This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “T-Independent B-cell Responses”.
1. Which of the following is a part of the chemical composition of T-independent Antigen (TI-Ag)?
a) Proteins
b) Polypeptides
c) Hapten Complexes
d) Capsular polysaccharides
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Explanation: TI Ags (T independent Antigens) are more diverse and usually exhibit highly repetitive epitopes or contain TLR ligands, such as LPS. The components of many natural pathogens, such as polysaccharides from bacterial cell walls and viral capsids, can enhance TI responses, making them an important defence mechanism against different infections. On the other hand, 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 proteins, polypeptides and hapten complexes.
2. TI antigens elicit weak BCR (B cell receptor) signalling.
a) True
b) False
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Explanation: It is thought that TI Ags can elicit strong BCR signalling or a combination of BCR and TLR signalling. In either case, it can bypass the necessity of T cell help for B cell proliferation and plasma cell (PC) formation. However, the strong activation of B cells by TI Ags may not necessarily exclude their further interactions with T cells.
3. T-independent antigens show high affinity to which of the following antibody isotype?
a) IgG
b) IgM
c) IgA
d) IgE
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Explanation: T-independent antigens are simple repetitive antigens and are often composed of polysaccharides. They show modest to higher affinity to IgM. Their main property is that they have no memory and act spontaneously against any infection. These antigens help in activating B cells by direct crosslinking of B cell receptors (BCRs). They can also be activated via Toll-like Receptors (TLRs).
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 helps 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. How many classes of T-independent Antigens exist?
a) 2 classes-TI-1 and TI-3
b) 3 classes-TI-1, TI-2, TI-3
c) 4 classes-TI-1, TI-2, TI-3, TI-5
d) 2 classes-TI-1, TI-2
View Answer
Explanation: T-Independent Antigens are classified and categorised into 2 major classes: TI-1 and TI-2. TI-1 antigens are responsible for proliferation and differentiation of B lymphocytes without carrying out T cell stimulation. This mechanism takes place independently of their BCR (B cell receptor) specificity. TI-2 antigens, on the other hand, are responsible for activating only mature B lymphocytes. Immature B cells undergo energy.
6. Which of the following is the property possessed by TI-2 (T-independent type 2) antigen?
a) It is flexible, hydrophilic and non-degradable
b) It shows mitogenic stimuli
c) It enhances polyclonal B cell activity
d) It recognises microbial molecules
View Answer
Explanation: T-independent antigens are classified in two types: TI-1 and TI-2. TI-2 antigen is composed of pure polysaccharides and it is able to activate complements. However, it lacks the ability to induce MHC dependent T cells. It is flexible, hydrophilic as well as non-degradable. It is also capable of engaging multiple BCRs which is one of the most important property of TI-2 antigen.
7. Which cells are responsible to play roles of T-independent antibody response in humoral defences?
a) B1 and B2 cells
b) B and T cells
c) B1 and marginal zone B cells
d) Central and marginal zone B cells
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Explanation: B1 and marginal zone B cells are mostly responsible for the roles of T-independent antibody response in humoral defences. This takes place as the cells are activated, migrated and differentiated into the antibody-producing cells in various lymphoid tissues. This can lead to a possible peripheral tolerance mechanism of autoreactive B cells at the target organs.
8. Which of the following is the property of TI type 1 (TI-1) antigen?
a) It activates complements
b) It functions by non-specifically or polyclonal activity
c) It is flexible and hydrophilic
d) Capable of engaging multiple BCRs
View Answer
Explanation: T-independent antigens are of two types: TI-1 and TI-2. TI-1 type of antigen is a mitogenic antigen as it shows mitogenic stimuli like LPS, CpG or poly IC and B cell mitogens. It functions by non-specifically or polyclonal activity. This is because it enhances the polyclonal B cell activation via Toll like receptors (TLRs). TI-1 also recognises microbial molecules and it signals the cell to secrete immunostimulatory cytokines.
9. Which of the following is a polysaccharide vaccine of TI-2 antigen?
a) Menozain
b) Covax
c) Pneumovax
d) Flumune
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Explanation: TI-2 antigens enhance the robust and long-lasting primary antibody responses but they cannot recall response i.e., secondary immunization. Polysaccharide vaccines like Pneumovax and Menomune confer long term humoral protection in adult humans. These are the vaccines in response to TI-2 antigen. These antigens stimulate extrafollicular foci of plasma cell production and short-lived abortive TI germinal centres.
10. Which of the following is not an example of polysaccharide of bacterial capsule?
a) Streptomycin
b) Streptococcus
c) Haemophilys
d) Neisseria
View Answer
Explanation: T-independent antigens (specifically TI-2) plays a very important role in shaping various vaccines and bacterial capsules as polysaccharide is the major component of these antigens. These antigens do not induce immunological memory. However, the antibodies to TI antigens develop after the age of 2 years in humans. Polysaccharides of bacterial capsule include Streptococcus, Haemophilys and Neisseria which play an important role in engaging BCRs.
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