This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “Negative Regulation of B-cells”.
1. Which of the following cytokine and chemokine (respectively) is useful for the early-stage development of B cells?
a) IL7 and CXCL12 respectively
b) IL7 and CXCL12 respectively
c) IL3 and IL7 respectively
d) CXCL13 and IL7 respectively
View Answer
Explanation: B cell development begins in the fetal liver and it continues in haematopoietic stem cells (HSCs) in the bone marrow where the stromal cells provide certain chemokine and cytokines for the initiation of the B cell development. Cytokines are nothing but the interleukins which take part in various immune system mechanisms. One of the most important cytokines that is involved in early-stage development of B cells is IL-7. On the other hand, chemokines are a family of small cytokines which act as signalling proteins. One such cytokine is C-X-C motif chemokine 12 (CXCL12) which is involved in the early-stage development of B cells.
2. All humans have autoreactive B cells.
a) True
b) False
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Explanation: Yes, it’s true that all humans have autoreactive B cells. These cells are quite important for every individual as they perform some beneficial functions in the host and they are regulated by regulatory T and B cells on the basis of homeostasis. These autoreactive B cells perform several mechanisms to prevent the body from any autoimmune diseases or disorders. They also produce some polyreactive natural antibodies (nAb) for tissue homeostasis.
3. Which antibody isotype expressed by B cells are negatively selected?
a) IgG
b) IgM
c) IgE
d) IgA
View Answer
Explanation: The negative selection of B cells takes place only if B cells express IgM antibody isotype. Negative selection of such B cells refer that these cells are killed and inactivated only when they associate and bind to multiple ligands. These type of B cells differ from the mature B cells as mature B cells activate with the help of their BCR (B cell receptors) which associate to only one ligand at a time. If a B cell binds to multivalent ligand, it may lead to apoptosis and clonal deletion.
4. Where do B cells undergo negative selection?
a) Secondary Lymphoid Organs
b) Bone marrow
c) Primary Lymphoid Organs
d) Tertiary Lymphoid Organs
View Answer
Explanation: B cells undergo negative as well as positive selection in the Primary Lymphoid Organs. To accompany the negative and positive selection, T cells also get negatively/positively selected, depending on their conditions, in the same area of the body. Negative selection leads to the near-end of these cells. It takes place only if these cells bind to the wrong antigen or to the self-antigen. However, positive selection requires certain signalling mechanisms which can be mediated by antigen receptor. This signalling is necessary for the cells to survive.
5. In adult mice, which of the following factors is considered as a base for negative selection of B cells?
a) Expression and antigen specificity of B cell receptor
b) Expression and antibody specificity of B cell receptor
c) Expression of B cell receptor
d) Antibody specificity of B cell receptor
View Answer
Expression: During their development, B cells are prone to both positive and negative selection events that shape the peripheral repertoire of antigen-reactive B cells. These selection events are based on the expression and antigen specificity of the B cell antigen receptor (BCR). The complete BCR complex, consists of both antigen recognition and signalling elements. It is first expressed at the immature stage of B lymphocyte development. B cells at this stage of development are highly sensitive to negative selection.
6. Negative selection of autoreactive B cells takes place by which of the following mechanisms?
a) Deletion ➔ Anergy ➔ Clonal Selection
b) Anergy ➔ Deletion ➔ Transgenic immunogloublation
c) Deletion ➔ Anergy ➔ Receptor Editing
d) Receptor Editing ➔ Clonal Selection ➔ Clonal Deletion
View Answer
Explanation: 3 main mechanisms take place for the B cells to undergo negative selection. These mechanisms are in an order as follows- deletion, anergy and receptor editing. This process has been studied and identified in mice which is used (in most cases) as a model organism. Mice expresses a transgenic immunoglobulin receptor which responds to membrane-bound antigen. This bond somehow deletes the immature B cells as these cells become lethargic) As and when these cells associate with immunoglobulin receptor, they attack the soluble antigen in order to undergo anergic state. If there are any errors in this stage, these cells automatically transfer to receptor editing phase. This is the last phase of the B cells as they eventually undergo apoptosis.
7. How are immature B cells distinguished from mature splenic B cells?
a) By increased IgD surface expression
b) By negative signalling to BCR engagement
c) High surface area of IgD expression
d) Lower surface area of BCR engagement
View Answer
Explanation: Immature B cells are distinguished from mature splenic B cells by their negative signalling to BCR engagement. They are also distinguished phenotypically by higher surface IgM and heat stable antigen (HSA) expression. IgM is one of the most important antibody isotypes during negative regulation and selection of B cells. On the other hand, the ‘transitional’ immature B cells are distinguished from bone marrow immature B cells by increased IgD surface expression.
8. Which of the following is NOT a fate of immature B cell during ligation?
a) Apoptosis
b) Anergy
c) Primary immunoglobulin rearrangement
d) Secondary immunoglobulin rearrangement
View Answer
Explanation: There are various evidences that exist for the mechanism of negative selection of B cells. There are different models that predict that the ligation of the BCR on an immature B cell leads to 3 possible cell fates: elimination by induction of apoptosis, induction of anergy, or secondary immunoglobulin rearrangement. In order to restore the different models of negative selection and predicting the fate pf B cells, a complex array of intrinsic and extrinsic factors of the B cells are considered. These factors are chosen on the basis of the criteria by which the mechanism of negative selection is determined.
9. Where do immature B cells exist principally?
a) Bone marrow and peripheral lymphoid organs
b) Bone marrow and liver
c) Spleen and secondary lymphoid organs
d) Liver and spleen
View Answer
Explanation: Bone marrow and peripheral lymphoid organs are the home to immature B cells. The B cells obtained from the bone marrow are termed as bone marrow-derived B cells and those obtained from peripheral lymphoid organs are termed as peripheral transitional immature B cells. If these cells undergo certain secondary signals, the BCR engagement starts becoming weaker and eventually these cells undergo apoptosis.
10. Which of the following is defined as Human Immature B cells in Blood?
a) CD20+ CD27– CD38hi CD24hi CD2+
b) CD20+ CD27– CD38hi CD24hi CD10+
c) CD38hi CD24hi CD2+
d) CD34+ CD27+ CD38hi CD24hi CD10+
View Answer
Explanation: Human immature B cells in blood can be defined as CD20+ CD27– CD38hi CD24hi CD10+ cells. These cells are further subdivided into CD21lo and CD21hi populations. The CD21lo subset is based on several criteria and it is less mature. In vitro it produces higher levels of autoantibodies (autoAb). The human spleen contains the highest levels of the CD21lo subset.
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