A defining feature of adaptive immunity, compared with innate immunity, is:

Memory that speeds up a later response

Full activity within minutes of entry

Killing of bacteria by neutrophils

Recognition through Toll-like receptors

Toll-like receptors on macrophages and dendritic cells bind:

Conserved microbial molecules such as LPS

Peptides displayed on MHC class II

Complement fragment C3b on microbes

Immune system physiology

10 ASCP MLS practice questions on Immune system physiology, part of Immunology. The first 10 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 9-year-old girl has had repeated Staphylococcus aureus skin abscesses that are swollen but barely warm or red, two pneumonias that left air-filled lung cysts (pneumatoceles), recurrent oral and nail candidiasis, and eczema since infancy. Two primary teeth have not fallen out. Results: WBC 9.8 x 10^3/µL [9.8 x 10^9/L]; neutrophils 6.0 x 10^3/µL; eosinophils 1.1 x 10^3/µL; dihydrorhodamine (DHR) oxidative burst normal; IgG, IgA and IgM within age ranges; IgE 4,600 IU/mL (reference < 200); CD4 and CD8 T-cell counts normal. Poor development of which CD4 T-cell subset best explains her infections?
1. ATh17 cells
2. BTh2 cells
3. CTh1 cells
4. DRegulatory T cells
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Answer: A · Th17 cells
Cold staphylococcal abscesses, pneumatoceles, mucocutaneous candidiasis, eczema, retained primary teeth and an IgE above 2,000 IU/mL are the picture of autosomal dominant hyper-IgE (Job) syndrome, usually caused by dominant-negative STAT3 variants. STAT3 signaling is needed for naive CD4 T cells to become Th17 cells, which make IL-17 and IL-22. These cytokines make skin and airway epithelium release neutrophil-attracting chemokines and antimicrobial peptides, so neutrophils that are normal in number and oxidative burst are not called into the tissue, and Candida is not controlled. The very high IgE and eosinophils are features of the syndrome, not signs of missing Th2 cells. The normal DHR test separates this from chronic granulomatous disease, which also causes staphylococcal abscesses.
- B: Th2 activity is not lacking here; IgE and eosinophils are raised.
- C: Th1 cells and IFN-gamma mainly defend against mycobacteria and Salmonella, not staphylococci and Candida.
- D: Failure of regulatory T cells (IPEX) causes autoimmunity and enteropathy, not cold abscesses.
Question 2 · Easy
Which cell is the most effective at presenting antigen to naive T cells in lymph nodes?
1. APlasma cell
2. BDendritic cell
3. CNeutrophil
4. DMast cell
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Answer: B · Dendritic cell
Dendritic cells capture antigen in tissues, mature, and travel in lymph to the T cell zones of lymph nodes. There they present peptides on MHC class I and II together with costimulatory molecules such as CD80 and CD86, which naive T cells need for activation. Macrophages and B cells also present antigen, but mainly to T cells that are already activated. Neutrophils, plasma cells and mast cells are not professional antigen-presenting cells.
- A: Plasma cells secrete antibody and express little MHC class II.
- C: Neutrophils phagocytose and kill microbes but do not prime naive T cells.
- D: Mast cells release histamine and other mediators.
Question 3 · Easy
A defining feature of adaptive immunity, compared with innate immunity, is:
1. AFull activity within minutes of entry
2. BKilling of bacteria by neutrophils
3. CRecognition through Toll-like receptors
4. DMemory that speeds up a later response
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Answer: D · Memory that speeds up a later response
Adaptive immunity uses T and B cells with antigen-specific receptors, and it leaves memory cells that respond faster and more strongly on re-exposure. Innate immunity acts within minutes to hours, uses germline-encoded receptors such as Toll-like receptors, and does not improve with repeated exposure. Vaccination works because of adaptive memory. Neutrophils, macrophages, NK cells and complement belong to the innate system.
- A: Innate defences act within minutes; a first adaptive response takes days.
- B: Neutrophil killing is an innate mechanism.
- C: Toll-like receptors are germline pattern receptors of innate cells.
Question 4 · Easy
Toll-like receptors on macrophages and dendritic cells bind:
1. AThe Fc portion of bound IgG
2. BPeptides displayed on MHC class II
3. CComplement fragment C3b on microbes
4. DConserved microbial molecules such as LPS
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Answer: D · Conserved microbial molecules such as LPS
Toll-like receptors are pattern recognition receptors that bind molecular patterns shared by whole groups of microbes. Examples are lipopolysaccharide (TLR4), bacterial lipoproteins (TLR2), flagellin (TLR5) and microbial nucleic acids (TLR3, 7, 8 and 9). Binding triggers release of cytokines such as TNF-alpha and IL-1, and helps dendritic cells activate T cells. These receptors are encoded in the germline and do not change with exposure.
- A: IgG Fc is bound by Fc gamma receptors, not Toll-like receptors.
- B: Peptide-MHC class II complexes are recognized by the T cell receptor of CD4 T cells.
- C: C3b is bound by complement receptor 1 (CR1).
Question 5 · Easy
Which cells are large granular lymphocytes that express CD16 and CD56 but lack CD3?
1. ACytotoxic T cells
2. BNatural killer cells
3. CRegulatory T cells
4. DMemory B cells
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Answer: B · Natural killer cells
NK cells are innate lymphocytes, identified by flow cytometry as CD3-negative and CD16- and/or CD56-positive. They kill virus-infected and tumor cells without prior sensitization, especially cells that have lost MHC class I. They also kill IgG-coated cells through CD16 (Fc gamma receptor III), which is antibody-dependent cellular cytotoxicity.
- A: Cytotoxic T cells are CD3-positive and CD8-positive.
- C: Regulatory T cells are CD3-positive T cells that carry CD4 and CD25.
- D: B cells carry CD19 and CD20, not CD16 and CD56.
Question 6 · Easy
CD8-positive cytotoxic T cells recognize peptide antigen bound to:
1. AMHC class II molecules
2. BMHC class I molecules
3. CMHC class III proteins
4. DFc gamma receptors
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Question 7 · Medium
In the thymus, negative selection removes developing T cells that:
1. ABind self-peptide-MHC too strongly
2. BHave not yet met foreign antigen
3. CExpress both CD4 and CD8
4. DFail to bind self-MHC at all
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Question 8 · Medium
Th2 helper T cells mainly support which type of immune response?
1. AMacrophage activation by interferon-gamma
2. BSuppression of responses by IL-10 and TGF-beta
3. CIgE production and eosinophil activity
4. DNeutrophil recruitment by IL-17
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Question 9 · Medium
Within a lymph node, B cells undergo class switching and affinity maturation mainly in the:
1. AParacortical T cell zone
2. BMedullary cords near the hilum
3. CSubcapsular sinus
4. DGerminal centers of the follicles
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Question 10 · Hard
A patient with rheumatoid arthritis received rituximab (anti-CD20) 6 months ago. Flow cytometry shows no CD19-positive cells, yet total IgG is still within the reference interval. What best explains this?
1. ANK cells switch to IgG secretion
2. BIgG has a half-life of about 6 months
3. CHelper T cells make IgG when B cells are gone
4. DLong-lived plasma cells lack CD20
Answer and explanation in LearnFree account

Immune system physiology

Which cell is the most effective at presenting antigen to naive T cells in lymph nodes?

A defining feature of adaptive immunity, compared with innate immunity, is:

Toll-like receptors on macrophages and dendritic cells bind:

Which cells are large granular lymphocytes that express CD16 and CD56 but lack CD3?

CD8-positive cytotoxic T cells recognize peptide antigen bound to:

In the thymus, negative selection removes developing T cells that:

Th2 helper T cells mainly support which type of immune response?

Within a lymph node, B cells undergo class switching and affinity maturation mainly in the:

A patient with rheumatoid arthritis received rituximab (anti-CD20) 6 months ago. Flow cytometry shows no CD19-positive cells, yet total IgG is still within the reference interval. What best explains this?