Innate and adaptive immunity

12 DOH Abu Dhabi (HAAD) lab licensing practice questions on Innate and adaptive immunity, part of Immunology and Serology. The first 12 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Medium

   Children under 2 years respond poorly to plain polysaccharide vaccines, so conjugate vaccines link the sugar to a protein. Why does this help?

   1. AIt lets the vaccine activate complement directly
   2. BIt makes the vaccine bind Toll-like receptors
   3. CIt allows maternal antibody to boost the response
   4. DIt recruits helper T cells, giving IgG and memory

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   Answer: D · It recruits helper T cells, giving IgG and memory

   Pure polysaccharides are T-independent antigens: they cross-link B-cell receptors directly but cannot be presented to helper T cells on MHC class II, so the response is mainly IgM with little class switching or memory. The marginal zone B cells that handle these antigens are immature until about age 2. Linking the polysaccharide to a carrier protein lets B cells present carrier peptides to helper T cells, giving class-switched IgG, affinity maturation and memory. This is the basis of the Hib, pneumococcal and meningococcal conjugate vaccines.

   • A: Complement activation does not create memory or class switching.
   • B: Toll-like receptor binding is not what conjugation adds; the protein carrier brings in T-cell help.
   • C: Maternal antibody tends to blunt, not boost, an infant's vaccine response.

2. Question 2 · Easy

   Lysozyme in tears and saliva protects against bacteria by:

   1. ABreaking down peptidoglycan in the cell wall
   2. BBinding iron that bacteria need to grow
   3. CCoating bacteria to promote phagocytosis
   4. DBlocking bacterial attachment to mucosa

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   Answer: A · Breaking down peptidoglycan in the cell wall

   Lysozyme splits the bond between N-acetylmuramic acid and N-acetylglucosamine in peptidoglycan, weakening the wall so the bacterium bursts. Gram-positive bacteria, with a thick exposed peptidoglycan layer, are the most affected, while the outer membrane of gram-negative bacteria limits access. It is part of the innate chemical barrier, together with lactoferrin, defensins and stomach acid. Lysozyme is also stored in neutrophil granules.

   • B: Binding iron is the action of lactoferrin.
   • C: Coating bacteria for phagocytosis (opsonization) is done by antibody and C3b.
   • D: Blocking attachment to mucosa is a main role of secretory IgA.

3. Question 3 · Easy

   In a lymph node, naive T cells meet antigen carried in from the tissues by dendritic cells mainly in the:

   1. AGerminal centres
   2. BParacortex
   3. COuter cortical follicles
   4. DMedullary cords

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   Answer: B · Paracortex

   Lymph nodes are divided into zones. T cells and dendritic cells fill the deeper cortex (paracortex), where naive T cells scan the antigen that dendritic cells carry in from the tissues. B cells gather in follicles in the outer cortex, which form germinal centres once they are activated, and plasma cells and macrophages sit in the medullary cords. In children with a missing thymus, the paracortex is poorly populated.

   • A: Germinal centres form inside B-cell follicles, where B cells mutate and are selected.
   • C: Follicles in the outer cortex are the B-cell areas.
   • D: Medullary cords hold mainly plasma cells and macrophages.

4. Question 4 · Easy

   MHC class II molecules are normally expressed on which cells?

   1. ADendritic cells, macrophages and B cells
   2. BNeutrophils and platelets
   3. CAll nucleated cells of the body
   4. DRed cells and hepatocytes

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   Answer: A · Dendritic cells, macrophages and B cells

   Class II molecules present peptides from ingested proteins to CD4 helper T cells, so they are found mainly on the professional antigen-presenting cells: dendritic cells, macrophages and B cells. Thymic epithelium and activated human T cells also express them. Class I molecules, by contrast, are on almost all nucleated cells and present peptides to CD8 T cells. HLA-DR, -DQ and -DP are the human class II molecules typed for transplantation.

   • B: Platelets carry class I but not class II, and neutrophils do not normally express class II.
   • C: Almost all nucleated cells carry MHC class I, not class II.
   • D: Mature red cells carry almost no HLA, and hepatocytes do not normally express class II.

5. Question 5 · Easy

   Virus-infected cells release cytokines that make neighbouring cells resistant to viral replication. These cytokines are:

   1. AInterleukin-10 and TGF-beta
   2. BInterleukin-4 and interleukin-5
   3. CInterferon-alpha and interferon-beta
   4. DTumor necrosis factor and interleukin-1

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   Answer: C · Interferon-alpha and interferon-beta

   Type I interferons (alpha and beta) are made by most virus-infected cells and in large amounts by plasmacytoid dendritic cells. They bind receptors on nearby cells and switch on genes that block viral protein synthesis and break down viral RNA, creating an antiviral state. They also raise MHC class I expression and activate NK cells. Interferon-alpha has been used to treat chronic hepatitis B and C.

   • A: IL-10 and TGF-beta are regulatory cytokines that suppress immune responses.
   • B: IL-4 and IL-5 are Th2 cytokines that drive IgE and eosinophil responses.
   • D: TNF and IL-1 cause inflammation and fever but do not create the antiviral state.

6. Question 6 · Easy

   Kupffer cells lining the liver sinusoids belong to which cell type?

   1. AResident macrophages
   2. BMast cells
   3. CPlasma cells
   4. DDendritic cells

   Answer and explanation in LearnFree account

7. Question 7 · Easy

   Which white cell is usually the first to arrive in large numbers at a site of acute bacterial infection?

   1. AMonocyte
   2. BLymphocyte
   3. CEosinophil
   4. DNeutrophil

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8. Question 8 · Medium

   Tumor cells sometimes escape cytotoxic T cells by losing their MHC class I molecules. Which cells are then best placed to kill them?

   1. ANatural killer cells
   2. BPlasma cells
   3. CCD8 cytotoxic T cells
   4. DCD4 helper T cells

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9. Question 9 · Medium

   Regulatory T cells, which suppress immune responses and help prevent autoimmunity, typically have which phenotype?

   1. ACD8+, perforin+ and granzyme+
   2. BCD4+, CD25 high and FOXP3+
   3. CCD3-, CD16+ and CD56+
   4. DCD19+, CD20+ and CD5+

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10. Question 10 · Medium

    Interferon-gamma released by Th1 cells and NK cells mainly helps the body by:

    1. AActivating macrophages to kill ingested microbes
    2. BRecruiting eosinophils against helminths
    3. CSwitching B cells to IgE production
    4. DSuppressing inflammation after infection

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11. Question 11 · Hard

    A 6-year-old with sickle cell anemia (HbSS) in Al Ain has a spleen that can no longer be felt, and his blood film shows Howell-Jolly bodies. Which infection risk is most increased, and why?

    1. AMycobacteria, because macrophage activation fails
    2. BHerpesviruses, because NK cell numbers fall
    3. CEncapsulated bacteria, because splenic filtering is lost
    4. DMolds, because neutrophil killing is impaired

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12. Question 12 · Easy

    The main T-cell growth factor, made by activated T cells themselves, is:

    1. AInterleukin-1
    2. BInterleukin-2
    3. CInterleukin-4
    4. DInterleukin-10

    Answer and explanation in LearnFree account