Weekly Year 2: Cellular Immunology Exam - March 13, 2026 (Se

Question 1

Which of the following microscopy techniques uses ultraviolet (UV) light for examining specimens?

Accepted Answer

Fluorescence microscopy — Fluorescence microscopy uses UV light to excite fluorochromes like FITC attached to specimens.

Question 2

Which of the following would be used as the most appropriate preliminary screening for the presence of antibodies to HIV proteins in a patient's blood sample?

Accepted Answer

ELISA — ELISA (Enzyme-Linked Immunosorbent Assay) is the standard preliminary screening tool for HIV due to its high sensitivity.

Question 3

What color light is emitted when antigens treated with fluorescein isothiocyanate (FITC) are exposed to UV light?

Accepted Answer

Apple-green — FITC emits a characteristic apple-green fluorescence when excited by UV light.

Question 4

Which of the following immunological tests frequently utilizes the enzyme horseradish peroxidase (HRP)?

Accepted Answer

ELISA — HRP is a common enzyme conjugated to secondary antibodies in ELISA and Western Blots to catalyze a colorimetric reaction.

Question 5

Which technique is used extensively to detect antigens in tissue sections or to screen for auto-antibodies like ANA (Anti-Nuclear Antibody)?

Accepted Answer

Immunocytochemistry/Immunofluorescence — Immunofluorescence is the gold standard for detecting auto-antibodies against cellular antigens in tissue substrates.

Question 6

Which of the following techniques involves separating protein antigens by molecular weight using SDS-PAGE before transferring them to a membrane for detection?

Accepted Answer

Western Blot — The Western Blot uses SDS-PAGE for size-based separation followed by antibody probing.

Question 7

Each polypeptide chain (heavy and light) of an immunoglobulin molecule contains which domains?

Accepted Answer

One Variable (V) and one Constant (C) region — Each Ig chain consists of a Variable domain for antigen binding and at least one Constant domain for effector functions.

Question 8

During somatic recombination of antibody genes, which chain rearranges its V, D, and J segments first?

Accepted Answer

Heavy chain — Heavy chain rearrangement (D-J then V-DJ) occurs before the light chain begins rearrangement.

Question 9

The two types of light chains found in human immunoglobulins are:

Accepted Answer

Kappa and Lambda — An antibody molecule contains either two kappa or two lambda light chains.

Question 10

Which of the following is NOT true regarding the mechanisms of generating antibody diversity?

Accepted Answer

Alternative splicing of mRNA — Alternative splicing generates different membrane vs. secreted forms or co-expression of IgM/IgD, but does not create primary sequence diversity.

Question 11

Which two classes of antibodies are co-expressed on the surface of mature, naive B cells due to alternative RNA processing?

Accepted Answer

IgM and IgD — Mature B cells express both IgM and IgD using the same VDJ region via alternative splicing of the primary transcript.

Question 12

If alternative processing of the heavy chain mRNA uses the first polyadenylation site (pAs), which form of the antibody is produced?

Accepted Answer

Secreted form — Cleavage at the first polyadenylation site removes the hydrophobic transmembrane coding region, resulting in secreted antibody.

Question 13

In liver cells, bilirubin is mainly conjugated with which molecule to become water-soluble?

Accepted Answer

Glucuronic acid — Bilirubin is conjugated with glucuronic acid by UDP-glucuronosyltransferase to form bilirubin diglucuronide.

Question 14

Which of the following pathways is critical for maintaining reduced glutathione in RBC energy metabolism?

Accepted Answer

Pentose Phosphate Pathway — The Hexose Monophosphate Shunt (PPP) produces NADPH, which is essential to keep glutathione in its reduced state.

Question 15

An abnormal increase in the total red blood cell count in the circulation is termed:

Accepted Answer

Polycythemia — Polycythemia refers to an increased concentration of hemoglobin and/or RBC mass.

Question 16

Which of the following is the brain’s preferred source of energy under normal physiological conditions?

Accepted Answer

Glucose — The brain relies almost exclusively on glucose, although it can adapt to ketone bodies during starvation.

Question 17

Which statement regarding Hemolytic Disease of the Newborn (HDN) is TRUE?

Accepted Answer

It occurs when an Rh- mother carries an Rh+ fetus — HDN (Erythroblastosis fetalis) occurs when maternal anti-Rh IgG antibodies cross the placenta and attack Rh+ fetal RBCs.

Question 18

Hematocrit is a clinical measure of:

Accepted Answer

The percentage of blood volume occupied by red blood cells — Hematocrit (Hct) represents the proportion of whole blood volume that is comprised of red blood cells.

Question 19

High-energy phosphate bonds for instant muscle contraction (first few seconds) are provided by:

Accepted Answer

Creatine phosphate — Phosphocreatine provides the fastest regeneration of ATP for short bursts of activity.

Question 20

The Rapoport-Luebering cycle in RBCs is responsible for the production of:

Accepted Answer

2,3-Bisphosphoglycerate (2,3-BPG) — This shunt off the glycolytic pathway produces 2,3-BPG, which regulates hemoglobin's affinity for oxygen.

Question 21

In healthy adults, the major site of erythrocyte production (erythropoiesis) is the:

Accepted Answer

Red bone marrow — While the liver/spleen produce RBCs in the fetus, the bone marrow takes over as the primary site after birth.

Question 22

Which of the following is FALSE regarding cardiac muscle compared to skeletal muscle?

Accepted Answer

Cardiac muscle lacks striations — Both cardiac and skeletal muscles are striated; smooth muscle is the only non-striated muscle type.

Question 23

Phagocytic white cells (e.g., macrophages) congregate within when foreign organisms penetrate the skin.

Accepted Answer

Inflamed tissue — Inflammation triggers the recruitment of phagocytes from the blood into the infected or damaged tissue.

Question 24

Which of the following mediates an early response to viral infections by inhibiting viral replication in neighboring cells?

Accepted Answer

Interferons (IFN-alpha/beta) — Type I interferons (IFN-α and IFN-β) are critical in the innate antiviral response.

Question 25

Which of the following serves as a critical messenger mediating the connection between innate and adaptive immunity?

Accepted Answer

Dendritic cells — Dendritic cells capture antigens in the periphery (innate) and migrate to lymph nodes to present them to T cells (adaptive).

Question 26

Which of the following immune components would NOT recognize a macromolecular epitope directly?

Accepted Answer

T cell receptor — TCRs require antigens to be processed into peptides and presented on MHC molecules, unlike BCRs which recognize intact macromolecules.

Question 27

Which of the following is a large genomic region essential for the presentation of peptide antigens to T cells?

Accepted Answer

MHC (Major Histocompatibility Complex) — MHC genes encode proteins that display antigens for T cell recognition.

Question 28

T cells are produced in the and complete their maturation/differentiation in the .

Accepted Answer

Bone marrow; Thymus — T cell precursors originate in the bone marrow and migrate to the thymus for selection.

Question 29

Which transmembrane glycoprotein serves as a co-receptor for MHC Class I and identifies Cytotoxic T cells?

Accepted Answer

CD8 — CD8 binds to the invariant region of MHC Class I molecules during antigen recognition by CTLs.

Question 30

Which cells produce large amounts of antibodies (Igs) following differentiation from B cells?

Accepted Answer

Plasma cells — Plasma cells are the effector form of B cells specialized in high-rate antibody secretion.

Question 31

Which of the following is a glycoprotein expressed on T helper cells that acts as a co-receptor for MHC Class II?

Accepted Answer

CD4 — CD4 is the marker for T helper cells and interacts with MHC Class II on APCs.

Question 32

Which APC type is highly specialized and most effective at initiating a primary T cell response to a new antigen?

Accepted Answer

Dendritic cells — Dendritic cells are the most potent professional APCs for activating naive T cells.

Question 33

Which APC uses surface immunoglobulin to capture specific antigens for internal processing and presentation?

Accepted Answer

B cell — B cells use their BCR (immunoglobulin) to endocytose specific soluble antigens for presentation to T cells.

Question 34

Which professional APC is particularly specialized for the degradation of particulate antigens and microbes via phagocytosis?

Accepted Answer

Macrophage — Macrophages are highly phagocytic and specialize in degrading large particles for presentation.

Question 35

The fragment of an antibody that contains the antigen-binding site is known as:

Accepted Answer

Fab fragment — The 'Fragment Antigen Binding' (Fab) consists of one light chain and the V and CH1 domains of one heavy chain.

Question 36

Which antibody isotype exists as a pentamer when secreted, providing high avidity despite lower affinity?

Accepted Answer

IgM — Secreted IgM forms a pentamer linked by a J-chain, offering 10 antigen-binding sites.

Question 37

In the context of immunological memory, which antibody class is predominantly produced during a secondary immune response?

Accepted Answer

IgG — Secondary responses are characterized by class switching to high-affinity IgG.

Question 38

The hypervariable regions that make direct contact with the antigen are also called:

Accepted Answer

Complementarity-determining regions (CDRs) — CDRs are the three loops on the variable domains of both heavy and light chains that form the binding pocket.

Question 39

Which heavy chain constant region defines the IgA isotype?

Accepted Answer

Alpha (α) — IgA is defined by the alpha heavy chain; IgM by mu; IgG by gamma; IgD by delta.

Question 40

The process where B cells change the constant region of the heavy chain but keep the same variable region is called:

Accepted Answer

Class switch recombination — Class switching allows B cells to produce different antibody classes (isotypes) with the same specificity.

Question 41

Which mechanism increases the affinity of antibodies for an antigen during a prolonged immune response?

Accepted Answer

Somatic hypermutation — Somatic hypermutation introduces point mutations in V regions, followed by selection for higher affinity binders.

Question 42

MHC Class II molecules display peptides to which type of cells?

Accepted Answer

CD4+ T cells — MHC Class II targets T helper (CD4+) cells, while MHC Class I targets Cytotoxic (CD8+) T cells.

Question 43

Which of the following is an example of a primary lymphoid organ?

Accepted Answer

Thymus — Primary lymphoid organs (Bone marrow and Thymus) are where lymphocytes develop and mature.

Question 44

The binding of an antibody to a toxin to prevent its interaction with host cells is called:

Accepted Answer

Neutralization — Neutralization involves antibodies blocking the functional sites of microbes or toxins.

Question 45

Which cell type is responsible for the 'missing self' hypothesis recognition resulting in target cell lysis?

Accepted Answer

Natural Killer (NK) cell — NK cells kill target cells that have downregulated MHC Class I, a common viral or tumor escape mechanism.

Question 46

Which complement component serves as the central 'hub' and acts as an opsonin when cleaved?

Accepted Answer

C1q — C3b is a major opsonin that coats pathogens for recognition by phagocytes.

Question 47

A lack of NADPH oxidase results in which primary immunodeficiency characterized by inability to kill phagocytosed microbes?

Accepted Answer

Chronic Granulomatous Disease — CGD is caused by defects in the oxidative burst mechanism within phagocytes.

Question 48

The enzyme RAG-1 and RAG-2 are essential for which process?

Accepted Answer

V(D)J recombination — Recombination-Activating Genes (RAG) are required to initiate the assembly of Ig and TCR gene segments.

Question 49

Which cytokine is the primary growth factor for T cell proliferation?

Accepted Answer

IL-2 — IL-2 acts in an autocrine and paracrine fashion to drive Clonal expansion of activated T cells.

Question 50

Which cell type expresses MHC Class II?

Accepted Answer

Dendritic cells — Professional APCs (Dendritic cells, Macrophages, B cells) are the primary expressors of MHC Class II.

Weekly Year 2: Cellular Immunology Exam - March 13, 2026 (Se

Questions, Answers & Explanations