This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “T-Dependent B-Cell Responses”.
1. Which of the following is NOT a part of the chemical composition of T-dependent Antigen (Td-Ag)?
a) Proteins
b) Polypeptides
c) Capsular polysaccharides
d) Hapten complexes
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Explanation: T-dependent antigens are the antigens which help in activation of only mature B cells by carrying out their interaction with Helper T cells. These antigens mainly consist of polypeptides, proteins and hapten complexes. T-dependent antigens are immunogenic over a wide range. On the other hand, T-independent antigens consist of capsular polysaccharides along with bacterial cell wall components like lipopolysaccharides. These antigens help in activation of mature as well as immature B cells.
2. The coordination between B cells and helper T cells that are specific to the same antigen is referred to as linked recognition.
a) True
b) False
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Explanation: Linked Recognition involves several immune processes of the adaptive immune system that occur in secondary lymphoid tissue. It mainly focuses on 1) Antigen processing and presentation. 2) Selection and expansion of epitope specific T and B cells. 3) Generation of antigen-specific antibody. Linked recognition initiates the activity of B cells with the help of interaction with helper T cells that respond to same antigen.
3. Which of the following types of T cells deliver activating signals to B cells?
a) Cytotoxic T cells
b) Helper T cells
c) Memory T cells
d) Regulatory T cells
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Explanation: T cells help antigens to respond to antibodies. B cells also require this help from T cells when they are in contact with the antigens. B cells interact with the antigens with the help of immunoglobulin present on the surface of B cells. T cells (more specifically helper T cells) help the B cells as it is regulated because of binding between MHC II molecule and peptides of the antigen. Helper T cells carry forward the activating signals to B cells as and when they recognize this peptide-MHCII complex.
4. Which cells are majorly involved in production and secretion of cytokines to activate B cells?
a) T cells
b) Th1 cells
c) Th2 cells
d) Memory T cells
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Explanation: After the initiation of activation by linked recognition, Th2 cells produce and secrete cytokines in order to continue the process of activation of B cells. Th2 cells cause proliferation and help the B cells to differentiate into clonal daughter cells. These activated clonal B cells further develop into Memory B cells. They also start secreting pentameric IgM.
5. Which of the following is the most important T-cell effector membrane-bound molecule that is essential for B cell responses to T-dependent antigens?
a) CD8
b) CD40
c) CD21
d) CD4
View Answer
Explanation: CD40 belongs to Tumour-Necrosis Factor (TNF) Family. However, it does not consist of death domains. It is the most important T cell effector membrane bound molecule which is involved in directing the B cell into cell cycle and is essential for its response to T-dependent antigen. The ligand of CD40 designated as CD40L (or also known as CD154) is expressed on T cell which helps in B cell activation.
6. How many B-cell receptor (BCR) isotypes can a mature B cell express?
a) Two
b) Three
c) Four
d) Only one
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Explanation: A mature B cell is capable of expressing two BCR isotypes namely IgM and IgD. The structure of BCR consists of four immunoglobulin domains (in case of IgD) and five immunoglobulin domains (in case of IgM) on the heavy chain which is linked by the hinge. The structure of BCR also includes a short intracellular domain which shows the linkage of three amino acids: Lysine-Valine-Lysine.
7. In the secondary response of T-dependent B cell activation, production of which antibody is extremely high as compared to its production in primary response?
a) IgD
b) IgM
c) IgG
d) IgA
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Explanation: During the secondary response of T-dependent B cell activation, the production of IgG is so high that it helps to stimulate the actions of B cells. This high production of IgG helps B cells to fight against infections. This entirely depends on the signals received from T cells. In addition, the antibodies produced during the secondary response are more effective. They have a higher affinity to bind to targeted epitopes. Plasma cells are produced during secondary responses and they live longer than those produced during the primary response.
8. What is the receptor of B-cell activating factor called?
a) B-cell Receptor
b) TACI
c) Follicular dendritic cell receptor
d) T-cell Receptor
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Explanation: TACI stands for Transmembrane activator and calcium-modulating cyclophilin ligand interactor. It acts as a receptor associated with the B cell activator. TACI is the part of Tumour-Necrosis Family (TNF). It plays an important role in T-cell dependent B cell responses by providing accurate and limited signals for their interaction. However, if there is any abnormality in the regular signalling response of TACI, it may result in autoimmune diseases. TACI is also responsible for isotype switching and B-cell homeostasis.
9. In the second phase of primary B cell immune response, what do the activated B cells form when they migrate to primary lymphoid follicles?
a) Follicular dendritic cell centre
b) Mantle zone
c) Germinal centre
d) Follicle centre
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Explanation: In the second phase of B cell immune response, B cells for germinal centers as and when they move towards the lymphoid follicles. These germinal centres consist of growing and differentiating B cells. They also show the presence of 5-10% of T cells that are antigen-specific. These germinal centres provide great help to B cells for their developmental processes.
10. What is the initial stage of primary response of T-dependent B cell activation called?
a) Lag Period
b) Log period
c) Stationary Period
d) Initial Period
View Answer
Explanation: Activation of B cells via T-cell dependent mechanism is very important as it showcases two types of responses: Primary and Secondary Responses. These responses always incline towards adaptive immunity. The first step or primary response mechanism is termed as lag phase. It is also sometimes called as latent period or latent phase. This phase lasts for around 10 days.
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