MLT GlobeDHA exam preparation (Dubai) – page 11
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
Which feature describes innate immunity?
Innate defences are present from birth and act immediately. Memory and antigen specificity are features of adaptive immunity.
Normal flora protect against pathogens mainly by:
Commensals block pathogens by competing for nutrients and attachment sites and by making bacteriocins and acids. Antibodies are made by the host.
Which is NOT a function of complement?
Complement opsonizes (C3b), lyses (MAC) and promotes inflammation (C3a, C5a); antibodies are made by plasma cells.
Which cell uses reactive oxygen species and lysozyme to kill ingested pathogens?
Macrophages kill phagocytosed microbes via oxidative burst and lysosomal enzymes. NK and T cells kill other cells by perforin and granzymes.
Toll-like receptors are:
TLRs on host cells recognize conserved microbial patterns such as LPS and trigger innate responses.
Which class of molecule is generally the most potent immunogen?
Large proteins are complex and T-dependent, so they are strongest immunogens.
Which cell is the most efficient antigen-presenting cell for naive T cells?
Dendritic cells capture and process antigen and present it to naive T cells in lymph nodes.
Which antibody usually exists as a pentamer?
Secreted IgM is a pentamer joined by J chain. IgA is mostly a dimer in secretions.
The antigen-binding site of an antibody is made up of:
The binding site is formed by the variable domains of both heavy and light chains.
Which cells synthesize and secrete immunoglobulins?
Plasma cells, terminally differentiated B cells, secrete large amounts of antibody.
How many types of light chain are found in human immunoglobulins?
Kappa and lambda; each molecule has only one type.
Which statement about complement is correct?
The alternative pathway is activated by microbial surfaces. The MAC is C5b-9; C3a and C5a are anaphylatoxins.
Classical pathway components act in which order?
C1 cleaves C4 then C2, forming C4b2a, which cleaves C3.
Which statement about complement is correct?
Complement proteins are mostly made by the liver and circulate inactive.
Which is NOT a cytokine?
Colistin is a polymyxin antibiotic; the others are cytokines.
Minutes after a bee sting, a child has wheezing and hypotension. Which antibody mediates this?
Anaphylaxis is type I: allergen cross-links IgE on mast cells, releasing histamine.
Which pair of conditions is driven by IgE bound to mast cells, i.e. immediate (type I) hypersensitivity?
Type I reactions follow allergen cross-linking of mast-cell IgE, as in anaphylaxis and atopy. Serum sickness/Arthus are immune-complex (type III); contact dermatitis and tuberculin reactions are T-cell mediated (type IV).
A porcine heart valve implanted in a human is an example of which type of graft?
Xenografts cross species; living xenografts face strong rejection, which is why porcine valves are chemically treated before use.
Immunological tolerance is best defined as:
Tolerance is antigen-specific non-reactivity (e.g. to self), while responses to other antigens remain intact; general failure is immunodeficiency.
A patient with thyroiditis has antibodies against thyroid peroxidase. This illustrates autoimmunity, meaning:
Autoimmunity is loss of self-tolerance, producing autoantibodies or autoreactive T cells against self antigens such as thyroid peroxidase.