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Questions and Answers
What is the fate of D.P-Thymocytes if they do not recognize and bind to MHC molecules?
What is the fate of D.P-Thymocytes if they do not recognize and bind to MHC molecules?
Which of the following surface markers is characteristic of B lymphocytes?
Which of the following surface markers is characteristic of B lymphocytes?
Which types of antigens do T lymphocytes primarily recognize?
Which types of antigens do T lymphocytes primarily recognize?
Which cell type is responsible for humoral immunity?
Which cell type is responsible for humoral immunity?
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What is the main function of natural killer (NK) cells?
What is the main function of natural killer (NK) cells?
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What receptors do NK cells have that facilitate their function?
What receptors do NK cells have that facilitate their function?
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How do positively selected T cells react when they bind strongly to self peptides?
How do positively selected T cells react when they bind strongly to self peptides?
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Which type of white blood cell primarily responds to acute bacterial infections?
Which type of white blood cell primarily responds to acute bacterial infections?
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What is a defining characteristic of basophils?
What is a defining characteristic of basophils?
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Which cells are classified as antigen presenting cells (APC)?
Which cells are classified as antigen presenting cells (APC)?
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What percentage of white blood cells do lymphocytes account for?
What percentage of white blood cells do lymphocytes account for?
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Which of the following T cell types is known as a helper T cell?
Which of the following T cell types is known as a helper T cell?
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Where do T lymphocytes mature before entering circulation?
Where do T lymphocytes mature before entering circulation?
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Which type of leukocyte is characterized by the presence of CD14 and CD40 markers?
Which type of leukocyte is characterized by the presence of CD14 and CD40 markers?
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Which leukocyte is mainly involved in allergic conditions and contains histamine?
Which leukocyte is mainly involved in allergic conditions and contains histamine?
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Study Notes
Basic Immunology: Immune Cells, Receptors & Markers
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Lymphoid Tissues: Classified into primary and secondary organs
- Primary organs: Thymus, bone marrow
- Secondary organs: Neck (cervical) lymph nodes, armpit (axillary) lymph nodes, spleen, Peyer's patches, groin (inguinal) lymph node
White Blood Cell Classification
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Myeloid Lineage:
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Granular leukocytes: Neutrophils, eosinophils, basophils, mast cells
- Neutrophils: ~60% of peripheral blood leukocytes; segmented (mature), band; activated in acute bacterial infection
- Eosinophils: Eosin-loving granules, 0-5% of WBCs; activated in helminths infection and allergies
- Basophils: Acidic cytoplasmic granules containing histamine; 0-1% of WBCs; activated in allergic conditions
- Mast cells: Scattered in connective tissues (especially skin, mucosa, and epithelia); contain histamine; activated in allergic conditions; from granulocytic-myeloid cells
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Agranular leukocytes: Monocytes, macrophages, dendritic cells
- Monocytes, macrophages & dendritic cells: Monocytes in circulation, macrophages and dendritic cells in tissues; 5-7% of peripheral blood leukocytes; antigen-presenting cells (APCs); scavenger cells for innate immunity; Macrophage markers: CD14, CD40, CD11b
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Granular leukocytes: Neutrophils, eosinophils, basophils, mast cells
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Lymphoid Lineage:
- Granular leukocytes: Natural killer (NK) cells
- Agranular leukocytes: T cells, B cells
Immune Cell Development
- A pluripotent hematopoietic stem cell gives rise to all leukocytes, erythrocytes, and platelets.
- This cell develops into myeloid and lymphoid lineages
T Lymphocytes
- Thymus-derived cells: Arise from bone marrow, mature in thymus, enter circulation
- Identified by presence of CD3 complex (TCR)
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Four subsets:
- CD4+ T cells (helper): recognize MHC class II
- CD8+ T cells (cytotoxic): recognize MHC class I
- CD4+ and CD25+ T regulatory (Treg)
- T suppressor (Ts) cells
T Lymphocyte Selection
- Double negative prothymocytes: Enter thymus; do not express CD4 or CD8; express TCR-CD3 complex, and both CD4 and CD8 (double positive cells; D.P).
- Positive selection: DP thymocytes die unless they recognize and bind to major histocompatibility complex (MHC-I, II).
- Negative selection: Positively selected T cells (CD4 or CD8) that bind strongly to self-peptides of the MHC I or MHC II on medullary APCs (phagocytes) undergo apoptotic death
B Lymphocytes
- Bone marrow-derived cells: Arise and mature within bone marrow
- Markers: B cell receptors (antibodies: IgM & IgD); CD19, CD20, & CD21 (complement receptor)
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Two types:
- B1: present in respiratory & GI systems
- B2: widely distributed in lymphoid organs and tissues
- Isotope switching is typical for B2 lineage
- Plasma cells: terminally differentiated B cells; immunoglobulin-producing cells
Natural Killer (NK) Cells
- Forms 5-10% of peripheral blood lymphocytes
- Lack B cell receptor
- Surface markers: CD16, CD56, and Fc receptor for IgG
- Some NK cells carry TCR and CD4 or CD8 markers
- Very active in killing virally infected cells and tumor cells
- Have two major receptors:
- Killing activation receptor (KAR)
- Killing inhibition receptor (KIR)
Natural Killer Cell Receptors
- Killer activation receptors (KARs): Recognize the presence of stress-related molecules expressed by virally infected cells and tumor cells.
- Killer inhibition receptors (KIRs): Recognize the presence of MHC class I, which is normally displayed on the host cell surfaces.
Somatically Generated Receptors
- T cell receptors (TCR): Associated with cluster of differentiation 3 (CD3); binds to antigen-MHC; CD4 and CD8 are co-receptors.
- B cell receptors (BCR): Immunoglobulins IgM & IgD serve as B-cell receptors.
Summary Table (Lymphocytes)
| Feature | B Lymphocytes | T Lymphocytes | NK Cells |
|---|---|---|---|
| Origin | Bone marrow | Thymus | Bone marrow |
| Percentage | ~10-15% | ~75-80% | ~5-10% |
| Surface Markers | CD19, CD20, CD21, CD35 | CD3, CD4, or CD8 | CD16, CD56, Fc receptor for IgG (some TCR) |
| Antigen Receptor | B cell receptor (BCR), IgM, IgD | T cell receptor (TCR), α and β chains | KARs and KIRs |
| Antigen Recognition | MHC-II, wide variety of antigens (proteins, polysaccharides) | MHC-I and II, Peptide+MHC molecules on APC | Stress-related molecules; MHC class I |
| Immunity Type | Humoral | Cell-mediated | Cell-mediated |
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Description
Explore the fundamentals of immunology with this quiz focused on immune cells, receptors, and lymphoid tissues. Learn about the classification and functions of various white blood cells and how they contribute to our immune response. This quiz is ideal for students studying basic immunology concepts.
