Structure and functions of thymus MCQs With Answer

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Structure and functions of thymus MCQs With Answer

The thymus is a primary lymphoid organ essential for T‑lymphocyte development, central tolerance, and adaptive immunity. This concise guide for B.Pharm students covers thymic anatomy, cortical and medullary microenvironments, thymic epithelial cells, Hassall’s corpuscles, T‑cell maturation stages (double‑negative, double‑positive, single‑positive), positive/negative selection, AIRE‑mediated tolerance, involution, and clinical links such as DiGeorge syndrome, thymoma, and immunomodulatory agents like thymosin. Emphasis is on functional histology, molecular markers (CD4/CD8, MHC), and pharmacological/clinical relevance to pharmacy practice. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the embryological origin of the thymus?

  • Neural crest cells
  • Third pharyngeal (branchial) pouch endoderm
  • Mesonephric (Wolffian) duct
  • Surface ectoderm of first pharyngeal arch

Correct Answer: Third pharyngeal (branchial) pouch endoderm

Q2. Which thymic region is primarily responsible for positive selection of thymocytes?

  • Medulla
  • Cortex
  • Hassall’s corpuscles
  • Subcapsular zone

Correct Answer: Cortex

Q3. Which cells express AIRE (autoimmune regulator) critical for negative selection?

  • Thymic cortical epithelial cells
  • Thymic medullary epithelial cells
  • Macrophages in cortex
  • Endothelial cells of thymic vasculature

Correct Answer: Thymic medullary epithelial cells

Q4. During thymocyte development, the double-positive stage refers to expression of which markers?

  • CD3 and TCRαβ
  • CD4 and CD8
  • CD19 and CD20
  • CD34 and CD45

Correct Answer: CD4 and CD8

Q5. The primary function of Hassall’s corpuscles is best described as:

  • Generating naive B cells
  • Supporting regulatory T cell development and cytokine production
  • Filtering blood like a spleen
  • Producing large quantities of antibodies

Correct Answer: Supporting regulatory T cell development and cytokine production

Q6. Which molecule is essential for positive selection by presenting self‑peptides to thymocytes?

  • Complement C3
  • MHC class I and II molecules on thymic epithelial cells
  • Immunoglobulin M on B cells
  • Toll‑like receptors on macrophages

Correct Answer: MHC class I and II molecules on thymic epithelial cells

Q7. Which genetic deletion is classically associated with thymic aplasia (DiGeorge syndrome)?

  • Chromosome 7q11.23 deletion
  • 22q11.2 deletion
  • X‑linked FOXP3 deletion
  • Trisomy 21

Correct Answer: 22q11.2 deletion

Q8. Thymic involution with age primarily results in:

  • Increased thymic epithelial cell proliferation
  • Reduced naive T‑cell output and smaller thymic size
  • Enhanced production of B cells
  • Greater susceptibility to autoimmune hyperplasia

Correct Answer: Reduced naive T‑cell output and smaller thymic size

Q9. Which hormone/peptide produced by the thymus has been used as an immunomodulatory agent?

  • Insulin
  • Thymosin alpha‑1
  • Corticotropin‑releasing hormone
  • Calcitonin

Correct Answer: Thymosin alpha‑1

Q10. Negative selection in the thymus eliminates thymocytes that:

  • Cannot rearrange TCR genes
  • React strongly to self‑antigens presented on MHC
  • Lack surface CD45 expression
  • Express only CD8 without CD4

Correct Answer: React strongly to self‑antigens presented on MHC

Q11. Which cell type in the thymus acts as a professional antigen-presenting cell for negative selection?

  • Keratinocytes
  • Dendritic cells and medullary epithelial cells
  • Neutrophils
  • Adipocytes

Correct Answer: Dendritic cells and medullary epithelial cells

Q12. The earliest thymocyte progenitors arriving from bone marrow lack which markers?

  • They are double‑positive for CD4 and CD8
  • They are double‑negative (CD4− CD8−)
  • They express mature TCR on surface
  • They are CD19+ B progenitors

Correct Answer: They are double‑negative (CD4− CD8−)

Q13. Which enzyme complex is required for V(D)J recombination during TCR gene rearrangement?

  • RNA polymerase II
  • RAG1 and RAG2 recombinases
  • DNA methyltransferase 3A
  • Telomerase

Correct Answer: RAG1 and RAG2 recombinases

Q14. Which statement about thymic epithelial cells (TECs) is true?

  • Cortical TECs are mainly involved in negative selection
  • Medullary TECs express peripheral tissue antigens under AIRE control
  • TECs are identical to bone marrow stromal cells
  • TECs produce antibodies

Correct Answer: Medullary TECs express peripheral tissue antigens under AIRE control

Q15. Myasthenia gravis is frequently associated with which thymic pathology?

  • Thymic carcinoma exclusively
  • Thymoma or thymic hyperplasia
  • Complete absence of thymus in adults
  • Pulmonary metastasis to thymus

Correct Answer: Thymoma or thymic hyperplasia

Q16. Which chemokine receptor guides positively selected thymocytes from cortex to medulla?

  • CCR7
  • CXCR5
  • CCR5
  • CCR9

Correct Answer: CCR7

Q17. The predominant cell surface marker of mature T lymphocytes is:

  • CD19
  • CD3
  • CD15
  • CD56

Correct Answer: CD3

Q18. Which process occurs in the thymic medulla more than in the cortex?

  • Positive selection
  • Negative selection and central tolerance induction
  • Somatic hypermutation of BCRs
  • Production of naive B cells

Correct Answer: Negative selection and central tolerance induction

Q19. Central tolerance in the thymus helps prevent:

  • Allergic rhinitis
  • Autoimmune disease by deleting self‑reactive T cells
  • Bacterial sepsis
  • Platelet aggregation disorders

Correct Answer: Autoimmune disease by deleting self‑reactive T cells

Q20. Which of the following reduces thymic mass and T‑cell production when administered chronically?

  • Growth hormone
  • Chronic corticosteroids
  • Interleukin‑7 therapy
  • Thymosin supplements

Correct Answer: Chronic corticosteroids

Q21. Thymic output of naive T cells can be measured clinically by detecting:

  • Serum immunoglobulin levels
  • T-cell receptor excision circles (TRECs)
  • Complement activity
  • CD19+ cell count

Correct Answer: T-cell receptor excision circles (TRECs)

Q22. In the thymus, positive selection ensures thymocytes:

  • Can recognize self‑MHC with low-to-moderate affinity
  • Are autoreactive to self‑peptides
  • Express B‑cell receptors
  • Become NK cells

Correct Answer: Can recognize self‑MHC with low-to-moderate affinity

Q23. Which molecule is a transcription factor essential for development of regulatory T cells?

  • GATA3
  • FOXP3
  • NFAT1
  • STAT3

Correct Answer: FOXP3

Q24. Which cell type clears apoptotic thymocytes during selection?

  • B cells in medulla
  • Macrophages and dendritic cells
  • Endothelial cells of venules
  • Myocytes adjacent to thymus

Correct Answer: Macrophages and dendritic cells

Q25. The subcapsular zone of the thymus is mainly the site of:

  • Late single‑positive T‑cell maturation
  • Early thymocyte proliferation and DN stage expansion
  • B cell affinity maturation
  • Plasma cell secretion

Correct Answer: Early thymocyte proliferation and DN stage expansion

Q26. Which marker combination identifies immature thymocytes that have not yet rearranged TCRβ?

  • CD4+ CD8+
  • CD34+ CD7+ (double‑negative early progenitors)
  • CD19+ CD20+
  • CD3+ TCR+ mature cells

Correct Answer: CD34+ CD7+ (double‑negative early progenitors)

Q27. A deficiency of AIRE in the thymus commonly leads to which condition?

  • Severe combined immunodeficiency
  • Autoimmune polyendocrine syndrome type 1 (APS‑1)
  • Chronic granulomatous disease
  • Hyper-IgM syndrome

Correct Answer: Autoimmune polyendocrine syndrome type 1 (APS‑1)

Q28. Which thymic stromal cell produces cytokines that influence thymocyte survival and proliferation?

  • Adipocytes
  • Thymic epithelial cells (TECs)
  • Red blood cells
  • Peripheral nerve fibers

Correct Answer: Thymic epithelial cells (TECs)

Q29. Good’s syndrome is characterized by thymoma with:

  • Selective IgA excess
  • Combined B‑cell immunodeficiency and hypogammaglobulinemia
  • Excessive neutrophil counts
  • Isolated thrombocytopenia

Correct Answer: Combined B‑cell immunodeficiency and hypogammaglobulinemia

Q30. Which MHC class is primarily involved in selection of CD8+ T cells?

  • MHC class II
  • MHC class I
  • Complement receptors
  • Fc receptors

Correct Answer: MHC class I

Q31. The thymic medulla contains which distinctive histological structures?

  • Peyer’s patches
  • Hassall’s corpuscles
  • Keratinized epidermal layers
  • Follicular dendritic cell networks

Correct Answer: Hassall’s corpuscles

Q32. Which of the following best describes central versus peripheral tolerance?

  • Central tolerance occurs in lymph nodes; peripheral tolerance in thymus
  • Central tolerance is thymic deletion of self‑reactive T cells; peripheral tolerance controls escaped autoreactive cells in tissues
  • Peripheral tolerance deletes B cells in bone marrow
  • They are identical processes occurring in spleen

Correct Answer: Central tolerance is thymic deletion of self‑reactive T cells; peripheral tolerance controls escaped autoreactive cells in tissues

Q33. Thymectomy in neonates typically results in:

  • Immediate increase in thymic size elsewhere
  • Long‑term reduction in naive T‑cell repertoire and immunodeficiency
  • Loss of myeloid cell production
  • Uncontrolled B‑cell proliferation

Correct Answer: Long‑term reduction in naive T‑cell repertoire and immunodeficiency

Q34. Which physiological change is associated with age-related thymic involution?

  • Increased thymic epithelial area and thymopoiesis
  • Replacement of thymic tissue with adipose tissue
  • Transformation into bone marrow tissue
  • Development of secondary follicles

Correct Answer: Replacement of thymic tissue with adipose tissue

Q35. Which of the following best explains positive selection outcome for thymocytes?

  • Only thymocytes that fail to bind MHC survive
  • Thymocytes that bind self‑MHC with appropriate affinity are rescued from apoptosis
  • All thymocytes expressing any TCR are allowed to mature
  • Positive selection deletes cells that bind foreign antigens

Correct Answer: Thymocytes that bind self‑MHC with appropriate affinity are rescued from apoptosis

Q36. Which cytokine produced in thymus is important for thymocyte survival and proliferation?

  • Interleukin‑7 (IL‑7)
  • Interleukin‑2 exclusively from peripheral T cells
  • Interferon‑gamma from epithelial cells
  • Insulin‑like growth factor 1 only

Correct Answer: Interleukin‑7 (IL‑7)

Q37. Which diagnostic finding suggests thymoma in a patient with myasthenia gravis?

  • High serum IgE levels
  • Mediastinal mass on chest imaging (anterior mediastinum)
  • Splenomegaly on ultrasound
  • Elevated peripheral neutrophil alkaline phosphatase

Correct Answer: Mediastinal mass on chest imaging (anterior mediastinum)

Q38. Which adhesion molecules are important for thymocyte migration and interactions with stromal cells?

  • Integrins and selectins
  • Hemoglobin and myoglobin
  • Albumin and globulins
  • Collagen IV exclusively

Correct Answer: Integrins and selectins

Q39. A defect in RAG1/RAG2 would primarily impair which process in thymocytes?

  • TCR gene V(D)J recombination and receptor assembly
  • MHC class II expression on TECs
  • Secretion of thymic hormones
  • Apoptosis of mature T cells in periphery

Correct Answer: TCR gene V(D)J recombination and receptor assembly

Q40. Which clinical syndrome is characterized by hypocalcemia due to parathyroid aplasia and thymic hypoplasia?

  • Severe combined immunodeficiency (SCID)
  • DiGeorge syndrome (22q11.2 deletion)
  • Autoimmune lymphoproliferative syndrome
  • Wiskott‑Aldrich syndrome

Correct Answer: DiGeorge syndrome (22q11.2 deletion)

Q41. Which thymic cell type contributes to presentation of tissue‑restricted antigens for central tolerance?

  • Medullary thymic epithelial cells (mTECs)
  • Pericytes of blood vessels
  • Adipocytes within cortex
  • Endothelial cells of capillaries

Correct Answer: Medullary thymic epithelial cells (mTECs)

Q42. The majority of thymocytes die in thymus due to:

  • Lack of cytokines in bone marrow
  • Failure of positive selection or strong self‑reactivity during negative selection
  • Infection by thymic parasites
  • Transformation into B cells

Correct Answer: Failure of positive selection or strong self‑reactivity during negative selection

Q43. Which marker is used to identify recent thymic emigrants among peripheral T cells?

  • High expression of CD45RA and presence of TRECs
  • CD19 positivity
  • Expression of CD56 NK marker
  • Elevated immunoglobulin G

Correct Answer: High expression of CD45RA and presence of TRECs

Q44. Which of the following best describes thymic epithelial network function?

  • It passively stores T cells without interactions
  • It provides structural support, presents self‑peptides, and secretes cytokines for thymocyte education
  • It only secretes digestive enzymes
  • It is primarily adipose tissue with no immune role

Correct Answer: It provides structural support, presents self‑peptides, and secretes cytokines for thymocyte education

Q45. Which thymic change is commonly seen on CT scan in elderly individuals?

  • Enlarged lymphoid cortex
  • Fatty replacement and decreased thymic density
  • Calcified Hassall’s corpuscles visible as dense nodules
  • Massive hyperplasia of thymic tissue

Correct Answer: Fatty replacement and decreased thymic density

Q46. Which transcription factor is important for thymic epithelial cell differentiation?

  • TP53 only
  • FOXN1
  • BRCA1 exclusively
  • MYOD

Correct Answer: FOXN1

Q47. In the context of immunopharmacology, why is thymic function relevant to vaccine response?

  • Thymus directly produces antibodies for vaccines
  • Thymic output of naive T cells influences ability to generate new T‑cell responses to vaccine antigens
  • Vaccine antigens are degraded by thymic enzymes before reaching lymph nodes
  • Thymus secretes complement that neutralizes vaccines

Correct Answer: Thymic output of naive T cells influences ability to generate new T‑cell responses to vaccine antigens

Q48. Which laboratory finding would suggest a severe T‑cell developmental defect in a newborn?

  • High TRECs and abundant naive T cells
  • Very low or absent TRECs and profoundly reduced CD3+ T cells
  • Elevated IgG with normal T‑cell numbers
  • Increased eosinophils only

Correct Answer: Very low or absent TRECs and profoundly reduced CD3+ T cells

Q49. Which of the following best characterizes thymic cortical epithelial cell function?

  • They express class II MHC to mediate positive selection of CD4+ T cells
  • They generate antibodies following antigen exposure
  • They store fat and have no immunologic role
  • They exclusively produce red blood cells

Correct Answer: They express class II MHC to mediate positive selection of CD4+ T cells

Q50. Which therapy or condition can accelerate thymic involution and impair T-cell immunity?

  • Intermittent exercise
  • Chronic stress and prolonged glucocorticoid exposure
  • Balanced diet and adequate sleep
  • IL‑7 supplementation

Correct Answer: Chronic stress and prolonged glucocorticoid exposure

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