Unit 2 Question Bank
The five tabs are the five sections of the real paper. Items tagged
Past Paper 2019 or 2020 are the genuine questions, reproduced verbatim.
Items tagged Slide come from the TMU lecture; items tagged Janeway's are built
from the textbook to cover examinable ground. Nothing is invented. Janeway's 10e is a reflowed
edition with no printed page numbers, so it is cited by numbered section (§1-14), not by page.
0 / 27 answered
1Haptens have:
Answer: C
A hapten is small enough to be bound by antibody but too small to induce antibody on its own — it has antigenicity (immunoreactivity) but lacks immunogenicity. Coupling it to a carrier protein makes the conjugate immunogenic. Penicillin binding covalently to serum albumin is the classic example.Past Papers 2019 & 2020, Section III Q2 — verbatim, both years
2Which property does a complete antigen possess that a hapten does not?
Answer: D
Both have antigenicity — both can be bound. Only the complete antigen has immunogenicity, the ability to induce the response in the first place. Specificity and valence are properties of the epitopes, not a point of difference here.TMU Lecture 2 (Lei Zhi) Slides 12–16
3An epitope is usually composed of approximately how many amino acid residues?
Answer: A
An epitope is a small patch — around 5 to 15 residues, or the equivalent in polysaccharide residues or nucleotides. That small size is why a single protein carries many epitopes and can raise many different antibodies at once.TMU Lecture 2 (Lei Zhi) Slide 23
4Which statement about a conformational epitope is correct?
Answer: B
A conformational (non-linear, discontinuous) epitope exists only while the molecule holds its native fold, so denaturation destroys it. A run of consecutive residues is a linear epitope, and it is linear peptides — produced by degrading the antigen — that the TCR sees on MHC.TMU Lecture 2 (Lei Zhi) Slides 26–30
5A T-cell epitope differs from a B-cell epitope in that it:
Answer: C
The TCR cannot see free antigen. The antigen must first be degraded to a linear peptide and displayed in the groove of an MHC molecule. The BCR, by contrast, binds the intact native antigen directly, usually at a conformational epitope on its surface.TMU Lecture 2 (Lei Zhi) Slides 28–30
6Antibody raised against group A haemolytic streptococcus can damage cardiac valves. This is an example of:
Answer: D
The streptococcal cell wall shares epitopes with cardiac valve glycoprotein, myocardium and glomerular basement membrane. Antibody raised against the bacterium therefore binds host tissue — a cross-reaction via a common (heterophilic) antigen, giving rheumatic fever and post-streptococcal glomerulonephritis. Nothing malfunctioned: the specificity was real but not unique.TMU Lecture 2 (Lei Zhi) Slides 31–34, 55
7Under the clonal selection theory, 'foreignness' means a substance that:
Answer: A
Foreignness is defined by what the developing repertoire was not shown. This is why a self molecule sequestered behind the blood–testis, blood–brain or blood–eye barrier can later be attacked as foreign — as in sympathetic ophthalmia. Coming from another species is the commonest case, not the definition.TMU Lecture 2 (Lei Zhi) Slide 37
8Which route of antigen administration produces the strongest immune response?
Answer: B
The order taught is intracutaneous > subcutaneous > intravenous > oral. Skin is densely populated with dendritic cells, so antigen deposited there is picked up and presented efficiently; oral antigen tends to induce tolerance instead.TMU Lecture 2 (Lei Zhi) Slide 45
9Which is characteristic of a thymus-independent (TI) antigen?
Answer: C
TI antigens are typically polysaccharides carrying one epitope repeated in a regular array, which cross-links many BCRs at once and activates the B cell without T help. The price is a poor response: IgM only, no class switching, no memory. Multiple classes and memory are TD features.TMU Lecture 2 (Lei Zhi) Slides 48–49
10Blood group ABO and HLA transplantation antigens are classified as:
Answer: D
They differ between individuals of the same species, which is the definition of allogeneic. Xenogeneic means from a different species (horse antitoxin); heterophilic means shared across unrelated species; an autoantigen is the host's own component.TMU Lecture 2 (Lei Zhi) Slide 58
11Therapeutic horse antitoxin serum has a dual nature because it acts as:
Answer: A
It neutralises the toxin as a specific antibody, while simultaneously being horse protein — a xenogeneic antigen that provokes the patient to make antibody against it. Repeat courses therefore risk serum sickness, a type III hypersensitivity (Unit 15). The treatment is also the next problem.TMU Lecture 2 (Lei Zhi) Slides 56–57
12Which is NOT a feature of a superantigen?
Answer: B
A superantigen needs no antigen processing — it clamps the outside of the MHC class II molecule to the outside of the TCR, bypassing the peptide groove entirely. That is also why it is not MHC restricted and why it activates a huge fraction of T cells at once, as in staphylococcal toxic shock syndrome.TMU Lecture 2 (Lei Zhi) Slide 67
13Which of the following are common T-cell mitogens?
Answer: C
Phytohaemagglutinin, concanavalin A and pokeweed mitogen bind lymphocyte surface receptors and drive resting cells to become lymphoblasts — polyclonally, without specificity. Alum, BCG and poly I:C are adjuvants, a different category of non-specific stimulator.TMU Lecture 2 (Lei Zhi) Slide 69 · Review sheet, verified against lecture
14An adjuvant is best defined as a substance which:
Answer: D
An adjuvant is given before or together with the antigen and amplifies or redirects the response non-specifically. Covalent coupling to confer immunogenicity describes a carrier; polyclonal activation without processing describes a superantigen; toxin neutralisation is what an antitoxin does.TMU Lecture 2 (Lei Zhi) Slide 70
15Which molecular feature makes a molecule a POOR immunogen?
Answer: A
Size alone is not enough — structural complexity is also required. Gelatin exceeds 100 kD yet is a poor immunogen because it is a monotonous straight-chain polymer; adding only about 2% tyrosine makes it markedly more immunogenic. High MW, particulate form and aromatic residues all increase immunogenicity.TMU Lecture 2 (Lei Zhi) Slides 40–43
1 Antigen (Ag) — 3 marks+
A molecule that can induce the production of antibodies and/or effector T cells and can in turn interact specifically with the antibodies and/or effector lymphocytes produced. It therefore possesses two properties: immunogenicity (the ability to induce a response) and immunoreactivity or antigenicity (the ability to combine specifically with the products of that response).Past Paper 2019, Section I Q1 · TMU Lecture 2 (Lei Zhi) Slides 7, 12
2 Epitope (antigenic determinant) — 3 marks+
The immunologically active region of an immunogen that binds to antigen-specific membrane receptors on lymphocytes (TCR or BCR) or to secreted antibodies. Usually composed of 5–15 amino acid residues, or of polysaccharide residues or nucleotides. Epitopes may be linear (a sequential fragment) or conformational (non-sequential residues brought together by folding).Past Paper 2020, Section I Q1 · TMU Lecture 2 (Lei Zhi) Slides 23, 26
3 Hapten — 3 marks+
A small-molecular-weight substance which is antigenic but incapable by itself of inducing a specific immune response — it lacks immunogenicity but reacts with specific antibody. Coupling to a carrier renders the conjugate immunogenic. A hapten is equivalent to a single epitope and is therefore monovalent. Penicillin is the classic example.TMU Lecture 2 (Lei Zhi) Slides 16–17, 25
4 Antigenic valence — 3 marks+
The total number of epitopes on an antigen molecule that can bind antibody. A hapten, being the equivalent of one epitope, binds only one site on a TCR, BCR or antibody and is monovalent.TMU Lecture 2 (Lei Zhi) Slide 25
5 Cross-reaction — 3 marks+
The reaction in which antibody induced by one antigen reacts with an unrelated antigen, because the two share an identical epitope or carry epitopes of similar conformation. The shared determinant is the common antigen. Antigenic specificity is therefore not absolute, and cross-reaction can occur between unrelated species.TMU Lecture 2 (Lei Zhi) Slides 31–33
6 Superantigen (SAg) — 3 marks+
A molecule that polyclonally activates a large fraction of T cells by binding simultaneously to MHC class II molecules and to the T-cell receptor, outside the peptide-binding groove. Features: polyclonal activation, no antigen processing required, and no MHC restriction.TMU Lecture 2 (Lei Zhi) Slide 67
7 Adjuvant — 3 marks+
A substance which, when injected before or together with an antigen, non-specifically enhances the immune response or changes its type. It acts by altering the antigen's physicochemical form, improving processing and presentation by macrophages, and non-specifically stimulating lymphocyte proliferation. Examples: Al(OH)₃, BCG, poly I:C, Freund's adjuvants.TMU Lecture 2 (Lei Zhi) Slides 70–71
8 TD and TI antigens — 3 marks+
Thymus-dependent (TD) antigens cannot induce antibody without T-cell help; they are mainly proteins, carry a few copies of many different epitopes, elicit both humoral and cellular immunity, produce multiple antibody classes and generate memory. Thymus-independent (TI) antigens stimulate B cells directly; they are mainly polysaccharides with one epitope repeated many times, give IgM only, and generate no memory.TMU Lecture 2 (Lei Zhi) Slides 47–49
1An antigen molecule generally possesses two properties: ? and ? .2 mark(s)
Immunogenicity = the ability to induce a response; antigenicity (immunoreactivity) = the ability to be bound by that response's products. A hapten has the second without the first.
TMU Lecture 2 (Lei Zhi) Slide 12 · phrasing confirmed by the student review sheet2Using a specific hapten coupled to a ? , a specific antibody can be produced.1 mark(s)
The carrier is usually a protein. It supplies the bulk and the T-cell epitopes the hapten lacks, so T-cell help can be recruited and antibody made against the hapten itself. Conjugate vaccines exploit exactly this.
TMU Lecture 2 (Lei Zhi) Slide 163Immunologically active structures of an antigen that bind to antigen receptors on lymphocytes or to secreted antibodies are called ? or ? .2 mark(s)
The two words are interchangeable. TMU uses both, and the 2020 paper set Epitope as a Section I definition.
TMU Lecture 2 (Lei Zhi) Slide 234The epitopes recognised by the TCR are called ? epitopes, and those recognised by the BCR are called ? epitopes.2 mark(s)
T-cell epitopes are linear peptides that must be presented on MHC; B-cell epitopes are usually conformational and are read directly off the native antigen surface.
TMU Lecture 2 (Lei Zhi) Slides 28–305TD antigens induce B-cell activation only when specific ? cells are present.1 mark(s)
That is what 'thymus-dependent' means. Without T help a protein antigen cannot drive class switching, affinity maturation or memory — which is why conjugating a polysaccharide to a protein carrier transforms the response.
TMU Lecture 2 (Lei Zhi) Slide 506The three features of a superantigen are ? activation, ? antigen processing, and ? MHC restriction.3 mark(s)
All three follow from one structural fact: the superantigen binds the outside of MHC II and the outside of the TCR, so the peptide groove is irrelevant.
TMU Lecture 2 (Lei Zhi) Slide 671Mitogens can specifically activate T cells or B cells.
FALSE
False. Mitogens activate lymphocytes non-specifically and polyclonally — which is precisely why they are classed as non-specific stimulators alongside superantigens and adjuvants. Every other word in the sentence is correct, so the trap is the adverb. Set in both papers, unchanged.Past Papers 2019 & 2020, Section IV Q1 — verbatim, both years
2A hapten can induce antibody production without being coupled to a carrier.
FALSE
False. That is the definition of a hapten — it lacks immunogenicity. It will bind antibody that already exists, but it cannot induce antibody until a carrier supplies the missing bulk and T-cell epitopes.TMU Lecture 2 (Lei Zhi) Slide 17
3Conformational epitopes are destroyed when the antigen is denatured.
TRUE
True. A conformational epitope is made of residues that are distant in the sequence and only adjacent because of folding. Unfold the protein and the epitope ceases to exist. Linear epitopes survive, and some previously buried ones are newly exposed.TMU Lecture 2 (Lei Zhi) Slide 26
4Thymus-independent antigens generate immunological memory.
FALSE
False. TI antigens give IgM only, with no class switching and no memory. This is the clinical reason plain polysaccharide pneumococcal vaccine protects infants poorly, and why the conjugate version — which converts it into a TD antigen — was developed.TMU Lecture 2 (Lei Zhi) Slide 49
5A molecule with a molecular weight above 100 kD is always a strong immunogen.
FALSE
False. Size helps but is not sufficient — complexity is also required. Gelatin exceeds 100 kD and is a poor immunogen because it is a monotonous straight-chain polymer; adding about 2% tyrosine makes it much stronger.TMU Lecture 2 (Lei Zhi) Slide 41
6Superantigens require processing by an antigen-presenting cell before they can activate T cells.
FALSE
False. Superantigens bypass processing entirely, clamping intact MHC class II to the TCR from the outside. No processing, no MHC restriction, and polyclonal activation of a large fraction of T cells — the mechanism behind toxic shock syndrome.TMU Lecture 2 (Lei Zhi) Slide 67
1
Compare complete antigen and hapten.
6 marks
| Complete antigen | Hapten | |
|---|---|---|
| Immunogenicity | Yes | No |
| Antigenicity | Yes | Yes |
| Molecular size | Large | Small |
| Valence | Multivalent | Monovalent |
| Needs a carrier? | No | Yes, to become immunogenic |
| Example | Bacterial protein, toxoid | Penicillin |
Marking guide: 1 mark per row. The two rows that must be present for a pass are immunogenicity and antigenicity — that contrast is the question.
2
Compare thymus-dependent (TD) and thymus-independent (TI) antigens.
6 marks
| TD antigen | TI antigen | |
|---|---|---|
| T-cell help | Required | Not required |
| Chemical nature | Mainly proteins | Mainly polysaccharides |
| Epitope structure | A few copies of many different epitopes | One epitope repeated many times |
| Response type | Humoral and cellular | Humoral only |
| Antibody classes | IgM, IgG, IgA | IgM only |
| Memory | Yes | No |
If there is room, add the clinical pay-off: because TI antigens give no memory and work poorly in infants, the pneumococcal polysaccharide is conjugated to a carrier protein to convert it into a TD antigen.
Marking guide: 1 mark per row. Memory and antibody class are the highest-value rows — they are what the distinction is for.
3
List the factors that affect the immunogenicity of an antigen.
6 marks
1 · Properties of the antigen — foreignness (the dominant factor); chemical nature (proteins and glycoproteins strongest); molecular weight (>100 kD strong, <10 kD poor); structural complexity; epitope conformation and accessibility; physical form (polymer > monomer, cyclic > linear, particulate > soluble).
2 · The host — genetic background, especially MHC type; age, sex and state of health; infection or immunosuppressive drugs.
3 · Method of administration — dose (a moderate dose is best; extremes induce tolerance); timing of injections; route (intracutaneous > subcutaneous > intravenous > oral); use of an adjuvant.
Marking guide: 2 marks per heading. The three-way structure — antigen, host, administration — is itself worth marks; an unstructured list of factors scores lower even if it contains the same items.