Ocular therapeutics Ð Part 7 Overview of the immune system

1 Which of the following lymphocyte sub-type is primarily responsible for antibody production? (A) B cells; (B) Cytotoxic T cells; (C) Helper T cells; (D) Natural killer cells. The correct answer is A. Lymphocytes are responsible for the recognition of antigens and are divided into two main lineages, B cells which produce antibodies and T cells. 2 What is 'clonal selection'? (A) Elimination of lymphocytes lacking a functional antigen receptor; (B) A mechanism by which specific pathogens propagate by evading the immune system; (C) The selection and propagation of lymphocytes that react with a particular pathogen; (D) The identification and elimination of self-reactive lymphocytes. The correct answer is C. The basis of all specific immune responses is that only the lymphocytes that recognise a pathogen react against it. 3 Which of the following cells plays an important role in targeting and eliminating virally infected cells? (A) Neutrophils; (B) Macrophages; (C) T cells; (D) B cells. The correct answer is C. T cells perform a variety of functions including the destruction of virally-infected cells. 4 Which of the following cell types expresses MHC Class II molecules on their surface? (A) NK cells; (B) Dendritic cells; (C) Neutrophils; (D) T cells. The correct answer is B. A rare but important group of leukocytes are the dendritic cells which act as antigen presenting cells. This is carried out by molecules encoded in the major histo-compatibility complex (MHC molecules). 5 Which lymphocyte sub-type secretes cytokines that activate macrophages? (A) Tc cells; (B) TH1 cells; (C) TH2 cells; (D) NK cells. The correct answer is B. One of the things that distinguishes the two types of T helper cells is the cytokines they produce. TH1 cells secrete cytokines that activate macrophages (such as interferon-g). 6 Which class of antibody plays a major role in the defence of mucosal surfaces? (A) IgG; (B) IgA; (C) IgM; (D) IgE. The correct answer is B. IgA is the major antibody protecting mucosal surfaces and is found in high concentration in secretions such as saliva, tears and breast milk. 7 Which class of antibody plays a major role on Type I hypersensitivity reactions? (A) IgG; (B) IgA; (C) IgM; (D) IgE. The correct answer is D. IgE binds with high affinity to receptors on mast cells and basophils and is therefore particularly important in type I hypersensitivity. 8 Which of the following is not a function of complement? (A) Induction of anti-viral proteins; (B) Cell lysis; (C) Opsonisation; (D) Mast cell activation. The correct answer is A. Induction of anti-viral is not a complement function. 9 Which group of cytokines are key elements in the defence against viruses? (A) Interleukins; (B) Tumour necrosis factors; (C) Interferons; (D) Colony stimulating factors. The correct answer is C. An infected cell releases interferons which promotes anti-viral resistance in neighbouring cells. 10 What is the principal defence mechanism against bacterial toxins? (A) Neutralisation by specific antibodies; (B) Complement binding; (C) Phagocytosis by neutrophils; (D) Proteolytic cleavage by enzymes released from phagocytes. The correct answer is A. Protection against toxins released by bacteria is primarily mediated by specific antibodies which can bind and neutralise the toxin. 11 Which HLA molecule has been linked to susceptibility to ankylosing spondylitis? (A) HLA-B27; (B) HLA-B67; (C) HLA-A29; (D) HLA-A27. The correct answer is A. The strongest known association between specific systemic disease and HLA molecules is between HLA-B27 and ankylosing spondylitis. 12 Which HLA molecule has been linked to susceptibility to birdshot chorioretinopathy? (A) HLA-B27; (B) HLA-B67; (C) HLA-A29; (D) HLA-A27. The correct answer is C. HLA-A29 has been associated with birdshot chorioretinopathy.