Weekly Year 2: Cellular Immunology Exam - April 3, 2026 (Sec

Question 1

Which of the following microscopy techniques utilizes ultraviolet (UV) light for examining specimens, often in conjunction with fluorochromes?

Accepted Answer

Fluorescence microscopy — Fluorescence microscopy uses a high-intensity UV or near-UV light source to excite fluorescent molecules (fluorochromes) in a specimen, which then emit light at a longer wavelength.

Question 2

Which laboratory method is commonly used as a preliminary screening tool for detecting the presence of antibodies against HIV proteins in a patient's serum?

Accepted Answer

ELISA (Enzyme-Linked Immunosorbent Assay) — ELISA is the standard primary screening test for HIV due to its high sensitivity; positive results are typically confirmed with a Western Blot or specialized PCR.

Question 3

When antigens are treated with fluorescein isothiocyanate (FITC) and exposed to UV light, what color light is characteristically emitted?

Accepted Answer

Apple-green — FITC is a fluorochrome that absorbs UV/blue light and emits a characteristic bright apple-green fluorescence.

Question 4

The use of the enzyme horseradish peroxidase (HRP) to catalyze a colorimetric reaction is most characteristic of which technique?

Accepted Answer

ELISA and Immunohistochemistry — Horseradish peroxidase (HRP) is a common enzyme conjugate used in ELISA and IHC to produce a visible color change in the presence of a substrate like DAB or TMB.

Question 5

Which technique is used extensively to detect specific antigens within tissue sections or to screen for auto-antibodies (e.g., ANA) in a patient's serum?

Accepted Answer

Immunohistochemistry/Immunofluorescence — Immunohistochemistry (IHC) and Immunofluorescence (IF) allow for the localization of antigens within preserved tissue architecture or cells.

Question 6

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

Accepted Answer

Western Blot — The Western Blot uses SDS-PAGE for size-based separation of proteins, followed by electroprinting onto a membrane and detection via specific antibodies.

Question 7

Each polypeptide chain (heavy and light) of an immunoglobulin molecule contains which of the following structural regions?

Accepted Answer

A Variable (V) and a Constant (C) region — All antibody chains consist of a Variable region (responsible for antigen binding) and a Constant region (responsible for effector functions).

Question 8

During B cell development and somatic recombination, which gene segments rearrange first, and what does the resulting region contain?

Accepted Answer

Heavy chain; Variable region — The heavy chain (D to J, then V to DJ) rearranges first. The resulting V region (rearranged VDJ) is what determines antigen specificity.

Question 9

In humans, the two distinct types of light chains found in immunoglobulin molecules are:

Accepted Answer

Kappa and Lambda — An antibody molecule will have either two kappa (κ) light chains or two lambda (λ) light chains, never one of each.

Question 10

Which of the following is NOT a mechanism for generating antibody diversity?

Accepted Answer

Alternative splicing of the C-region to change antigen specificity — Splicing of C-regions (class switching) changes the effector function (isotype) but does NOT change the antigen specificity (the V region).

Question 11

Which two classes of immunoglobulins are frequently co-expressed on the surface of a mature B cell via alternative RNA processing?

Accepted Answer

IgM and IgD — Mature, naive B cells co-express IgM and IgD. This occurs because the primary RNA transcript includes both the mu and delta constant regions, which are differentially spliced.

Question 12

In B cells, if alternative processing of the primary RNA transcript utilizes the first polyadenylation site, which form of the heavy chain is produced?

Accepted Answer

IgM (mu) heavy chain — The mu constant region genes are located upstream of the delta constant region genes. Using the first polyadenylation site results in an IgM transcript.

Question 13

In hepatocytes, bilirubin is primarily conjugated with which molecule to increase its water solubility?

Accepted Answer

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

Question 14

Which metabolic pathway is essential in red blood cells (RBCs) to maintain hemoglobin in its reduced (Fe2+) state?

Accepted Answer

Hexose Monophosphate (HMP) Shunt — The HMP shunt produces NADPH, which is vital for maintaining reduced glutathione, which in turn keeps hemoglobin in the functional reduced state.

Question 15

An abnormal increase in the total red blood cell count and hemoglobin concentration is known as:

Accepted Answer

Polycythemia — Polycythemia refers to an increased concentration of erythrocytes in the blood.

Question 16

Under normal physiological conditions, what is the brain's preferred primary source of energy?

Accepted Answer

Glucose — Glucose is the primary and preferred fuel for the brain. It can use ketones only during prolonged starvation.

Question 17

Which of the following statements regarding erythrocyte physiology is TRUE?

Accepted Answer

Mature RBCs lack a nucleus and organelles — Mature erythrocytes lack a nucleus, mitochondria, and ribosomes to maximize space for hemoglobin and prevent internal oxygen consumption.

Question 18

One of the following is TRUE regarding Hemolytic Disease of the Newborn (HDN):

Accepted Answer

It involves maternal IgG antibodies crossing the placenta and attacking fetal RBCs — HDN (Erythroblastosis fetalis) occurs when an Rh-negative mother is sensitized to Rh-positive fetal blood. Her IgG antibodies can then cross the placenta in subsequent pregnancies.

Question 19

Hematocrit is a clinical measurement of:

Accepted Answer

The percentage of total blood volume occupied by red blood cells — Hematocrit (Hct) is the ratio of the volume of red blood cells to the total volume of blood.

Question 20

High-energy phosphate bonds for immediate muscle contraction are provided by the rapid transfer of phosphate from:

Accepted Answer

Creatine phosphate (Phosphocreatine) — Creatine phosphate acts as a rapid mobilizable reserve of high-energy phosphates in skeletal muscle and the brain to recycle ATP.

Question 21

The Rapoport-Luebering cycle is a metabolic pathway unique to which cell type, producing 2,3-BPG?

Accepted Answer

Erythrocytes — The Rapoport-Luebering cycle is a shunt of glycolysis in RBCs that produces 2,3-bisphosphoglycerate (2,3-BPG), which regulates hemoglobin's oxygen affinity.

Question 22

In a healthy adult, what is the major site of erythrocyte production (erythropoiesis)?

Accepted Answer

Red bone marrow — In adults, erythropoiesis occurs almost exclusively in the red bone marrow of flat and long bones.

Question 23

The most rapid method to resynthesize ATP during short bursts of high-intensity exercise is:

Accepted Answer

Phosphocreatine breakdown — The phosphagen system (ATP-CP) provides the fastest resynthesis of ATP, though its capacity is very limited.

Question 24

Which of the following statements is FALSE regarding cardiac and skeletal muscles?

Accepted Answer

Both are strictly under voluntary control — Skeletal muscle is voluntary, but cardiac muscle is involuntary (autonomic control).

Question 25

Phagocytic white cells like macrophages congregate within which of the following areas when foreign organisms enter through a cutaneous wound?

Accepted Answer

Inflamed tissue/local site of infection — Inflammation signals phagocytes to exit the bloodstream (diapedesis) and congregate at the site of trauma or infection.

Question 26

Which of the following components mediates an early, non-specific response to viral infections by inhibiting viral replication in neighboring cells?

Accepted Answer

Interferons (Type I) — Interferon-alpha and beta are produced by virus-infected cells to induce an 'antiviral state' in nearby uninfected cells.

Question 27

Which of the following acts as a critical messenger (cytokine) that bridges the gap between innate and adaptive immunity by activating T cells?

Accepted Answer

Interleukin-12 (IL-12) — IL-12 is produced by APCs (innate) to stimulate the differentiation of naive T cells into Th1 cells (adaptive).

Question 28

Which of the following immune components would typically NOT recognize a macromolecule epitope directly (requiring instead processed peptides on MHC)?

Accepted Answer

T cell receptor (TCR) — TCRs recognize only processed peptide fragments presented on MHC molecules, whereas BCRs and antibodies can recognize 3D epitopes on intact macromolecules.

Question 29

Which genomic region, also known as the HLA complex in humans, encodes proteins that present antigens to T cells?

Accepted Answer

Major Histocompatibility Complex (MHC) — The MHC (Major Histocompatibility Complex) is essential for antigen presentation and self/non-self recognition.

Question 30

T cells are produced in the and then migrate to the to complete their maturation and differentiation.

Accepted Answer

Bone marrow; Thymus — Progenitor T cells are born in the bone marrow but must travel to the thymus for education (positive and negative selection).

Question 31

Which transmembrane glycoprotein serves as a co-receptor for the TCR on Cytotoxic T cells (CTLs) and recognizes MHC Class I?

Accepted Answer

CD8 — CD8 is the marker for cytotoxic T cells and binds to the constant portion of MHC class I molecules.

Question 32

Which cells differentiate into plasma cells to produce large quantities of antibodies after receiving help from CD4+ T cells?

Accepted Answer

B cells — B cells are the precursors to antibody-secreting plasma cells.

Question 33

Which of the following is a glycoprotein expressed on T helper cells that recognizes MHC Class II molecules?

Accepted Answer

CD4 — CD4 is a co-receptor on T helper cells that binds to MHC Class II.

Question 34

Which type of Antigen Presenting Cell (APC) is considered the most professional and critical for the initial activation of naive T cells?

Accepted Answer

Dendritic cells — Dendritic cells are the most potent APCs for initiating primary immune responses.

Question 35

Which APC uses surface immunoglobulin as a receptor to internalize specific antigens for presentation to T cells?

Accepted Answer

B cell — B cells are unique APCs that use their membrane-bound antibody (BCR) to capture specific antigens.

Question 36

Which antigen-presenting cell is highly specialized for the phagocytosis, degradation, and presentation of particulate (large) antigens?

Accepted Answer

Macrophage — Macrophages are professional phagocytes that clear debris and pathogens, presenting the resulting peptides to T cells.

Question 37

What is the primary function of the variable (V) region of an antibody?

Accepted Answer

Antigen binding specificity — The V regions of the heavy and light chains form the antigen-binding site, determining the specificity of the antibody.

Question 38

Alternative RNA processing in B cells allows for the production of which two forms of an immunoglobulin?

Accepted Answer

Membrane-bound and Secreted forms — A B cell can produce either a membrane-bound or a secreted version of the same antibody by using different polyadenylation sites at the end of the heavy chain transcript.

Question 39

Which enzyme is responsible for 'nicking' DNA during V(D)J recombination?

Accepted Answer

RAG-1 and RAG-2 — Recombination-Activating Genes (RAG-1 and RAG-2) recognize RSS sequences and initiate the DNA breaks required for recombination.

Question 40

In the erythrocyte, the Pentose Phosphate Pathway is the sole source of:

Accepted Answer

NADPH — Because RBCs lack mitochondria, the PPP (HMP shunt) is their only source of NADPH, which is needed to keep glutathione reduced.

Question 41

Hyperbilirubinemia leading to jaundice in a patient with excessive RBC breakdown (hemolysis) is classified as:

Accepted Answer

Pre-hepatic jaundice — Pre-hepatic jaundice occurs when the rate of bilirubin production exceeds the liver's conjugation capacity, usually due to hemolysis.

Question 42

Which antibody isotype is found in highest concentration in mucosal secretions (saliva, tears, breast milk)?

Accepted Answer

IgA — Secretory IgA is the primary antibody protecting mucosal surfaces.

Question 43

Somatic hypermutation occurs primarily in which location during an immune response?

Accepted Answer

Germinal centers of secondary lymphoid organs — Somatic hypermutation and affinity maturation occur in B cells within the germinal centers of lymph nodes or spleen.

Question 44

Affinity maturation is a process that results in:

Accepted Answer

B cells producing antibodies with higher binding strength for an antigen — Affinity maturation involves somatic hypermutation and selection for B cells with TCRs that have higher affinity for the antigen.

Question 45

Which of the following is an example of an innate immune barrier?

Accepted Answer

Low pH of the stomach — The acidity of the stomach is a physiological barrier that is part of the innate (non-specific) immune system.

Question 46

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

Accepted Answer

Isotype (Class) — The heavy chain constant region (CH) determines the class (IgM, IgG, IgA, IgE, or IgD) and therefore the effector function.

Question 47

Which cell type is most associated with the killing of helminthic parasites and participates in allergic reactions?

Accepted Answer

Eosinophils — Eosinophils release granular contents like Major Basic Protein to destroy large parasites that cannot be phagocytosed.

Question 48

MHC Class II molecules are expressed ON which of the following cell types?

Accepted Answer

Professional Antigen Presenting Cells (APCs) — MHC Class II is restricted to professional APCs (dendritic cells, macrophages, B cells).

Question 49

The process by which a B cell changes the class of antibody it produces (e.g., from IgM to IgG) without changing specificity is called:

Accepted Answer

Isotype switching (Class switch recombination) — Isotype switching involves changing the constant region of the heavy chain but keeping the same rearranged VDJ variable region.

Question 50

Which of the following is produced during the Rapoport-Luebering path and decreases hemoglobin's affinity for oxygen?

Accepted Answer

2,3-Bisphosphoglycerate (2,3-BPG) — 2,3-BPG stabilizes the 'T' (tense) state of hemoglobin, facilitating oxygen release to tissues.

Weekly Year 2: Cellular Immunology Exam - April 3, 2026 (Sec

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