Which of the following cells is involved in cell-mediated immunity?
Answer: B
Correct answer: T cells
T cells carry cell-mediated immunity, killing infected cells directly and orchestrating the rest of the response. Mast cells belong to the inflammatory and allergic response; thrombocytes are platelets, for clotting; and leukaemia is a disease, not a cell type.
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Segments of antigen that are recognized by antibody are
Answer: B
Correct answer: Epitopes
An epitope (antigenic determinant) is the small part of an antigen that an antibody actually binds - a few amino acids or sugar residues on the surface. A single large antigen carries many different epitopes, which is why one protein provokes many different antibodies.
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Which is involved in body defence?
Answer: D
Correct answer: All the above
All three are white cells of the defence system: neutrophils are the first phagocytes to arrive at an infection, macrophages engulf and also present antigen, and lymphocytes carry the specific response. Between them they cover both the innate and the acquired arms.
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What is the behavior in which T cells and B cells constantly travel throughout the body seeking out and destroying foreign substances?
Answer: B
Correct answer: Immune surveillance
Immune surveillance is the continual patrolling of the body by lymphocytes, which circulate through blood, tissue and lymph, passing through the lymph nodes, so that an antigen appearing anywhere is met by the cells that recognise it. It is also the mechanism credited with picking off cells that have turned cancerous.
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Which of the following conveys the longest-lasting immunity to an infectious agent?
Answer: A
Correct answer: Active immunity
Active immunity lasts because the body has made the response itself: it retains memory cells that can be roused quickly on re-exposure, so protection can last years or a lifetime. Passive immunity supplies ready-made antibodies but leaves no memory, so it fades as those antibodies are broken down.
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An Rh- individual receives Rh+ blood. The recipient becomes
Answer: D
Correct answer: Isoimmunised
The Rh-negative recipient has no D antigen, so the transfused Rh-positive cells are foreign and provoke an immune response - the recipient becomes isoimmunised, that is, sensitised, and now carries anti-D antibodies. The first transfusion often passes without a dramatic reaction; the danger is the next exposure, and, in a woman, a later Rh-positive pregnancy.
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Which type of interferons is associated with an antiviral innate response?
Answer: A
In a type of antiviral response initiated within the cell, type I interferons (IFN-alpha and IFN-beta) are produced and secreted into the extracellular space where they bind to noninfected cells and render them resistant to subsequent viral infections.
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Which of the following blood proteins can destroy pathogens?
Answer: D
Correct answer: Complement system
The complement system is a cascade of some thirty plasma proteins. Once triggered - by antibody bound to a surface, or directly by microbial surfaces - it opsonises the pathogen for phagocytosis, recruits inflammatory cells, and assembles the membrane attack complex that punches a hole in the microbe and lyses it. Fibrinogen is for clotting, platelets are cell fragments, and MHC molecules present antigen rather than destroying it.
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A rare disease congenital agammaglobulinemia is caused due to abnormality in __________________
Answer: A
Correct answer: humoral antibody
Congenital agammaglobulinaemia - Bruton’s disease - is a failure of B cells to mature, so almost no immunoglobulin is made. The defect is therefore in the humoral (antibody) arm. Cell-mediated immunity is intact, which is why such patients handle viruses reasonably well but suffer repeated bacterial infections, the very ones antibody normally controls.
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B and T lymphocytes arise from _____________
Answer: A
Correct answer: hematopoietic stem cells
Both arise from the haematopoietic stem cells of the bone marrow. B cells complete their maturation there; T cells migrate to the thymus to mature, which is what the T stands for. Germ cells give rise to gametes, and have nothing to do with it.
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