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Questions and Answers
What is the primary function of antigen presenting cells (APCs)?
Which of the following is NOT considered a primary lymphoid organ?
What major role do secondary lymphoid organs serve?
What type of lymphocyte is primarily developed in the thymus?
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In which condition is there a significant reduction in T cells due to the absence of the thymus?
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Which of the following statements about MALT is true?
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What are Peyer patches primarily associated with?
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Langerhans cells are primarily found in which location?
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Which type of cell can act as an APC and also produce antibodies?
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What is the primary function of lymph nodes?
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Which type of T lymphocyte is primarily responsible for assisting other immune cells?
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What is the main function of granulocytes in the immune system?
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Which of the following cells are classified as antigen presenting cells?
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In which primary tissue of the immune system does hematopoiesis primarily occur?
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Which type of cell is NOT part of the myeloid lineage?
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What defines totipotent stem cells?
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What is the role of platelets in the immune response?
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Which of the following is a characteristic of cytotoxic T cells?
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Which immune cells are primarily involved in an allergic response?
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Which secondary tissue of the immune system is a key site for filtering lymphatic fluid?
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What is the primary function of neutrophils in the immune response?
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Which cells are classified as myeloid cells?
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What type of granules are found in neutrophils that contain hydrolytic enzymes?
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What characterizes the nuclei of neutrophils?
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What promotes the extravasation of polymorphonuclear granulocytes?
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Which type of cell forms from a common ancestor, a totipotent cell?
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What is a significant secondary function of neutrophils?
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Basophils and mast cells are characterized by which of the following nuclei shapes?
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Which products stimulate neutrophils' chemotactic response?
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What role do lysosomes play in neutrophils?
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What types of chemical mediators are released by basophils and mast cells during immediate hypersensitivity reactions?
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What is the primary function of eosinophils in response to parasites?
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Which of the following describes the maturation pathway of monocytes?
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What distinguishes T cells from B cells in terms of development location?
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What do natural killer (NK) cells lack compared to T and B cells?
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Which of the following statements is true regarding the reticuloendothelial system?
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What is the role of platelets following injury to endothelial cells?
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How are B cells distinguished from resting B cells upon activation?
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Which leukocyte is the least prevalent in the white blood cell count?
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Which type of lymphocyte primarily expresses T-cell receptors?
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Study Notes
Connective Tissue Mast Cells (CTMC)
- Release mediators like heparin, histamine, slow-reacting substance of anaphylaxis (SRS-A) and eosinophil chemotactic factor A (ECF-A)
Basophils and Mast Cells
- Least prevalent leukocytes
- Possess high affinity Fc receptors for IgE
- Release mediators like histamine, prostaglandins, thromboxanes, leukotrienes, and heparin
- Produce eosinophil chemotactic factor (ECF) which attracts eosinophils to areas of worm infestation or allergen
Eosinophils
- Have bilobed nucleus
- Granules stain with acid dyes (eosin)
- Capable of phagocytosing and killing microorganisms
- Release granule contents into surrounding area (degranulation)
- Kill parasites using basic proteins and cationic proteins, such as Schistosoma mansoni
Monocytes/Macrophages
- Monocytes enter circulation from bone marrow and migrate to various tissues
- Mature into macrophages, Kupffer cells (liver), histiocytes (connective tissue), dendritic cells (lymph nodes and spleen), glial cells (brain), and Langerhans' cells (skin)
- Collectively form the reticuloendothelial system (RES) or mononuclear phagocyte system
Differential White Blood Cell Count
- Neutrophils: 50-60% of WBCs, 3000-7000 cells/cmm
- Eosinophils: 1-4% of WBCs, 50-400 cells/cmm
- Basophils: 0.5-2% of WBCs, 25-100 cells/cmm
- Lymphocytes: 20-40% of WBCs, 1000-4000 cells/cmm
- T cells: 80-85% of lymphocytes
- B cells: 5-15% of lymphocytes
- NK cells: 5-15% of lymphocytes
- Monocytes: 2-9% of WBCs, 100-600 cells/cmm
Reticuloendothelial System (RES)
- Also known as mononuclear phagocyte system
Platelets
- Anucleate cell fragments derived from megakaryocytes
- Contain granules
- Major functions include blood clotting and inflammation
- Adhere to damaged tissue, releasing substances that increase vascular permeability, activate complement, and attract leukocytes.
Classes of Lymphocytes
- Include T cells, B cells, and NK cells
Maturation of Lymphocytes
- Includes the development of both T and B cells
Functions of Lymphocytes
- T cells and B cells contribute to adaptive immunity
- NK cells contribute to innate immunity
B and T lymphocytes
- T cells develop in the thymus
- B cells differentiate in the fetal liver and postnatal bone marrow
- T cells and B cells recognize antigens via specific receptors
- NK cells lack antigen receptors
- Lymphocytes have a high nucleus-to-cytoplasm ratio
- Large granular lymphocytes (NK cells) have lower nucleus-to-cytoplasm ratio
T Cells
- Majority of T cells express αβ TCR
- T cell subpopulations:
- T helper cells (TH) express CD4
- T cytotoxic cells (Tc) express CD8
- TCR is an immunoglobulin
- Contain Gall bodies (Gb) in the cytoplasm (cluster of lysosomes and a lipid droplet)
- Recognize MHC-I
Subpopulations of T cells
- T cytotoxic (Tc) cells express CD8
- T helper (TH) cells express CD4
- TH1
- TH2
- αβ T cells
- γδ T cells
B Cells
- Express MHC-I and MHC II proteins
- Resting B cells lack Gall bodies and have monoribosomes scattered in the cytoplasm
- Activated B cells have rough ER
- Function as antigen-presenting cells (APCs)
- Express CR1 (CD35) and CR2 (CD21) complement receptors
- CR2 is the target for Epstein-Barr virus (EBV) binding
NK Cells
- Have large granular lymphocyte morphology
- Contain large number of azurophilic granules compared to granular T cells
- Lack specific antigen receptors
- Derived from lymphoid progenitors in the bone marrow
- Can lyse certain tumor cell lines in vitro without prior sensitization
Antigen Presenting Cells (APCs)
- Heterogenous leukocytes that present antigens to TH or Tc cells
- Able to digest protein antigens
- Found primarily in skin, spleen, and lymph nodes
Cells that can serve as APCs
- Langerhans cells (LC)
- Dendritic cells
- Interdigitating dendritic cells (IDC)
- Follicular dendritic cells (FDC)
- Germinal center dendritic cells (GCDC)
- B cells
- Macrophages
Lymphoid Organs
- Organs involved in the maturation, differentiation, and proliferation of lymphocytes
- Primary (central) lymphoid organs:
- Where T and B lymphocytes begin expressing their antigen receptors
- Bone marrow: where B cells develop
- Thymus: where T cells develop
- Secondary lymphoid organs
- Site of antigen-dependent proliferation and differentiation
- Spleen
- Lymph nodes
- Mucosa-associated lymphoid tissue (MALT)
Primary Lymphoid Organs
- Bone marrow: where B cells develop
- Thymus: where T cells develop
- Progenitor cells from bone marrow migrate to the thymus
- Bilobed structure
- Maximum size at birth
- Atrophy with age
- Cortex contains immature thymocytes that mature and migrate to the medulla
- In the medulla, T cells learn to discriminate between self and nonself during fetal development and shortly after birth
Primary Lymphoid Organs - T Cells
- Leave the medulla
- Enter peripheral blood circulation
- Transported to secondary lymphoid organs
- DiGeorge syndrome: congenital absence of thymus, leading to severe reduction in T cells and potentially lethal wasting disease
Secondary Lymphoid Organs
- Trap and concentrate foreign substances
- Sites of antibody and T cell production
- Major secondary lymphoid organs:
- Spleen: responsive to blood-borne antigens
- Lymph nodes: protect against antigens that enter through skin and internal surfaces via the lymphatic system
- Mucosa-associated lymphoid tissue (MALT): scattered along mucosal linings, protecting against antigens entering through mucosal surfaces
Spleen
- Responsive to blood-borne antigens
Lymph nodes
- Clustered at strategic points in the body (neck, axillae, groin, mediastinum, abdominal cavity)
- Filter antigens from interstitial tissue fluid and lymph during its passage from the periphery to the thoracic duct.
- Two types:
- Somatic lymph nodes: protect the skin
- Visceral lymph nodes: protect the respiratory, digestive, and genitourinary tracts.
MALT
- Over 50% of the body's lymphoid tissue
- Composed of:
- GALT: lines the intestinal tract
- BALT: lines the respiratory tract
- Genitourinary tract lining lymphoid tissue
- Secretory IgA (sIgA) is a major effector mechanism, secreted onto mucosal epithelial surfaces.
MALT - Components
- Peyer patches lining the small intestine
- Tonsils
- Appendix
- "M" cells
- Have microfolds that absorb, transport, process, and present antigens to subepithelial lymphocytes.
Cells of the Immune System
- Lymphoid lineage:
- T helper cells (TH)
- Cytotoxic T cells (Tc or CTL)
- B cells
- Natural Killer (NK) cells
- Myeloid lineage:
- Polymorphonuclear granulocytes: neutrophils, basophils, mast cells, and eosinophils
- Mononuclear phagocytes: dendritic cells and macrophages
- Megakaryocytic lineage: platelets
Hematopoiesis
- Process of blood cell maturation from stem cell to active, functional blood cell
- Red blood cells and white blood cells are formed in the bone marrow
- Stem cells are totipotent or pluripotent:
- Totipotent: ability to give rise to unlike cells and develop into a new organism
- Pluripotent: potential to develop into more than one type of mature cell
- Myeloid cells and lymphoid cells are pluripotent with a common ancestor, a totipotent cell
Hematopoiesis - Myeloid and Lymphoid Cells
- Myeloid cells:
- Erythrocytes
- Neutrophils
- Monocytes → Macrophages
- Eosinophils
- Basophils & Mast cells
- Megakaryocytes → Platelets
- Lymphoid cells:
- Lymphocytes:
- T cells
- B cells → Plasma cells
- NK cells
- Lymphocytes:
Polymorphonuclear Granulocytes (PMNs)
- Includes neutrophils, eosinophils, basophils, and mast cells
- Produced in bone marrow at a rate of 7 million/minute
- Short lifespan (2-3 days)
- Account for 60-70% of WBCs
- Undergo extravasation (diapedesis)
Extravasation (Diapedesis)
- PMNs leave circulation by adhering to the endothelium and squeezing out
- Promoted by chemokines, such as IL-1
Neutrophil
- Subject to chemotactic stimulation by:
- Complement fragments (C5a)
- Products of platelets and leukocytes
- Bacterial products
- Protein products of fibrinolysis
- Contain lysosomes:
- Primary granules: contain hydrolases, peroxidases, and lysozyme
- Secondary (specific) granules: contain lactoferrin and lysozyme
Neutrophils
- Have multilobed nuclei
- Primary function is phagocytosis (enhanced by opsonization with complement and antibodies)
- Promote inflammation
- Kill by producing:
- Reactive oxygen metabolites
- Hydrolytic enzymes (granules)
- Nitric oxide
- Antibiotic proteins: defensins and bacterial permeability inducing protein
Basophils and Mast Cells
- Basophils in circulation
- Have S-shaped nucleus
- Round shape
- Mast cells are stationary:
- Mucosal mast cells (MMC)
- Connective tissue mast cells (CTMC)
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Description
This quiz focuses on the characteristics and functions of connective tissue mast cells, basophils, eosinophils, and monocytes/macrophages. Dive into the roles these cells play in immune response, including mediator release and interactions with allergens and parasites. Test your knowledge on their functions and clinical significance.
