MLT GlobeImmunology & Serology: Immune system principles – page 6
257 Immunology & Serology MCQs on Immune system principles with answers and explanations.
Which immunoglobulin binds with high affinity to Fc receptors on mast cells and basophils?
IgE binds FcεRI on mast cells and basophils. Cross-linking by allergen triggers degranulation and histamine release, the basis of type I hypersensitivity.
Which complement component is shared by all three complement pathways and is the point where they converge?
The classical, lectin and alternative pathways all generate a C3 convertase that cleaves C3. C1q, C2 and C4 are used by the classical (and lectin, for C2/C4) pathways but not the alternative pathway.
Which cytokine is the main T-cell growth factor produced by activated T cells?
IL-2 drives proliferation of activated T cells (autocrine and paracrine). IL-5 acts on eosinophils and IL-10 is mainly anti-inflammatory.
Coating of bacteria with IgG or C3b so that phagocytes ingest them more easily is called:
Opsonins such as IgG and C3b bind Fc and complement receptors on phagocytes, increasing phagocytosis. Chemotaxis is directed cell migration and diapedesis is movement through vessel walls.
The primary lymphoid organ where T cells mature and undergo positive and negative selection is the:
T-cell precursors from the bone marrow mature in the thymus, where positive selection (MHC recognition) and negative selection (self-tolerance) occur. Spleen and lymph nodes are secondary lymphoid organs.
Compared with a primary antibody response, a secondary (anamnestic) response shows:
Memory B cells respond faster on re-exposure, producing higher titres of mainly IgG with increased affinity (affinity maturation). A primary response has a longer lag and is dominated by IgM.
In flow cytometry, which marker is expressed on essentially all leukocytes and is used to gate white cells away from red cells and debris?
CD45 (leukocyte common antigen) is present on all nucleated haematopoietic cells, so CD45 versus side scatter is the standard leukocyte gate. CD34 marks only stem/progenitor cells.
Which surface marker is most characteristic of monocytes and macrophages?
CD14, the receptor for LPS-binding protein complexes, is strongly expressed by monocytes. CD19 is a B-cell marker and CD56 is found on NK cells.
Kupffer cells are resident macrophages found in the:
Kupffer cells line the hepatic sinusoids. Resident macrophages of the brain are microglia, and in bone they are osteoclasts.
Lysozyme in tears and saliva protects against bacteria by:
Lysozyme breaks the bonds between N-acetylmuramic acid and N-acetylglucosamine in peptidoglycan, mainly damaging Gram-positive bacteria. Iron binding is the action of lactoferrin.
A patient with a helminth infection has marked eosinophilia. Which cytokine mainly drives eosinophil production and activation?
IL-5, produced by Th2 cells and ILC2s, stimulates eosinophil growth, differentiation and activation. IL-12 and IFN-γ drive Th1 responses instead.
The T-cell receptor is associated with a signalling complex that is used as a pan-T-cell marker. This complex is:
CD3 transmits the activation signal after the TCR binds peptide–MHC and is present on all mature T cells. CD33 is myeloid and CD41 is a platelet marker.
In adult humans, B lymphocytes develop from progenitors mainly in the:
The bone marrow is the primary lymphoid organ for B-cell development in humans. The thymus is where T cells mature.
The first immunoglobulin chain produced by a developing pre-B cell, found in the cytoplasm, is the:
Heavy-chain genes rearrange first; cytoplasmic μ chain pairs with a surrogate light chain as the pre-B-cell receptor. Light chains rearrange afterwards.
Mature plasma cells usually lose CD20 and strongly express which marker?
CD138 (syndecan-1) is the standard plasma-cell marker, along with strong CD38. CD3 is a T-cell marker and CD14 marks monocytes.
In a lymph node, T lymphocytes are found mainly in the:
The paracortex (deep cortex) is the T-cell zone, where dendritic cells present antigen. Follicles and germinal centres are B-cell areas.
In the spleen, the periarteriolar lymphoid sheath (PALS) of the white pulp contains mainly:
The PALS surrounding central arterioles is the splenic T-cell zone; B-cell follicles lie next to it. Red cell removal takes place in the red pulp.
Which cell type normally lacks MHC class I molecules?
MHC class I is expressed on almost all nucleated cells and platelets; mature red cells have lost their nucleus and have essentially no class I. Hepatocytes, neutrophils and B cells all express it.
HLA-B27 is most strongly associated with which disease?
About 90% of patients with ankylosing spondylitis carry HLA-B27. Coeliac disease is linked to HLA-DQ2/DQ8.
Immature dendritic cells of the epidermis that capture antigen and migrate to lymph nodes are called:
Langerhans cells are skin dendritic cells that carry antigen to draining nodes and present it to naive T cells. Kupffer cells are liver macrophages.