MLT GlobeImmunology & Serology: Immune system principles – page 7
257 Immunology & Serology MCQs on Immune system principles with answers and explanations.
The heavy chain of IgA is designated:
Immunoglobulin class is defined by heavy chain: α for IgA, γ for IgG, δ for IgD, ε for IgE and μ for IgM.
Which immunoglobulin class has the highest concentration in normal adult serum?
IgG makes up about 70–75% of serum immunoglobulin (roughly 7–16 g/L). IgA is second in serum but is the main antibody in secretions.
Which IgG subclass makes up the largest proportion of total serum IgG?
IgG1 is about 60–70% of total IgG, followed by IgG2, IgG3 and IgG4. IgG2 is second.
Which complement fragments act as anaphylatoxins, causing mast cell degranulation and smooth muscle contraction?
The small 'a' fragments C3a and C5a (and weakly C4a) trigger histamine release and increase vascular permeability. C3b and C4b are opsonins and parts of convertases.
The measles–mumps–rubella (MMR) vaccine is an example of a:
MMR contains weakened live viruses that replicate briefly and give strong, long-lasting immunity. Toxoid vaccines contain inactivated bacterial toxins, as in tetanus.
The tetanus vaccine contains:
Tetanus disease is caused by toxin, so the vaccine uses an inactivated toxin (toxoid) that induces neutralising antibody. There is no live tetanus vaccine.
Aluminium salts are added to many inactivated vaccines to act as:
Alum adjuvants form an antigen depot and activate innate immune cells, increasing antibody responses. Preservatives such as thiomersal have a different role.
An mRNA vaccine produces immunity mainly because:
The lipid-nanoparticle mRNA is translated by host cells into the antigen, which is then presented to B and T cells. mRNA does not enter the nucleus or integrate into DNA.
Which type of bond is NOT involved in antigen–antibody binding?
Antigen–antibody binding uses only weak non-covalent forces, which is why the reaction is reversible. Hydrogen, ionic, van der Waals and hydrophobic interactions all contribute.
The overall binding strength between a multivalent antibody and a multivalent antigen, combining all binding sites, is called:
Avidity is the combined strength of many binding sites, so IgM can bind strongly even with low-affinity sites. Affinity is the strength of one binding site with one epitope.
Which white blood cells are usually the first to arrive in large numbers at a site of acute bacterial infection?
Neutrophils are recruited within hours to acute bacterial inflammation and phagocytose the organisms. Plasma cells are part of the later antibody response.
Which tissue cell releases histamine when IgE bound to its surface is cross-linked by antigen?
Mast cells carry high-affinity IgE receptors. Cross-linking of bound IgE by allergen causes degranulation and release of histamine and other mediators.
A child recovers from chickenpox and is then immune to it. This is an example of:
The child's own immune system made the antibodies and memory cells after natural infection, so the immunity is natural and active.
Which of these is a secondary (peripheral) lymphoid organ?
Lymph nodes, spleen and mucosa-associated lymphoid tissue are secondary lymphoid organs where immune responses start. Thymus and bone marrow are primary lymphoid organs where lymphocytes develop.
Natural killer (NK) cells belong to which part of the immune system?
NK cells kill virus-infected and tumour cells without prior sensitisation and without antigen-specific receptors, so they are part of innate immunity.
Eosinophils are especially important in defence against:
Eosinophils release toxic granule proteins such as major basic protein that damage large parasites like helminths. They also take part in allergic reactions.
How many subclasses of IgG are found in humans?
Human IgG has four subclasses, IgG1 to IgG4, which differ in their heavy chains, hinge regions and functions.
Which part of an antibody molecule binds to Fc receptors on phagocytes?
The Fc region, formed by the constant domains of the heavy chains, binds Fc receptors and complement. The Fab region binds antigen.
Which is the largest secondary lymphoid organ in the body and filters blood?
The spleen is the largest secondary lymphoid organ; it filters blood, removes old red cells and mounts immune responses to blood-borne antigens.
The resident macrophages of the brain and spinal cord are called:
Microglia are the tissue macrophages of the central nervous system. Kupffer cells are in the liver, osteoclasts in bone and Langerhans cells in the epidermis.