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Questions and Answers
What percentage of the recirculating pool of small lymphocytes do B cells form?
Which of the following does not represent a subtype of B lymphocytes?
Which surface molecules do mature B cells express?
Which organ is primarily involved in the maturation of B lymphocytes?
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What is the primary function of B cells after antigen stimulation?
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Which cluster of differentiation (CD) molecule is expressed on immature B cells?
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Where do mature B cells primarily await the arrival of specific antigens?
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What type of immunity are lymphocytes primarily associated with?
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What is the origin of T lymphocytes?
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Which type of cells mature T lymphocytes in the thymus?
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What is true about double-negative immature thymocytes?
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What component of the TCR is responsible for recognizing specific peptide antigens?
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What function does CD3 serve in T cells?
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How do T lymphocytes recognize antigens?
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What distinguishes different clones of T lymphocytes?
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Which of the following statements about T lymphocyte maturation is incorrect?
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Which receptor is NOT associated with natural killer cells?
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What percentage of peripheral lymphocytes do natural killer cells comprise?
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Which of the following is a main function of natural killer cells?
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What role do LAK cells serve in cancer therapy?
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In immunotherapy, which lymphocyte subtype is known for its spontaneous non-specific killing of tumor cells?
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What happens to T cells that recognize MHC class I on thymic epithelial cells during maturation?
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What is the main function of T helper cells (CD4) within the immune response?
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Which T cell subtype is primarily responsible for terminating the immune response?
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What is the typical ratio of CD4 to CD8 T cells in most tissues?
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During negative selection, what normally happens to self-reactive T cell clones?
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Which T cell subtype is responsible for the fast and strong secondary immune response upon re-exposure to an antigen?
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What is a characteristic function of T cytotoxic (CD8) cells?
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Which statement accurately describes the life span and location of T helper cells?
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Study Notes
Lymphocytes
- Lymphocytes are a type of white blood cell and the unique cells of adaptive immunity.
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CD molecules (Cluster of Differentiation):
- Cell surface molecules expressed on all immune cells
- Each type of immune cell has a particular CD number
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Examples:
- T cells: CD3
- Th cells: CD4
- Tc cells: CD8
- B cells: CD19
B Lymphocytes
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Origin and Maturation:
- Develop from bone marrow stem cells
- Mature in the generative lymphoid organs (bone marrow)
- Circulate through the blood to complete maturation in secondary lymphoid organs
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Subtypes:
- Pre-B cells: Lack surface immunoglobulins but express IgM heavy chains mu in their cytoplasm
- Immature B cells: Express IgM receptors on the surface
- Mature B cells: Express IgM and IgD molecules on the surface as receptors for antigens
- **Memory B cells: ** Express IgG, IgA, or IgE on the surface
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Percentage, Life Span, and Location:
- B cells constitute about 15% of the recirculating pool of small lymphocytes
- Short life span (days or weeks)
- Found in the germinal center of lymph nodes, the white pulp of the spleen, and the gut-associated lymphoid tissue
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Function:
- Important antigen-presenting cells
- Mature B cells differentiate to plasma cells which synthesize and secrete antibodies.
T Lymphocytes
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Origin:
- From lymphoid stem cells in bone marrow
- Immature thymocytes circulate in blood without surface markers
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Maturation:
- Develop from bone marrow stem cells
- Mature in the thymus
- Circulate through blood to secondary lymphoid organs.
- Naive lymphocytes respond to foreign antigens in these secondary tissues or return to the blood via lymphatic drainage
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T lymphocyte receptor (TCR):
- Recognizes only processed protein antigens (epitopes)
- Recognizes epitopes in association with MHC molecules
- MHC molecules are found on the surface of antigen-presenting cells (APCs)
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Maturation in the Thymus:
- The thymus consists of an outer cortex and an inner medulla
- Contains thymic epithelial cells, dendritic cells, and macrophages
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Stages of Maturation:
- Double-negative immature thymocytes (in cortex): Don't express CD4 or CD8 molecules
- Double-positive immature thymocytes (in cortex): Express TCR complex, CD4, and CD8
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Expression of TCR/CD3 complex:
- TCR: Composed of alpha and beta polypeptide chains with constant and variable regions
- Variable region: Recognizes specific peptide antigens (epitopes) on MHC molecules of APCs
- CD3: Associated with the TCR and transmits intracellular activation signals
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Single-positive mature T lymphocytes: Express either CD4 or CD8 based on TCR recognition of MHC class I or II
- CD8 + cells: Become T cytotoxic cells
- CD4 + cells: Become T helper cells
- Negative selection: Ensures self-tolerance by deleting T cell clones that recognize self-peptides (self-reactive clones)
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Subtypes:
- T cytotoxic cells (Tc) or killer cells: Kill cells infected with intracellular organisms or abnormal host cells (e.g., graft cells and tumor cells) by releasing cytotoxic proteins like perforins and granzymes
- T regulatory cells (Treg): Terminate the immune response by suppressing the functions of activated immune cells, express CD25
- T helper cells (Th): Orchestrate immune responses through cytokine secretion, resulting in the activation, proliferation, and differentiation of B cells, T cells, and macrophages
- Th1 and Th2: Subtypes of T helper cells
- T memory cells: Recognize antigens upon re-exposure, resulting in a faster and stronger secondary immune response
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Percentage, Life Span, and Location:
- T cells constitute 65-80% of circulating lymphocytes (Th cells 65%, Tc cells 35%)
- Relatively long life span (months or years)
- T helper cells predominate in the thymic medulla, tonsils, and blood.
Natural Killer Cells (NK cells)
- Origin: Lymphoid stem cells in the bone marrow
- Receptors: CD56 and CD16 (receptor for the Fc portion of IgG)
- Percentage: 5-10% of peripheral lymphocytes
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Function:
- Innate immunity: Have spontaneous non-specific cytotoxic activity on virus-infected cells, tumor cells, and graft cells.
- Cytokine production: Produce INF-γ, TNF α, and GM-CSF (Granulocytes monocytes colony stimulating factor)
- LAK cells: IL-2-activated NK cells with more efficient killing effects than NK cells alone, showing promising results in metastatic cancer therapy
- ADCC (Antibody-dependent cellular cytotoxicity): Through the Fc receptor of IgG, NK cells can interact with and kill IgG-coated cells (Acquired immunity)
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Description
This quiz explores the essential characteristics of lymphocytes, focusing particularly on B lymphocytes. It covers their origin and maturation, subtypes, and the surface molecules that define their function within the immune system. Test your knowledge of these critical components of adaptive immunity.
