MLT GlobeImmunology & Serology: Immune system principles
257 Immunology & Serology MCQs on Immune system principles with answers and explanations.
The immune system is broadly divided into which two arms?
The primary division is innate versus adaptive immunity. Humoral and cell-mediated responses are subdivisions of the adaptive arm.
Intact skin, mucus, cilia and gastric acid make up which line of defence?
Surface barriers are the first line of defence. Phagocytes and inflammation are the second line, and lymphocytes and antibodies are the third (adaptive) line.
What is the main role of epidermal Langerhans (dendritic) cells?
Langerhans cells are skin dendritic cells that take up antigens and carry them to lymph nodes for presentation. Arrector pili muscles raise hairs, and melanocytes make pigment.
A person receives a booster dose of tetanus toxoid. Compared with the first exposure, the antibody response is:
Memory B cells produce a secondary response with a shorter lag, higher titres, more IgG and higher affinity than the primary response.
Neutrophils engulfing bacteria at a wound within minutes, without prior exposure, illustrates which arm of immunity?
Phagocytosis by neutrophils is non-specific and needs no previous sensitisation, so it belongs to innate immunity. Adaptive responses depend on antigen-specific lymphocytes and take days to develop.
Compared with the primary response, a secondary antibody response to a protein antigen is characterised by:
Memory B and T cells give a rapid, larger response dominated by class-switched, affinity-matured IgG. Such switching and maturation require T-cell help; IgM predominance is typical of a primary response.
CD8 is a transmembrane glycoprotein co-receptor characteristically found on:
CD8 binds MHC class I and marks cytotoxic T cells. Helper T cells carry CD4 and bind MHC class II. The older term 'suppressor T cell' is no longer used as a distinct CD8 category.
How many classes of heavy-chain constant region (isotypes) define the human immunoglobulin classes?
The γ, α, μ, δ and ε heavy chains define IgG, IgA, IgM, IgD and IgE. Two is the number of light-chain types (κ and λ).
Activation of the complement cascade proceeds mainly by:
Each activated component is a protease that cleaves the next (e.g. C3 convertase splits C3 into C3a and C3b), amplifying the cascade, much like coagulation. Kinase-type phosphorylation is not involved.
A single IgG molecule is made of how many polypeptide chains?
The basic immunoglobulin unit has two identical heavy and two identical light chains linked by disulfide bonds. Five refers to the number of units in pentameric IgM.
A patient's serology shows specific antibodies of only one class early in a new infection. Which class is it?
IgM is the first antibody made in a primary immune response, so specific IgM indicates recent or current infection. IgG rises later and persists.
Which immunoglobulin class crosses the placenta and gives passive immunity to the newborn?
IgG is the only class transported across the placenta via neonatal Fc receptors. It also has four subclasses and is the most abundant serum immunoglobulin.
Which immunoglobulin class circulates mainly as a pentamer joined by a J chain?
Serum IgM is a pentamer, making it efficient at agglutination and complement activation. Secretory IgA is a dimer; IgG, IgE and IgD are monomers.
Which immunoglobulin class, bound to mast cells and eosinophils, mediates defense against helminths?
IgE binds Fc-epsilon receptors on mast cells and basophils and triggers eosinophil-mediated killing of worms. It also drives immediate allergic reactions.
Which cell is the main source of circulating antibody?
Plasma cells are terminally differentiated B cells that secrete large amounts of immunoglobulin. Helper T cells assist B cells but do not make antibody.
Which immunoglobulin circulates as a pentamer of five monomers joined by a J chain?
Serum IgM is pentameric (10 antigen-binding sites), making it an efficient agglutinator and complement activator. Secretory IgA is dimeric; IgG and IgE are monomers.
The small region of an antigen that a specific antibody binds is called the:
The epitope is on the antigen; the paratope is the complementary binding site on the antibody. Fc receptors bind antibody constant regions.
Which complement component is present at the highest concentration in normal serum?
C3 (about 1-1.5 g/L) is the most abundant complement protein and the convergence point of all three pathways.
Neutrophils migrate toward C5a and IL-8 released at an infection site. This directed movement is called:
Chemotaxis is directional movement along a gradient of chemoattractants. Opsonisation coats microbes for uptake; phagocytosis is engulfment.
A foreign molecule that can trigger an immune response and bind specific antibodies is called an:
Antigens are usually complex molecules such as proteins or polysaccharides recognised by B- and T-cell receptors.