imunology general mcq to sort out
Where do precursor T-lymphocytes develop into fully competent but not yet activated T-cells? a) The thymus gland b) The bone marrow c) The lymph nodes d) The splee
a) The thymus gland Feedback: Lymphoid stem cells derived from the bone marrow develop into competent T-lymphocytes, with a functioning T-cell receptor and co-receptor, in the thymus gland. Mature competent lymphocytes can also develop in the bone marrow, but these become B-cells capable of producing antibody molecules. Mature but non-activated lymphocytes leave these two primary lymphoid tissues and enter the blood and lymph, where they remain inactive until they encounter an antigen they recognize, presented by an antigen presenting cell. This happens in secondary lymphoid tissues, which include the lymph nodes and the white pulp areas of the spleen, as well as the mucosal associated lymphoid tissues of the gut and airways.
What is the normal immunological role of the CD8+ve T-cell? a) Helps B-lymphocytes to develop into plasma cells. b) Kills virus infected cells. c) Secretes antibodies. d) Rejects transplanted tissue.
b) Kills virus infected cells. Feedback: A CD8+ve (cytotoxic) T-cell recognizes small peptides derived from viral proteins being synthesized within an infected cell, and presented on the cell surface attached to a class I MHC antigen. It kills the infected cell, interrupting the virus life cycle. A CD4+ve (helper) T-cell recognizes peptides derived from antigens and presented on B-cell surfaces attached to class II MHC antigens. It stimulates the B-cell to develop into an antibody secreting plasma cell. Cytotoxic T-cells, helper T-cells and antibodies can all play a part in rejecting transplanted tissue, but this cannot be regarded as their normal immunological role since a tissue transplant is physiologically abnormal.
Cancer cells often have reduced amounts of cell surface proteins, including class I MHC antigens. Which of the following cells of the immune system can exploit this property to kill cancer cells? a) Cytotoxic T-cells b) Natural killer cells c) Helper T-cells d) Macrophages
b) Natural killer cells Feedback: Natural killer cells are lymphocytes which do not carry a specific antigen receptor (antibody or T-cell receptor) on their surface. Instead they recognize cells which express a lowered amount of MHC class I antigen, and they mount a cytotoxic attack against such cells. These cells may be virus infected, because some viruses attempt to avoid cytotoxic T-cell attack by suppressing expression of class I MHC antigen by the cells they infect, or they may be cancer cells. Cytotoxic T-cells kill virus infected cells but recognize viral peptides presented on the cell surface by class I MHC proteins. Helper T-cells recognize cells carrying foreign peptides presented by class II MHC proteins, and they stimulate the cells they recognize. Macrophages, the tissue based phagocytes, recognize pathogen specific surface molecules, and apoptotic cells, but do not recognize live tumour cells.
Which of the following is not true about antibody structure? a) Antibodies have multiple identical antigen binding sites. b) Antibodies are built from equal numbers of large (heavy) and small (light) peptide chains. c) Antibodies are secreted and function away from the cell. They are not attached to the cell membrane. d) The class of the antibody molecule is determined solely by its heavy chain
c) Antibodies are secreted and function away from the cell. They are not attached to the cell membrane. All antibody units are made up of two identical heavy chains and two identical light chains. The Y shaped antibody unit has an antigen binding site at the end of each arm of the Y so all antibody units have at least two antigen binding sites. Those antibodies which are polymers of antibody units (IgM and secreted IgA) have more than two. The antigen binding sites within an antibody are derived from the interaction of identical light and heavy chains so they are identical. There are nine alternative genes coding for the constant region of the heavy chain. The class of antibody produced is determined by which one of these is expressed. There are just two types of light chain, either of which can occur in any class of antibody. Non-activated B-cells carry a sample of the antibody they are capable of secreting attached to their cell membrane. Additionally IgE functions attached to the membrane of the mast cell forming an antigen receptor for that cell
Which of the following is not a feature of a secondary immune response to an antigen, when compared to the first response to the same antigen? a) The antibody is generated faster. b) More antibody is produced. c) The antibody produced has greater affinity for the antigen. d) Antibody is generated without T-cell help.
d) Antibody is generated without T-cell help. Feedback: After the first response to an antigen, the lymphocyte circulation contains many memory cells displaying antibody specific for that antigen. Therefore on a second encounter specific lymphocytes are located more quickly and in greater numbers than they were the first time, so antibody production starts more quickly and much more antibody is produced. As the immune response progresses the amount of antigen displayed by antigen presenting cells decreases, creating competition for binding between B-cells, which ensures that only those producing a high affinity antibody are selected and survive. Thus the antigen binding affinity of the antibody produced increases. This is aided by mutation within the antibody gene in activated B-cells, primarily affecting the antigen binding regions. B-cell activation in the secondary immune response requires T-cell help, exactly as it does in the primary response.
Which of the following cell types or systems is not part of an innate immune response to a pathogen? a) Phagocytes. b) Natural killer cells. c) The inflammatory response. d) Cytotoxic T-lymphocytes.
d) Cytotoxic T-lymphocytes. Feedback: Cytotoxic T-lymphocytes identify virus infected cells by means of viral peptide antigens displayed on the cell surface attached to class 1 major histocompatibility antigens. This is a classic adaptive response and cytotoxic T-cells take no part in an innate immune response. Both major phagocyte types, the blood based neutrophils and tissues based macrophages, can recognise prokaryote surface components without the need for an adaptive immune response, and so are part of the innate immune response. Binding of antibodies to pathogens helps their recognition by phagocytes (a process called opsonisation), but phagocytes can recognise pathogens in the absence of antibodies. Natural killer (NK) cells are a type of lymphocyte, but they do not produce antibodies or carry a T-cell receptor, so are not part of the adaptive immune response. They recognise cells which do not express very much class 1 major histocompatibility antigen (MHC antigens) on their surfaces. Some viruses can reduce the amount of MHC antigen expressed and tumour cells often express lower amounts of surface protein, so NK cells mount an innate attack on some virally infected cells and tumour cells. An inflammatory response can be triggered by tissue injury, or by presence of pathogens. It is initially activated by a range of chemokines produced by phagocytes, generated by innate activation of the complement system, or produced by the blood clotting mechanism. In sensitised individuals antibodies bound to mast cells can play a part in activation of inflammation but they are not essential.
In order to initiate an adaptive immune response, antigenic peptide must be presented to antigen-specific T cells. Which one type of cell presents this antigen to T cells? a) Dendritic cell b) Epithelial cell c) Neutrophil d) Plasma cel
d) Plasma cell Feedback: T cell activation is dependent on specific antigen presentation by dendritic cells. Epithelial cells can help to initiate inflammation but they do not present antigen to T cells. Neutrophils are essential for removing encapsulated bacterial infections but they do not present antigens to T cells. Plasma cells are antibody-secreting cells that have differentiated from activated B cells. While they are unable to present antigen to T cells, their activated B cell precursors are also effective at antigen presentation to helper T
There is huge variation in the specificity of antibodies and T cell receptors to different antigens. The genetic basis of this variation comes from: a) A large number of germline genes each coding for a different specificity. b) A small number of germline genes that undergo somatic hypermutation to create a large number of different specificities. c) Programmed selection of gene segments from a small number of genes. d) Random selection of gene segments and recombination from a small number of genes.
d) Random selection of gene segments and recombination from a small number of genes. Feedback: Gene segments are randomly selected for recombination. This has the advantage that each individual is likely to have a different repertoire, but has the disadvantage that not every recombination will lead to a functional gene product. Developing lymphocytes that have non-functional gene rearrangements do not survive. It is estimated that there are >1011 different lymphocyte specificities but humans have only about 30,000 genes in the germline. Somatic hypermutation plays an important role in increasing the affinity of an antibody for its antigen, but it plays no role in the initial generation of the immune repertoire or in the affinity of T cell receptors. There is no programmed selection of gene segments. It is a random process.
