Weekly Year 2: Cellular Immunology Exam - March 27, 2026 (Se

Question 1

Which of the following cell types is primarily responsible for mediating the specific, adaptive immune response by producing antibodies?

Accepted Answer

B lymphocyte — B lymphocytes (B cells) differentiate into plasma cells, which are the primary producers of antibodies, mediating humoral immunity, a key component of the adaptive immune response.

Question 2

Which of the following is a key characteristic that distinguishes innate immunity from adaptive immunity?

Accepted Answer

Rapid, non-specific response — Innate immunity provides an immediate, non-specific defense against pathogens, lacking memory and specific antigen recognition, which are hallmarks of adaptive immunity.

Question 3

The primary lymphoid organ where T lymphocytes mature and undergo selection processes is the:

Accepted Answer

Thymus — T lymphocytes originate in the bone marrow but migrate to the thymus for maturation, where they undergo positive and negative selection to ensure self-tolerance and MHC restriction.

Question 4

Which cell surface marker is characteristic of cytotoxic T lymphocytes (CTLs) and helps them recognize MHC Class I molecules?

Accepted Answer

CD8 — CD8 is a co-receptor found on cytotoxic T lymphocytes (CTLs) that binds to MHC Class I molecules, which present intracellular antigens to CD8+ T cells.

Question 5

Which component of an antibody molecule is responsible for its antigen-binding specificity?

Accepted Answer

Variable region of both heavy and light chains — The variable regions (V regions) of both the heavy and light chains form the antigen-binding site (Fab region) and determine the antibody's specificity for a particular epitope.

Question 6

Somatic recombination, a critical process for generating antibody diversity, involves the rearrangement of gene segments. Which segments are involved in generating the light chain variable region?

Accepted Answer

V, J segments — The light chain variable region is formed by the rearrangement of Variable (V) and Joining (J) gene segments. The heavy chain also includes Diversity (D) segments.

Question 7

Which immunoglobulin class is typically found as a pentamer in serum and is the first antibody produced in a primary immune response?

Accepted Answer

IgM — IgM exists as a pentamer in its secreted form and is the predominant antibody produced early in a primary immune response. It also functions as a monomer on the surface of B cells.

Question 8

MHC Class II molecules primarily present antigens that are derived from:

Accepted Answer

Extracellular pathogens — MHC Class II molecules present antigens derived from extracellular pathogens and proteins, which are internalized by antigen-presenting cells (APCs) and processed in endosomal/lysosomal compartments.

Question 9

What is the main function of dendritic cells in the immune system?

Accepted Answer

Presenting antigens to naive T cells — Dendritic cells are the most potent antigen-presenting cells (APCs) and are crucial for initiating primary T cell responses by presenting processed antigens to naive T cells in lymphoid organs.

Question 10

Which of the following cytokines is critical for the proliferation and differentiation of T cells, often referred to as T cell growth factor?

Accepted Answer

IL-2 — Interleukin-2 (IL-2) is a potent T cell growth factor, promoting the proliferation and differentiation of activated T cells, including cytotoxic T cells and regulatory T cells.

Question 11

The process by which B cells change the class of antibody they produce (e.g., from IgM to IgG) while maintaining the same antigen specificity is called:

Accepted Answer

Class switch recombination — Class switch recombination (or isotype switching) allows B cells to change the constant region of their heavy chain, thereby changing the antibody class (e.g., from IgM to IgG, IgA, or IgE) without altering antigen specificity.

Question 12

Natural Killer (NK) cells are part of the innate immune system and primarily target:

Accepted Answer

Virally infected cells and tumor cells — NK cells are lymphocytes of the innate immune system that recognize and kill virally infected cells and tumor cells, typically by detecting changes in MHC Class I expression on their surface.

Question 13

Which of the following is an example of an immunological technique that uses an enzyme (e.g., horseradish peroxidase) conjugated to an antibody for detection, often resulting in a colorimetric readout?

Accepted Answer

Enzyme-linked immunosorbent assay (ELISA) — ELISA (Enzyme-Linked Immunosorbent Assay) commonly uses enzyme-conjugated antibodies (like HRP) to detect antigens or antibodies, with the enzyme converting a substrate into a detectable product, often a color change.

Question 14

The CD4 co-receptor on T helper cells binds to a non-polymorphic region of which MHC molecule?

Accepted Answer

MHC Class II — CD4 is a co-receptor on T helper cells that binds to the beta-2 domain of MHC Class II molecules, stabilizing the T cell receptor-MHC interaction.

Question 15

Which of the following terms describes the ability of a single B cell clone to express both IgM and IgD simultaneously on its surface, with identical antigen specificity?

Accepted Answer

Alternative RNA splicing — Mature naive B cells co-express IgM and IgD on their surface with the same antigen specificity. This is achieved by alternative RNA splicing of a single primary RNA transcript, not class switching.

Question 16

The complement system is a crucial part of innate immunity. Which pathway is activated by antigen-antibody complexes?

Accepted Answer

Classical pathway — The classical pathway of complement activation is primarily triggered by the binding of C1q to antibody-antigen complexes (typically IgM or IgG) or directly to pathogen surfaces.

Question 17

Which type of immunoglobulin is primarily found in external secretions like mucus, tears, saliva, and breast milk, providing mucosal immunity?

Accepted Answer

IgA — Secretory IgA (sIgA), often found as a dimer, is the predominant antibody in mucosal secretions, playing a crucial role in protecting mucosal surfaces from pathogens.

Question 18

Negative selection in the thymus ensures that developing T cells do not react strongly against self-antigens. What happens to T cells that bind too strongly to self-MHC/self-peptide complexes?

Accepted Answer

They undergo apoptosis (programmed cell death). — During negative selection, T cells that bind too strongly to self-MHC/self-peptide complexes expressed by medullary thymic epithelial cells or dendritic cells undergo apoptosis to prevent autoimmunity.

Question 19

What is the primary role of the CD3 complex associated with the T cell receptor (TCR)?

Accepted Answer

Signal transduction — The CD3 complex (composed of CD3γ, CD3δ, CD3ε, and ζ chains) is non-covalently associated with the TCR and is essential for transmitting the signal from the antigen-bound TCR into the cell.

Question 20

Which of the following is NOT a mechanism contributing to antibody diversity?

Accepted Answer

Class switch recombination — Class switch recombination changes the constant region (isotype) of the antibody but does not alter the antigen-binding specificity or diversity of the variable region. Somatic recombination, junctional diversity, and somatic hypermutation all contribute to creating diverse antigen-binding sites.

Question 21

A patient presents with a severe bacterial infection. Which type of leukocyte would you expect to be significantly elevated in their blood count?

Accepted Answer

Neutrophils — Neutrophils are the most abundant type of white blood cell and are typically the first responders to bacterial infections, making their count elevated during such conditions (neutrophilia).

Question 22

Which cytokine is known for its potent antiviral effects and is produced by virally infected cells, leading to an 'antiviral state' in neighboring cells?

Accepted Answer

Interferon-alpha (IFN-α) — Type I interferons, primarily IFN-α and IFN-β, are produced by virally infected cells and induce an antiviral state in uninfected cells, inhibiting viral replication and enhancing immune responses.

Question 23

The process of opsonization, which enhances phagocytosis, can be mediated by which of the following immune components?

Accepted Answer

Complement proteins (e.g., C3b) — Opsonization is the process by which pathogens are marked for ingestion and destruction by phagocytes. Antibodies (IgG) and complement proteins (especially C3b) are major opsonins.

Question 24

Which professional antigen-presenting cell (APC) is highly efficient at cross-presentation, allowing it to present exogenous antigens on MHC Class I molecules?

Accepted Answer

Dendritic cell — Dendritic cells are uniquely capable of cross-presentation, where they can take up extracellular antigens and present them on MHC Class I molecules to activate naive CD8+ T cells, important for antiviral and anti-tumor immunity.

Question 25

An individual with a defect in the RAG (Recombination Activating Gene) enzymes would most likely suffer from a severe deficiency in which cell types?

Accepted Answer

T cells and B cells — RAG enzymes are essential for V(D)J recombination, the process that rearranges gene segments to form functional T cell receptors (TCRs) and B cell receptors (BCRs). A defect would severely impair the development of both T and B cells, leading to Severe Combined Immunodeficiency (SCID).

Question 26

What is the primary function of regulatory T cells (Tregs)?

Accepted Answer

To suppress immune responses and maintain self-tolerance — Regulatory T cells (Tregs) play a critical role in maintaining immunological self-tolerance and preventing excessive immune responses by suppressing the activity of other immune cells.

Question 27

Which of the following describes the immunological term for the small part of an antigen that is recognized by an antibody or T cell receptor?

Accepted Answer

Epitope — An epitope (or antigenic determinant) is the specific molecular structure on an antigen that is recognized and bound by an antibody or T cell receptor.

Question 28

The constant region of the heavy chain of an antibody determines its:

Accepted Answer

Class (isotype) and effector function — The constant region (Fc region) of the heavy chain determines the antibody's class (e.g., IgG, IgM, IgA) and its biological effector functions, such as complement activation, opsonization, and placental transfer.

Question 29

Which immunological technique is commonly used to identify and quantify different cell populations in a heterogeneous sample based on their surface markers, using fluorochrome-conjugated antibodies and a laser?

Accepted Answer

Flow cytometry — Flow cytometry uses fluorescently labeled antibodies to detect specific cell surface or intracellular markers, allowing for the rapid identification and quantification of different cell types in a mixed population.

Question 30

The process by which B cells increase the binding strength (affinity) of their antibodies to a specific antigen over time is called:

Accepted Answer

Somatic hypermutation and affinity maturation — Somatic hypermutation introduces point mutations in the variable regions of immunoglobulin genes, followed by affinity maturation, where B cells producing higher-affinity antibodies are preferentially selected and proliferate.

Question 31

Which of the following is NOT a primary function of the complement system?

Accepted Answer

Antigen presentation to T cells — While complement components can enhance antigen presentation by B cells, the complement system itself does not directly present antigens to T cells. Its primary functions include lysis, opsonization, and promoting inflammation/chemotaxis.

Question 32

A patient with a defect in phagolysosome formation in macrophages would likely have impaired clearance of which type of pathogens?

Accepted Answer

Extracellular bacteria and fungi — Phagolysosomes are formed by the fusion of phagosomes (containing internalized pathogens) with lysosomes. This is crucial for killing and degrading extracellular bacteria and fungi that are internalized by phagocytosis.

Question 33

Which type of hypersensitivity reaction is mediated by IgE antibodies and involves mast cell degranulation and histamine release?

Accepted Answer

Type I (Immediate) — Type I hypersensitivity (immediate hypersensitivity) is mediated by IgE antibodies binding to mast cells and basophils, leading to rapid degranulation upon re-exposure to the allergen and release of inflammatory mediators like histamine.

Question 34

The process by which immune cells are attracted to a site of infection or inflammation by chemical signals is known as:

Accepted Answer

Chemotaxis — Chemotaxis is the movement of a cell or organism in response to a chemical stimulus. In immunology, it refers to the directed migration of immune cells (e.g., neutrophils, macrophages) towards chemoattractants at sites of infection or injury.

Question 35

What is the primary role of perforin and granzymes, secreted by cytotoxic T lymphocytes (CTLs)?

Accepted Answer

To induce apoptosis in target cells — Cytotoxic T lymphocytes (CTLs) use perforin to create pores in the target cell membrane and granzymes (serine proteases) to enter the cell and initiate apoptotic pathways, leading to the destruction of infected or cancerous cells.

Question 36

Which of the following cell types is primarily involved in host defense against parasitic infections and allergic reactions?

Accepted Answer

Eosinophils — Eosinophils are granulocytes that play a key role in defense against parasitic helminths (worms) and are also heavily involved in allergic and asthmatic responses.

Question 37

The Major Histocompatibility Complex (MHC) genes are highly polymorphic. What does 'polymorphic' mean in this context?

Accepted Answer

They have multiple alleles within the population. — Polymorphism refers to the existence of multiple different alleles (variants) for a gene within a population. The high polymorphism of MHC genes ensures that a wide variety of peptides can be presented, contributing to population-level immunity.

Question 38

Which co-stimulatory molecule, found on antigen-presenting cells (APCs), is crucial for full activation of naive T cells by binding to CD28 on the T cell?

Accepted Answer

B7 (CD80/CD86) — B7 molecules (CD80 and CD86) on APCs provide the crucial co-stimulatory signal by binding to CD28 on naive T cells, which is necessary for complete T cell activation and proliferation, preventing anergy.

Question 39

Central tolerance for T cells occurs in the thymus, while peripheral tolerance mechanisms typically occur in:

Accepted Answer

Lymph nodes and peripheral tissues — Central tolerance eliminates self-reactive lymphocytes during their development in primary lymphoid organs (thymus for T cells, bone marrow for B cells). Peripheral tolerance mechanisms function in secondary lymphoid organs and peripheral tissues to control self-reactive lymphocytes that escape central tolerance.

Question 40

Which immunoglobulin is associated with immediate hypersensitivity reactions and defense against parasitic infections, primarily by binding to Fc receptors on mast cells and basophils?

Accepted Answer

IgE — IgE antibodies are strongly associated with allergic reactions (Type I hypersensitivity) and play a role in immunity against parasites. They bind with high affinity to Fc receptors (FcεRI) on mast cells and basophils.

Question 41

The specific region on the T cell receptor (TCR) that binds to an antigen-MHC complex is formed by:

Accepted Answer

Variable regions of alpha and beta chains — Similar to antibodies, the antigen-binding site of the TCR is formed by the variable regions of its alpha and beta (or gamma and delta) chains, allowing it to specifically recognize a processed peptide presented by an MHC molecule.

Question 42

Which of the following is a key feature of memory T and B cells, crucial for a more rapid and robust secondary immune response?

Accepted Answer

Lower activation threshold and increased numbers — Memory lymphocytes (T and B cells) are more numerous than naive cells specific for the same antigen, have a lower activation threshold, and respond more quickly and effectively upon re-exposure to the antigen, leading to a faster and stronger secondary immune response.

Question 43

What is the role of the invariant chain (Ii) in MHC Class II antigen presentation?

Accepted Answer

To prevent endogenous peptides from binding to MHC Class II in the ER — The invariant chain (Ii) binds to the peptide-binding groove of MHC Class II molecules in the ER, preventing premature binding of endogenous peptides. It also directs MHC Class II to endosomal compartments where it eventually dissociates, allowing exogenous peptides to bind.

Question 44

Which type of cytokine typically acts locally to induce inflammation and recruit immune cells to a site of infection?

Accepted Answer

Chemokines — Chemokines are a family of small cytokines that act as chemoattractants, guiding the migration of various immune cells to sites of inflammation or to specific lymphoid organs.

Question 45

A defect in which complement protein would primarily impair the ability to form the Membrane Attack Complex (MAC)?

Accepted Answer

C1q — C9 is the terminal component of the complement cascade. Multiple C9 molecules polymerize to form the pore-like structure of the Membrane Attack Complex (MAC), which causes osmotic lysis of target cells.

Question 46

The phenomenon where only one allele of an immunoglobulin heavy chain and one allele of an immunoglobulin light chain are expressed in a B cell is known as:

Accepted Answer

Allelic exclusion — Allelic exclusion ensures that each B cell expresses only one functional heavy chain allele and one functional light chain allele, leading to the production of antibodies with a single antigen specificity.

Question 47

Which cell type is crucial for activating naive CD8+ T cells against intracellular pathogens via cross-presentation?

Accepted Answer

Dendritic cells — Dendritic cells are the most efficient APCs for initiating primary T cell responses, including the cross-presentation of exogenous antigens on MHC Class I molecules to activate naive CD8+ T cells.

Question 48

What is the function of AID (Activation-Induced Cytidine Deaminase) enzyme in B cells?

Accepted Answer

To mediate somatic hypermutation and class switch recombination — AID is a critical enzyme in activated B cells that initiates somatic hypermutation and class switch recombination by deaminating cytosine to uracil in immunoglobulin genes, leading to DNA damage and subsequent repair pathways that introduce mutations or promote recombination.

Question 49

Which type of T helper cell is primarily involved in host defense against intracellular bacteria and viruses by activating macrophages and promoting cytotoxic T cell responses?

Accepted Answer

Th1 cells — Th1 cells produce cytokines like IFN-gamma, which activate macrophages to kill phagocytosed microbes and promote the differentiation of cytotoxic T cells, crucial for cell-mediated immunity against intracellular pathogens.

Question 50

A lack of MHC Class I molecules on the surface of a host cell would make it a primary target for which immune cell?

Accepted Answer

Natural Killer cells — Natural Killer (NK) cells recognize and kill cells that have downregulated their MHC Class I expression, a common strategy used by viruses to evade cytotoxic T cell detection.

Weekly Year 2: Cellular Immunology Exam - March 27, 2026 (Se

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