MLT GlobeImmunology & Serology: Immune system principles – page 10
257 Immunology & Serology MCQs on Immune system principles with answers and explanations.
Before a peripheral blood stem cell transplant, the harvested product is counted for haematopoietic progenitor cells. Which marker is used?
CD34 identifies haematopoietic stem and progenitor cells and is used to calculate the graft dose. CD138 marks plasma cells, and CD25 is the IL-2 receptor alpha chain.
Cytotoxic T lymphocytes kill virus-infected target cells mainly by releasing:
Perforin forms pores in the target membrane and granzymes enter to trigger apoptosis. Major basic protein is an eosinophil product used against helminths.
A virus reduces MHC class I expression on infected cells so that cytotoxic T cells cannot recognise them. Which cell is best able to kill these infected cells?
NK cells are inhibited by self MHC class I; when class I is lost ('missing self'), the inhibition is removed and the NK cell kills. Plasma cells secrete antibody but do not kill cells directly.
NK cells perform antibody-dependent cellular cytotoxicity (ADCC) against IgG-coated target cells by using which receptor?
CD16 is a low-affinity Fc receptor for IgG; binding IgG on a target cell triggers NK degranulation. CD21 and CD35 are complement receptors, not Fc receptors.
During the neutrophil respiratory burst, which enzyme complex produces superoxide from molecular oxygen?
NADPH oxidase reduces oxygen to superoxide, which is converted to hydrogen peroxide. Myeloperoxidase then uses hydrogen peroxide to make hypochlorite; it does not make superoxide.
The main action of type I interferons (IFN-α and IFN-β) is to:
Virus-infected cells release IFN-α/β, which induce nearby cells to make proteins that block viral replication and increase MHC class I. IgE switching is driven by IL-4.
Which chemokine released by macrophages and epithelial cells is a major attractant for neutrophils?
CXCL8 (IL-8) binds CXCR1/CXCR2 on neutrophils and draws them to sites of infection. IL-7 is a lymphocyte growth factor, not a chemokine.
Which pair of cytokines is mainly anti-inflammatory and immunosuppressive?
IL-10 and TGF-β inhibit macrophage activation and T-cell proliferation and are produced by regulatory T cells. IL-1 and TNF-α are classic pro-inflammatory cytokines.
Differentiation of a naive CD4 T cell into a Th1 cell is mainly driven by which cytokine from dendritic cells and macrophages?
IL-12 induces T-bet and IFN-γ production, leading to Th1 cells that activate macrophages. IL-4 drives Th2 differentiation instead.
Besides TCR binding to peptide–MHC, full activation of a naive T cell requires a costimulatory signal between:
CD28 binding B7 molecules on activated antigen-presenting cells provides 'signal 2'. CD8 binds MHC class I, not class II.
CTLA-4, expressed on activated and regulatory T cells, mainly:
CTLA-4 competes with CD28 for B7 with higher affinity and delivers an inhibitory signal, limiting immune responses. The IL-2 receptor alpha chain is CD25.
For a B cell to switch from IgM to IgG production in response to a protein antigen, helper T cells must engage the B cell through:
CD40L on activated helper T cells binding CD40 on B cells, together with cytokines, drives class switching and germinal-centre formation. Absence of CD40L causes hyper-IgM syndrome.
A student has infectious mononucleosis. Epstein–Barr virus enters B lymphocytes by binding which molecule?
EBV glycoprotein gp350 binds CD21 (CR2), the receptor for C3d, on B cells. CD4 is the main receptor for HIV.
HIV enters CD4 T cells by binding CD4 together with which coreceptor?
HIV gp120 binds CD4 and then a chemokine receptor, CCR5 (R5 strains) or CXCR4 (X4 strains). CD21 is the EBV receptor.
During T-cell development, positive selection in the thymic cortex ensures that surviving thymocytes:
Only thymocytes whose TCR binds self-MHC weakly receive survival signals, giving MHC restriction. Removal of strongly self-reactive cells is negative selection.
During negative selection in the thymus, thymocytes are deleted when their T-cell receptor:
Strong binding to self-peptide–MHC signals a potentially autoreactive cell, which dies by apoptosis (central tolerance). Cells that bind no MHC die by neglect, not negative selection.
Thymocytes that express both CD4 and CD8 on their surface are:
Thymocytes progress from double-negative to double-positive (CD4+CD8+) in the cortex, then become single-positive cells after selection. Mature blood T cells are normally single-positive.
Each B cell produces antibody from only one of its two heavy-chain alleles. This is called:
Once one allele is productively rearranged, rearrangement of the other is stopped, so each B cell has a single specificity. Isotype switching changes the constant region, not the allele used.
Antibody affinity for an antigen increases during the weeks after immunisation. This is mainly due to:
Point mutations in variable-region genes, followed by selection of B cells that bind antigen best, produce affinity maturation. Light-chain type does not change affinity in this way.
Germinal centres, where B cells proliferate and undergo selection, are found in:
Antigen stimulation turns primary follicles into secondary follicles with germinal centres. Primary follicles contain resting naive B cells without germinal centres.