity, and platelets (thrombocytes) for blood clotting.
  2. B-Cell Maturation: As a primary lymphoid organ, the bone marrow is the site where B lymphocytes originate and mature. During maturation, B cells that react against self-antigens are eliminated, establishing central B-cell tolerance.
  3. Immune Cell Reservoir: It stores a reserve of mature immune cells, which can be rapidly mobilized to sites of infection.
  4. Fat Storage: Yellow marrow stores fat, which can be used as an energy source by the body.
  5. Bone and Cartilage Maintenance: The stromal cells within the bone marrow contribute to the maintenance of bone and cartilage.

  Q4. Differentiate between any two of the following : 5+5 (a) Humoral immunity and Cell-mediated immunity (b) Antigen and Hapten (c) Isotypes and Allotypes

  Ans. (a) Difference between Humoral and Cell-mediated Immunity:

  Feature	Humoral Immunity	Cell-mediated Immunity
  Primary Mediator	Mediated by B-lymphocytes and their secreted products, antibodies .	Mediated directly by T-lymphocytes (Helper T-cells, Cytotoxic T-cells).
  Target	Primarily targets extracellular pathogens (e.g., bacteria, viruses in body fluids) and their toxins.	Primarily targets intracellular pathogens (e.g., viruses inside cells), cancerous cells, and foreign tissue grafts.
  Mechanism	Antibodies bind to antigens, leading to neutralization, opsonization (enhancing phagocytosis), and activation of the complement system.	Cytotoxic T-lymphocytes (CTLs) directly kill infected host cells. Helper T-cells activate other immune cells like macrophages and B-cells.
  Memory	Long-term protection is provided by memory B-cells .	Long-term protection is provided by memory T-cells .
  Passive Transfer	Immunity can be transferred to a non-immune individual by transferring serum containing antibodies.	Immunity can only be transferred by transferring viable T-lymphocytes, not by serum.

  (b) Difference between Antigen and Hapten:

  Feature	Antigen	Hapten
  Definition	A substance that can induce a specific immune response (is immunogenic) and can react with the products of that response (e.g., antibodies).	A small molecule that is not immunogenic by itself but can react with pre-existing antibodies.
  Immunogenicity	It is immunogenic , meaning it can trigger an immune response on its own.	It is not immunogenic on its own. It becomes immunogenic only when it binds to a larger carrier protein.
  Antigenicity	It is antigenic (can bind to antibodies or T-cell receptors).	It is antigenic (can bind to antibodies), but only after an immune response has been generated against the hapten-carrier conjugate.
  Molecular Weight	Typically large molecules, such as proteins and polysaccharides, with a high molecular weight (usually >10,000 Daltons).	Small molecules with a low molecular weight (usually <1,000 Daltons).
  Example	Bacterial cell wall proteins, viral glycoproteins, pollen, toxins.	Penicillin, certain drugs, poison ivy’s urushiol, dinitrophenol (DNP).

  (c) Difference between Isotypes and Allotypes:

  Feature	Isotype	Allotype
  Definition	Variants of immunoglobulin constant regions that define the different classes and subclasses of heavy chains (e.g., μ, γ, α) and types of light chains (κ, λ).	Genetically determined, minor variations in the amino acid sequence of the constant regions of immunoglobulins that differ between individuals within a species.
  Presence	All isotypes are found in every healthy individual of a given species.	All individuals of a species do not share the same allotypes; their presence is determined by the specific alleles inherited from parents.
  Genetic Basis	Encoded by different constant region genes (e.g., Cμ, Cγ, Cα genes).	Encoded by different alleles of the same constant region gene.
  Location	These differences are located in the constant (C) regions of both heavy and light chains. Isotypes determine the function of the antibody.	These minor differences are also located in the constant regions of heavy or light chains but do not significantly alter the function.
  Example	The five major classes of antibodies: IgM, IgG, IgA, IgD, and IgE are different isotypes. Subclasses like IgG1, IgG2 are also isotypes.	Gm markers on the IgG heavy chain and Km markers on the kappa light chain are examples of human allotypes.

  Q5. (a) Discuss the role of growth factors in Haematopoiesis. 5 (b) Elaborate the different types of vaccines. 5

  Ans. (a) Role of Growth Factors in Haematopoiesis: Haematopoiesis is the process of blood cell formation, originating from Hematopoietic Stem Cells (HSCs) in the bone marrow. This complex process is tightly regulated by a group of signaling proteins known as hematopoietic growth factors . These factors, which are a type of cytokine, are essential for the survival, proliferation, and differentiation of HSCs and their progenitor cells into all the different mature blood cell lineages. The key roles and examples of these growth factors include:

  • Survival and Proliferation: Growth factors bind to specific receptors on the surface of hematopoietic cells, triggering intracellular signaling pathways that prevent apoptosis (programmed cell death) and stimulate cell division. Stem Cell Factor (SCF) is crucial for the survival and proliferation of early HSCs.
  • Lineage-Specific Differentiation: Different growth factors guide progenitor cells to commit to a specific lineage. They act in a hierarchical and often synergistic manner.
    • Erythropoietin (EPO): Primarily produced by the kidneys, EPO is the main regulator of red blood cell (erythrocyte) production.
    • Thrombopoietin (TPO): Produced by the liver, TPO stimulates the development of megakaryocytes and the subsequent production of platelets (thrombocytes).
    • Colony-Stimulating Factors (CSFs): This family is critical for white blood cell production.
      • Granulocyte-Macrophage CSF (GM-CSF) promotes the production of neutrophils, eosinophils, basophils, and monocytes.
      • Granulocyte CSF (G-CSF) specifically stimulates the production of neutrophils.
      • Macrophage CSF (M-CSF) drives the differentiation of monocytes and macrophages.
    • Interleukins (ILs): Many interleukins also function as hematopoietic growth factors. For example, IL-7 is vital for the development of lymphocytes (B and T cells), while IL-5 is a key factor for eosinophil production.

    In summary, hematopoietic growth factors act as a sophisticated communication network, ensuring that the body produces the right number and type of blood cells to meet physiological demands and respond to challenges like infection or injury.

    (b) Different Types of Vaccines: Vaccines are biological preparations that provide active acquired immunity to a specific infectious disease. They work by introducing an agent that resembles a disease-causing microorganism, stimulating the immune system to produce antibodies and memory cells. The major types of vaccines are:

    1. Live-Attenuated Vaccines: These contain a weakened (attenuated) form of the living microbe. Because it is so similar to the natural infection, it creates a very strong and long-lasting immune response.
       • Examples: MMR (Measles, Mumps, Rubella), Chickenpox, Oral Polio Vaccine (OPV).
    2. Inactivated (Killed) Vaccines: These are made from the microbe that has been killed with heat, chemicals, or radiation. They cannot cause disease, but the immune response is generally weaker than with live vaccines, often requiring multiple booster doses.
       • Examples: Inactivated Polio Vaccine (IPV) , Hepatitis A, Rabies.
    3. Toxoid Vaccines: These are used for diseases caused by a toxin produced by the bacteria, rather than the bacteria itself. The vaccine contains an inactivated toxin, called a toxoid, which is no longer harmful but elicits an immune response against the toxin.
       • Examples: Tetanus and Diphtheria vaccines.
    4. Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines: These use only specific pieces of the pathogen—such as its protein, sugar, or capsid—to provoke an immune response.
       • Subunit vaccines: Contain purified antigens. Example: Hepatitis B , acellular Pertussis.
       • Conjugate vaccines: These link a polysaccharide (a type of sugar) from the microbe’s outer coat to a carrier protein. This is particularly effective for evoking a strong immune response in infants against bacteria with polysaccharide capsules. Examples: Hib (Haemophilus influenzae type b) , Pneumococcal vaccine.
    5. mRNA Vaccines: A modern type where a piece of genetic material, messenger RNA (mRNA), is used. The mRNA instructs the body’s cells to produce a specific antigen (e.g., a viral spike protein), which then triggers an immune response.
       • Examples: Pfizer-BioNTech and Moderna COVID-19 vaccines.
    6. Viral Vector Vaccines: These use a modified, harmless virus (the vector) to deliver the genetic code for an antigen into the body’s cells. The cells then produce the antigen, stimulating an immune response.
       • Examples: Johnson & Johnson and AstraZeneca COVID-19 vaccines.

    Q6. (a) Enlist the actions and properties of cytokines. 5 (b) Define proteosome. How does it degrade antigen protein into peptides ? 2+3

    Ans. (a) Properties and Actions of Cytokines: Cytokines are a broad category of small, secreted proteins that are crucial for cell-to-cell communication, particularly in the immune system. They act as chemical messengers that regulate the intensity and duration of immune responses. Properties of Cytokines:

    • Pleiotropy: A single cytokine can have multiple, different effects on various cell types. For example, Interleukin-4 (IL-4) can promote B-cell proliferation, T-cell differentiation, and macrophage activation.
    • Redundancy: Different cytokines can have similar or overlapping functions. This ensures that if one cytokine pathway is deficient, another can often compensate. For instance, IL-2, IL-4, and IL-5 can all induce B-cell proliferation.
    • Synergy: The combined effect of two or more cytokines is greater than the sum of their individual effects. For example, IFN-γ and TNF-α work synergistically to increase the expression of MHC class I molecules.
    • Antagonism: The action of one cytokine can inhibit or counteract the effects of another. For example, IL-10 (an anti-inflammatory cytokine) can inhibit the production of IFN-γ (a pro-inflammatory cytokine).
    • Cascade Induction: The action of one cytokine on a target cell can induce that cell to produce other cytokines, creating a signaling cascade that amplifies the response.

    
    Actions of Cytokines:
    

    • Mediation and regulation of innate and adaptive immunity.
    • Regulation of inflammation.
    • Control of the proliferation and differentiation of immune cells (hematopoiesis).
    • Induction of chemotaxis (movement of cells towards a chemical signal).
    • Stimulation of effector functions, such as antibody production by B cells or cytotoxic activity of NK cells and CTLs.
    • Communication between leukocytes (interleukins) and interference with viral replication (interferons).

    (b)
    
    Proteasome and its Role in Antigen Degradation:
    
    Definition (2 marks):
    

    A
    
    proteasome
    
    is a large, cylindrical, multi-protein complex found in the cytoplasm and nucleus of all eukaryotic cells. Its primary function is to degrade unneeded, damaged, or misfolded proteins by proteolysis, a chemical reaction that breaks peptide bonds. It is the central component of the
    
    ubiquitin-proteasome system
    
    , which is the cell’s main pathway for non-lysosomal protein degradation.

    
    Degradation of Antigen Protein into Peptides (3 marks):
    

    The proteasome plays a critical role in the
    
    MHC class I antigen processing pathway
    
    , which is essential for the immune system to detect and eliminate cells infected with intracellular pathogens (like viruses) or cancerous cells.

    The process is as follows:

    1. Tagging for Destruction (Ubiquitination): Intracellular proteins, such as a viral protein or a mutated self-protein, are targeted for degradation. They are “tagged” by the covalent attachment of multiple copies of a small protein called ubiquitin . This polyubiquitin chain acts as a signal for the proteasome.
    2. Recognition and Unfolding: The 19S regulatory cap of the proteasome recognizes the polyubiquitinated protein. Using ATP, it unfolds the protein and threads it into the central proteolytic core of the proteasome.
    3. Proteolysis: The 20S core particle of the proteasome contains the active proteolytic sites. It cleaves the unfolded protein into short peptide fragments, typically 8-11 amino acids in length.
    4. Transport and Loading: These peptides are then transported from the cytoplasm into the endoplasmic reticulum (ER) by a specific transporter protein called TAP (Transporter associated with Antigen Processing) .
    5. MHC Class I Presentation: Inside the ER, these peptides are loaded onto newly synthesized MHC class I molecules. The stable peptide-MHC I complex is then transported to the cell surface, where it is displayed for recognition by the T-cell receptors on Cytotoxic T-Lymphocytes (CTLs) .

    Q7. (a) Explain the major steps of western blotting technique with suitable diagram. 5 (b) Give a brief account on probiotics and prebiotics. 5

    Ans. (a) Western Blotting Technique: Western blotting, also known as immunoblotting, is a widely used analytical technique to detect and quantify a specific protein within a complex mixture of proteins extracted from cells or tissues. The method identifies proteins based on their molecular weight and their specific interaction with a corresponding antibody. The major steps are:

    1. Sample Preparation and Gel Electrophoresis (SDS-PAGE): First, proteins are extracted from the sample (e.g., cells, tissue). This protein mixture is then loaded onto a polyacrylamide gel . An electric current is applied (electrophoresis), causing the proteins, which have been coated with a negative charge by the detergent SDS, to migrate through the gel. They are separated primarily based on their size (molecular weight), with smaller proteins moving faster and farther.
    2. Blotting/Transfer: The separated proteins are transferred from the gel onto a solid support membrane, typically made of nitrocellulose or PVDF . This transfer is usually achieved by applying an electric field (electroblotting) that moves the proteins from the gel to the membrane, creating a mirror image of the protein separation pattern.
    3. Blocking: To prevent non-specific binding of antibodies to the membrane surface, the membrane is incubated in a “blocking” solution, which is a solution of an irrelevant protein like bovine serum albumin (BSA) or non-fat milk. This step ensures that the antibodies will only bind to the target protein.
    4. Antibody Incubation (Primary and Secondary):
       • The membrane is first incubated with a primary antibody that is specific to the protein of interest. This antibody binds only to its target protein on the membrane.
       • After washing away unbound primary antibody, the membrane is incubated with a secondary antibody . This antibody is engineered to bind to the primary antibody and is conjugated (linked) to a reporter enzyme (like Horseradish Peroxidase, HRP) or a fluorescent tag.
    5. Detection and Visualization: The final step is to detect the location of the secondary antibody. If an enzyme-linked antibody was used, a chemical substrate is added that the enzyme converts into a product that emits light (chemiluminescence) or has a visible color. This signal is captured on X-ray film or with a digital imager, appearing as a band that confirms the presence and indicates the molecular weight of the target protein.

    
    (A suitable diagram would be a flowchart showing: SDS-PAGE Gel → Transfer Setup → Membrane with protein bands → Blocking Step → Primary Antibody Incubation → Secondary Antibody Incubation → Detection, showing a final band on a film.)
    

    (b) Probiotics and Prebiotics: Probiotics and prebiotics are both related to promoting a healthy gut microbiome, which is crucial for digestion, nutrient absorption, and immune function. Although they work together, they are fundamentally different. Probiotics:

    • Definition: Probiotics are live microorganisms (beneficial bacteria and yeasts) which, when administered in adequate amounts, confer a health benefit on the host. They are often called “good” or “friendly” bacteria.
    • Mechanism: They work by improving or restoring the gut flora. They can compete with harmful pathogens for nutrients and attachment sites on the intestinal wall, produce antimicrobial substances, and modulate the host’s immune system by enhancing the production of certain antibodies (like IgA) and regulating inflammatory responses.
    • Sources: Probiotics are found in fermented foods such as yogurt, kefir, sauerkraut, kimchi, and kombucha, as well as in dietary supplements. Common probiotic strains belong to the Lactobacillus and Bifidobacterium groups.

    
    Prebiotics:
    

    • Definition: Prebiotics are a type of non-digestible dietary fiber that acts as “food” for the beneficial bacteria already living in the gut. They selectively stimulate the growth and/or activity of these beneficial microbes.
    • Mechanism: Prebiotics pass through the upper gastrointestinal tract undigested and are fermented by the gut microbiota in the colon. This fermentation process produces short-chain fatty acids (SCFAs) , such as butyrate, acetate, and propionate. These SCFAs serve as an energy source for colon cells, lower the pH of the colon (inhibiting pathogens), and have systemic anti-inflammatory effects.
    • Sources: Prebiotics are found naturally in many plant-based foods, including garlic, onions, leeks, asparagus, bananas, oats, and chicory root. Common prebiotics include fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), and inulin.

    In essence, probiotics are the beneficial bacteria themselves, while prebiotics are the food that helps these bacteria thrive.

    Q8. Write short notes on any two of the following : 2×5=10 (a) Type-IV hypersensitivity (b) Tumor antigen (c) Humoral response (d) T-cell differentiation

    Ans. (a) Type-IV Hypersensitivity: Type-IV hypersensitivity, also known as Delayed-Type Hypersensitivity (DTH) , is a cell-mediated immune response, distinct from the other three types which are antibody-mediated. The term “delayed” refers to the fact that the reaction takes 24 to 72 hours to develop after exposure to the antigen. Mediators: The primary mediators of this response are antigen-specific T-lymphocytes , specifically T helper 1 ( Th1 ) cells, and macrophages . Cytotoxic T-lymphocytes (CTLs) can also be involved. Mechanism: The response occurs in two phases:

    1. Sensitization Phase: Upon initial exposure to the antigen (e.g., proteins from Mycobacterium tuberculosis or urushiol from poison ivy), antigen-presenting cells (APCs) process the antigen and present it to naive helper T-cells. These T-cells then proliferate and differentiate into sensitized memory Th1 cells.
    2. Elicitation Phase: Upon subsequent exposure to the same antigen, the sensitized memory Th1 cells are re-activated. They release a variety of cytokines, most notably interferon-gamma (IFN-γ) . These cytokines recruit large numbers of macrophages and other inflammatory cells to the site. The recruited macrophages are activated by IFN-γ, causing them to release lytic enzymes and reactive oxygen species, which leads to inflammation and tissue damage.

    
    Examples:
    
    The classic example is the
    
    tuberculin (Mantoux) skin test
    
    . Other examples include contact dermatitis from exposure to poison ivy or nickel, and the granulomatous inflammation seen in diseases like tuberculosis and sarcoidosis.

    (b) Tumor Antigen: Tumor antigens are molecules, typically proteins or carbohydrates, expressed by tumor cells that can be recognized by the host’s immune system, particularly by T-cells or antibodies. The ability of the immune system to recognize these antigens is the basis of cancer immunotherapy. Tumor antigens are broadly classified into two categories:

    1. Tumor-Specific Antigens (TSAs):
       • These antigens are found exclusively on tumor cells and not on any normal cells.
       • They often arise from mutations in genes (e.g., mutated p53, RAS) that are unique to the cancer cell. They can also be proteins encoded by oncogenic viruses, such as the E6 and E7 proteins from Human Papillomavirus (HPV) in cervical cancer.
       • Because they are truly “foreign” to the immune system, TSAs are considered ideal targets for highly specific cancer immunotherapies.
    2. Tumor-Associated Antigens (TAAs):
       • These antigens are present on both tumor cells and some normal cells, but they are expressed abnormally or at much higher levels (overexpressed) on tumor cells.
       • Categories include: differentiation antigens (e.g., PSA in prostate cancer), overexpressed antigens (e.g., HER2 in breast cancer), and cancer-testis antigens (e.g., MAGE family), which are normally expressed only in immune-privileged sites like the testes.

    The identification of tumor antigens has been crucial for developing diagnostic biomarkers, prognostic tools, and therapeutic strategies like cancer vaccines and CAR-T cell therapy, which engineer a patient’s T-cells to recognize and attack cells bearing a specific tumor antigen.