FYUG Even Semester Exam, 2025 Biotechnology (2nd Semester) Immunology (Course No: BTCSEC-151)

Full Marks: 50 | Pass Marks: 20 | Time: 2 Hours

UNIT-I

Question 1 (Answer any three) 1 x 3 = 3

(a) What is innate immunity?

Innate immunity is the non-specific, first line of defense that is present from birth. It provides immediate protection against pathogens through physical barriers (skin), chemical barriers, and cellular responses like phagocytosis.

(b) What is the function of cytotoxic T-cell?

The primary function of cytotoxic T-cells (CD8+) is to monitor body cells and eliminate those that are infected by viruses or have become cancerous by inducing apoptosis.

(c) Define antibody.

An antibody, also known as an immunoglobulin, is a Y-shaped protein produced by B-lymphocytes (plasma cells) that specifically binds to a particular antigen to neutralize or mark it for destruction.

(d) What is Fab fragment?

The Fab (Fragment antigen-binding) fragment is the region of an antibody that binds to antigens. It is composed of one constant and one variable domain of each of the heavy and light chains.

Question 2 (Answer any one) 2

Option A

(a) Write about adaptive immunity.

Adaptive (acquired) immunity is characterized by specificity and memory. It involves the activation of T and B lymphocytes that recognize specific antigens. Unlike innate immunity, it takes longer to initiate but provides a more potent and long-lasting defense upon subsequent exposure.

Option B

(b) Write a note on B-lymphocyte.

B-lymphocytes are a type of white blood cell that matures in the bone marrow. They are central to humoral immunity; upon activation by an antigen, they differentiate into plasma cells that secrete antibodies.

Question 3 (Answer any one) 5

Option A

(a) Give a brief account of the structure and function of immunoglobulins.

Structure: Immunoglobulins consist of four polypeptide chains—two identical heavy (H) chains and two identical light (L) chains—linked by disulfide bonds to form a Y-shaped molecule. Each chain has a variable (V) region for antigen binding and a constant (C) region that determines biological activity.

Functions:

  • Neutralization: Blocking the active sites of toxins or viruses.
  • Opsonization: Coating pathogens to enhance phagocytosis.
  • Complement Activation: Triggering the complement system to lyse bacteria.
  • Agglutination: Clumping together particulate antigens for easier clearance.

UNIT-II

Question 4 (Answer any three) 1 x 3 = 3

(b) What do you mean by allelic exclusion?

Allelic exclusion is a process by which only one of the two alleles for an immunoglobulin heavy or light chain is expressed in a single B-cell, ensuring that each B-cell produces antibodies with a single specificity.

(c) Write about immunologic memory.

Immunologic memory refers to the ability of the immune system to recognize an antigen that it has previously encountered and initiate a faster, stronger, and more specific secondary immune response.

Question 5 (Answer any one) 2

Option A

(a) Write a note on clonal selection theory.

This theory states that specific antigen receptors exist on lymphocytes before they encounter an antigen. When an antigen enters the body, it "selects" the specific lymphocyte that has a matching receptor, triggering that cell to proliferate and form a clone of identical cells to fight the infection.

Question 6 (Answer any one) 5

Option B

(b) Describe the genetic basis of antibody diversity.

Antibody diversity is generated through several genetic mechanisms:

  1. V(D)J Recombination: The random joining of different V (variable), D (diversity), and J (joining) gene segments.
  2. Junctional Flexibility: Random addition or subtraction of nucleotides at the joints between segments.
  3. Somatic Hypermutation: High-rate mutations in the variable regions of activated B-cells.
  4. Combinatorial Association: The random pairing of different heavy and light chains.

UNIT-III

Question 7 (Answer any three) 1 x 3 = 3

(a) What do you mean by MHC?

MHC stands for Major Histocompatibility Complex. It is a set of cell surface proteins essential for the acquired immune system to recognize foreign molecules.

(c) What is antigen-presenting cell?

An antigen-presenting cell (APC) is a specialized immune cell (like dendritic cells, macrophages, or B-cells) that captures, processes, and displays antigens on its surface via MHC molecules to activate T-cells.

Question 9 (Answer any one) 2 + 3 = 5

Option A

(a) Describe the structure of Class-I MHC molecule. Add a note on the function of Class-I MHC molecule.

Structure: It consists of a large transmembrane alpha (a) chain with three domains (a1, a2, a3) and a smaller, non-covalently linked protein called beta-2 microglobulin (B2m). The peptide-binding cleft is formed by the a1 and a2 domains.

Function: Class-I MHC molecules are expressed on nearly all nucleated cells. They present endogenous (cytosolic) antigens to CD8+ cytotoxic T-cells, signaling that the cell is infected and should be destroyed.

UNIT-IV

Question 10 (Answer any three) 1 x 3 = 3

(a) Define cytokines.

Cytokines are small signaling proteins secreted by immune cells that act as chemical messengers to regulate the intensity and duration of the immune response.

Question 12 (Answer any one) 1 + 4 = 5

Option A

(a) What is ELISA? Write down the principle and applications of ELISA.

ELISA (Enzyme-Linked Immunosorbent Assay): A biochemical technique used to detect the presence of an antibody or an antigen in a sample.

Principle: It relies on the specific binding between an antigen and an antibody. An enzyme-linked secondary antibody is used to generate a color change when a substrate is added, which is proportional to the amount of target substance present.

Applications: Diagnosis of HIV/AIDS, pregnancy testing, detection of food allergens, and screening for various viral/bacterial infections.

UNIT-V

Question 13 (Answer any three) 1 x 3 = 3

(a) What do you mean by passive immunization?

Passive immunization is the transfer of ready-made antibodies (from another human or animal) to an individual to provide immediate but temporary protection.

Question 15 (Answer any one) 5

Option B

(b) Write about immunodeficiency. Add a note on the structure of HIV.

Immunodeficiency is a state in which the immune system's ability to fight infectious disease and cancer is compromised or entirely absent.

Structure of HIV:

  • Envelope: Outer lipid bilayer containing gp120 and gp41 glycoproteins.
  • Capsid: Cone-shaped protein core (p24).
  • Genome: Two single-stranded RNA molecules.
  • Enzymes: Contains reverse transcriptase, integrase, and protease for replication.

Exam Focus Enhancements

Exam Tips: Immunology papers often focus on structures. [span_33](start_span)Practice drawing the Immunoglobulin (Antibody) and MHC Class I/II structures as they carry high marks[span_33](end_span).

Common Mistakes: Do not confuse "Innate" (non-specific) with "Adaptive" (specific) immunity. [span_35](start_span)Also, remember MHC-I is for CD8+ T-cells while MHC-II is for CD4+ T-cells[span_35](end_span).

Important Definitions:

  • Adjuvant: A substance added to a vaccine to boost the immune response.
  • Autoimmunity: A condition where the immune system mistakenly attacks the body's own tissues.

Answer Presentation: For genetic diversity (Q6), listing the mechanisms in a numbered list helps examiners quickly identify key points.