T Cell and B Cell Activation Questions and Answers

Q: The membrane of mature B cells have

Mature B cells carry both IgM and IgD on their membranes.A mature naive B cell, leaving the bone marrow and circulating in the periphery, expresses membrane IgM and IgD with the same antigen specificity. Both are made from one long primary transcript by alternative splicing of the heavy-chain constant regions Cμ and Cδ.IgG and IgE appear only after the cell has been activated and undergone class switching, which replaces the constant region; immature B cells express IgM alone. So any option including IgG or IgE does not describe a mature naive B cell.

Q: Pick the correctly matched pairs.P. Immature B cells - Terminal deoxynucleotidyl transferaseQ. Activated B cells - Class switchingR. Pre B cells - Surrogate light chainS. Mature B cells - Recombination activating gene 1

The correctly matched pairs are Q and R.Q is correct: once activated by antigen and T-cell help, B cells undergo class switching (for example from IgM to IgG, IgA or IgE) in germinal centres. R is correct: pre-B cells pair their newly rearranged μ heavy chain with the surrogate light chain (VpreB and λ5) to form the pre-B cell receptor.P is wrong because terminal deoxynucleotidyl transferase adds N-nucleotides during heavy-chain rearrangement in pro-B cells, and is switched off by the immature stage. S is wrong because the recombination activating genes RAG1 and RAG2 work in developing B cells and are turned off in mature B cells. So pairs containing P or S are excluded.

Q: If a naive T cell recognizes an antigen-MHC complex on an appropriate antigen-presenting cell or target cell, it will be activated, initiating :

The response initiated is a primary response.A naive T cell has never met its antigen. When it first recognises its antigen-MHC complex on an antigen-presenting cell (with co-stimulation), it proliferates and differentiates into effector and memory cells; that first encounter is the primary immune response.A secondary response is mounted by memory cells when the same antigen returns, faster and stronger. Prophylactic describes preventive measures such as vaccination, not a stage of the response, and degranulation of mast cells is an IgE-mediated effector event, not T-cell activation.

Q: When you are continuously exposed to specific antigen for a longer period which of the following statements falls wrong ?

The wrong statement is The body produces same antibody always.Repeated or prolonged exposure to an antigen changes the antibody response. Activated B cells switch class from IgM to IgG, IgA or IgE, and somatic hypermutation followed by selection in germinal centres raises the affinity of the antibodies (affinity maturation). The first encounter gives a slower primary response dominated by IgM, and later encounters a faster, larger secondary response dominated by IgG.The other three statements describe exactly these changes, so they are correct. Only the claim that the same antibody is made throughout contradicts them.

The membrane of mature B cells have

A.both IgG and IgM
B.both IgG and IgD
C.both IgM and IgE
D.both IgM and IgD

Exam Year(s)

GATE Life Sciences - 2012,

Answer: D

Mature B cells carry both IgM and IgD on their membranes.

A mature naive B cell, leaving the bone marrow and circulating in the periphery, expresses membrane IgM and IgD with the same antigen specificity. Both are made from one long primary transcript by alternative splicing of the heavy-chain constant regions Cμ and Cδ.

IgG and IgE appear only after the cell has been activated and undergone class switching, which replaces the constant region; immature B cells express IgM alone. So any option including IgG or IgE does not describe a mature naive B cell.

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Pick the correctly matched pairs.

P. Immature B cells - Terminal deoxynucleotidyl transferase
Q. Activated B cells - Class switching
R. Pre B cells - Surrogate light chain
S. Mature B cells - Recombination activating gene 1

A.P and R
B.Q and R
C.Q and S
D.Q and P

Exam Year(s)

GATE Life Sciences - 2012,

Answer: B

The correctly matched pairs are Q and R.

Q is correct: once activated by antigen and T-cell help, B cells undergo class switching (for example from IgM to IgG, IgA or IgE) in germinal centres. R is correct: pre-B cells pair their newly rearranged μ heavy chain with the surrogate light chain (V_preB and λ5) to form the pre-B cell receptor.

P is wrong because terminal deoxynucleotidyl transferase adds N-nucleotides during heavy-chain rearrangement in pro-B cells, and is switched off by the immature stage. S is wrong because the recombination activating genes RAG1 and RAG2 work in developing B cells and are turned off in mature B cells. So pairs containing P or S are excluded.

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If a naive T cell recognizes an antigen-MHC complex on an appropriate antigen-presenting cell or target cell, it will be activated, initiating :

A.a primary response
B.a secondary response
C.a prophylactic response
D.degranulation of mast cells

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: A

The response initiated is a primary response.

A naive T cell has never met its antigen. When it first recognises its antigen-MHC complex on an antigen-presenting cell (with co-stimulation), it proliferates and differentiates into effector and memory cells; that first encounter is the primary immune response.

A secondary response is mounted by memory cells when the same antigen returns, faster and stronger. Prophylactic describes preventive measures such as vaccination, not a stage of the response, and degranulation of mast cells is an IgE-mediated effector event, not T-cell activation.

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When you are continuously exposed to specific antigen for a longer period which of the following statements falls wrong ?

A.There will be antibody class switching happening in the body
B.There will be affinity maturation happening in the body
C.The body produces same antibody always
D.There will be primary and secondary response happening

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: C

The wrong statement is The body produces same antibody always.

Repeated or prolonged exposure to an antigen changes the antibody response. Activated B cells switch class from IgM to IgG, IgA or IgE, and somatic hypermutation followed by selection in germinal centres raises the affinity of the antibodies (affinity maturation). The first encounter gives a slower primary response dominated by IgM, and later encounters a faster, larger secondary response dominated by IgG.

The other three statements describe exactly these changes, so they are correct. Only the claim that the same antibody is made throughout contradicts them.

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T Cell and B Cell Activation Questions and Answers

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