Question 1

As we age,our thymus shrinks,or atrophies,by a process called involution,yet T-cell immunity is still functional in old age.
A.Explain how T-cell numbers in the periphery remain constant in the absence of continual replenishment from the thymus.
B.How does this differ from the maintenance of the B-cell repertoire?

Accepted Answer

The answer of As we age,our thymus shrinks,or atrophies,by a...

Question 2

If the process of positive selection did not occur,then

Accepted Answer

Positive selection ensures that T cells can recognize self-MHC molecules, which is crucial for their activation. Without it, very few T cells would be capable of activation.

Question 3

Allelic exclusion occurs for all of the following except

Accepted Answer

Allelic exclusion occurs for all antigen receptor genes except for T-cell receptor α genes, which can undergo additional rearrangements if the first attempt is unsuccessful.

Question 4

Immediately after positive selection

Accepted Answer

Positive selection occurs in the thymus, where thymocytes with T-cell receptors (TCRs) capable of recognizing self-MHC molecules are selected for survival. After positive selection, RAG proteins, which are involved in TCR gene rearrangement, are degraded and no longer synthesized, as the TCR is already successfully rearranged and functional.

Question 5

The function of negative selection of thymocytes in the thymus is to eliminate

Accepted Answer

The function of negative selection is to eliminate autoreactive thymocytes, which are T cells that recognize and attack the body's own tissues. This is an important mechanism for preventing autoimmune diseases. Single-positive and double-positive thymocytes are not eliminated during negative selection. Alloreactive T cells are those that recognize and attack foreign tissues with different MHC molecules, but they are not eliminated during negative selection. Apoptotic thymocytes refer to dying or dead thymocytes and are not relevant to negative selection.

Question 6

Healthy individuals have approximately ____ of CD4 T cells compared with CD8 T cells.

Accepted Answer

Healthy individuals typically have about twice the number of CD4 T cells compared to CD8 T cells.

Question 7

In T cells,allelic exclusion of the α-chain locus is relatively ineffective,resulting in the production of some T cells with two T-cell receptors of differing antigen specificity on their cell surface.
A.Will both these receptors have to pass positive selection for the cell to survive? Explain your answer.
B.Will both receptors have to pass negative selection for the cell to survive? Explain your answer.
C.Is there a potential problem in having T cells with dual specificity surviving these selection processes and being exported to the periphery?

Accepted Answer

The answer of In T cells,allelic exclusion of the α-chain...

Question 8

Giulia McGettigan was born full term with a malformed jaw,cleft palate,a ventricular septal defect,and hypocalcemia.Within 48 hours of birth she developed muscle tetany,convulsions,tachypnea,and a systolic murmur.A chest X-ray showed an enlarged heart and the absence of a thymic shadow.Blood tests showed severely depleted levels of CD4 and CD8 T cells; B-cell numbers were low but within normal range.Parathyroid hormone was undetectable.Fluorescence in situ hybridization of the buccal mucosa revealed a small deletion in the long arm of chromosome 22.Giulia failed to thrive and battled chronic diarrhea and opportunistic infections,including oral candidiasis and Pneumocystis jirovecii,the latter infection causing her death.Giulia most probably had which of the following immunodeficiency diseases?

Accepted Answer

Depletion of T cells, but not of B cells, and the absence of a thymic shadow on the X-ray are critical clues. Development of both CD8 and CD4 T cells is affected in this patient because the thymus is the primary lymphoid organ required for T-cell development. Bare lymphocyte syndrome affects either CD8 (type I) or CD4 (type II), but not both. Although patients without a thymus succumb to infections also common in individuals with AIDS, this option can be ruled out because Giulia lacks CD8 T cells, a condition not seen in AIDS patients. Chronic granulomatous disease is a defect of neutrophil, not T-cell, function.

Question 9

MHC class II deficiency is inherited as an autosomal recessive trait and involves a defect in the coordination of transcription factors involved in regulating the expression of all MHC class II genes (HLA-DP,HLA-DQ,and HLA-DR).
A.What is the effect of MHC class II deficiency?
B.Explain why hypogammaglobulinemia is associated with this deficiency.

Accepted Answer

The answer of MHC class II deficiency is inherited as...

Question 10

A.What is the role of regulatory CD4 T cells (T_reg)? B.How can T_reg be distinguished from other non-regulatory CD4 T cells?

Accepted Answer

The answer of A.What is the role of regulatory CD4...

Question 11

Mature B cells undergo somatic hypermutation after activation,which,after affinity maturation,results in the production of antibody with a higher affinity for antigen than in the primary antibody response.Suggest some reasons why T cells have not evolved the same capacity.

Accepted Answer

The answer of Mature B cells undergo somatic hypermutation after...

Question 12

Double-negative thymocytes initiate rearrangement at the _____ locus (loci)before all other T-cell receptor genes.

Accepted Answer

The answer of Double-negative thymocytes initiate rearrangement at the _____...

Question 13

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED)is caused by a defect in

Accepted Answer

APECED is caused by a defect in the AIRE (autoimmune regulator) gene, which codes for a transcription factor that regulates tissue-specific gene expression in the thymus. This results in a failure of central tolerance, leading to the production of autoantibodies and autoimmune conditions such as candidiasis and endocrine dysfunction.

Question 14

Individuals with a defective autoimmune regulator gene (AIRE)exhibit

Accepted Answer

A defective AIRE gene leads to autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED).

Question 15

Identify which of the following describes how antigen processing and presentation of self antigens by thymic epithelial cells differs from that of antigen-presenting cells in peripheral tissues.(Select all that apply.)

Accepted Answer

- Thymic epithelial cells use cathepsin L for the proteolytic degradation of self proteins, which is different from the proteases used by antigen-presenting cells in peripheral tissues.- The transcription factor AIRE (Autoimmune Regulator) is uniquely expressed in thymic epithelial cells and is responsible for the activation of a wide array of tissue-specific genes, allowing for the presentation of a diverse set of self antigens to developing T cells, which is not a feature of peripheral antigen-presenting cells.

Question 16

The surrogate light chain operating during pre-B-cell development is made up of VpreB:λ.Its expression with μ on the pre-B-cell surface is an important checkpoint in B-cell maturation.Name the T-cell analog of VpreB:λ5 and discuss how it is functionally similar.

Accepted Answer

The answer of The surrogate light chain operating during pre-B-cell...

Question 17

A.Explain two ways in which the expression and processing of self antigens in thymic epithelium differs from the expression and processing of self antigens outside the thymus.
B.In what way is the thymic situation advantageous for the purposes of negative selection?

Accepted Answer

The answer of A.Explain two ways in which the expression...

Question 18

All of the following types of protein are processed and presented by macrophages in the thymus except _____ proteins.

Accepted Answer

Tissue-specific proteins are typically not processed and presented by macrophages in the thymus. The thymus is involved in the education of T cells, which requires exposure to a wide variety of antigens, but tissue-specific proteins are generally not presented in this context because they are not representative of antigens that T cells need to learn to recognize systemically.

Question 19

Which of the following statements is correct?

Accepted Answer

The answer of Which of the following statements is correct?
...

Question 20

The human thymus begins to degenerate as early as one year after birth.This process is called ______ and is marked by the accumulation of ___ once occupied by thymocytes.

Accepted Answer

The answer of The human thymus begins to degenerate as...

Quiz 7: The Development of T Lymphocytes

If the process of positive selection did not occur,then

Allelic exclusion occurs for all of the following except

Immediately after positive selection

The function of negative selection of thymocytes in the thymus is to eliminate

Healthy individuals have approximately ____ of CD4 T cells compared with CD8 T cells.

A.What is the role of regulatory CD4 T cells (T_reg)? B.How can T_reg be distinguished from other non-regulatory CD4 T cells?

Mature B cells undergo somatic hypermutation after activation,which,after affinity maturation,results in the production of antibody with a higher affinity for antigen than in the primary antibody response.Suggest some reasons why T cells have not evolved the same capacity.

Double-negative thymocytes initiate rearrangement at the _____ locus (loci) before all other T-cell receptor genes.

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is caused by a defect in

Individuals with a defective autoimmune regulator gene (AIRE) exhibit

Identify which of the following describes how antigen processing and presentation of self antigens by thymic epithelial cells differs from that of antigen-presenting cells in peripheral tissues.(Select all that apply.)

The surrogate light chain operating during pre-B-cell development is made up of VpreB:λ.Its expression with μ on the pre-B-cell surface is an important checkpoint in B-cell maturation.Name the T-cell analog of VpreB:λ5 and discuss how it is functionally similar.

A.Explain two ways in which the expression and processing of self antigens in thymic epithelium differs from the expression and processing of self antigens outside the thymus. B.In what way is the thymic situation advantageous for the purposes of negative selection?

All of the following types of protein are processed and presented by macrophages in the thymus except _____ proteins.

Which of the following statements is correct?

The human thymus begins to degenerate as early as one year after birth.This process is called ____ and is marked by the accumulation of _ once occupied by thymocytes.

Quiz 7: The Development of T Lymphocytes

If the process of positive selection did not occur,then

Allelic exclusion occurs for all of the following except

Immediately after positive selection

The function of negative selection of thymocytes in the thymus is to eliminate

Healthy individuals have approximately ____ of CD4 T cells compared with CD8 T cells.

A.What is the role of regulatory CD4 T cells (Treg)? B.How can Treg be distinguished from other non-regulatory CD4 T cells?

Mature B cells undergo somatic hypermutation after activation,which,after affinity maturation,results in the production of antibody with a higher affinity for antigen than in the primary antibody response.Suggest some reasons why T cells have not evolved the same capacity.

Double-negative thymocytes initiate rearrangement at the _____ locus (loci) before all other T-cell receptor genes.

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is caused by a defect in

Individuals with a defective autoimmune regulator gene (AIRE) exhibit

Identify which of the following describes how antigen processing and presentation of self antigens by thymic epithelial cells differs from that of antigen-presenting cells in peripheral tissues.(Select all that apply.)

The surrogate light chain operating during pre-B-cell development is made up of VpreB:λ.Its expression with μ on the pre-B-cell surface is an important checkpoint in B-cell maturation.Name the T-cell analog of VpreB:λ5 and discuss how it is functionally similar.

A.Explain two ways in which the expression and processing of self antigens in thymic epithelium differs from the expression and processing of self antigens outside the thymus. B.In what way is the thymic situation advantageous for the purposes of negative selection?

All of the following types of protein are processed and presented by macrophages in the thymus except _____ proteins.

Which of the following statements is correct?

The human thymus begins to degenerate as early as one year after birth.This process is called ______ and is marked by the accumulation of ___ once occupied by thymocytes.

A.What is the role of regulatory CD4 T cells (T_reg)? B.How can T_reg be distinguished from other non-regulatory CD4 T cells?

The human thymus begins to degenerate as early as one year after birth.This process is called ____ and is marked by the accumulation of _ once occupied by thymocytes.